"Clang" CFE Internals Manual
- Introduction
- LLVM Support Library
- The Clang 'Basic' Library
- The Driver Library
- Precompiled Headers
- The Frontend Library
- The Lexer and Preprocessor Library
- The Parser Library
- The AST Library
- Howto guides
Introduction
This document describes some of the more important APIs and internal design decisions made in the Clang C front-end. The purpose of this document is to both capture some of this high level information and also describe some of the design decisions behind it. This is meant for people interested in hacking on Clang, not for end-users. The description below is categorized by libraries, and does not describe any of the clients of the libraries.
LLVM Support Library
The LLVM libsupport library provides many underlying libraries and data-structures, including command line option processing, various containers and a system abstraction layer, which is used for file system access.
The Clang 'Basic' Library
This library certainly needs a better name. The 'basic' library contains a number of low-level utilities for tracking and manipulating source buffers, locations within the source buffers, diagnostics, tokens, target abstraction, and information about the subset of the language being compiled for.
Part of this infrastructure is specific to C (such as the TargetInfo class), other parts could be reused for other non-C-based languages (SourceLocation, SourceManager, Diagnostics, FileManager). When and if there is future demand we can figure out if it makes sense to introduce a new library, move the general classes somewhere else, or introduce some other solution.
We describe the roles of these classes in order of their dependencies.
The Diagnostics Subsystem
The Clang Diagnostics subsystem is an important part of how the compiler communicates with the human. Diagnostics are the warnings and errors produced when the code is incorrect or dubious. In Clang, each diagnostic produced has (at the minimum) a unique ID, an English translation associated with it, a SourceLocation to "put the caret", and a severity (e.g. WARNING or ERROR). They can also optionally include a number of arguments to the dianostic (which fill in "%0"'s in the string) as well as a number of source ranges that related to the diagnostic.
In this section, we'll be giving examples produced by the Clang command line driver, but diagnostics can be rendered in many different ways depending on how the DiagnosticClient interface is implemented. A representative example of a diagnostic is:
t.c:38:15: error: invalid operands to binary expression ('int *' and '_Complex float') P = (P-42) + Gamma*4; ~~~~~~ ^ ~~~~~~~
In this example, you can see the English translation, the severity (error), you can see the source location (the caret ("^") and file/line/column info), the source ranges "~~~~", arguments to the diagnostic ("int*" and "_Complex float"). You'll have to believe me that there is a unique ID backing the diagnostic :).
Getting all of this to happen has several steps and involves many moving pieces, this section describes them and talks about best practices when adding a new diagnostic.
The Diagnostic*Kinds.td files
Diagnostics are created by adding an entry to one of the clang/Basic/Diagnostic*Kinds.td files, depending on what library will be using it. From this file, tblgen generates the unique ID of the diagnostic, the severity of the diagnostic and the English translation + format string.
There is little sanity with the naming of the unique ID's right now. Some start with err_, warn_, ext_ to encode the severity into the name. Since the enum is referenced in the C++ code that produces the diagnostic, it is somewhat useful for it to be reasonably short.
The severity of the diagnostic comes from the set {NOTE, WARNING, EXTENSION, EXTWARN, ERROR}. The ERROR severity is used for diagnostics indicating the program is never acceptable under any circumstances. When an error is emitted, the AST for the input code may not be fully built. The EXTENSION and EXTWARN severities are used for extensions to the language that Clang accepts. This means that Clang fully understands and can represent them in the AST, but we produce diagnostics to tell the user their code is non-portable. The difference is that the former are ignored by default, and the later warn by default. The WARNING severity is used for constructs that are valid in the currently selected source language but that are dubious in some way. The NOTE level is used to staple more information onto previous diagnostics.
These severities are mapped into a smaller set (the Diagnostic::Level enum, {Ignored, Note, Warning, Error, Fatal }) of output levels by the diagnostics subsystem based on various configuration options. Clang internally supports a fully fine grained mapping mechanism that allows you to map almost any diagnostic to the output level that you want. The only diagnostics that cannot be mapped are NOTEs, which always follow the severity of the previously emitted diagnostic and ERRORs, which can only be mapped to Fatal (it is not possible to turn an error into a warning, for example).
Diagnostic mappings are used in many ways. For example, if the user specifies -pedantic, EXTENSION maps to Warning, if they specify -pedantic-errors, it turns into Error. This is used to implement options like -Wunused_macros, -Wundef etc.
Mapping to Fatal should only be used for diagnostics that are considered so severe that error recovery won't be able to recover sensibly from them (thus spewing a ton of bogus errors). One example of this class of error are failure to #include a file.
The Format String
The format string for the diagnostic is very simple, but it has some power. It takes the form of a string in English with markers that indicate where and how arguments to the diagnostic are inserted and formatted. For example, here are some simple format strings:
"binary integer literals are an extension" "format string contains '\\0' within the string body" "more '%%' conversions than data arguments" "invalid operands to binary expression (%0 and %1)" "overloaded '%0' must be a %select{unary|binary|unary or binary}2 operator" " (has %1 parameter%s1)"
These examples show some important points of format strings. You can use any plain ASCII character in the diagnostic string except "%" without a problem, but these are C strings, so you have to use and be aware of all the C escape sequences (as in the second example). If you want to produce a "%" in the output, use the "%%" escape sequence, like the third diagnostic. Finally, Clang uses the "%...[digit]" sequences to specify where and how arguments to the diagnostic are formatted.
Arguments to the diagnostic are numbered according to how they are specified by the C++ code that produces them, and are referenced by %0 .. %9. If you have more than 10 arguments to your diagnostic, you are doing something wrong :). Unlike printf, there is no requirement that arguments to the diagnostic end up in the output in the same order as they are specified, you could have a format string with "%1 %0" that swaps them, for example. The text in between the percent and digit are formatting instructions. If there are no instructions, the argument is just turned into a string and substituted in.
Here are some "best practices" for writing the English format string:
- Keep the string short. It should ideally fit in the 80 column limit of the DiagnosticKinds.td file. This avoids the diagnostic wrapping when printed, and forces you to think about the important point you are conveying with the diagnostic.
- Take advantage of location information. The user will be able to see the line and location of the caret, so you don't need to tell them that the problem is with the 4th argument to the function: just point to it.
- Do not capitalize the diagnostic string, and do not end it with a period.
- If you need to quote something in the diagnostic string, use single quotes.
Diagnostics should never take random English strings as arguments: you shouldn't use "you have a problem with %0" and pass in things like "your argument" or "your return value" as arguments. Doing this prevents translating the Clang diagnostics to other languages (because they'll get random English words in their otherwise localized diagnostic). The exceptions to this are C/C++ language keywords (e.g. auto, const, mutable, etc) and C/C++ operators (/=). Note that things like "pointer" and "reference" are not keywords. On the other hand, you can include anything that comes from the user's source code, including variable names, types, labels, etc. The 'select' format can be used to achieve this sort of thing in a localizable way, see below.
Formatting a Diagnostic Argument
Arguments to diagnostics are fully typed internally, and come from a couple different classes: integers, types, names, and random strings. Depending on the class of the argument, it can be optionally formatted in different ways. This gives the DiagnosticClient information about what the argument means without requiring it to use a specific presentation (consider this MVC for Clang :).
Here are the different diagnostic argument formats currently supported by Clang:
| "s" format | |
| Example: | "requires %1 parameter%s1" |
| Class: | Integers |
| Description: | This is a simple formatter for integers that is useful when producing English diagnostics. When the integer is 1, it prints as nothing. When the integer is not 1, it prints as "s". This allows some simple grammatical forms to be to be handled correctly, and eliminates the need to use gross things like "requires %1 parameter(s)". |
| "select" format | |
| Example: | "must be a %select{unary|binary|unary or binary}2 operator" |
| Class: | Integers |
| Description: | This format specifier is used to merge multiple related diagnostics together into one common one, without requiring the difference to be specified as an English string argument. Instead of specifying the string, the diagnostic gets an integer argument and the format string selects the numbered option. In this case, the "%2" value must be an integer in the range [0..2]. If it is 0, it prints 'unary', if it is 1 it prints 'binary' if it is 2, it prints 'unary or binary'. This allows other language translations to substitute reasonable words (or entire phrases) based on the semantics of the diagnostic instead of having to do things textually. The selected string does undergo formatting. |
| "plural" format | |
| Example: | "you have %1 %plural{1:mouse|:mice}1 connected to your computer" |
| Class: | Integers |
| Description: | This is a formatter for complex plural forms. It is designed to handle even the requirements of languages with very complex plural forms, as many Baltic languages have. The argument consists of a series of expression/form pairs, separated by ':', where the first form whose expression evaluates to true is the result of the modifier. An expression can be empty, in which case it is always true. See the example at the top. Otherwise, it is a series of one or more numeric conditions, separated by ','. If any condition matches, the expression matches. Each numeric condition can take one of three forms.
The parser is very unforgiving. A syntax error, even whitespace, will abort, as will a failure to match the argument against any expression. |
| "ordinal" format | |
| Example: | "ambiguity in %ordinal0 argument" |
| Class: | Integers |
| Description: | This is a formatter which represents the argument number as an ordinal: the value 1 becomes 1st, 3 becomes 3rd, and so on. Values less than 1 are not supported. This formatter is currently hard-coded to use English ordinals. |
| "objcclass" format | |
| Example: | "method %objcclass0 not found" |
| Class: | DeclarationName |
| Description: | This is a simple formatter that indicates the DeclarationName corresponds to an Objective-C class method selector. As such, it prints the selector with a leading '+'. |
| "objcinstance" format | |
| Example: | "method %objcinstance0 not found" |
| Class: | DeclarationName |
| Description: | This is a simple formatter that indicates the DeclarationName corresponds to an Objective-C instance method selector. As such, it prints the selector with a leading '-'. |
| "q" format | |
| Example: | "candidate found by name lookup is %q0" |
| Class: | NamedDecl* |
| Description | This formatter indicates that the fully-qualified name of the declaration should be printed, e.g., "std::vector" rather than "vector". |
| "diff" format | |
| Example: | "no known conversion %diff{from | to | }1,2" |
| Class: | QualType |
| Description | This formatter takes two QualTypes and attempts to print a template difference between the two. If tree printing is off, the text inside the braces before the pipe is printed, with the formatted text replacing the $. If tree printing is on, the text after the pipe is printed and a type tree is printed after the diagnostic message. |
It is really easy to add format specifiers to the Clang diagnostics system, but they should be discussed before they are added. If you are creating a lot of repetitive diagnostics and/or have an idea for a useful formatter, please bring it up on the cfe-dev mailing list.
