[clang] [clang] Don't crash when module directive `export module foo` not following a semicolon and there are no rest pp-tokens in current module file (PR #187845)

[via cfe-commits]

https://github.com/yronglin updated https://github.com/llvm/llvm-project/pull/187845

>From f0394ded3e23fb3fbcc7ac948ae0f2851b9378b1 Mon Sep 17 00:00:00 2001
From: yronglin <yronglin777 at gmail.com>
Date: Sat, 21 Mar 2026 15:16:18 +0800
Subject: [PATCH 1/2] [clang] Don't crash when module directive export module
 foo not following a semicolon and there are no rest pp-tokens in current
 module file

Signed-off-by: yronglin <yronglin777 at gmail.com>
---
 clang/docs/ReleaseNotes.rst                   |  1 +
 clang/lib/Lex/PPDirectives.cpp                | 19 ++++++++++---------
 .../test/CXX/module/dcl.dcl/dcl.module/p1.cpp |  5 +++++
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index b13171f7ecafc..dd2f3e25b9223 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -339,6 +339,7 @@ Bug Fixes in This Version
 - Fixed a crash when normalizing constraints involving concept template parameters whose index coincided with non-concept template parameters in the same parameter mapping.
 - Fixed a crash caused by accessing dependent diagnostics of a non-dependent context.
 - Fixed a crash when substituting into a non-type template parameter that has a type containing an undeduced placeholder type.
+- Fixed a crash when module directive ``export module foo`` not following a semicolon and there are no rest pp-tokens in current module file. (#GH187771)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index 09f0c3fe8c61e..c89402fa137c0 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -4407,18 +4407,19 @@ void Preprocessor::HandleCXXModuleDirective(Token ModuleTok) {
 
   // Consume the pp-import-suffix and expand any macros in it now, if we're not
   // at the semicolon already.
-  std::optional<Token> NextPPTok = DirToks.back();
-  if (DirToks.back().is(tok::eod)) {
-    NextPPTok = peekNextPPToken();
-    if (NextPPTok && NextPPTok->is(tok::raw_identifier))
-      LookUpIdentifierInfo(*NextPPTok);
-  }
+  std::optional<Token> NextPPTok =
+      DirToks.back().is(tok::eod) ? peekNextPPToken() : DirToks.back();
 
   // Only ';' and '[' are allowed after module name.
   // We also check 'private' because the previous is not a module name.
-  if (!NextPPTok->isOneOf(tok::semi, tok::eod, tok::l_square, tok::kw_private))
-    Diag(*NextPPTok, diag::err_pp_unexpected_tok_after_module_name)
-        << getSpelling(*NextPPTok);
+  if (NextPPTok) {
+    if (NextPPTok->is(tok::raw_identifier))
+      LookUpIdentifierInfo(*NextPPTok);
+    if (!NextPPTok->isOneOf(tok::semi, tok::eod, tok::l_square,
+                            tok::kw_private))
+      Diag(*NextPPTok, diag::err_pp_unexpected_tok_after_module_name)
+          << getSpelling(*NextPPTok);
+  }
 
   if (!DirToks.back().isOneOf(tok::semi, tok::eod)) {
     // Consume the pp-import-suffix and expand any macros in it now. We'll add
diff --git a/clang/test/CXX/module/dcl.dcl/dcl.module/p1.cpp b/clang/test/CXX/module/dcl.dcl/dcl.module/p1.cpp
index 95d087e0f6c78..190d4f5ef4871 100644
--- a/clang/test/CXX/module/dcl.dcl/dcl.module/p1.cpp
+++ b/clang/test/CXX/module/dcl.dcl/dcl.module/p1.cpp
@@ -7,6 +7,7 @@
 // RUN: %clang_cc1 -std=c++20 %t/D.cppm -fmodule-file=foo=%t/C.pcm
 // RUN: %clang_cc1 -std=c++20 %t/E.cppm -fmodule-file=foo=%t/C.pcm
 // RUN: %clang_cc1 -std=c++20 -verify %t/F.cppm -fmodule-file=foo=%t/C.pcm
+// RUN: %clang_cc1 -std=c++20 -verify %t/NoSemi.cppm
 
 //--- A.cppm
 export module foo; // expected-note {{previous module declaration is here}}
@@ -28,3 +29,7 @@ export module bar;
 //--- F.cppm
 module foo; // expected-note {{previous module declaration is here}}
 export module bar; // expected-error {{translation unit contains multiple module declarations}}
+
+//--- NoSemi.cppm
+// This test checked issue: https://github.com/llvm/llvm-project/issues/187771
+export module foo //expected-error {{module directive must end with a ';'}}

>From 9422ea51de5db274f41e168de4014191fb2e6749 Mon Sep 17 00:00:00 2001
From: yronglin <yronglin777 at gmail.com>
Date: Tue, 24 Mar 2026 20:58:56 +0800
Subject: [PATCH 2/2] Update clang/docs/ReleaseNotes.rst

Co-authored-by: Aaron Ballman <aaron at aaronballman.com>
---
 clang/docs/ReleaseNotes.rst | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index dd2f3e25b9223..92a5324a61a68 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -339,7 +339,8 @@ Bug Fixes in This Version
 - Fixed a crash when normalizing constraints involving concept template parameters whose index coincided with non-concept template parameters in the same parameter mapping.
 - Fixed a crash caused by accessing dependent diagnostics of a non-dependent context.
 - Fixed a crash when substituting into a non-type template parameter that has a type containing an undeduced placeholder type.
-- Fixed a crash when module directive ``export module foo`` not following a semicolon and there are no rest pp-tokens in current module file. (#GH187771)
+- Correctly diagnosing and no longer crashing when ``export module foo``
+  (without a semicolon) are the final tokens in a module file. (#GH187771)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^