[clang-tidy] Add StrictMode to cppcoreguidelines-pro-type-static-cast-downcast (#69529)

Add StrictMode option that controls behavior whatever
warnings are emitted for casts on non-polymorphic types.

Fixes: #69414

Author: PiotrZSL

clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeStaticCastDowncastCheck.cpp

@@ -14,17 +14,24 @@ using namespace clang::ast_matchers;
 
 namespace clang::tidy::cppcoreguidelines {
 
+ProTypeStaticCastDowncastCheck::ProTypeStaticCastDowncastCheck(
+    StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      StrictMode(Options.getLocalOrGlobal("StrictMode", true)) {}
+
+void ProTypeStaticCastDowncastCheck::storeOptions(
+    ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "StrictMode", StrictMode);
+}
+
 void ProTypeStaticCastDowncastCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
-      cxxStaticCastExpr(unless(isInTemplateInstantiation())).bind("cast"),
-      this);
+      cxxStaticCastExpr(hasCastKind(CK_BaseToDerived)).bind("cast"), this);
 }
 
 void ProTypeStaticCastDowncastCheck::check(
     const MatchFinder::MatchResult &Result) {
   const auto *MatchedCast = Result.Nodes.getNodeAs<CXXStaticCastExpr>("cast");
-  if (MatchedCast->getCastKind() != CK_BaseToDerived)
-    return;
 
   QualType SourceType = MatchedCast->getSubExpr()->getType();
   const auto *SourceDecl = SourceType->getPointeeCXXRecordDecl();
@@ -33,15 +40,20 @@ void ProTypeStaticCastDowncastCheck::check(
   if (!SourceDecl)
     return;
 
-  if (SourceDecl->isPolymorphic())
+  if (SourceDecl->isPolymorphic()) {
     diag(MatchedCast->getOperatorLoc(),
          "do not use static_cast to downcast from a base to a derived class; "
          "use dynamic_cast instead")
         << FixItHint::CreateReplacement(MatchedCast->getOperatorLoc(),
                                         "dynamic_cast");
-  else
-    diag(MatchedCast->getOperatorLoc(),
-         "do not use static_cast to downcast from a base to a derived class");
+    return;
+  }
+
+  if (!StrictMode)
+    return;
+
+  diag(MatchedCast->getOperatorLoc(),
+       "do not use static_cast to downcast from a base to a derived class");
 }
 
 } // namespace clang::tidy::cppcoreguidelines

clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeStaticCastDowncastCheck.h

@@ -20,13 +20,19 @@ namespace clang::tidy::cppcoreguidelines {
 /// http://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines/pro-type-static-cast-downcast.html
 class ProTypeStaticCastDowncastCheck : public ClangTidyCheck {
 public:
-  ProTypeStaticCastDowncastCheck(StringRef Name, ClangTidyContext *Context)
-      : ClangTidyCheck(Name, Context) {}
+  ProTypeStaticCastDowncastCheck(StringRef Name, ClangTidyContext *Context);
   bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
     return LangOpts.CPlusPlus;
   }
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+  std::optional<TraversalKind> getCheckTraversalKind() const override {
+    return TK_IgnoreUnlessSpelledInSource;
+  }
+
+private:
+  const bool StrictMode;
 };
 
 } // namespace clang::tidy::cppcoreguidelines

clang-tools-extra/docs/ReleaseNotes.rst

@@ -269,6 +269,11 @@ Changes in existing checks
   <clang-tidy/checks/cppcoreguidelines/pro-type-member-init>` check to ignore
   dependent delegate constructors.
 
+- Improved :doc:`cppcoreguidelines-pro-type-static-cast-downcast
+  <clang-tidy/checks/cppcoreguidelines/pro-type-static-cast-downcast>` check to
+  disregard casts on non-polymorphic types when the `StrictMode` option is set
+  to `false`.
+
 - Improved :doc:`cppcoreguidelines-pro-type-vararg
   <clang-tidy/checks/cppcoreguidelines/pro-type-vararg>` check to ignore
   false-positives in unevaluated context (e.g., ``decltype``, ``sizeof``, ...).

clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/pro-type-static-cast-downcast.rst

@@ -14,3 +14,11 @@ unrelated type ``Z``.
 This rule is part of the `Type safety (Type.2)
 <https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Pro-type-downcast>`_
 profile from the C++ Core Guidelines.
+
+Options
+-------
+
+.. option:: StrictMode
+
+  When set to `false`, no warnings are emitted for casts on non-polymorphic
+  types. Default is `true`.