Producing the Diagnostic
Now that you've created the diagnostic in the DiagnosticKinds.td file, you need to write the code that detects the condition in question and emits the new diagnostic. Various components of Clang (e.g. the preprocessor, Sema, etc) provide a helper function named "Diag". It creates a diagnostic and accepts the arguments, ranges, and other information that goes along with it.
For example, the binary expression error comes from code like this:
if (various things that are bad) Diag(Loc, diag::err_typecheck_invalid_operands) << lex->getType() << rex->getType() << lex->getSourceRange() << rex->getSourceRange();
This shows that use of the Diag method: they take a location (a SourceLocation object) and a diagnostic enum value (which matches the name from DiagnosticKinds.td). If the diagnostic takes arguments, they are specified with the << operator: the first argument becomes %0, the second becomes %1, etc. The diagnostic interface allows you to specify arguments of many different types, including int and unsigned for integer arguments, const char* and std::string for string arguments, DeclarationName and const IdentifierInfo* for names, QualType for types, etc. SourceRanges are also specified with the << operator, but do not have a specific ordering requirement.
As you can see, adding and producing a diagnostic is pretty straightforward. The hard part is deciding exactly what you need to say to help the user, picking a suitable wording, and providing the information needed to format it correctly. The good news is that the call site that issues a diagnostic should be completely independent of how the diagnostic is formatted and in what language it is rendered.
Fix-It Hints
In some cases, the front end emits diagnostics when it is clear that some small change to the source code would fix the problem. For example, a missing semicolon at the end of a statement or a use of deprecated syntax that is easily rewritten into a more modern form. Clang tries very hard to emit the diagnostic and recover gracefully in these and other cases.
However, for these cases where the fix is obvious, the diagnostic can be annotated with a hint (referred to as a "fix-it hint") that describes how to change the code referenced by the diagnostic to fix the problem. For example, it might add the missing semicolon at the end of the statement or rewrite the use of a deprecated construct into something more palatable. Here is one such example from the C++ front end, where we warn about the right-shift operator changing meaning from C++98 to C++11:
test.cpp:3:7: warning: use of right-shift operator ('>>') in template argument will require parentheses in C++11 A<100 >> 2> *a; ^ ( )
Here, the fix-it hint is suggesting that parentheses be added, and showing exactly where those parentheses would be inserted into the source code. The fix-it hints themselves describe what changes to make to the source code in an abstract manner, which the text diagnostic printer renders as a line of "insertions" below the caret line. Other diagnostic clients might choose to render the code differently (e.g., as markup inline) or even give the user the ability to automatically fix the problem.
Fix-it hints on errors and warnings need to obey these rules:
- Since they are automatically applied if
-Xclang -fixit
is passed to the driver, they should only be used when it's very likely they match the user's intent. - Clang must recover from errors as if the fix-it had been applied.
If a fix-it can't obey these rules, put the fix-it on a note. Fix-its on notes are not applied automatically.
All fix-it hints are described by the FixItHint
class,
instances of which should be attached to the diagnostic using the
<< operator in the same way that highlighted source ranges and
arguments are passed to the diagnostic. Fix-it hints can be created
with one of three constructors:
FixItHint::CreateInsertion(Loc, Code)
- Specifies that the given
Code
(a string) should be inserted before the source locationLoc
. FixItHint::CreateRemoval(Range)
- Specifies that the code in the given source
Range
should be removed. FixItHint::CreateReplacement(Range, Code)
- Specifies that the code in the given source
Range
should be removed, and replaced with the givenCode
string.
The DiagnosticClient Interface
Once code generates a diagnostic with all of the arguments and the rest of the relevant information, Clang needs to know what to do with it. As previously mentioned, the diagnostic machinery goes through some filtering to map a severity onto a diagnostic level, then (assuming the diagnostic is not mapped to "Ignore") it invokes an object that implements the DiagnosticClient interface with the information.
It is possible to implement this interface in many different ways. For example, the normal Clang DiagnosticClient (named 'TextDiagnosticPrinter') turns the arguments into strings (according to the various formatting rules), prints out the file/line/column information and the string, then prints out the line of code, the source ranges, and the caret. However, this behavior isn't required.
Another implementation of the DiagnosticClient interface is the 'TextDiagnosticBuffer' class, which is used when Clang is in -verify mode. Instead of formatting and printing out the diagnostics, this implementation just captures and remembers the diagnostics as they fly by. Then -verify compares the list of produced diagnostics to the list of expected ones. If they disagree, it prints out its own output. Full documentation for the -verify mode can be found in the Clang API documentation for VerifyDiagnosticConsumer, here.
There are many other possible implementations of this interface, and this is why we prefer diagnostics to pass down rich structured information in arguments. For example, an HTML output might want declaration names be linkified to where they come from in the source. Another example is that a GUI might let you click on typedefs to expand them. This application would want to pass significantly more information about types through to the GUI than a simple flat string. The interface allows this to happen.
Adding Translations to Clang
Not possible yet! Diagnostic strings should be written in UTF-8, the client can translate to the relevant code page if needed. Each translation completely replaces the format string for the diagnostic.
The SourceLocation and SourceManager classes
Strangely enough, the SourceLocation class represents a location within the source code of the program. Important design points include:
- sizeof(SourceLocation) must be extremely small, as these are embedded into many AST nodes and are passed around often. Currently it is 32 bits.
- SourceLocation must be a simple value object that can be efficiently copied.
- We should be able to represent a source location for any byte of any input file. This includes in the middle of tokens, in whitespace, in trigraphs, etc.
- A SourceLocation must encode the current #include stack that was active when the location was processed. For example, if the location corresponds to a token, it should contain the set of #includes active when the token was lexed. This allows us to print the #include stack for a diagnostic.
- SourceLocation must be able to describe macro expansions, capturing both the ultimate instantiation point and the source of the original character data.
In practice, the SourceLocation works together with the SourceManager class to encode two pieces of information about a location: its spelling location and its instantiation location. For most tokens, these will be the same. However, for a macro expansion (or tokens that came from a _Pragma directive) these will describe the location of the characters corresponding to the token and the location where the token was used (i.e. the macro instantiation point or the location of the _Pragma itself).
The Clang front-end inherently depends on the location of a token being tracked correctly. If it is ever incorrect, the front-end may get confused and die. The reason for this is that the notion of the 'spelling' of a Token in Clang depends on being able to find the original input characters for the token. This concept maps directly to the "spelling location" for the token.
SourceRange and CharSourceRange
Clang represents most source ranges by [first, last], where first and last each point to the beginning of their respective tokens. For example consider the SourceRange of the following statement:
x = foo + bar; ^first ^last
To map from this representation to a character-based
representation, the 'last' location needs to be adjusted to point to
(or past) the end of that token with either
Lexer::MeasureTokenLength()
or
Lexer::getLocForEndOfToken()
. For the rare cases
where character-level source ranges information is needed we use
the CharSourceRange
class.
The Driver Library
The clang Driver and library are documented here.
Precompiled Headers
Clang supports two implementations of precompiled headers. The default implementation, precompiled headers (PCH) uses a serialized representation of Clang's internal data structures, encoded with the LLVM bitstream format. Pretokenized headers (PTH), on the other hand, contain a serialized representation of the tokens encountered when preprocessing a header (and anything that header includes).
The Frontend Library
The Frontend library contains functionality useful for building tools on top of the clang libraries, for example several methods for outputting diagnostics.
The Lexer and Preprocessor Library
The Lexer library contains several tightly-connected classes that are involved with the nasty process of lexing and preprocessing C source code. The main interface to this library for outside clients is the large Preprocessor class. It contains the various pieces of state that are required to coherently read tokens out of a translation unit.
The core interface to the Preprocessor object (once it is set up) is the Preprocessor::Lex method, which returns the next Token from the preprocessor stream. There are two types of token providers that the preprocessor is capable of reading from: a buffer lexer (provided by the Lexer class) and a buffered token stream (provided by the TokenLexer class).
The Token class
The Token class is used to represent a single lexed token. Tokens are intended to be used by the lexer/preprocess and parser libraries, but are not intended to live beyond them (for example, they should not live in the ASTs).
Tokens most often live on the stack (or some other location that is efficient to access) as the parser is running, but occasionally do get buffered up. For example, macro definitions are stored as a series of tokens, and the C++ front-end periodically needs to buffer tokens up for tentative parsing and various pieces of look-ahead. As such, the size of a Token matter. On a 32-bit system, sizeof(Token) is currently 16 bytes.
Tokens occur in two forms: "Annotation Tokens" and normal tokens. Normal tokens are those returned by the lexer, annotation tokens represent semantic information and are produced by the parser, replacing normal tokens in the token stream. Normal tokens contain the following information:
- A SourceLocation - This indicates the location of the start of the token.
- A length - This stores the length of the token as stored in the SourceBuffer. For tokens that include them, this length includes trigraphs and escaped newlines which are ignored by later phases of the compiler. By pointing into the original source buffer, it is always possible to get the original spelling of a token completely accurately.
- IdentifierInfo - If a token takes the form of an identifier, and if identifier lookup was enabled when the token was lexed (e.g. the lexer was not reading in 'raw' mode) this contains a pointer to the unique hash value for the identifier. Because the lookup happens before keyword identification, this field is set even for language keywords like 'for'.
