[clang-tools-extra] [clang-tidy] Do not warn on const variables in misc-use-internal-linkage (PR #97969)

[Carlos Galvez via cfe-commits]

https://github.com/carlosgalvezp updated https://github.com/llvm/llvm-project/pull/97969

>From a1fec907b5d3920d5dda8761b6e173e153b7f281 Mon Sep 17 00:00:00 2001
From: Carlos Galvez <carlosgalvezp at gmail.com>
Date: Sun, 7 Jul 2024 21:11:54 +0200
Subject: [PATCH] [clang-tidy] Do not warn on const variables in
 misc-use-internal-linkage

Since in C++ they already have implicit internal linkage.
https://eel.is/c++draft/diff#basic-3

Also, ensure that the check is only active in C++ code, since the
warning message presents anonymous namespaces as a solution, which
is not applicable to C.

Fixes #97947
---
 .../clang-tidy/misc/UseInternalLinkageCheck.cpp              | 5 ++++-
 clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.h  | 3 +++
 .../clang-tidy/checkers/misc/use-internal-linkage-var.cpp    | 3 +++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.cpp b/clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.cpp
index 44ccc2bc906a5b..bc3fc50ca75dff 100644
--- a/clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.cpp
@@ -103,7 +103,10 @@ void UseInternalLinkageCheck::registerMatchers(MatchFinder *Finder) {
       functionDecl(Common, unless(cxxMethodDecl()), unless(isMain()))
           .bind("fn"),
       this);
-  Finder->addMatcher(varDecl(Common, hasGlobalStorage()).bind("var"), this);
+  Finder->addMatcher(
+      varDecl(Common, hasGlobalStorage(), unless(hasType(isConstQualified())))
+          .bind("var"),
+      this);
 }
 
 static constexpr StringRef Message =
diff --git a/clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.h b/clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.h
index 0d6c3e43aa9457..1ad28333ddc49d 100644
--- a/clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.h
+++ b/clang-tools-extra/clang-tidy/misc/UseInternalLinkageCheck.h
@@ -21,6 +21,9 @@ namespace clang::tidy::misc {
 class UseInternalLinkageCheck : public ClangTidyCheck {
 public:
   UseInternalLinkageCheck(StringRef Name, ClangTidyContext *Context);
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;
+  }
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
   void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc/use-internal-linkage-var.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc/use-internal-linkage-var.cpp
index 01b8d28e612301..6777ce4bb0265e 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/misc/use-internal-linkage-var.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc/use-internal-linkage-var.cpp
@@ -42,3 +42,6 @@ int global_in_extern_c_1;
 }
 
 extern "C" int global_in_extern_c_2;
+
+const int const_global = 123;
+constexpr int constexpr_global = 123;