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/pro-type-static-cast-downcast.cpp

@@ -1,4 +1,5 @@
-// RUN: %check_clang_tidy %s cppcoreguidelines-pro-type-static-cast-downcast %t
+// RUN: %check_clang_tidy  -check-suffixes=NSTRICT,STRICT %s cppcoreguidelines-pro-type-static-cast-downcast %t
+// RUN: %check_clang_tidy  -check-suffix=NSTRICT %s cppcoreguidelines-pro-type-static-cast-downcast %t -- -config="{CheckOptions: {StrictMode: false}}"
 
 class Base {
 };
@@ -26,11 +27,11 @@ class PolymorphicMultiDerived : public Base, public PolymorphicBase {
 void pointers() {
 
   auto P0 = static_cast<Derived*>(new Base());
-  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-MESSAGES-STRICT: :[[@LINE-1]]:13: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
 
   const Base* B0;
   auto PC0 = static_cast<const Derived*>(B0);
-  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-MESSAGES-STRICT: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
 
   auto P1 = static_cast<Base*>(new Derived()); // OK, upcast to a public base
   auto P2 = static_cast<Base*>(new MultiDerived()); // OK, upcast to a public base
@@ -40,13 +41,13 @@ void pointers() {
 void pointers_polymorphic() {
 
   auto PP0 = static_cast<PolymorphicDerived*>(new PolymorphicBase());
-  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead [cppcoreguidelines-pro-type-static-cast-downcast]
-  // CHECK-FIXES: auto PP0 = dynamic_cast<PolymorphicDerived*>(new PolymorphicBase());
+  // CHECK-MESSAGES-NSTRICT: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-FIXES-NSTRICT: auto PP0 = dynamic_cast<PolymorphicDerived*>(new PolymorphicBase());
 
   const PolymorphicBase* B0;
   auto PPC0 = static_cast<const PolymorphicDerived*>(B0);
-  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead [cppcoreguidelines-pro-type-static-cast-downcast]
-  // CHECK-FIXES: auto PPC0 = dynamic_cast<const PolymorphicDerived*>(B0);
+  // CHECK-MESSAGES-NSTRICT: :[[@LINE-1]]:15: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-FIXES-NSTRICT: auto PPC0 = dynamic_cast<const PolymorphicDerived*>(B0);
 
 
   auto B1 = static_cast<PolymorphicBase*>(new PolymorphicDerived()); // OK, upcast to a public base
@@ -57,27 +58,27 @@ void pointers_polymorphic() {
 void arrays() {
   Base ArrayOfBase[10];
   auto A0 = static_cast<Derived*>(ArrayOfBase);
-  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-MESSAGES-STRICT: :[[@LINE-1]]:13: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
 }
 
 void arrays_polymorphic() {
   PolymorphicBase ArrayOfPolymorphicBase[10];
   auto AP0 = static_cast<PolymorphicDerived*>(ArrayOfPolymorphicBase);
-  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead
-  // CHECK-FIXES: auto AP0 = dynamic_cast<PolymorphicDerived*>(ArrayOfPolymorphicBase);
+  // CHECK-MESSAGES-NSTRICT: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead
+  // CHECK-FIXES-NSTRICT: auto AP0 = dynamic_cast<PolymorphicDerived*>(ArrayOfPolymorphicBase);
 }
 
 void references() {
   Base B0;
   auto R0 = static_cast<Derived&>(B0);
-  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-MESSAGES-STRICT: :[[@LINE-1]]:13: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
   Base& RefToBase = B0;
   auto R1 = static_cast<Derived&>(RefToBase);
-  // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-MESSAGES-STRICT: :[[@LINE-1]]:13: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
 
   const Base& ConstRefToBase = B0;
   auto RC1 = static_cast<const Derived&>(ConstRefToBase);
-  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-MESSAGES-STRICT: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class [cppcoreguidelines-pro-type-static-cast-downcast]
 
 
   Derived RD1;
@@ -87,18 +88,18 @@ void references() {
 void references_polymorphic() {
   PolymorphicBase B0;
   auto RP0 = static_cast<PolymorphicDerived&>(B0);
-  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead
-  // CHECK-FIXES: auto RP0 = dynamic_cast<PolymorphicDerived&>(B0);
+  // CHECK-MESSAGES-NSTRICT: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead
+  // CHECK-FIXES-NSTRICT: auto RP0 = dynamic_cast<PolymorphicDerived&>(B0);
 
   PolymorphicBase& RefToPolymorphicBase = B0;
   auto RP1 = static_cast<PolymorphicDerived&>(RefToPolymorphicBase);
-  // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead [cppcoreguidelines-pro-type-static-cast-downcast]
-  // CHECK-FIXES: auto RP1 = dynamic_cast<PolymorphicDerived&>(RefToPolymorphicBase);
+  // CHECK-MESSAGES-NSTRICT: :[[@LINE-1]]:14: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-FIXES-NSTRICT: auto RP1 = dynamic_cast<PolymorphicDerived&>(RefToPolymorphicBase);
 
   const PolymorphicBase& ConstRefToPolymorphicBase = B0;
   auto RPC2 = static_cast<const PolymorphicDerived&>(ConstRefToPolymorphicBase);
-  // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead [cppcoreguidelines-pro-type-static-cast-downcast]
-  // CHECK-FIXES: auto RPC2 = dynamic_cast<const PolymorphicDerived&>(ConstRefToPolymorphicBase);
+  // CHECK-MESSAGES-NSTRICT: :[[@LINE-1]]:15: warning: do not use static_cast to downcast from a base to a derived class; use dynamic_cast instead [cppcoreguidelines-pro-type-static-cast-downcast]
+  // CHECK-FIXES-NSTRICT: auto RPC2 = dynamic_cast<const PolymorphicDerived&>(ConstRefToPolymorphicBase);
 
   PolymorphicDerived d1;
   auto RP2 = static_cast<PolymorphicBase&>(d1); // OK, upcast to a public base