- TokenKind - This indicates the kind of token as classified by the lexer. This includes things like tok::starequal (for the "*=" operator), tok::ampamp for the "&&" token, and keyword values (e.g. tok::kw_for) for identifiers that correspond to keywords. Note that some tokens can be spelled multiple ways. For example, C++ supports "operator keywords", where things like "and" are treated exactly like the "&&" operator. In these cases, the kind value is set to tok::ampamp, which is good for the parser, which doesn't have to consider both forms. For something that cares about which form is used (e.g. the preprocessor 'stringize' operator) the spelling indicates the original form.
- Flags - There are currently four flags tracked by the
lexer/preprocessor system on a per-token basis:
- StartOfLine - This was the first token that occurred on its input source line.
- LeadingSpace - There was a space character either immediately before the token or transitively before the token as it was expanded through a macro. The definition of this flag is very closely defined by the stringizing requirements of the preprocessor.
- DisableExpand - This flag is used internally to the preprocessor to represent identifier tokens which have macro expansion disabled. This prevents them from being considered as candidates for macro expansion ever in the future.
- NeedsCleaning - This flag is set if the original spelling for the token includes a trigraph or escaped newline. Since this is uncommon, many pieces of code can fast-path on tokens that did not need cleaning.
One interesting (and somewhat unusual) aspect of normal tokens is that they don't contain any semantic information about the lexed value. For example, if the token was a pp-number token, we do not represent the value of the number that was lexed (this is left for later pieces of code to decide). Additionally, the lexer library has no notion of typedef names vs variable names: both are returned as identifiers, and the parser is left to decide whether a specific identifier is a typedef or a variable (tracking this requires scope information among other things). The parser can do this translation by replacing tokens returned by the preprocessor with "Annotation Tokens".
Annotation Tokens
Annotation Tokens are tokens that are synthesized by the parser and injected into the preprocessor's token stream (replacing existing tokens) to record semantic information found by the parser. For example, if "foo" is found to be a typedef, the "foo" tok::identifier token is replaced with an tok::annot_typename. This is useful for a couple of reasons: 1) this makes it easy to handle qualified type names (e.g. "foo::bar::baz<42>::t") in C++ as a single "token" in the parser. 2) if the parser backtracks, the reparse does not need to redo semantic analysis to determine whether a token sequence is a variable, type, template, etc.
Annotation Tokens are created by the parser and reinjected into the parser's token stream (when backtracking is enabled). Because they can only exist in tokens that the preprocessor-proper is done with, it doesn't need to keep around flags like "start of line" that the preprocessor uses to do its job. Additionally, an annotation token may "cover" a sequence of preprocessor tokens (e.g. a::b::c is five preprocessor tokens). As such, the valid fields of an annotation token are different than the fields for a normal token (but they are multiplexed into the normal Token fields):
- SourceLocation "Location" - The SourceLocation for the annotation token indicates the first token replaced by the annotation token. In the example above, it would be the location of the "a" identifier.
- SourceLocation "AnnotationEndLoc" - This holds the location of the last token replaced with the annotation token. In the example above, it would be the location of the "c" identifier.
- void* "AnnotationValue" - This contains an opaque object that the parser gets from Sema. The parser merely preserves the information for Sema to later interpret based on the annotation token kind.
- TokenKind "Kind" - This indicates the kind of Annotation token this is. See below for the different valid kinds.
Annotation tokens currently come in three kinds:
- tok::annot_typename: This annotation token represents a resolved typename token that is potentially qualified. The AnnotationValue field contains the QualType returned by Sema::getTypeName(), possibly with source location information attached.
- tok::annot_cxxscope: This annotation token represents a C++ scope specifier, such as "A::B::". This corresponds to the grammar productions "::" and ":: [opt] nested-name-specifier". The AnnotationValue pointer is a NestedNameSpecifier* returned by the Sema::ActOnCXXGlobalScopeSpecifier and Sema::ActOnCXXNestedNameSpecifier callbacks.
- tok::annot_template_id: This annotation token represents a C++ template-id such as "foo<int, 4>", where "foo" is the name of a template. The AnnotationValue pointer is a pointer to a malloc'd TemplateIdAnnotation object. Depending on the context, a parsed template-id that names a type might become a typename annotation token (if all we care about is the named type, e.g., because it occurs in a type specifier) or might remain a template-id token (if we want to retain more source location information or produce a new type, e.g., in a declaration of a class template specialization). template-id annotation tokens that refer to a type can be "upgraded" to typename annotation tokens by the parser.
As mentioned above, annotation tokens are not returned by the preprocessor, they are formed on demand by the parser. This means that the parser has to be aware of cases where an annotation could occur and form it where appropriate. This is somewhat similar to how the parser handles Translation Phase 6 of C99: String Concatenation (see C99 <IP_ADDRESS>). In the case of string concatenation, the preprocessor just returns distinct tok::string_literal and tok::wide_string_literal tokens and the parser eats a sequence of them wherever the grammar indicates that a string literal can occur.
In order to do this, whenever the parser expects a tok::identifier or tok::coloncolon, it should call the TryAnnotateTypeOrScopeToken or TryAnnotateCXXScopeToken methods to form the annotation token. These methods will maximally form the specified annotation tokens and replace the current token with them, if applicable. If the current tokens is not valid for an annotation token, it will remain an identifier or :: token.
The Lexer class
The Lexer class provides the mechanics of lexing tokens out of a source buffer and deciding what they mean. The Lexer is complicated by the fact that it operates on raw buffers that have not had spelling eliminated (this is a necessity to get decent performance), but this is countered with careful coding as well as standard performance techniques (for example, the comment handling code is vectorized on X86 and PowerPC hosts).
The lexer has a couple of interesting modal features:
- The lexer can operate in 'raw' mode. This mode has several features that make it possible to quickly lex the file (e.g. it stops identifier lookup, doesn't specially handle preprocessor tokens, handles EOF differently, etc). This mode is used for lexing within an "#if 0" block, for example.
- The lexer can capture and return comments as tokens. This is required to support the -C preprocessor mode, which passes comments through, and is used by the diagnostic checker to identifier expect-error annotations.
- The lexer can be in ParsingFilename mode, which happens when preprocessing after reading a #include directive. This mode changes the parsing of '<' to return an "angled string" instead of a bunch of tokens for each thing within the filename.
- When parsing a preprocessor directive (after "#") the ParsingPreprocessorDirective mode is entered. This changes the parser to return EOD at a newline.
- The Lexer uses a LangOptions object to know whether trigraphs are enabled, whether C++ or ObjC keywords are recognized, etc.
In addition to these modes, the lexer keeps track of a couple of other features that are local to a lexed buffer, which change as the buffer is lexed:
- The Lexer uses BufferPtr to keep track of the current character being lexed.
- The Lexer uses IsAtStartOfLine to keep track of whether the next lexed token will start with its "start of line" bit set.
- The Lexer keeps track of the current #if directives that are active (which can be nested).
- The Lexer keeps track of an MultipleIncludeOpt object, which is used to detect whether the buffer uses the standard "#ifndef XX / #define XX" idiom to prevent multiple inclusion. If a buffer does, subsequent includes can be ignored if the XX macro is defined.
The TokenLexer class
The TokenLexer class is a token provider that returns tokens from a list of tokens that came from somewhere else. It typically used for two things: 1) returning tokens from a macro definition as it is being expanded 2) returning tokens from an arbitrary buffer of tokens. The later use is used by _Pragma and will most likely be used to handle unbounded look-ahead for the C++ parser.
The MultipleIncludeOpt class
The MultipleIncludeOpt class implements a really simple little state machine that is used to detect the standard "#ifndef XX / #define XX" idiom that people typically use to prevent multiple inclusion of headers. If a buffer uses this idiom and is subsequently #include'd, the preprocessor can simply check to see whether the guarding condition is defined or not. If so, the preprocessor can completely ignore the include of the header.
The Parser Library
The AST Library
The Type class and its subclasses
The Type class (and its subclasses) are an important part of the AST. Types are accessed through the ASTContext class, which implicitly creates and uniques them as they are needed. Types have a couple of non-obvious features: 1) they do not capture type qualifiers like const or volatile (See QualType), and 2) they implicitly capture typedef information. Once created, types are immutable (unlike decls).
Typedefs in C make semantic analysis a bit more complex than it would be without them. The issue is that we want to capture typedef information and represent it in the AST perfectly, but the semantics of operations need to "see through" typedefs. For example, consider this code:
void func() {
typedef int foo;
foo X, *Y;
typedef foo* bar;
bar Z;
*X; // error
**Y; // error
**Z; // error
}
The code above is illegal, and thus we expect there to be diagnostics emitted on the annotated lines. In this example, we expect to get:
test.c:6:1: error: indirection requires pointer operand ('foo' invalid) *X; // error ^~ test.c:7:1: error: indirection requires pointer operand ('foo' invalid) **Y; // error ^~~ test.c:8:1: error: indirection requires pointer operand ('foo' invalid) **Z; // error ^~~
While this example is somewhat silly, it illustrates the point: we want to retain typedef information where possible, so that we can emit errors about "std::string" instead of "std::basic_string<char, std:...". Doing this requires properly keeping typedef information (for example, the type of "X" is "foo", not "int"), and requires properly propagating it through the various operators (for example, the type of *Y is "foo", not "int"). In order to retain this information, the type of these expressions is an instance of the TypedefType class, which indicates that the type of these expressions is a typedef for foo.
Representing types like this is great for diagnostics, because the user-specified type is always immediately available. There are two problems with this: first, various semantic checks need to make judgements about the actual structure of a type, ignoring typedefs. Second, we need an efficient way to query whether two types are structurally identical to each other, ignoring typedefs. The solution to both of these problems is the idea of canonical types.
Canonical Types
Every instance of the Type class contains a canonical type pointer. For simple types with no typedefs involved (e.g. "int", "int*", "int**"), the type just points to itself. For types that have a typedef somewhere in their structure (e.g. "foo", "foo*", "foo**", "bar"), the canonical type pointer points to their structurally equivalent type without any typedefs (e.g. "int", "int*", "int**", and "int*" respectively).
This design provides a constant time operation (dereferencing the canonical type pointer) that gives us access to the structure of types. For example, we can trivially tell that "bar" and "foo*" are the same type by dereferencing their canonical type pointers and doing a pointer comparison (they both point to the single "int*" type).
