[C23] Correctly handle missing embed with -MG

[AaronBallman]

-MG is supposed to suppress "file not found" diagnostics and instead treat those as generated files for purposes of dependency scanning. Clang was previously emitting the diagnostic instead of emitting the name of the embedded file.

Fixes #165632

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-driver

Author: Aaron Ballman (AaronBallman)

Changes

-MG is supposed to suppress "file not found" diagnostics and instead treat those as generated files for purposes of dependency scanning. Clang was previously emitting the diagnostic instead of emitting the name of the embedded file.

Fixes #165632

---

Full diff: https://github.com/llvm/llvm-project/pull/166188.diff

4 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/lib/Frontend/DependencyFile.cpp (+11)
• (modified) clang/lib/Lex/PPDirectives.cpp (+1-1)
• (modified) clang/test/Driver/mg.c (+3-1)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 6959e61cac980..cbf1c1922c59f 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -209,6 +209,8 @@ C23 Feature Support
   `WG14 N2710 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2710.htm>`_.
 - Fixed accepting as compatible unnamed tag types with the same fields within
   the same translation unit but from different types.
+- ``-MG`` now silences the "file not found" errors with ``#embed`` when
+  scanning for dependencies and encountering an unknown file. #GH165632
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------
diff --git a/clang/lib/Frontend/DependencyFile.cpp b/clang/lib/Frontend/DependencyFile.cpp
index 15fa7de35df97..d65740a03acd3 100644
--- a/clang/lib/Frontend/DependencyFile.cpp
+++ b/clang/lib/Frontend/DependencyFile.cpp
@@ -75,6 +75,17 @@ struct DepCollectorPPCallbacks : public PPCallbacks {
                                     /*IsMissing*/ false);
   }
 
+  bool EmbedFileNotFound(StringRef FileName) override {
+    DepCollector.maybeAddDependency(
+        llvm::sys::path::remove_leading_dotslash(FileName),
+        /*FromModule*/ false,
+        /*IsSystem*/ false,
+        /*IsModuleFile*/ false,
+        /*IsMissing*/ false);
+    // Return true to silence the file not found diagnostic.
+    return true;
+  }
+
   void InclusionDirective(SourceLocation HashLoc, const Token &IncludeTok,
                           StringRef FileName, bool IsAngled,
                           CharSourceRange FilenameRange,
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index 6a5e5d4bad3a6..891c8ab7f3155 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -4018,7 +4018,7 @@ void Preprocessor::HandleEmbedDirective(SourceLocation HashLoc, Token &EmbedTok,
       this->LookupEmbedFile(Filename, isAngled, true, LookupFromFile);
   if (!MaybeFileRef) {
     // could not find file
-    if (Callbacks && Callbacks->EmbedFileNotFound(OriginalFilename)) {
+    if (Callbacks && Callbacks->EmbedFileNotFound(Filename)) {
       return;
     }
     Diag(FilenameTok, diag::err_pp_file_not_found) << Filename;
diff --git a/clang/test/Driver/mg.c b/clang/test/Driver/mg.c
index 82d8a6084e5e0..b7458a08698d3 100644
--- a/clang/test/Driver/mg.c
+++ b/clang/test/Driver/mg.c
@@ -1,5 +1,7 @@
-// RUN: %clang -M -MG -include nonexistent-preinclude.h %s | FileCheck %s
+// RUN: %clang -M -MG -include nonexistent-preinclude.h -std=c23 %s | FileCheck %s
 // CHECK: nonexistent-preinclude.h
 // CHECK: nonexistent-ppinclude.h
+// CHECK: nonexistent-embed
 
 #include "nonexistent-ppinclude.h"
+#embed "nonexistent-embed"

[Fznamznon]

Thanks!

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.