[clang-tools-extra] [clang-tidy] Added check 'bugprone-function-visibility-change' (PR #140086)

[Piotr Zegar via cfe-commits]

================
@@ -0,0 +1,74 @@
+//===--- FunctionVisibilityChangeCheck.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 "FunctionVisibilityChangeCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::bugprone {
+
+void FunctionVisibilityChangeCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      cxxMethodDecl(
+          ofClass(cxxRecordDecl().bind("class")),
+          forEachOverridden(cxxMethodDecl(ofClass(cxxRecordDecl().bind("base")))
+                                .bind("base_func")))
+          .bind("func"),
+      this);
+}
+
+void FunctionVisibilityChangeCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *MatchedFunction = Result.Nodes.getNodeAs<FunctionDecl>("func");
+  const auto *ParentClass = Result.Nodes.getNodeAs<CXXRecordDecl>("class");
+  const auto *OverriddenFunction =
+      Result.Nodes.getNodeAs<FunctionDecl>("base_func");
+  const auto *BaseClass = Result.Nodes.getNodeAs<CXXRecordDecl>("base");
+
+  if (!MatchedFunction->isCanonicalDecl())
+    return;
+
+  AccessSpecifier ActualAccess = MatchedFunction->getAccess();
+  AccessSpecifier OverriddenAccess = OverriddenFunction->getAccess();
+
+  CXXBasePaths Paths;
+  if (!ParentClass->isDerivedFrom(BaseClass, Paths))
+    return;
+  const CXXBaseSpecifier *InheritanceWithStrictVisibility = nullptr;
+  for (const CXXBasePath &Path : Paths) {
+    for (auto Elem : Path) {
+      if (Elem.Base->getAccessSpecifier() > OverriddenAccess) {
+        OverriddenAccess = Elem.Base->getAccessSpecifier();
+        InheritanceWithStrictVisibility = Elem.Base;
+      }
+    }
+  }
+
+  if (ActualAccess != OverriddenAccess) {
+    if (InheritanceWithStrictVisibility) {
+      diag(MatchedFunction->getLocation(),
+           "visibility of function %0 is changed from %1 (through %1 "
+           "inheritance of class %2) to %3")
+          << MatchedFunction << OverriddenAccess
+          << InheritanceWithStrictVisibility->getType() << ActualAccess;
+      diag(InheritanceWithStrictVisibility->getBeginLoc(),
+           "this inheritance would make %0 %1", DiagnosticIDs::Note)
----------------
PiotrZSL wrote:

maybe better "%0 is inherited as %1 here".
I do not like that "this" at the begining

https://github.com/llvm/llvm-project/pull/140086