[clang-tidy] Added check 'bugprone-function-visibility-change'

clang-tools-extra/clang-tidy/misc/CMakeLists.txt

@@ -42,6 +42,7 @@ add_clang_library(clangTidyMiscModule STATIC
   UnusedUsingDeclsCheck.cpp
   UseAnonymousNamespaceCheck.cpp
   UseInternalLinkageCheck.cpp
+  VisibilityChangeToVirtualFunctionCheck.cpp
 
   LINK_LIBS
   clangTidy

clang-tools-extra/clang-tidy/misc/MiscTidyModule.cpp

@@ -32,6 +32,7 @@
 #include "UnusedUsingDeclsCheck.h"
 #include "UseAnonymousNamespaceCheck.h"
 #include "UseInternalLinkageCheck.h"
+#include "VisibilityChangeToVirtualFunctionCheck.h"
 
 namespace clang::tidy {
 namespace misc {
@@ -81,6 +82,8 @@ class MiscModule : public ClangTidyModule {
         "misc-use-anonymous-namespace");
     CheckFactories.registerCheck<UseInternalLinkageCheck>(
         "misc-use-internal-linkage");
+    CheckFactories.registerCheck<VisibilityChangeToVirtualFunctionCheck>(
+        "misc-visibility-change-to-virtual-function");
   }
 };
 

clang-tools-extra/clang-tidy/misc/VisibilityChangeToVirtualFunctionCheck.cpp

@@ -0,0 +1,147 @@
+//===--- VisibilityChangeToVirtualFunctionCheck.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 "VisibilityChangeToVirtualFunctionCheck.h"
+#include "../utils/Matchers.h"
+#include "../utils/OptionsUtils.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+using namespace clang;
+
+namespace {
+AST_MATCHER(NamedDecl, isOperatorDecl) {
+  DeclarationName::NameKind NK = Node.getDeclName().getNameKind();
+  return NK != DeclarationName::Identifier &&
+         NK != DeclarationName::CXXConstructorName &&
+         NK != DeclarationName::CXXDestructorName;
+}
+} // namespace
+
+namespace clang::tidy {
+
+template <>
+struct OptionEnumMapping<
+    misc::VisibilityChangeToVirtualFunctionCheck::ChangeKind> {
+  static llvm::ArrayRef<std::pair<
+      misc::VisibilityChangeToVirtualFunctionCheck::ChangeKind, StringRef>>
+  getEnumMapping() {
+    static constexpr std::pair<
+        misc::VisibilityChangeToVirtualFunctionCheck::ChangeKind, StringRef>
+        Mapping[] = {
+            {misc::VisibilityChangeToVirtualFunctionCheck::ChangeKind::Any,
+             "any"},
+            {misc::VisibilityChangeToVirtualFunctionCheck::ChangeKind::Widening,
+             "widening"},
+            {misc::VisibilityChangeToVirtualFunctionCheck::ChangeKind::
+                 Narrowing,
+             "narrowing"},
+        };
+    return {Mapping};
+  }
+};
+
+namespace misc {
+
+VisibilityChangeToVirtualFunctionCheck::VisibilityChangeToVirtualFunctionCheck(
+    StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      DetectVisibilityChange(
+          Options.get("DisallowedVisibilityChange", ChangeKind::Any)),
+      CheckDestructors(Options.get("CheckDestructors", false)),
+      CheckOperators(Options.get("CheckOperators", false)),
+      IgnoredFunctions(utils::options::parseStringList(
+          Options.get("IgnoredFunctions", ""))) {}
+
+void VisibilityChangeToVirtualFunctionCheck::storeOptions(
+    ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "DisallowedVisibilityChange", DetectVisibilityChange);
+  Options.store(Opts, "CheckDestructors", CheckDestructors);
+  Options.store(Opts, "CheckOperators", CheckOperators);
+  Options.store(Opts, "IgnoredFunctions",
+                utils::options::serializeStringList(IgnoredFunctions));
+}
+
+void VisibilityChangeToVirtualFunctionCheck::registerMatchers(
+    MatchFinder *Finder) {
+  auto IgnoredDecl =
+      namedDecl(matchers::matchesAnyListedName(IgnoredFunctions));
+  auto FilterDestructors =
+      CheckDestructors ? decl() : decl(unless(cxxDestructorDecl()));
+  auto FilterOperators =
+      CheckOperators ? namedDecl() : namedDecl(unless(isOperatorDecl()));
+  Finder->addMatcher(
+      cxxMethodDecl(
+          isVirtual(), FilterDestructors, FilterOperators,
+          ofClass(
+              cxxRecordDecl(unless(isExpansionInSystemHeader())).bind("class")),
+          forEachOverridden(cxxMethodDecl(ofClass(cxxRecordDecl().bind("base")),
+                                          unless(IgnoredDecl))
+                                .bind("base_func")))
+          .bind("func"),
+      this);
+}
+
+void VisibilityChangeToVirtualFunctionCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const auto *MatchedFunction = Result.Nodes.getNodeAs<FunctionDecl>("func");
+  if (!MatchedFunction->isCanonicalDecl())
+    return;
+
+  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");
+
+  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 (const CXXBasePathElement &Elem : Path) {
+      if (Elem.Base->getAccessSpecifier() > OverriddenAccess) {
+        OverriddenAccess = Elem.Base->getAccessSpecifier();
+        InheritanceWithStrictVisibility = Elem.Base;
+      }
+    }
+  }
+
+  if (ActualAccess != OverriddenAccess) {
+    if (DetectVisibilityChange == ChangeKind::Widening &&
+        ActualAccess > OverriddenAccess)
+      return;
+    if (DetectVisibilityChange == ChangeKind::Narrowing &&
+        ActualAccess < OverriddenAccess)
+      return;
+
+    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(),
+           "%0 is inherited as %1 here", DiagnosticIDs::Note)
+          << InheritanceWithStrictVisibility->getType() << OverriddenAccess;
+    } else {
+      diag(MatchedFunction->getLocation(),
+           "visibility of function %0 is changed from %1 in class %2 to %3")
+          << MatchedFunction << OverriddenAccess << BaseClass << ActualAccess;
+    }
+    diag(OverriddenFunction->getLocation(), "function declared here as %0",
+         DiagnosticIDs::Note)
+        << OverriddenFunction->getAccess();
+  }
+}
+
+} // namespace misc
+
+} // namespace clang::tidy

