[clang] [clang] Don't crash in invalid #module directive (PR #208695)

[Yihan Wang via cfe-commits]

https://github.com/yronglin created https://github.com/llvm/llvm-project/pull/208695

The following preprocessing directive is not a C++ module directive, don't handle it in C++ module subroutine.

```cpp
#module
```

Fixes https://github.com/llvm/llvm-project/issues/179220.

>From 924c8c8eab54a19115b7747d0174373f89087d0e Mon Sep 17 00:00:00 2001
From: yronglin <yronglin777 at gmail.com>
Date: Fri, 10 Jul 2026 03:58:44 -0700
Subject: [PATCH] [clang] Don't crash in invalid #module directive

Signed-off-by: yronglin <yronglin777 at gmail.com>
---
 clang/docs/ReleaseNotes.md             | 1 +
 clang/lib/Lex/PPDirectives.cpp         | 7 +++++--
 clang/test/Lexer/invalid-directive.cpp | 3 +++
 3 files changed, 9 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/Lexer/invalid-directive.cpp

diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index 449a3792eb4ba..3dff6efac576d 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -883,6 +883,7 @@ latest release, please see the [Clang Web Site](https://clang.llvm.org) or the
 - Correctly diagnose invalid non-dependent calls in dependent contexts. (#GH135694)
 - Fix initialization of GRO when GRO-return type mismatches, as part of CWG2563. (#GH98744)
 - Fix an error using an initializer list with array new for a type that is not default-constructible. (#GH81157)
+- Fixed a crash in invalid ``#module`` preprocessing directive. (#GH179220)
 - We no longer consider conversion operators when copy-initializing from the same type. This was non
   conforming and could lead to recursive constraint satisfaction checking. (#GH149443)
 - Fixed a crash in Itanium C++ name mangling for a lambda in a local class field initializer inside a constructor/destructor. (#GH176395)
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index 20f2575254e7b..76ea6b6a6e19b 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -1455,10 +1455,11 @@ void Preprocessor::HandleDirective(Token &Result) {
       return HandlePragmaDirective({PIK_HashPragma, Introducer.getLocation()});
     case tok::pp_module:
     case tok::pp___preprocessed_module:
-      return HandleCXXModuleDirective(Result);
+      if (Introducer.isModuleContextualKeyword())
+        return HandleCXXModuleDirective(Result);
+      break;
     case tok::pp___preprocessed_import:
       return HandleCXXImportDirective(Result);
-    // GNU Extensions.
     case tok::pp_import:
       switch (Introducer.getKind()) {
       case tok::hash:
@@ -1470,6 +1471,8 @@ void Preprocessor::HandleDirective(Token &Result) {
       default:
         llvm_unreachable("not a valid import directive");
       }
+
+    // GNU Extensions.
     case tok::pp_include_next:
       return HandleIncludeNextDirective(Introducer.getLocation(), Result);
 
diff --git a/clang/test/Lexer/invalid-directive.cpp b/clang/test/Lexer/invalid-directive.cpp
new file mode 100644
index 0000000000000..c20cc885e7a7b
--- /dev/null
+++ b/clang/test/Lexer/invalid-directive.cpp
@@ -0,0 +1,3 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
+
+#module // expected-error {{invalid preprocessing directive}}