[PATCH] D50462: Try building complete AST after a fatal error was emitted if further diagnostics are expected

[Dmitry via Phabricator via cfe-commits]

Dmitry.Kozhevnikov created this revision.
Dmitry.Kozhevnikov added reviewers: ilya-biryukov, sammccall, milianw.
Herald added subscribers: cfe-commits, ioeric.

Related to https://reviews.llvm.org/D50455

There is some code here and there that assume that no sane output is required if a fatal error has occurred. When using clangd/libclang, it's no longer true: diagnostics might still be requested, and AST might still be required for other IDE/tooling features, so it has to be as complete as possible.

Here I try to separate the following use cases:

1. Some clients check `hasFatalErrorOccurred()` because they are known to work unstable in presence of compile errors and want to mitigate it - they'll work as before
2. However, we don't want to take shortcuts in PP and Sema and still want to process include directives and instantiate templates

Note: I've found out that initially the flag in `DiagnosticsEngine` (which is now called `SuppressAfterFatalError`) had different meaning and was just demoting all fatal errors to non-fatal (https://reviews.llvm.org/rL262318). This would also fix this issue, however, it was partly reverted in https://reviews.llvm.org/rL301992 to the current state. Maybe we should go with the old approach instead (I assume the issue was that this flag was not serialized/restored, but probably should?)


Repository:
  rCTE Clang Tools Extra

https://reviews.llvm.org/D50462

Files:
  include/clang/Basic/Diagnostic.h
  lib/Lex/PPDirectives.cpp
  lib/Sema/SemaTemplateInstantiate.cpp
  unittests/Frontend/PCHPreambleTest.cpp

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