clang-tools-extra/clang-tidy/misc/VisibilityChangeToVirtualFunctionCheck.h

@@ -0,0 +1,43 @@
+//===--- VisibilityChangeToVirtualFunctionCheck.h - clang-tidy --*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_VISIBILITYCHANGETOVIRTUALFUNCTIONCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_VISIBILITYCHANGETOVIRTUALFUNCTIONCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::misc {
+
+/// Finds virtual function overrides with different visibility than the function
+/// in the base class.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/misc/visibility-change-to-virtual-function.html
+class VisibilityChangeToVirtualFunctionCheck : public ClangTidyCheck {
+public:
+  enum class ChangeKind { Any, Widening, Narrowing };
+
+  VisibilityChangeToVirtualFunctionCheck(StringRef Name,
+                                         ClangTidyContext *Context);
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;
+  }
+
+private:
+  ChangeKind DetectVisibilityChange;
+  bool CheckDestructors;
+  bool CheckOperators;
+  std::vector<llvm::StringRef> IgnoredFunctions;
+};
+
+} // namespace clang::tidy::misc
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_VISIBILITYCHANGETOVIRTUALFUNCTIONCHECK_H

clang-tools-extra/docs/ReleaseNotes.rst

@@ -142,6 +142,12 @@ New checks
   Finds unscoped (non-class) ``enum`` declarations and suggests using
   ``enum class`` instead.
 
