[PATCH] D127452: [clang-cl][MSVC] Map /external:Wn n=1-4 to -Wsystem-headers

[Stephen Long via Phabricator via cfe-commits]

steplong added a comment.

I don't think /external:Wn behaves exactly like -Wsystem-headers. /external:Wn applies /Wn to the system headers, while -Wsystem-headers applies whatever is on the command line to the system headers. I think /external:Wn behaves more like:

  // foo.c
  #pragma clang diagnostic push
  #pragma clang diagnostic warning "-Wall"
  #include <foo.h>
  #pragma clang diagnostic pop
  
  
  void foo() {
    int i = 10;
  }

  // foo.h
  void bar() {
     int i = 11;
  }

Passing `-Wno-unused-variables` only suppresses the warnings for the rest of `foo.c`. It looks like the pragma is calling `setSeverityForGroup(diag::Flavor::WarningOrError, "-Wall", diag::Serverity::Warning, Loc)`, but I'm not sure where we can detect that we are including a system header.


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https://reviews.llvm.org/D127452