[clang-tools-extra] Fix #35272: Don't replace typedefs in extern c scope (PR #69102)

[via cfe-commits]

https://github.com/Da-Viper updated https://github.com/llvm/llvm-project/pull/69102

>From 21156656433fb8d2dc5a805d97cbd20fa916fff9 Mon Sep 17 00:00:00 2001
From: Ezike Ebuka <yerimyah1 at gmail.com>
Date: Sun, 15 Oct 2023 11:39:42 +0100
Subject: [PATCH 1/2] Fix #35272: Don't replace typedefs in extern c scope

---
 .../clang-tidy/modernize/UseUsingCheck.cpp       | 16 ++++++++++++----
 .../clang-tidy/checkers/modernize/use-using.cpp  | 14 ++++++++++++++
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/modernize/UseUsingCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseUsingCheck.cpp
index e6293ed48bfddbb..841ffb4c9bfe66e 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseUsingCheck.cpp
+++ b/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.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-using.cpp b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-using.cpp
index 422abee11a71962..0f8f14502d5ca3c 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-using.cpp
+++ b/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;
+
+}

>From 521dec9325285d1e1819a8bee1bd20eadb7c4158 Mon Sep 17 00:00:00 2001
From: Ezike Ebuka <yerimyah1 at gmail.com>
Date: Mon, 16 Oct 2023 23:26:25 +0100
Subject: [PATCH 2/2] Add: Update docs with the new changes. Update
 ReleaseNotes.rst with the changes made

---
 clang-tools-extra/docs/ReleaseNotes.rst                  | 5 +++++
 .../docs/clang-tidy/checks/modernize/use-using.rst       | 9 +++++++++
 2 files changed, 14 insertions(+)

diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index c1b926b296b055a..af6b20369c9dcff 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -285,6 +285,10 @@ Changes in existing checks
   <clang-tidy/checks/modernize/use-using>` check to fix function pointer and
   forward declared ``typedef`` correctly.
 
+- Improved :doc:`modernize-use-using
+  <clang-tidy/checks/modernize/use-using>` by ignoring ``typedef`` declaration in
+  ``extern "C"`` scope.
+
 - Improved :doc:`performance-faster-string-find
   <clang-tidy/checks/performance/faster-string-find>` check to properly escape
   single quotes.
@@ -325,6 +329,7 @@ Changes in existing checks
   identify calls to static member functions with out-of-class inline definitions.
 
 
+
 Removed checks
 ^^^^^^^^^^^^^^
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-using.rst b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-using.rst
index eeddaf8d8d65abe..048fc26617b7b73 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/modernize/use-using.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/modernize/use-using.rst
@@ -28,6 +28,15 @@ After:
   using R_t = struct { int a; };
   using R_p = R_t*;
 
+The checker ignores `typedef` within `extern "C" { ... }` blocks.
+
+.. code-block:: c++
+
+  extern "C" {
+
+    typedef int InExternC; // Left intact.
+  }
+
 This check requires using C++11 or higher to run.
 
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