https://github.com/AaronBallman created 
https://github.com/llvm/llvm-project/pull/166188

-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

>From e89037e8d5c5ec944a51a6ab9c45cac656d2c63e Mon Sep 17 00:00:00 2001
From: Aaron Ballman <[email protected]>
Date: Mon, 3 Nov 2025 11:16:24 -0500
Subject: [PATCH] [C23] Correctly handle missing embed with -MG

-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
---
 clang/docs/ReleaseNotes.rst           |  2 ++
 clang/lib/Frontend/DependencyFile.cpp | 11 +++++++++++
 clang/lib/Lex/PPDirectives.cpp        |  2 +-
 clang/test/Driver/mg.c                |  4 +++-
 4 files changed, 17 insertions(+), 2 deletions(-)

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"

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