[clang] [Clang][Parser] Fix crash of clang when using C++ constructs like :: in C code (PR #74926)

[via cfe-commits]

https://github.com/ChipsSpectre updated https://github.com/llvm/llvm-project/pull/74926

>From cb46f3aab771133e3987c65bcbd1f6011792e74c Mon Sep 17 00:00:00 2001
From: ChipsSpectre <maximilian.hornung at tum.de>
Date: Sat, 30 Dec 2023 23:01:12 +0100
Subject: [PATCH] [clang][Parse] `TryAnnotateCXXScopeToken` to be called only
 when parsing C++

Assume `TryAnnotateCXXScopeToken` to be parsing C++ code in all of its paths.

Fixes: https://github.com/llvm/llvm-project/issues/73559.
---
 clang/docs/ReleaseNotes.rst      | 6 ++++--
 clang/lib/Parse/ParseDecl.cpp    | 3 ++-
 clang/lib/Parse/ParseDeclCXX.cpp | 2 ++
 clang/test/Parser/cxx-in-c.c     | 3 +++
 4 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 0c8fec691bf3c9..da9b78b60bee8c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -685,9 +685,11 @@ Bug Fixes in This Version
   (`#65568 <https://github.com/llvm/llvm-project/issues/65568>`_)
 - Fix an issue where clang doesn't respect detault template arguments that
   are added in a later redeclaration for CTAD.
-  Fixes (#69987 <https://github.com/llvm/llvm-project/issues/69987>`_)
+  Fixes (`#69987 <https://github.com/llvm/llvm-project/issues/69987>`_)
 - Fix an issue where CTAD fails for explicit type conversion.
-  Fixes (#64347 <https://github.com/llvm/llvm-project/issues/64347>`_)
+  Fixes (`#64347 <https://github.com/llvm/llvm-project/issues/64347>`_)
+- Fix crash when using C++ only tokens like ``::`` in C compiler clang.
+  Fixes (`#73559 https://github.com/llvm/llvm-project/issues/73559`_)
 
 
 Bug Fixes to Compiler Builtins
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index ed006f9d67de45..b60ae293ef8c20 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -3483,7 +3483,8 @@ void Parser::ParseDeclarationSpecifiers(
 
     case tok::coloncolon: // ::foo::bar
       // C++ scope specifier.  Annotate and loop, or bail out on error.
-      if (TryAnnotateCXXScopeToken(EnteringContext)) {
+      if (getLangOpts().CPlusPlus &&
+          TryAnnotateCXXScopeToken(EnteringContext)) {
         if (!DS.hasTypeSpecifier())
           DS.SetTypeSpecError();
         goto DoneWithDeclSpec;
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 910112ecae964c..d97081da4200de 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -2679,6 +2679,8 @@ Parser::ParseCXXClassMemberDeclaration(AccessSpecifier AS,
                                        ParsedAttributes &AccessAttrs,
                                        const ParsedTemplateInfo &TemplateInfo,
                                        ParsingDeclRAIIObject *TemplateDiags) {
+  assert(getLangOpts().CPlusPlus &&
+         "ParseCXXClassMemberDeclaration should only be called in C++ mode");
   if (Tok.is(tok::at)) {
     if (getLangOpts().ObjC && NextToken().isObjCAtKeyword(tok::objc_defs))
       Diag(Tok, diag::err_at_defs_cxx);
diff --git a/clang/test/Parser/cxx-in-c.c b/clang/test/Parser/cxx-in-c.c
index f5fa39bd0cb99b..034a44cdf12bfa 100644
--- a/clang/test/Parser/cxx-in-c.c
+++ b/clang/test/Parser/cxx-in-c.c
@@ -3,3 +3,6 @@
 // PR9137
 void f0(int x) : {}; // expected-error{{expected function body after function declarator}}
 void f1(int x) try {}; // expected-error{{expected function body after function declarator}}
+
+// GH73559
+::; // expected-error{{expected identifier or '('}}