Canonical types and typedef types bring up some complexities that must be carefully managed. Specifically, the "isa/cast/dyncast" operators generally shouldn't be used in code that is inspecting the AST. For example, when type checking the indirection operator (unary '*' on a pointer), the type checker must verify that the operand has a pointer type. It would not be correct to check that with "isa<PointerType>(SubExpr->getType())", because this predicate would fail if the subexpression had a typedef type.
The solution to this problem are a set of helper methods on Type, used to check their properties. In this case, it would be correct to use "SubExpr->getType()->isPointerType()" to do the check. This predicate will return true if the canonical type is a pointer, which is true any time the type is structurally a pointer type. The only hard part here is remembering not to use the isa/cast/dyncast operations.
The second problem we face is how to get access to the pointer type once we know it exists. To continue the example, the result type of the indirection operator is the pointee type of the subexpression. In order to determine the type, we need to get the instance of PointerType that best captures the typedef information in the program. If the type of the expression is literally a PointerType, we can return that, otherwise we have to dig through the typedefs to find the pointer type. For example, if the subexpression had type "foo*", we could return that type as the result. If the subexpression had type "bar", we want to return "foo*" (note that we do not want "int*"). In order to provide all of this, Type has a getAsPointerType() method that checks whether the type is structurally a PointerType and, if so, returns the best one. If not, it returns a null pointer.
This structure is somewhat mystical, but after meditating on it, it will make sense to you :).
The QualType class
The QualType class is designed as a trivial value class that is small, passed by-value and is efficient to query. The idea of QualType is that it stores the type qualifiers (const, volatile, restrict, plus some extended qualifiers required by language extensions) separately from the types themselves. QualType is conceptually a pair of "Type*" and the bits for these type qualifiers.
By storing the type qualifiers as bits in the conceptual pair, it is extremely efficient to get the set of qualifiers on a QualType (just return the field of the pair), add a type qualifier (which is a trivial constant-time operation that sets a bit), and remove one or more type qualifiers (just return a QualType with the bitfield set to empty).
Further, because the bits are stored outside of the type itself, we do not need to create duplicates of types with different sets of qualifiers (i.e. there is only a single heap allocated "int" type: "const int" and "volatile const int" both point to the same heap allocated "int" type). This reduces the heap size used to represent bits and also means we do not have to consider qualifiers when uniquing types (Type does not even contain qualifiers).
In practice, the two most common type qualifiers (const and restrict) are stored in the low bits of the pointer to the Type object, together with a flag indicating whether extended qualifiers are present (which must be heap-allocated). This means that QualType is exactly the same size as a pointer.
Declaration names
The DeclarationName class represents the name of a
declaration in Clang. Declarations in the C family of languages can
take several different forms. Most declarations are named by
simple identifiers, e.g., "f
" and "x
" in
the function declaration f(int x)
. In C++, declaration
names can also name class constructors ("Class
"
in struct Class { Class(); }
), class destructors
("~Class
"), overloaded operator names ("operator+"),
and conversion functions ("operator void const *
"). In
Objective-C, declaration names can refer to the names of Objective-C
methods, which involve the method name and the parameters,
collectively called a selector, e.g.,
"setWidth:height:
". Since all of these kinds of
entities - variables, functions, Objective-C methods, C++
constructors, destructors, and operators - are represented as
subclasses of Clang's common NamedDecl
class, DeclarationName
is designed to efficiently
represent any kind of name.
Given
a DeclarationName
N
, N.getNameKind()
will produce a value that describes what kind of name N
stores. There are 8 options (all of the names are inside
the DeclarationName
class)
- Identifier
- The name is a simple
identifier. Use
N.getAsIdentifierInfo()
to retrieve the correspondingIdentifierInfo*
pointing to the actual identifier. Note that C++ overloaded operators (e.g., "operator+
") are represented as special kinds of identifiers. UseIdentifierInfo
'sgetOverloadedOperatorID
function to determine whether an identifier is an overloaded operator name. - ObjCZeroArgSelector, ObjCOneArgSelector, ObjCMultiArgSelector
- The name is an Objective-C selector, which can be retrieved as a
Selector
instance viaN.getObjCSelector()
. The three possible name kinds for Objective-C reflect an optimization within theDeclarationName
class: both zero- and one-argument selectors are stored as a maskedIdentifierInfo
pointer, and therefore require very little space, since zero- and one-argument selectors are far more common than multi-argument selectors (which use a different structure). - CXXConstructorName
- The name is a C++ constructor
name. Use
N.getCXXNameType()
to retrieve the type that this constructor is meant to construct. The type is always the canonical type, since all constructors for a given type have the same name. - CXXDestructorName
- The name is a C++ destructor
name. Use
N.getCXXNameType()
to retrieve the type whose destructor is being named. This type is always a canonical type. - CXXConversionFunctionName
- The name is a C++ conversion function. Conversion functions are
named according to the type they convert to, e.g., "
operator void const *
". UseN.getCXXNameType()
to retrieve the type that this conversion function converts to. This type is always a canonical type. - CXXOperatorName
- The name is a C++ overloaded operator name. Overloaded operators
are named according to their spelling, e.g.,
"
operator+
" or "operator new []
". UseN.getCXXOverloadedOperator()
to retrieve the overloaded operator (a value of typeOverloadedOperatorKind
).
DeclarationName
s are cheap to create, copy, and
compare. They require only a single pointer's worth of storage in
the common cases (identifiers, zero-
and one-argument Objective-C selectors) and use dense, uniqued
storage for the other kinds of
names. Two DeclarationName
s can be compared for
equality (==
, !=
) using a simple bitwise
comparison, can be ordered
with <
, >
, <=
,
and >=
(which provide a lexicographical ordering for
normal identifiers but an unspecified ordering for other kinds of
names), and can be placed into LLVM DenseMap
s
and DenseSet
s.
DeclarationName
instances can be created in different
ways depending on what kind of name the instance will store. Normal
identifiers (IdentifierInfo
pointers) and Objective-C selectors
(Selector
) can be implicitly converted
to DeclarationName
s. Names for C++ constructors,
destructors, conversion functions, and overloaded operators can be retrieved from
the DeclarationNameTable
, an instance of which is
available as ASTContext::DeclarationNames
. The member
functions getCXXConstructorName
, getCXXDestructorName
,
getCXXConversionFunctionName
, and getCXXOperatorName
, respectively,
return DeclarationName
instances for the four kinds of
C++ special function names.
Declaration contexts
Every declaration in a program exists within some declaration
context, such as a translation unit, namespace, class, or
function. Declaration contexts in Clang are represented by
the DeclContext
class, from which the various
declaration-context AST nodes
(TranslationUnitDecl
, NamespaceDecl
, RecordDecl
, FunctionDecl
,
etc.) will derive. The DeclContext
class provides
several facilities common to each declaration context:
- Source-centric vs. Semantics-centric View of Declarations
DeclContext
provides two views of the declarations stored within a declaration context. The source-centric view accurately represents the program source code as written, including multiple declarations of entities where present (see the section Redeclarations and Overloads), while the semantics-centric view represents the program semantics. The two views are kept synchronized by semantic analysis while the ASTs are being constructed.- Storage of declarations within that context
- Every declaration context can contain some number of
declarations. For example, a C++ class (represented
by
RecordDecl
) contains various member functions, fields, nested types, and so on. All of these declarations will be stored within theDeclContext
, and one can iterate over the declarations via [DeclContext::decls_begin()
,DeclContext::decls_end()
). This mechanism provides the source-centric view of declarations in the context. - Lookup of declarations within that context
- The
DeclContext
structure provides efficient name lookup for names within that declaration context. For example, ifN
is a namespace we can look for the nameN::f
usingDeclContext::lookup
. The lookup itself is based on a lazily-constructed array (for declaration contexts with a small number of declarations) or hash table (for declaration contexts with more declarations). The lookup operation provides the semantics-centric view of the declarations in the context. - Ownership of declarations
- The
DeclContext
owns all of the declarations that were declared within its declaration context, and is responsible for the management of their memory as well as their (de-)serialization.
All declarations are stored within a declaration context, and one
can query
information about the context in which each declaration lives. One
can retrieve the DeclContext
that contains a
particular Decl
using Decl::getDeclContext
. However, see the
section Lexical and Semantic
Contexts for more information about how to interpret this
context information.
Redeclarations and Overloads
Within a translation unit, it is common for an entity to be declared several times. For example, we might declare a function "f" and then later re-declare it as part of an inlined definition:
void f(int x, int y, int z = 1); inline void f(int x, int y, int z) { /* ... */ }
The representation of "f" differs in the source-centric and semantics-centric views of a declaration context. In the source-centric view, all redeclarations will be present, in the order they occurred in the source code, making this view suitable for clients that wish to see the structure of the source code. In the semantics-centric view, only the most recent "f" will be found by the lookup, since it effectively replaces the first declaration of "f".
In the semantics-centric view, overloading of functions is represented explicitly. For example, given two declarations of a function "g" that are overloaded, e.g.,
void g(); void g(int);
the DeclContext::lookup
operation will return
a DeclContext::lookup_result
that contains a range of iterators
over declarations of "g". Clients that perform semantic analysis on a
program that is not concerned with the actual source code will
primarily use this semantics-centric view.
Lexical and Semantic Contexts
Each declaration has two potentially different
declaration contexts: a lexical context, which corresponds to
the source-centric view of the declaration context, and
a semantic context, which corresponds to the
semantics-centric view. The lexical context is accessible
via Decl::getLexicalDeclContext
while the
semantic context is accessible
via Decl::getDeclContext
, both of which return
DeclContext
pointers. For most declarations, the two
contexts are identical. For example:
class X { public: void f(int x); };
Here, the semantic and lexical contexts of X::f
are
the DeclContext
associated with the
class X
(itself stored as a RecordDecl
AST
node). However, we can now define X::f
out-of-line:
void X::f(int x = 17) { /* ... */ }
This definition of has different lexical and semantic
contexts. The lexical context corresponds to the declaration
context in which the actual declaration occurred in the source
code, e.g., the translation unit containing X
. Thus,
this declaration of X::f
can be found by traversing
the declarations provided by
[decls_begin()
, decls_end()
) in the
translation unit.
