[clang] [Clang] Fix infinite loop on '::' inside parens in C mode (PR #195377)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Petr Beneš (wbenny)

<details>
<summary>Changes</summary>

`Parser::isTypeSpecifierQualifier` was recursing on the same `::` token forever when called from `isTypeIdInParens` while parsing a parenthesized expression in C mode.

Fixes: #<!-- -->195367

---
Full diff: https://github.com/llvm/llvm-project/pull/195377.diff


2 Files Affected:

- (modified) clang/lib/Parse/ParseDecl.cpp (+2) 
- (added) clang/test/Parser/c-global-scope-coloncolon.c (+3) 


``````````diff
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 434a1a8fcb223..b5f06c9e01077 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -5632,6 +5632,8 @@ bool Parser::isTypeSpecifierQualifier(const Token &Tok) {
     return isTypeSpecifierQualifier(getCurToken());
 
   case tok::coloncolon:   // ::foo::bar
+    if (!getLangOpts().CPlusPlus && !getLangOpts().ObjC)
+      return false;
     if (NextToken().is(tok::kw_new) ||    // ::new
         NextToken().is(tok::kw_delete))   // ::delete
       return false;
diff --git a/clang/test/Parser/c-global-scope-coloncolon.c b/clang/test/Parser/c-global-scope-coloncolon.c
new file mode 100644
index 0000000000000..508b89ef6a180
--- /dev/null
+++ b/clang/test/Parser/c-global-scope-coloncolon.c
@@ -0,0 +1,3 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+int x = (::h); // expected-error {{expected expression}}

``````````

</details>


https://github.com/llvm/llvm-project/pull/195377