+- New :doc:`misc-visibility-change-to-virtual-function
+  <clang-tidy/checks/misc/visibility-change-to-virtual-function>` check.
+
+  Finds virtual function overrides with different visibility than the function
+  in the base class.
+
 - New :doc:`modernize-use-scoped-lock
   <clang-tidy/checks/modernize/use-scoped-lock>` check.
 

clang-tools-extra/docs/clang-tidy/checks/list.rst

@@ -278,6 +278,7 @@ Clang-Tidy Checks
    :doc:`misc-unused-using-decls <misc/unused-using-decls>`, "Yes"
    :doc:`misc-use-anonymous-namespace <misc/use-anonymous-namespace>`,
    :doc:`misc-use-internal-linkage <misc/use-internal-linkage>`, "Yes"
+   :doc:`misc-visibility-change-to-virtual-function <misc/visibility-change-to-virtual-function>`,
    :doc:`modernize-avoid-bind <modernize/avoid-bind>`, "Yes"
    :doc:`modernize-avoid-c-arrays <modernize/avoid-c-arrays>`,
    :doc:`modernize-concat-nested-namespaces <modernize/concat-nested-namespaces>`, "Yes"

clang-tools-extra/docs/clang-tidy/checks/misc/visibility-change-to-virtual-function.rst

@@ -0,0 +1,87 @@
+.. title:: clang-tidy - misc-visibility-change-to-virtual-function
+
+misc-visibility-change-to-virtual-function
+==========================================
+
+Finds virtual function overrides with different visibility than the function
+in the base class. This includes for example if a virtual function declared as
+``private`` is overridden and declared as ``public`` in a subclass. The detected
+change is the modification of visibility resulting from keywords ``public``,
+``protected``, ``private`` at overridden virtual functions. The check applies to
+any normal virtual function and optionally to destructors or operators. Use of
+the ``using`` keyword is not considered as visibility change by this check.
+
+
+.. code-block:: c++
+
+  class A {
+  public:
+    virtual void f_pub();
+  private:
+    virtual void f_priv();
+  };
+
+  class B: public A {
+  public:
+    void f_priv(); // warning: changed visibility from private to public
+  private:
+    void f_pub(); // warning: changed visibility from public to private
+  };
+
+  class C: private A {
+    // no warning: f_pub becomes private in this case but this is from the
+    // private inheritance
+  };
+
+  class D: private A {
+  public:
+    void f_pub(); // warning: changed visibility from private to public
+                  // 'f_pub' would have private access but is forced to be
+                  // public
+  };
+
+If the visibility is changed in this way, it can indicate bad design or
+programming error.
+
+If a virtual function is private in a subclass but public in the base class, it
+can still be accessed from a pointer to the subclass if the pointer is converted
+to the base type. Probably private inheritance can be used instead.
+
+A protected virtual function that is made public in a subclass may have valid
+use cases but similar (not exactly same) effect can be achieved with the
+``using`` keyword.
+
+Options
+-------
+
+.. option:: DisallowedVisibilityChange
+
+  Controls what kind of change to the visibility will be detected by the check.
+  Possible values are `any`, `widening`, `narrowing`. For example the
+  `widening` option will produce warning only if the visibility is changed
+  from more restrictive (``private``) to less restrictive (``public``).
+  Default value is `any`.
+
+.. option:: CheckDestructors
+
+  If turned on, the check does apply to destructors too. Otherwise destructors
+  are ignored by the check.
+  Default value is `false`.
+
+.. option:: CheckOperators
+
+  If turned on, the check does apply to overloaded C++ operators (as virtual
+  member functions) too. This includes other special member functions (like
+  conversions) too. This option is probably useful only in rare cases because
+  operators and conversions are not often virtual functions.
+  Default value is `false`.
+
+.. option:: IgnoredFunctions
+
+  This option can be used to ignore the check at specific functions.
+  To configure this option, a semicolon-separated list of function names
+  should be provided. The list can contain regular expressions, in this way it
+  is possible to select all functions of a specific class (like `MyClass::.*`)
+  or a specific function of any class (like `my_function` or
+  `::.*::my_function`). The function names are matched at the base class.
+  Default value is empty string.

clang-tools-extra/test/clang-tidy/checkers/misc/Inputs/visibility-change-to-virtual-function/test-system-header.h

@@ -0,0 +1,14 @@
+#pragma clang system_header
+
+namespace sys {
+
+struct Base {
+  virtual void publicF();
+};
+
+struct Derived: public Base {
+private:
+  void publicF() override;
+};
+
+}