The semantic context of X::f
corresponds to the
class X
, since this member function is (semantically) a
member of X
. Lookup of the name f
into
the DeclContext
associated with X
will
then return the definition of X::f
(including
information about the default argument).
Transparent Declaration Contexts
In C and C++, there are several contexts in which names that are logically declared inside another declaration will actually "leak" out into the enclosing scope from the perspective of name lookup. The most obvious instance of this behavior is in enumeration types, e.g.,
enum Color { Red, Green, Blue };
Here, Color
is an enumeration, which is a declaration
context that contains the
enumerators Red
, Green
,
and Blue
. Thus, traversing the list of declarations
contained in the enumeration Color
will
yield Red
, Green
,
and Blue
. However, outside of the scope
of Color
one can name the enumerator Red
without qualifying the name, e.g.,
Color c = Red;
There are other entities in C++ that provide similar behavior. For example, linkage specifications that use curly braces:
extern "C" { void f(int); void g(int); } // f and g are visible here
For source-level accuracy, we treat the linkage specification and enumeration type as a declaration context in which its enclosed declarations ("Red", "Green", and "Blue"; "f" and "g") are declared. However, these declarations are visible outside of the scope of the declaration context.
These language features (and several others, described below) have
roughly the same set of
requirements: declarations are declared within a particular lexical
context, but the declarations are also found via name lookup in
scopes enclosing the declaration itself. This feature is implemented
via transparent declaration contexts
(see DeclContext::isTransparentContext()
), whose
declarations are visible in the nearest enclosing non-transparent
declaration context. This means that the lexical context of the
declaration (e.g., an enumerator) will be the
transparent DeclContext
itself, as will the semantic
context, but the declaration will be visible in every outer context
up to and including the first non-transparent declaration context (since
transparent declaration contexts can be nested).
The transparent DeclContexts
are:
- Enumerations (but not C++11 "scoped enumerations"):
enum Color { Red, Green, Blue }; // Red, Green, and Blue are in scope
- C++ linkage specifications:
extern "C" { void f(int); void g(int); } // f and g are in scope
- Anonymous unions and structs:
struct LookupTable { bool IsVector; union { std::vector<Item> *Vector; std::set<Item> *Set; }; }; LookupTable LT; LT.Vector = 0; // Okay: finds Vector inside the unnamed union
- C++11 inline namespaces:
namespace mylib { inline namespace debug { class X; } } mylib::X *xp; // okay: mylib::X refers to mylib::debug::X
Multiply-Defined Declaration Contexts
C++ namespaces have the interesting--and, so far, unique--property that the namespace can be defined multiple times, and the declarations provided by each namespace definition are effectively merged (from the semantic point of view). For example, the following two code snippets are semantically indistinguishable:
// Snippet #1: namespace N { void f(); } namespace N { void f(int); } // Snippet #2: namespace N { void f(); void f(int); }
In Clang's representation, the source-centric view of declaration
contexts will actually have two separate NamespaceDecl
nodes in Snippet #1, each of which is a declaration context that
contains a single declaration of "f". However, the semantics-centric
view provided by name lookup into the namespace N
for
"f" will return a DeclContext::lookup_result
that contains
a range of iterators over declarations of "f".
DeclContext
manages multiply-defined declaration
contexts internally. The
function DeclContext::getPrimaryContext
retrieves the
"primary" context for a given DeclContext
instance,
which is the DeclContext
responsible for maintaining
the lookup table used for the semantics-centric view. Given the
primary context, one can follow the chain
of DeclContext
nodes that define additional
declarations via DeclContext::getNextContext
. Note that
these functions are used internally within the lookup and insertion
methods of the DeclContext
, so the vast majority of
clients can ignore them.
The CFG class
The CFG class is designed to represent a source-level control-flow graph for a single statement (Stmt*). Typically instances of CFG are constructed for function bodies (usually an instance of CompoundStmt), but can also be instantiated to represent the control-flow of any class that subclasses Stmt, which includes simple expressions. Control-flow graphs are especially useful for performing flow- or path-sensitive program analyses on a given function.
Basic Blocks
Concretely, an instance of CFG is a collection of basic blocks. Each basic block is an instance of CFGBlock, which simply contains an ordered sequence of Stmt* (each referring to statements in the AST). The ordering of statements within a block indicates unconditional flow of control from one statement to the next. Conditional control-flow is represented using edges between basic blocks. The statements within a given CFGBlock can be traversed using the CFGBlock::*iterator interface.
A CFG object owns the instances of CFGBlock within the control-flow graph it represents. Each CFGBlock within a CFG is also uniquely numbered (accessible via CFGBlock::getBlockID()). Currently the number is based on the ordering the blocks were created, but no assumptions should be made on how CFGBlocks are numbered other than their numbers are unique and that they are numbered from 0..N-1 (where N is the number of basic blocks in the CFG).
Entry and Exit Blocks
Each instance of CFG contains two special blocks: an entry block (accessible via CFG::getEntry()), which has no incoming edges, and an exit block (accessible via CFG::getExit()), which has no outgoing edges. Neither block contains any statements, and they serve the role of providing a clear entrance and exit for a body of code such as a function body. The presence of these empty blocks greatly simplifies the implementation of many analyses built on top of CFGs.Conditional Control-Flow
Conditional control-flow (such as those induced by if-statements and loops) is represented as edges between CFGBlocks. Because different C language constructs can induce control-flow, each CFGBlock also records an extra Stmt* that represents the terminator of the block. A terminator is simply the statement that caused the control-flow, and is used to identify the nature of the conditional control-flow between blocks. For example, in the case of an if-statement, the terminator refers to the IfStmt object in the AST that represented the given branch.
To illustrate, consider the following code example:
int foo(int x) {
x = x + 1;
if (x > 2) x++;
else {
x += 2;
x *= 2;
}
return x;
}
After invoking the parser+semantic analyzer on this code fragment, the AST of the body of foo is referenced by a single Stmt*. We can then construct an instance of CFG representing the control-flow graph of this function body by single call to a static class method:
Stmt* FooBody = ...
CFG* FooCFG = CFG::buildCFG(FooBody);
It is the responsibility of the caller of CFG::buildCFG to delete the returned CFG* when the CFG is no longer needed.
Along with providing an interface to iterate over its CFGBlocks, the CFG class also provides methods that are useful for debugging and visualizing CFGs. For example, the method CFG::dump() dumps a pretty-printed version of the CFG to standard error. This is especially useful when one is using a debugger such as gdb. For example, here is the output of FooCFG->dump():
[ B5 (ENTRY) ]
Predecessors (0):
Successors (1): B4
[ B4 ]
1: x = x + 1
2: (x > 2)
T: if [B4.2]
Predecessors (1): B5
Successors (2): B3 B2
[ B3 ]
1: x++
Predecessors (1): B4
Successors (1): B1
[ B2 ]
1: x += 2
2: x *= 2
Predecessors (1): B4
Successors (1): B1
[ B1 ]
1: return x;
Predecessors (2): B2 B3
Successors (1): B0
[ B0 (EXIT) ]
Predecessors (1): B1
Successors (0):
For each block, the pretty-printed output displays for each block the number of predecessor blocks (blocks that have outgoing control-flow to the given block) and successor blocks (blocks that have control-flow that have incoming control-flow from the given block). We can also clearly see the special entry and exit blocks at the beginning and end of the pretty-printed output. For the entry block (block B5), the number of predecessor blocks is 0, while for the exit block (block B0) the number of successor blocks is 0.
The most interesting block here is B4, whose outgoing control-flow represents the branching caused by the sole if-statement in foo. Of particular interest is the second statement in the block, (x > 2), and the terminator, printed as if [B4.2]. The second statement represents the evaluation of the condition of the if-statement, which occurs before the actual branching of control-flow. Within the CFGBlock for B4, the Stmt* for the second statement refers to the actual expression in the AST for (x > 2). Thus pointers to subclasses of Expr can appear in the list of statements in a block, and not just subclasses of Stmt that refer to proper C statements.
The terminator of block B4 is a pointer to the IfStmt object in the AST. The pretty-printer outputs if [B4.2] because the condition expression of the if-statement has an actual place in the basic block, and thus the terminator is essentially referring to the expression that is the second statement of block B4 (i.e., B4.2). In this manner, conditions for control-flow (which also includes conditions for loops and switch statements) are hoisted into the actual basic block.
Constant Folding in the Clang AST
There are several places where constants and constant folding matter a lot to the Clang front-end. First, in general, we prefer the AST to retain the source code as close to how the user wrote it as possible. This means that if they wrote "5+4", we want to keep the addition and two constants in the AST, we don't want to fold to "9". This means that constant folding in various ways turns into a tree walk that needs to handle the various cases.
However, there are places in both C and C++ that require constants to be folded. For example, the C standard defines what an "integer constant expression" (i-c-e) is with very precise and specific requirements. The language then requires i-c-e's in a lot of places (for example, the size of a bitfield, the value for a case statement, etc). For these, we have to be able to constant fold the constants, to do semantic checks (e.g. verify bitfield size is non-negative and that case statements aren't duplicated). We aim for Clang to be very pedantic about this, diagnosing cases when the code does not use an i-c-e where one is required, but accepting the code unless running with -pedantic-errors.
Things get a little bit more tricky when it comes to compatibility with real-world source code. Specifically, GCC has historically accepted a huge superset of expressions as i-c-e's, and a lot of real world code depends on this unfortuate accident of history (including, e.g., the glibc system headers). GCC accepts anything its "fold" optimizer is capable of reducing to an integer constant, which means that the definition of what it accepts changes as its optimizer does. One example is that GCC accepts things like "case X-X:" even when X is a variable, because it can fold this to 0.
