[cfe-dev] Possible bug with ASTUnit::LoadFromASTFile and setting the main file ID

[Tom Honermann]

This is based on Clang 2.9.  I haven't tested with 3.0, but I briefly 
looked at the 3.0 source and I don't see anything that would have 
changed this...

When loading an AST file produced with something like:
   clang -emit-ast file.c
with ASTUnit::LoadFromASTFile(), calling ASTUnit::isMainFileAST() will 
return true.  However, the SourceManager instance will not have a main 
file ID as determined by SourceManager::getMainFileID() - this returns 
an invalid FileID instance.

ASTReader will call SourceManager::setPreambleFileID() if the AST file 
is a pre-compiled preamble, but there are no corresponding conditions 
under which SourceManager::createMainFileID() will be called.  Note that 
SourceManager::setPreambleFileID() and SourceManager::createMainFileID() 
are mutually exclusive and both set SourceManager::MainFileID in Clang 
2.9.  In Clang 3.0, SourceManager has separate fields and these methods 
are not mutually exclusive.

Does this sound like the way things should be?  I would expect 
ASTUnit::isMainFileAST() returning true to imply that 
SourceManager::getMainFileID() should return a valid FileID.

Basically, it seems like another case like the following from the Clang 
3.0 ASTReader.cpp is needed:

   // If this AST file is a precompiled preamble, then set the preamble 
file ID
   // of the source manager to the file source file from which the 
preamble was
   // built.
   if (Type == MK_Preamble) {
     if (!OriginalFileID.isInvalid()) {
       OriginalFileID = 
FileID::get(ModuleMgr.getPrimaryModule().SLocEntryBaseID
                                         + 
OriginalFileID.getOpaqueValue() - 1);
       SourceMgr.setPreambleFileID(OriginalFileID);
     }
   }

If someone can confirm that SourceManager::getMainFileID() should return 
a valid ID for AST files loaded via ASTUnit::LoadFromASTFile(), I'll 
submit a patch.

Tom.