[clang-tools-extra] [clang-tidy] Add bugprone-custom-errno-declaration check (PR #213015)

[Zeyi Xu via cfe-commits]

================
@@ -0,0 +1,38 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "CustomErrnoDeclarationCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+void CustomErrnoDeclarationCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(varDecl(hasType(asString("int")), hasName("errno"), hasExternalFormalLinkage()).bind("errnoDecl"), this);
+}
+
+void CustomErrnoDeclarationCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *MatchedDecl = Result.Nodes.getNodeAs<VarDecl>("errnoDecl"); // NULL?
+  const SourceManager &SM = *Result.SourceManager;
+  const auto Location = MatchedDecl->getLocation();
+  const auto FileID = SM.getFileID(Location);
+
+  unsigned Line = SM.getSpellingLineNumber(MatchedDecl->getBeginLoc());
+
+  const auto Diag = diag(Location, "errno declaration detected, include cerrno instead")
+      << FixItHint::CreateRemoval(CharSourceRange::getCharRange(SM.translateLineCol(FileID, Line, 1), SM.translateLineCol(FileID, Line + 1, 1)));
+
+  if (alreadyInserted)
+    return;
+
+  Diag << FixItHint::CreateInsertion(SM.getLocForStartOfFile(FileID), "#include <cerrno>\n");
----------------
zeyi2 wrote:

We should use `utils::IncludeInserter` for inserting includes.

Also we should support inserting `<errno.h>` as well:

```cpp
StringRef Header =
    Result.Context->getLangOpts().CPlusPlus ? "<cerrno>" : "<errno.h>";
```

https://github.com/llvm/llvm-project/pull/213015