Another issue are how constants interact with the extensions we support, such as __builtin_constant_p, __builtin_inf, __extension__ and many others. C99 obviously does not specify the semantics of any of these extensions, and the definition of i-c-e does not include them. However, these extensions are often used in real code, and we have to have a way to reason about them.
Finally, this is not just a problem for semantic analysis. The code generator and other clients have to be able to fold constants (e.g. to initialize global variables) and has to handle a superset of what C99 allows. Further, these clients can benefit from extended information. For example, we know that "foo()||1" always evaluates to true, but we can't replace the expression with true because it has side effects.
Implementation Approach
After trying several different approaches, we've finally converged on a design (Note, at the time of this writing, not all of this has been implemented, consider this a design goal!). Our basic approach is to define a single recursive method evaluation method (Expr::Evaluate), which is implemented in AST/ExprConstant.cpp. Given an expression with 'scalar' type (integer, fp, complex, or pointer) this method returns the following information:
- Whether the expression is an integer constant expression, a general constant that was folded but has no side effects, a general constant that was folded but that does have side effects, or an uncomputable/unfoldable value.
- If the expression was computable in any way, this method returns the APValue for the result of the expression.
- If the expression is not evaluatable at all, this method returns information on one of the problems with the expression. This includes a SourceLocation for where the problem is, and a diagnostic ID that explains the problem. The diagnostic should be have ERROR type.
- If the expression is not an integer constant expression, this method returns information on one of the problems with the expression. This includes a SourceLocation for where the problem is, and a diagnostic ID that explains the problem. The diagnostic should be have EXTENSION type.
This information gives various clients the flexibility that they want, and we will eventually have some helper methods for various extensions. For example, Sema should have a Sema::VerifyIntegerConstantExpression method, which calls Evaluate on the expression. If the expression is not foldable, the error is emitted, and it would return true. If the expression is not an i-c-e, the EXTENSION diagnostic is emitted. Finally it would return false to indicate that the AST is ok.
Other clients can use the information in other ways, for example, codegen can just use expressions that are foldable in any way.
Extensions
This section describes how some of the various extensions Clang supports interacts with constant evaluation:
- __extension__: The expression form of this extension causes any evaluatable subexpression to be accepted as an integer constant expression.
- __builtin_constant_p: This returns true (as an integer constant expression) if the operand evaluates to either a numeric value (that is, not a pointer cast to integral type) of integral, enumeration, floating or complex type, or if it evaluates to the address of the first character of a string literal (possibly cast to some other type). As a special case, if __builtin_constant_p is the (potentially parenthesized) condition of a conditional operator expression ("?:"), only the true side of the conditional operator is considered, and it is evaluated with full constant folding.
- __builtin_choose_expr: The condition is required to be an integer constant expression, but we accept any constant as an "extension of an extension". This only evaluates one operand depending on which way the condition evaluates.
- __builtin_classify_type: This always returns an integer constant expression.
- __builtin_inf,nan,..: These are treated just like a floating-point literal.
- __builtin_abs,copysign,..: These are constant folded as general constant expressions.
- __builtin_strlen and strlen: These are constant folded as integer constant expressions if the argument is a string literal.
How to change Clang
How to add an attribute
To add an attribute, you'll have to add it to the list of attributes, add it to the parsing phase, and look for it in the AST scan. r124217 has a good example of adding a warning attribute.
(Beware that this hasn't been reviewed/fixed by the people who designed the attributes system yet.)
include/clang/Basic/Attr.td
Each attribute gets a def inheriting from Attr or one of its subclasses. InheritableAttr means that the attribute also applies to subsequent declarations of the same name.
Spellings lists the strings that can appear in __attribute__((here)) or [[here]]. All such strings will be synonymous. If you want to allow the [[]] C++11 syntax, you have to define a list of Namespaces, which will let users write [[namespace:spelling]]. Using the empty string for a namespace will allow users to write just the spelling with no ":".
Subjects restricts what kinds of AST node to which this attribute can appertain (roughly, attach).
Args names the arguments the attribute takes, in order. If Args is [StringArgument<"Arg1">, IntArgument<"Arg2">] then __attribute__((myattribute("Hello", 3))) will be a valid use.
Boilerplate
Write a new HandleYourAttr() function in lib/Sema/SemaDeclAttr.cpp, and add a case to the switch in ProcessNonInheritableDeclAttr() or ProcessInheritableDeclAttr() forwarding to it.
If your attribute causes extra warnings to fire, define a DiagGroup in include/clang/Basic/DiagnosticGroups.td named after the attribute's Spelling with "_"s replaced by "-"s. If you're only defining one diagnostic, you can skip DiagnosticGroups.td and use InGroup<DiagGroup<"your-attribute">> directly in DiagnosticSemaKinds.td
The meat of your attribute
Find an appropriate place in Clang to do whatever your attribute needs to do. Check for the attribute's presence using Decl::getAttr<YourAttr>().
Update the Clang Language Extensions document to describe your new attribute.
How to add an expression or statement
Expressions and statements are one of the most fundamental constructs within a compiler, because they interact with many different parts of the AST, semantic analysis, and IR generation. Therefore, adding a new expression or statement kind into Clang requires some care. The following list details the various places in Clang where an expression or statement needs to be introduced, along with patterns to follow to ensure that the new expression or statement works well across all of the C languages. We focus on expressions, but statements are similar.
- Introduce parsing actions into the parser. Recursive-descent
parsing is mostly self-explanatory, but there are a few things that
are worth keeping in mind:
- Keep as much source location information as possible! You'll want it later to produce great diagnostics and support Clang's various features that map between source code and the AST.
- Write tests for all of the "bad" parsing cases, to make sure your recovery is good. If you have matched delimiters (e.g., parentheses, square brackets, etc.), use Parser::BalancedDelimiterTracker to give nice diagnostics when things go wrong.
- Introduce semantic analysis actions into Sema. Semantic
analysis should always involve two functions: an ActOnXXX
function that will be called directly from the parser, and a
BuildXXX function that performs the actual semantic
analysis and will (eventually!) build the AST node. It's fairly
common for the ActOnCXX function to do very little (often
just some minor translation from the parser's representation to
Sema's representation of the same thing), but the separation
is still important: C++ template instantiation, for example,
should always call the BuildXXX variant. Several notes on
semantic analysis before we get into construction of the AST:
- Your expression probably involves some types and some subexpressions. Make sure to fully check that those types, and the types of those subexpressions, meet your expectations. Add implicit conversions where necessary to make sure that all of the types line up exactly the way you want them. Write extensive tests to check that you're getting good diagnostics for mistakes and that you can use various forms of subexpressions with your expression.
- When type-checking a type or subexpression, make sure to first check whether the type is "dependent" (Type::isDependentType()) or whether a subexpression is type-dependent (Expr::isTypeDependent()). If any of these return true, then you're inside a template and you can't do much type-checking now. That's normal, and your AST node (when you get there) will have to deal with this case. At this point, you can write tests that use your expression within templates, but don't try to instantiate the templates.
- For each subexpression, be sure to call Sema::CheckPlaceholderExpr() to deal with "weird" expressions that don't behave well as subexpressions. Then, determine whether you need to perform lvalue-to-rvalue conversions (Sema::DefaultLvalueConversione) or the usual unary conversions (Sema::UsualUnaryConversions), for places where the subexpression is producing a value you intend to use.
- Your BuildXXX function will probably just return ExprError() at this point, since you don't have an AST. That's perfectly fine, and shouldn't impact your testing.
- Introduce an AST node for your new expression. This starts with
declaring the node in include/Basic/StmtNodes.td and
creating a new class for your expression in the appropriate
include/AST/Expr*.h header. It's best to look at the class
for a similar expression to get ideas, and there are some specific
things to watch for:
- If you need to allocate memory, use the ASTContext allocator to allocate memory. Never use raw malloc or new, and never hold any resources in an AST node, because the destructor of an AST node is never called.
- Make sure that getSourceRange() covers the exact source range of your expression. This is needed for diagnostics and for IDE support.
- Make sure that children() visits all of the subexpressions. This is important for a number of features (e.g., IDE support, C++ variadic templates). If you have sub-types, you'll also need to visit those sub-types in the RecursiveASTVisitor.
- Add printing support (StmtPrinter.cpp) and dumping support (StmtDumper.cpp) for your expression.
- Add profiling support (StmtProfile.cpp) for your AST node, noting the distinguishing (non-source location) characteristics of an instance of your expression. Omitting this step will lead to hard-to-diagnose failures regarding matching of template declarations.
- Teach semantic analysis to build your AST node! At this point,
you can wire up your Sema::BuildXXX function to actually
create your AST. A few things to check at this point:
- If your expression can construct a new C++ class or return a new Objective-C object, be sure to update and then call Sema::MaybeBindToTemporary for your just-created AST node to be sure that the object gets properly destructed. An easy way to test this is to return a C++ class with a private destructor: semantic analysis should flag an error here with the attempt to call the destructor.
- Inspect the generated AST by printing it using clang -cc1 -ast-print, to make sure you're capturing all of the important information about how the AST was written.
- Inspect the generated AST under clang -cc1 -ast-dump to verify that all of the types in the generated AST line up the way you want them. Remember that clients of the AST should never have to "think" to understand what's going on. For example, all implicit conversions should show up explicitly in the AST.
- Write tests that use your expression as a subexpression of other, well-known expressions. Can you call a function using your expression as an argument? Can you use the ternary operator?
- Teach code generation to create IR to your AST node. This step
is the first (and only) that requires knowledge of LLVM IR. There
are several things to keep in mind:
- Code generation is separated into scalar/aggregate/complex and lvalue/rvalue paths, depending on what kind of result your expression produces. On occasion, this requires some careful factoring of code to avoid duplication.
- CodeGenFunction contains functions ConvertType and ConvertTypeForMem that convert Clang's types (clang::Type* or clang::QualType) to LLVM types. Use the former for values, and the later for memory locations: test with the C++ "bool" type to check this. If you find that you are having to use LLVM bitcasts to make the subexpressions of your expression have the type that your expression expects, STOP! Go fix semantic analysis and the AST so that you don't need these bitcasts.
