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

[Congcong Cai 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);
+  });
----------------
HerrCai0907 wrote:

It will match more cases which I cannot understand the code style.
e.g.
```c++
/// a.cpp
void f(); // decl-1

/// b.cpp
#include <a.cpp>
void f() {} // decl-2
```
The current version will ignore this cases because decl-1 is not in main file.
But the suggestion version will catch this cases because both file is source fill extensions.

Actually I don't understand and didn't meet this code style, so I keep conservative to avoid false positive.


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