Fix #35272: Don't replace typedefs in extern c scope

Author: da-viper

clang-tools-extra/clang-tidy/modernize/UseUsingCheck.cpp

@@ -11,6 +11,12 @@
 #include "clang/Lex/Lexer.h"
 
 using namespace clang::ast_matchers;
+namespace {
+
+AST_MATCHER(clang::LinkageSpecDecl, isExternCLinkage) {
+  return Node.getLanguage() == clang::LinkageSpecDecl::lang_c;
+}
+} // namespace
 
 namespace clang::tidy::modernize {
 
@@ -27,10 +33,12 @@ void UseUsingCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
 }
 
 void UseUsingCheck::registerMatchers(MatchFinder *Finder) {
-  Finder->addMatcher(typedefDecl(unless(isInstantiated()),
-                                 hasParent(decl().bind(ParentDeclName)))
-                         .bind(TypedefName),
-                     this);
+  Finder->addMatcher(
+      typedefDecl(unless(anyOf(isInstantiated(), hasAncestor(linkageSpecDecl(
+                                                     isExternCLinkage())))),
+                  hasParent(decl().bind(ParentDeclName)))
+          .bind(TypedefName),
+      this);
 
   // This matcher is used to find tag declarations in source code within
   // typedefs. They appear in the AST just *prior* to the typedefs.

clang-tools-extra/test/clang-tidy/checkers/modernize/use-using.cpp

@@ -325,3 +325,17 @@ typedef bool (*ISSUE_65055_2)(int);
 typedef class ISSUE_67529_1 *ISSUE_67529;
 // CHECK-MESSAGES: :[[@LINE-1]]:1: warning: use 'using' instead of 'typedef'
 // CHECK-FIXES: using ISSUE_67529 = class ISSUE_67529_1 *;
+
+// Some Header
+extern "C" {
+
+typedef int InExternC;
+}
+
+extern "C++" {
+
+typedef int InExternCPP;
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: use 'using' instead of 'typedef' [modernize-use-using]
+// CHECK-FIXES: using InExternCPP = int;
+
+}