- The CodeGenFunction class has a number of helper functions to make certain operations easy, such as generating code to produce an lvalue or an rvalue, or to initialize a memory location with a given value. Prefer to use these functions rather than directly writing loads and stores, because these functions take care of some of the tricky details for you (e.g., for exceptions).
- If your expression requires some special behavior in the event of an exception, look at the push*Cleanup functions in CodeGenFunction to introduce a cleanup. You shouldn't have to deal with exception-handling directly.
- Testing is extremely important in IR generation. Use clang -cc1 -emit-llvm and FileCheck to verify that you're generating the right IR.
- Teach template instantiation how to cope with your AST
node, which requires some fairly simple code:
- Make sure that your expression's constructor properly computes the flags for type dependence (i.e., the type your expression produces can change from one instantiation to the next), value dependence (i.e., the constant value your expression produces can change from one instantiation to the next), instantiation dependence (i.e., a template parameter occurs anywhere in your expression), and whether your expression contains a parameter pack (for variadic templates). Often, computing these flags just means combining the results from the various types and subexpressions.
- Add TransformXXX and RebuildXXX functions to the TreeTransform class template in Sema. TransformXXX should (recursively) transform all of the subexpressions and types within your expression, using getDerived().TransformYYY. If all of the subexpressions and types transform without error, it will then call the RebuildXXX function, which will in turn call getSema().BuildXXX to perform semantic analysis and build your expression.
- To test template instantiation, take those tests you wrote to make sure that you were type checking with type-dependent expressions and dependent types (from step #2) and instantiate those templates with various types, some of which type-check and some that don't, and test the error messages in each case.
- There are some "extras" that make other features work better.
It's worth handling these extras to give your expression complete
integration into Clang:
- Add code completion support for your expression in SemaCodeComplete.cpp.
- If your expression has types in it, or has any "interesting" features other than subexpressions, extend libclang's CursorVisitor to provide proper visitation for your expression, enabling various IDE features such as syntax highlighting, cross-referencing, and so on. The c-index-test helper program can be used to test these features.


1. Don't give up
Most babies and young children need to try something new seven to ten times before they like it. So don’t be afraid to introduce children to new or more exotic tastes.
A good tactic to get kids to eat a wide variety of foods is to tell them that tasting new things is a sign they’re growing up. Or, take them shopping and let them choose a new, healthy food to serve at home with something they already like.
2. Learn when to stop
Although children are born with the ability to stop eating when they are full, it can often be hard for parents to judge whether their kids have eaten the right foods, and enough of them.
Teaching children to listen to their tummies and to ask themselves questions about quantity and quality, such as “Is my tummy full?” or “Will I feel sick if I eat those extra biscuits?” will give them the opportunity to develop their ability to sense fullness.
3. Be creative
All the vibrant colours in fruit and vegetables come from natural plant chemicals that have healthy effects on our bodies. Different colours have different effects, so it’s good to eat a variety of different colours each day.
Offer your kids a colourful snack of different fruits and berries, or chop vegetables into interesting shapes to make them seem more fun and exciting.
4. Slow it down
Eating slowly is great for weight control at any age. It’s a fantastic way to show kids that it takes about 20 minutes for the message that they are full to get from their stomachs to their brains.
As much as we’d love our children to finish their meal in minutes, rather than hours, it’s much more important that they learn to slow down and chew their food properly.
5. Have fun in the kitchen
Children are more likely to become adventurous eaters if they know how to cook. Make it fun by giving them their own aprons and letting them help you regularly with small tasks in the kitchen.
As they get older and more confident, let them cook dinner once a week. If the thought of kids in the kitchen sounds like a recipe for disaster, why not enrol them in cooking classes during the school holidays?
6.

7. Grow your own
Growing vegetables and herbs at home can be a fun way to teach children where food comes from and to encourage them to eat a more varied diet.
They’re more likely to take at least a little bite of broccoli or carrots if they’ve helped to plant and pick them. If you don’t have a garden, a window box can be just as effective.
8. Drink water
Make water the drink of choice at meal times, and keep juice and sweet drinks as occasional treats.
While juice has valuable nutrients and gives a concentrated energy boost for active, growing bodies, kids should go for water first when they are thirsty, not sugar-sweetened drinks.
9. Choose healthier snacks
It’s easy to reach for chips or biscuits when you and your children feel like nibbling on something, but these snacks tend to be low in nutrients and high in calories.
Instead, try to keep your cupboards stocked with healthier snacks such as fruit, air-popped popcorn, unsalted nuts and unsweetened yoghurt.
10. Eat breakfast
Eating breakfast, even if it’s just a banana and a glass of milk, kick-starts the body and makes it easier to maintain lasting energy throughout the day.
If you can get your kids to establish the habit of eating a good breakfast at a young age, it should stay with them as they get older.


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lib/core/string.rb
Generated on Tue Nov 24 14:08:16 -0800 2009 with rcov <IP_ADDRESS>
Code reported as executed by Ruby looks like this...and this: this line is also marked as covered.Lines considered as run by rcov, but not reported by Ruby, look like this,and this: these lines were inferred by rcov (using simple heuristics).Finally, here's a line marked as not executed.
| Name |
Total lines |
Lines of code |
Total coverage |
Code coverage |
| lib/core/string.rb |
3 |
3 |
|
|
1 class String |
2 include WordPairs::ReverseAlternate |
3 end |
Generated on Tue Nov 24 14:08:16 -0800 2009 with rcov <IP_ADDRESS>


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object TextUtil
An utility class that provides methods that allow to handle texts.
Author
Michael Rapp
Since
2.2.0
fun hasNoText(text: CharSequence?): Boolean
Returns whether a specific text is null, empty or contains only whitespace. |
|
fun hasText(text: CharSequence?): Boolean
Returns whether a specific text is neither null, empty or contains only whitespace. |
|
fun isEmpty(text: CharSequence?): Boolean
Returns whether a specific text is null or empty. |
|
fun isNotEmpty(text: CharSequence?): Boolean
Returns whether a specific text is neither null or empty. |


|
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| PREV NEXT | FRAMES NO FRAMES |
| Packages that use SerializationHandler | |
|---|---|
| org.apache.xml.dtm.ref.sax2dtm | |
| org.apache.xml.serializer | Processes SAX events into streams. |
| org.apache.xml.serializer.dom3 |
| Uses of SerializationHandler in org.apache.xml.dtm.ref.sax2dtm |
|---|
| Methods in org.apache.xml.dtm.ref.sax2dtm with parameters of type SerializationHandler | |
|---|---|
protected void |
SAX2DTM2.copyAttribute(int nodeID,
int exptype,
SerializationHandler handler)
Copy an Attribute node to a SerializationHandler |
protected void |
SAX2DTM2.copyAttributes(int nodeID,
SerializationHandler handler)
Copy attribute nodes from an element . |
protected java.lang.String |
SAX2DTM2.copyElement(int nodeID,
int exptype,
SerializationHandler handler)
Copy an Element node to a SerializationHandler. |
protected void |
SAX2DTM2.copyNS(int nodeID,
SerializationHandler handler,
boolean inScope)
Copy namespace nodes. |
protected void |
SAX2DTM2.copyTextNode(int nodeID,
SerializationHandler handler)
Copy the String value of a Text node to a SerializationHandler |
| Uses of SerializationHandler in org.apache.xml.serializer |
|---|
| Classes in org.apache.xml.serializer that implement SerializationHandler | |
|---|---|
class |
EmptySerializer
This class is an adapter class. |
class |
SerializerBase
This class acts as a base class for the XML "serializers" and the stream serializers. |
class |
ToHTMLSAXHandler
Deprecated. As of Xalan 2.7.1, replaced by the use of ToXMLSAXHandler . |
class |
ToHTMLStream
This serializer takes a series of SAX or SAX-like events and writes its output to the given stream. |
class |
ToSAXHandler
This class is used to provide a base behavior to be inherited by other To...SAXHandler serializers. |
class |
ToStream
This abstract class is a base class for other stream serializers (xml, html, text ...) that write output to a stream. |
class |
ToTextSAXHandler
Deprecated. As of Xalan 2.7.1, replaced by the use of ToXMLSAXHandler . |
class |
ToTextStream
This class is not a public API. |
class |
ToUnknownStream
This class wraps another SerializationHandler. |
class |
ToXMLSAXHandler
This class receives notification of SAX-like events, and with gathered information over these calls it will invoke the equivalent SAX methods on a handler, the ultimate xsl:output method is known to be "xml". |
class |
ToXMLStream
This class converts SAX or SAX-like calls to a serialized xml document. |
| Fields in org.apache.xml.serializer declared as SerializationHandler | |
|---|---|
private SerializationHandler |
ToUnknownStream.m_handler
The wrapped handler, initially XML but possibly switched to HTML |
private SerializationHandler |
TreeWalker.m_Serializer
If m_contentHandler is a SerializationHandler, then this is a reference to the same object. |
| Uses of SerializationHandler in org.apache.xml.serializer.dom3 |
|---|
| Fields in org.apache.xml.serializer.dom3 declared as SerializationHandler | |
|---|---|
private SerializationHandler |
DOM3SerializerImpl.fSerializationHandler
|
private SerializationHandler |
DOM3TreeWalker.fSerializer
The SerializationHandler, it extends ContentHandler and when this class is instantiated via the constructor provided, a SerializationHandler object is passed to it. |
| Methods in org.apache.xml.serializer.dom3 with parameters of type SerializationHandler | |
|---|---|
void |
DOM3SerializerImpl.setSerializationHandler(SerializationHandler handler)
Sets a SerializationHandler on the DOM Serializer. |
| Constructors in org.apache.xml.serializer.dom3 with parameters of type SerializationHandler | |
|---|---|
DOM3SerializerImpl(SerializationHandler handler)
Constructor |
|
DOM3TreeWalker(SerializationHandler serialHandler,
org.w3c.dom.DOMErrorHandler errHandler,
org.w3c.dom.ls.LSSerializerFilter filter,
java.lang.String newLine)
Constructor. |
|
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Umut Sargut
2006-10-30
Hi all,
I tried to setup the source code in eclipse. Initially, I had to add all the required import statements for the utilized libraries. Now it compiles, but I get the following error when I run it:
Exception in thread "main" jadex.runtime.AgentCreationException: Error loading agent model: jadex.adapter.standalone.ams.AMS
at jadex.adapter.JadexAgentFactory.createJadexAgent(JadexAgentFactory.java:48)
at jadex.adapter.standalone.StandaloneAgentAdapter.<init>(StandaloneAgentAdapter.java:83)
at jadex.adapter.standalone.ams.AMS.createAgent(AMS.java:54)
at jadex.adapter.standalone.Platform.<init>(Platform.java:152)
at jadex.adapter.standalone.Platform.main(Platform.java:280)
Caused by: java.io.IOException: Unable to access binding information for class jadex.model.jibximpl.MBDIAgent
Make sure the binding has been compiled
java.lang.NoSuchFieldException: JiBX_bindingList
at java.lang.Class.getDeclaredField(Class.java:1854)
at org.jibx.runtime.BindingDirectory.getBindingList(Unknown Source)
at org.jibx.runtime.BindingDirectory.getFactory(Unknown Source)
at jadex.model.jibximpl.JibxLoader.loadAgentModel(JibxLoader.java:108)
at jadex.model.SXML.loadAgentModel(SXML.java:99)
at jadex.adapter.JadexAgentFactory.createJadexAgent(JadexAgentFactory.java:35)
at jadex.adapter.standalone.StandaloneAgentAdapter.<init>(StandaloneAgentAdapter.java:83)
at jadex.adapter.standalone.ams.AMS.createAgent(AMS.java:54)
at jadex.adapter.standalone.Platform.<init>(Platform.java:152)
at jadex.adapter.standalone.Platform.main(Platform.java:280)
at jadex.model.jibximpl.JibxLoader.loadAgentModel(JibxLoader.java:145)
at jadex.model.SXML.loadAgentModel(SXML.java:99)
at jadex.adapter.JadexAgentFactory.createJadexAgent(JadexAgentFactory.java:35)
... 4 more
I checked similar messages posted before but they didn't help much. An eclipse specific description of jadex execution would be a great help.
