[PATCH] D53866: [Preamble] Fix preamble for circular #includes

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov added a comment.

In https://reviews.llvm.org/D53866#1301086, @nik wrote:

> I still don't have feedback for a real world case except "unintentional #include". Unfortunately, in real world cases the cyclic include might be not obvious at all.
>  @ilya: As far as I understand you prefer to make the preamble generation rather fail as long as we don't have more information. How do you suggest to implement this? I see that Clang->getPreprocessor().addPPCallbacks() is called in PrecompiledPreamble::Build(). Adding a custom PPCallbacks there that overrides "void InclusionDirective()" might be enough to detect the cyclic #include and to set a flag that is checked before PrecompiledPreamble::Build() returns - BuildPreambleError could get a new enumerator. Is there a better way to do this? For example, it would be desirable to not only observe this case, but then to also stop/abort/skip all the further parsing that is done for the preamble only as it's pointless then.


Maybe produce a **fatal** error in the preprocessor? That seems to be the simplest option: the preprocessor is aware it's building the preamble and there's definitely some logic to produce fatal errors in other cases (include not found).
A fatal error currently aborts other stages of the compilation pipeline and producing one would make the run of the compiler that tries to produce the preamble fail, giving the empty preamble as a result.


Repository:
  rC Clang

https://reviews.llvm.org/D53866