[clang-tools-extra] [clang-tidy] new check misc-use-internal-linkage (PR #90830)

[Piotr Zegar via cfe-commits]

================
@@ -0,0 +1,78 @@
+//===--- UseInternalLinkageCheck.cpp - clang-tidy--------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "UseInternalLinkageCheck.h"
+#include "../utils/FileExtensionsUtils.h"
+#include "clang/AST/Decl.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/ASTMatchers/ASTMatchersMacros.h"
+#include "clang/Basic/SourceLocation.h"
+#include "clang/Basic/Specifiers.h"
+#include "llvm/ADT/STLExtras.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::misc {
+
+namespace {
+
+AST_MATCHER(Decl, isFirstDecl) { return Node.isFirstDecl(); }
+
+AST_MATCHER_P(Decl, isInMainFile, FileExtensionsSet, HeaderFileExtensions) {
+  return llvm::all_of(Node.redecls(), [&](const Decl *D) {
+    SourceManager &SM = Finder->getASTContext().getSourceManager();
+    const SourceLocation L = D->getLocation();
+    return SM.isInMainFile(L) &&
+           !utils::isSpellingLocInHeaderFile(L, SM, HeaderFileExtensions);
+  });
+}
+
+AST_POLYMORPHIC_MATCHER(isExternStorageClass,
+                        AST_POLYMORPHIC_SUPPORTED_TYPES(FunctionDecl,
+                                                        VarDecl)) {
+  return Node.getStorageClass() == SC_Extern;
+}
+
+} // namespace
+
+void UseInternalLinkageCheck::registerMatchers(MatchFinder *Finder) {
+  auto Common = allOf(isFirstDecl(), isInMainFile(HeaderFileExtensions),
----------------
PiotrZSL wrote:

isFirstDecl wont work if someone do:

```
void foo()
{
}
#include "foo.h"
```

but thats, fine, just would be good if documentation mention that it checks first declaration

https://github.com/llvm/llvm-project/pull/90830