Thanks,
Umut
Alexander Pokahr
2006-10-30
Hi Umut,
when you want to compile the Jadex sources yourself,
you need to apply the JiBX compiler afterwards.
Have a look at the first entry in the FAQ to learn
how this can be done:
http://vsis-www.informatik.uni-hamburg.de/projects/jadex/jadex-0.94x/userguide/faq.html
Is there any special reason, why you want to
compile the sources instead of using the precompiled
jars?
Kind regrads,
Alex
Umut Sargut
2006-11-02
Hi Alex,
Thanks for your immediate response.
I've been trying to setup eclipse to use jibx compiler but I couldn't still make it work. When I run org.jibx.binding.Compile with jibx binding, the compilation doesn't stop and it continuously prints a number of messages.
Then I tried to run it through the command prompt. But this time I get the following error message.
Error running binding compiler
*** Error during code generation - please enter a bug report for this error in Jira if the problem is not list
ed as fixed on the online status page ***
org.jibx.runtime.JiBXException: One or more <mapping> elements must be defined in <binding>
at org.jibx.binding.Utility.loadBinding(Utility.java:322)
at org.jibx.binding.Utility.loadFileBinding(Utility.java:413)
at org.jibx.binding.Compile.compile(Compile.java:296)
at org.jibx.binding.Compile.main(Compile.java:385)
I'm a PhD student and I'm working on a BDI agent model. I'm thinking of a conversion from the model to JADEX. It may require some extensions to the language, and I'd like to play with JADEX now as a warm-up. That's why I would like to compile the code myself.
Thanks again for the help,
Umut
Alexander Pokahr
2006-11-02
Hi Umut,
there is a build.xml in the distribution, which includes a
java task to execute the jibx compiler (part of the
"compile" target).
As a start, you could just run the build file.
For better eclipse integration, I use a custom build file,
with the following target, which I have added as a custom
builder in eclipse:
<target name="jibx_compile" description="apply jibx compiler">
<java classname="org.jibx.binding.Compile" failonerror="true" fork="true">
<classpath refid="compile.classpath"/>
<classpath location="${build.dir}"/>
<!--<arg value="-v" />-->
<arg value="${build.dir}/jadex/model/jibximpl/binding.xml" />
</java>
</target>
where ${build.dir} is my output folder, and
<path id="compile.classpath">
<fileset dir="lib" includes="*.jar" />
</path>
Let me know about your progress.
Also, we would be curious to know some more
details about your project and plans, if you are
willing to tell something about it.
Kind regards,
Alex
Umut Sargut
2006-11-07
Hi Alex,
Thanks so much for your help. Now I can compile the source code.
I am currently in the initial phases of my research. I am trying to create a goal oriented analysis and design model for BDI agents. The model will provide the required information for detecting and avoiding conflicts among the agent plans (propagating to the goals). I am inspired with the work of Thangarajah et. al.
Jadex is a good candidate for my research to implement some other extensions I have in my mind. I would be glad to share my ideas with you as a I proceed.
Thanks again for the help,
Umut
Alexander Pokahr
2006-11-07
Hi Umut,
an interesting topic, indeed.
You might be interested to know, that
one of our master students already implemented
one of the deliberation strategies proposed
by John Thangarajah as a prototypical extension
to Jadex. Unfortunately, the thesis is written
german, but I could also make available some
(probably not so well documented ;-) sample code.
In the near future, we plan to make Jadex even more
extensible along the lines already described in our
2005 MATES and IAT papers, which you may already have
found on our publications page.
Therefore, we are very interested in different kinds
of extensions and will try to make sure that these
can be easily implemented.
All the best for your project and hope to stay in touch.
Kind regards,
Alex
Umut Sargut
2006-11-11
Hi Alex,
Actually I would be glad if you could provide the code for the extension. I know a little German, but not enough to read a thesis. But the code itself would also help a lot.
By the way, I have another question. In the user guide, it's mentioned that related actions are added as child nodes to the current node. Does it mean that all the related actions are also executed before any other agenda entries (like external or other top level actions)?
Best regards,
Umut
Alexander Pokahr
2006-11-11
Hi Umut,
I will send you the sources on monday, as I don't
have them at hand at the moment.
You are right about the agenda actions.
As we see it, the agent behaviour appears more
consistent, when side-effects (e.g. caused by belief
changes) are computed directly, that is before other
unrelated actions, such as different plan steps or
processing of received messages.
But there might be other ways. We didn't experiment
a lot with different strategies. The main reason we
implemented it this way (besides finding it natural) was,
that it quite nicely resembles the execution style we had,
before we invented the agenda based interpreter. ;-)
Cheers,
Alex
Umut Sargut
2007-04-23
Hi Alex,
I just installed Jadex 0.96 beta version and tried to run it through Eclipse again.
It builds with no errors. However, when I try to run Plaform.java file from Eclipse, I get the following error message:
This is Jadex 0.96-beta1 - 2007/03/20
Using configuration: jar:file:/C:/Documents%20and%20Settings/Umut/My%20Documents/CISE/research/research%20papers/programming%20languages/jadex/kod/jadex-0.96-beta1/lib/jadex_standalone.jar!/jadex.properties
Exception in thread "main" jadex.runtime.AgentCreationException: Error loading agent model: jadex.adapter.standalone.ams.AMS
at jadex.adapter.JadexAgentFactory.createJadexAgent(JadexAgentFactory.java:45)
at jadex.adapter.standalone.StandaloneAgentAdapter.<init>(StandaloneAgentAdapter.java:74)
at jadex.adapter.standalone.ams.AMS.createAgent(AMS.java:94)
at jadex.adapter.standalone.Platform.<init>(Platform.java:190)
at jadex.adapter.standalone.Platform.main(Platform.java:566)
Caused by: java.io.IOException: Unable to access binding information for class jadex.model.jibximpl.MBDIAgent
Make sure the binding has been compiled
java.lang.NoSuchFieldException: JiBX_bindingList
at java.lang.Class.getDeclaredField(Unknown Source)
at org.jibx.runtime.BindingDirectory.getBindingList(BindingDirectory.java:70)
at org.jibx.runtime.BindingDirectory.getFactory(BindingDirectory.java:207)
at jadex.model.jibximpl.JibxLoader.loadAgentModel(JibxLoader.java:96)
at jadex.model.SXML.loadAgentModel(SXML.java:87)
at jadex.adapter.JadexAgentFactory.createJadexAgent(JadexAgentFactory.java:30)
at jadex.adapter.standalone.StandaloneAgentAdapter.<init>(StandaloneAgentAdapter.java:74)
at jadex.adapter.standalone.ams.AMS.createAgent(AMS.java:94)
at jadex.adapter.standalone.Platform.<init>(Platform.java:190)
at jadex.adapter.standalone.Platform.main(Platform.java:566)
at jadex.model.jibximpl.JibxLoader.loadAgentModel(JibxLoader.java:133)
at jadex.model.SXML.loadAgentModel(SXML.java:87)
at jadex.adapter.JadexAgentFactory.createJadexAgent(JadexAgentFactory.java:30)
... 4 more
If I run the created class file through the command line it works fine.
I am using java jre 1.6.
How can I get rid of this error?
Best regards,
Umut
Alexander Pokahr
2007-04-24
Hi Umut,
when compiling Jadex yourself, you need to manually apply
the JiBX compiler as described in an earlier message to this thread:
http://sourceforge.net/forum/message.php?msg_id=3993415
The problem is indicated by this part of the stack trace:
"java.io.IOException: Unable to access binding information for class jadex.model.jibximpl.MBDIAgent
Make sure the binding has been compiled"
Guess we should put this in the user guide somewhere...
Cheers,
Alex
Umut Sargut
2007-04-28
Hi Alex,
Now I understood that my problem was with the settings of classpath location while compiling with jibx. Eclipse creates a bin folder to keep the class files and the classpath should be set to this folder. I thought this may be useful for other Jadex users.
Best regards,
Umut