Another attempt to add a clang-tidy check for flagging C-style casts.

[alexfh]

Summary

The first version failed the SubstNonTypeTempateParmExpr-related test
on some buildbots. This one uses the new substNonTypeTempateParmExpr matcher to
filter out implicit C-style casts.

This patch depends on D4327.

[djasper]

Looks good, assuming that nothing else changed.

[dblaikie]

I don't see the initial email to the mailing list for this thread
(thus no patch was sent to the ML/archived/etc) - Manuel, Any idea why
this one got lost?

clang-tidy/google/AvoidCStyleCastsCheck.h

+//===--- AvoidCStyleCastsCheck.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_GOOGLE_AVOID_C_STYLE_CASTS_CHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_AVOID_C_STYLE_CASTS_CHECK_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+/// \brief Finds usages of C-style casts.
+///
+/// http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Casting#Casting
+/// Corresponding cpplint.py check name: 'readability/casting'.
+class AvoidCStyleCastsCheck : public ClangTidyCheck {
+public:
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_AVOID_C_STYLE_CASTS_CHECK_H

clang-tidy/google/AvoidCStyleCastsCheck.cpp

+//===--- AvoidCStyleCastsCheck.cpp - clang-tidy -----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AvoidCStyleCastsCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+void
+AvoidCStyleCastsCheck::registerMatchers(ast_matchers::MatchFinder *Finder) {
+  Finder->addMatcher(
+      cStyleCastExpr(
+          // Filter out (EnumType)IntegerLiteral construct, which is generated
+          // for non-type template arguments of enum types.
+          // FIXME: Remove this once this is fixed in the AST.
+          unless(hasParent(substNonTypeTemplateParmExpr()))).bind("cast"),
+      this);
+}
+
+void AvoidCStyleCastsCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *CastExpr = Result.Nodes.getNodeAs<CStyleCastExpr>("cast");
+
+  // Ignore casts in macros for now.
+  if (CastExpr->getLocStart().isMacroID())
+    return;
+
+  // Casting to void is an idiomatic way to mute "unused variable" and similar
+  // warnings.
+  if (CastExpr->getTypeAsWritten()->isVoidType())
+    return;
+
+  diag(CastExpr->getLocStart(), "C-style casts are discouraged. Use "
+                                "static_cast/const_cast/reinterpret_cast "
+                                "instead.");
+  // FIXME: Suggest appropriate C++ cast. See [expr.cast] for cast notation
+  // semantics.
+}
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang

clang-tidy/google/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyGoogleModule
+  AvoidCStyleCastsCheck.cpp
   ExplicitConstructorCheck.cpp
   GoogleTidyModule.cpp
 
   LINK_LIBS
   clangAST
   clangASTMatchers
   clangBasic
   clangTidy
   )

clang-tidy/google/GoogleTidyModule.cpp

 //===--- GoogleTidyModule.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 "AvoidCStyleCastsCheck.h"
 #include "ExplicitConstructorCheck.h"
 
 using namespace clang::ast_matchers;
 
 namespace clang {
 namespace tidy {
 
 class GoogleModule : public ClangTidyModule {
 public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.addCheckFactory(
         "google-explicit-constructor",
         new ClangTidyCheckFactory<ExplicitConstructorCheck>());
+    CheckFactories.addCheckFactory(
+        "google-readability-casting",
+        new ClangTidyCheckFactory<readability::AvoidCStyleCastsCheck>());
   }
 };
 
 // Register the GoogleTidyModule using this statically initialized variable.
 static ClangTidyModuleRegistry::Add<GoogleModule> X("google-module",
                                                     "Adds Google lint checks.");
 
 // This anchor is used to force the linker to link in the generated object file
 // and thus register the GoogleModule.
 volatile int GoogleModuleAnchorSource = 0;
 
 } // namespace tidy
 } // namespace clang

test/clang-tidy/avoid-c-style-casts.cpp

+// RUN: clang-tidy -checks=-*,google-readability-casting %s -- | FileCheck %s
+
+// CHECK-NOT: warning:
+
+bool g() { return false; }
+
+void f(int a, double b) {
+  int b1 = (int)b;
+  // CHECK: :[[@LINE-1]]:12: warning: C-style casts are discouraged. Use static_cast{{.*}}
+
+  // CHECK-NOT: warning:
+  int b2 = int(b);
+  int b3 = static_cast<double>(b);
+  int b4 = b;
+  double aa = a;
+  (void)b2;
+  return (void)g();
+}
+
+// CHECK-NOT: warning:
+enum E { E1 = 1 };
+template <E e>
+struct A { static const E ee = e; };
+struct B : public A<E1> {};