[cfe-dev] Building AST at runtime

[Daniel Albuschat]

Hello there,

I'm having a hard time building a simple AST at runtime. I think that only
small pieces are missing, but it's rather difficult for me to find which
ones and where.

The code I have has been created by trial and error regarding the
CompilerInstance initialization and the ASTDumpAction.
The sema-part was inspired by what happens in
https://github.com/tritao/clang/blob/master/lib/Sema/SemaCLI.cpp.

I'm first trying to create a namespace, for a start.

I get the following error mesage from the code:
> error: unknown target triple '', please use -triple or -arch

I thought I provided the required triple in the call to
clang::TargetInfo::CreateTargetInfo, passing targetOptions, which "Triple"
member has been set to "i386-pc-win32" (which was only a guess, since I did
not find a reference for the string syntax of a target triple).

Here's the code:

#include <clang/Frontend/ASTConsumers.h>
#include <clang/Frontend/CompilerInstance.h>
#include <clang/Frontend/FrontendActions.h>
#include <clang/CodeGen/CodeGenAction.h>
#include <clang/Tooling/Tooling.h>
#include <clang/Sema/Sema.h>
#include <clang/Lex/Preprocessor.h>
#include <clang/AST/Decl.h>
#include <clang/AST/ASTContext.h>
#include <clang/Basic/FileManager.h>
#include <clang/Basic/TargetInfo.h>
#include <clang/Basic/IdentifierTable.h>
#include <clang/Basic/SourceLocation.h>
#include <llvm/Support/raw_os_ostream.h>
#include <iostream>
#include <string>

void clang_sandbox ()
{
    clang::FileManager fileManager = clang::FileManager
(clang::FileSystemOptions ());
    auto targetOptions = new clang::TargetOptions ();
    targetOptions->Triple = "i386-pc-win32";

    clang::CompilerInstance instance;
    instance.createDiagnostics ();
    clang::TargetInfo * target (clang::TargetInfo::CreateTargetInfo
(instance.getDiagnostics (), targetOptions));
    instance.setTarget (target);
    instance.createFileManager ();
    instance.createSourceManager (fileManager);
    instance.createPreprocessor ();
    instance.setASTConsumer (clang::CreateASTPrinter (nullptr,
llvm::StringRef ()));
    instance.createASTContext ();

    auto sema = new clang::Sema (instance.getPreprocessor (),
instance.getASTContext (), instance.getASTConsumer (), clang::TU_Complete);

    clang::IdentifierTable & identifierTable = sema->getPreprocessor
().getIdentifierTable ();
    clang::IdentifierInfo & identifier = identifierTable.get ("blubb");

    clang::TranslationUnitDecl* tu =
sema->getASTContext().getTranslationUnitDecl();
    clang::DeclContext* declContext = tu->getPrimaryContext();

    clang::SourceLocation declSourceLocation;
    clang::NamespaceDecl::Create (sema->getASTContext (), declContext,
false, declSourceLocation, declSourceLocation, & identifier, nullptr);

    instance.setSema (sema);
    clang::ASTDumpAction action;
    instance.ExecuteAction (action);

    std::cout << "\nEnd CLang Sandbox!\n";
}

Greetings,
Daniel Albuschat

P.S.: Yes, I have been recommended to create C++ code instead of trying to
build an AST. But I'd still like to try the AST approach, since I'd like to
skip the (time consuming) parsing of the C++ code.
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