[clang][driver] Suppress gnu-line-marker when saving temps (#134621)

When passing `-save-temps` to clang, the generated preprocessed output
uses gnu line markers. This unexpectedly triggers gnu-line-marker
warnings when used with `-Weverything` or `-pedantic`. Even worse,
compilation fails if `-Werror` is used.

This change suppresses gnu-line-marker warnings when invoking clang with
input from a preprocessor job and the user has not otherwise explictly
specified `-Wgnu-line-marker` somewhere on the command line. Note that
this does apply to user provided preprocessed files.

fixes #63802

1 files changed, 8 insertions, 0 deletions

diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 69a91ee..f64613f 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/Basic/DiagnosticLex.h"
 #include "clang/Basic/HLSLRuntime.h"
 #include "clang/Basic/MacroBuilder.h"
 #include "clang/Basic/SourceManager.h"
@@ -1644,4 +1645,11 @@ void clang::InitializePreprocessor(Preprocessor &PP,
 
   // Copy PredefinedBuffer into the Preprocessor.
   PP.setPredefines(std::move(PredefineBuffer));
+
+  // Match gcc behavior regarding gnu-line-directive diagnostics, assuming that
+  // '-x <*>-cpp-output' is analogous to '-fpreprocessed'.
+  if (FEOpts.DashX.isPreprocessed()) {
+    PP.getDiagnostics().setSeverity(diag::ext_pp_gnu_line_directive,
+                                    diag::Severity::Ignored, SourceLocation());
+  }
 }