[clang-tidy] add check cppcoreguidelines-pro-type-const-cast

[mgehre]

Summary

This check flags all uses of const_cast in C++ code.

Modifying a variable that was declared const is undefined behavior, even
with const_cast.

This rule is part of the "Type safety" profile of the C++ Core
Guidelines, see
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#-type3-dont-use-const_cast-to-cast-away-const-ie-at-all.

Depends on D13313

[aaron.ballman]

LGTM, despite being bizarrely restrictive guidance.

~Aaron

[mgehre]

Rebased

[alexfh]

It looks like potentially we're going to have tens of checks in this module. I wonder whether we should start organizing the checks somehow right away. For example, create a directory (and a namespace) for each profile. We'd need to adapt the add_new_check.py script to support this then.

Just a thought. The patch LG.

[aaron.ballman]

Thanks for the patch! I've commit in r249540.

Given the number of checkers that you're working on, I would recommend getting commit privileges if you'd like them.

clang-tidy/cppcoreguidelines/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyCppCoreGuidelinesModule
   CppCoreGuidelinesTidyModule.cpp
+  ProTypeConstCastCheck.cpp
   ProTypeReinterpretCastCheck.cpp
 
   LINK_LIBS
   clangAST
   clangASTMatchers
   clangBasic
   clangLex
   clangTidy
   clangTidyUtils
   clangTooling
   )

clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp

 //===--- CppCoreGuidelinesModule.cpp - clang-tidy -------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "../ClangTidy.h"
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
+#include "ProTypeConstCastCheck.h"
 #include "ProTypeReinterpretCastCheck.h"
 
 namespace clang {
 namespace tidy {
 namespace cppcoreguidelines {
 
 class CppCoreGuidelinesModule : public ClangTidyModule {
 public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
+    CheckFactories.registerCheck<ProTypeConstCastCheck>(
+        "cppcoreguidelines-pro-type-const-cast");
     CheckFactories.registerCheck<ProTypeReinterpretCastCheck>(
         "cppcoreguidelines-pro-type-reinterpret-cast");
   }
 };
 
 // Register the LLVMTidyModule using this statically initialized variable.
 static ClangTidyModuleRegistry::Add<CppCoreGuidelinesModule>
     X("cppcoreguidelines-module", "Adds checks for the C++ Core Guidelines.");

clang-tidy/cppcoreguidelines/ProTypeConstCastCheck.h

+//===--- ProTypeConstCastCheck.h - clang-tidy--------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CPPCOREGUIDELINES_PRO_TYPE_CONST_CAST_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CPPCOREGUIDELINES_PRO_TYPE_CONST_CAST_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+
+/// This check flags all instances of const_cast
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines-pro-type-const-cast.html
+class ProTypeConstCastCheck : public ClangTidyCheck {
+public:
+  ProTypeConstCastCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CPPCOREGUIDELINES_PRO_TYPE_CONST_CAST_H
+

clang-tidy/cppcoreguidelines/ProTypeConstCastCheck.cpp

+//===--- ProTypeConstCastCheck.cpp - clang-tidy----------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ProTypeConstCastCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+
+void ProTypeConstCastCheck::registerMatchers(MatchFinder *Finder) {
+  if(!getLangOpts().CPlusPlus)
+    return;
+
+  Finder->addMatcher(cxxConstCastExpr().bind("cast"), this);
+}
+
+void ProTypeConstCastCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *MatchedCast = Result.Nodes.getNodeAs<CXXConstCastExpr>("cast");
+  diag(MatchedCast->getOperatorLoc(), "do not use const_cast");
+}
+
+} // namespace tidy
+} // namespace clang
+

docs/clang-tidy/checks/cppcoreguidelines-pro-type-const-cast.rst

+cppcoreguidelines-pro-type-const-cast
+=====================================
+
+This check flags all uses of const_cast in C++ code.
+
+Modifying a variable that was declared const is undefined behavior, even with const_cast.
+
+This rule is part of the "Type safety" profile of the C++ Core Guidelines, see
+https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#-type3-dont-use-const_cast-to-cast-away-const-ie-at-all.

docs/clang-tidy/checks/list.rst

 List of clang-tidy Checks
 =========================
 
 .. toctree::
    cert-variadic-function-def
+   cppcoreguidelines-pro-type-const-cast
    cppcoreguidelines-pro-type-reinterpret-cast
    google-build-explicit-make-pair
    google-build-namespaces
    google-build-using-namespace
    google-explicit-constructor
    google-global-names-in-headers
    google-readability-braces-around-statements
    google-readability-casting

test/clang-tidy/cppcoreguidelines-pro-type-const-cast.cpp

+// RUN: %python %S/check_clang_tidy.py %s cppcoreguidelines-pro-type-const-cast %t
+
+const int* i;
+int* j;
+void f() { j = const_cast<int*>(i); }
+// CHECK-MESSAGES: :[[@LINE-1]]:16: warning: do not use const_cast [cppcoreguidelines-pro-type-const-cast]