[clang-tidy] add new check cppcoreguidelines-pro-type-cstyle-cast

Summary:
This check flags all use of c-style casts that perform a static_cast
downcast, const_cast, or reinterpret_cast.

Use of these casts can violate type safety and cause the program to
access a
variable that is actually of type X to be accessed as if it were of an
unrelated type Z. Note that a C-style (T)expression cast means to
perform
the first of the following that is possible: a const_cast, a
static_cast, a
static_cast followed by a const_cast, a reinterpret_cast, or a
reinterpret_cast followed by a const_cast. This rule bans (T)expression
only when used to perform an unsafe 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#-type4-dont-use-c-style-texpression-casts-that-would-perform-a-static_cast-downcast-const_cast-or-reinterpret_cast.

Reviewers: alexfh, sbenza, bkramer, aaron.ballman

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D14096

llvm-svn: 252425

4 files changed, 145 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt b/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
index 506a90741ba..3bf729cbd10 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
@@ -5,6 +5,7 @@ add_clang_library(clangTidyCppCoreGuidelinesModule
   ProBoundsArrayToPointerDecayCheck.cpp
   ProBoundsPointerArithmeticCheck.cpp
   ProTypeConstCastCheck.cpp
+  ProTypeCstyleCastCheck.cpp
   ProTypeReinterpretCastCheck.cpp
   ProTypeStaticCastDowncastCheck.cpp
   ProTypeUnionAccessCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
index d77954b51a1..1ef55da14ab 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
@@ -14,6 +14,7 @@
 #include "ProBoundsArrayToPointerDecayCheck.h"
 #include "ProBoundsPointerArithmeticCheck.h"
 #include "ProTypeConstCastCheck.h"
+#include "ProTypeCstyleCastCheck.h"
 #include "ProTypeReinterpretCastCheck.h"
 #include "ProTypeStaticCastDowncastCheck.h"
 #include "ProTypeUnionAccessCheck.h"
@@ -33,6 +34,8 @@ public:
         "cppcoreguidelines-pro-bounds-pointer-arithmetic");
     CheckFactories.registerCheck<ProTypeConstCastCheck>(
         "cppcoreguidelines-pro-type-const-cast");
+    CheckFactories.registerCheck<ProTypeCstyleCastCheck>(
+        "cppcoreguidelines-pro-type-cstyle-cast");
     CheckFactories.registerCheck<ProTypeReinterpretCastCheck>(
         "cppcoreguidelines-pro-type-reinterpret-cast");
     CheckFactories.registerCheck<ProTypeStaticCastDowncastCheck>(
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeCstyleCastCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeCstyleCastCheck.cpp
new file mode 100644
index 00000000000..542dd854c43
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeCstyleCastCheck.cpp
@@ -0,0 +1,107 @@
+//===--- ProTypeCstyleCastCheck.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 "ProTypeCstyleCastCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+
+static bool needsConstCast(QualType SourceType, QualType DestType) {
+  SourceType = SourceType.getNonReferenceType();
+  DestType = DestType.getNonReferenceType();
+  while (SourceType->isPointerType() && DestType->isPointerType()) {
+    SourceType = SourceType->getPointeeType();
+    DestType = DestType->getPointeeType();
+    if (SourceType.isConstQualified() && !DestType.isConstQualified())
+      return true;
+  }
+  return false;
+}
+
+void ProTypeCstyleCastCheck::registerMatchers(MatchFinder *Finder) {
+  if (!getLangOpts().CPlusPlus)
+    return;
+
+  Finder->addMatcher(
+      cStyleCastExpr(unless(isInTemplateInstantiation())).bind("cast"), this);
+}
+
+void ProTypeCstyleCastCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *MatchedCast = Result.Nodes.getNodeAs<CStyleCastExpr>("cast");
+
+  if (MatchedCast->getCastKind() == CK_BitCast ||
+      MatchedCast->getCastKind() == CK_LValueBitCast ||
+      MatchedCast->getCastKind() == CK_IntegralToPointer ||
+      MatchedCast->getCastKind() == CK_PointerToIntegral ||
+      MatchedCast->getCastKind() == CK_ReinterpretMemberPointer) {
+    diag(MatchedCast->getLocStart(),
+         "do not use C-style cast to convert between unrelated types");
+    return;
+  }
+
+  QualType SourceType = MatchedCast->getSubExpr()->getType();
+
+  if (MatchedCast->getCastKind() == CK_BaseToDerived) {
+    const auto *SourceDecl = SourceType->getPointeeCXXRecordDecl();
+    if (!SourceDecl) // The cast is from object to reference.
+      SourceDecl = SourceType->getAsCXXRecordDecl();
+    if (!SourceDecl)
+      return;
+
+    if (SourceDecl->isPolymorphic()) {
+      // Leave type spelling exactly as it was (unlike
+      // getTypeAsWritten().getAsString() which would spell enum types 'enum
+      // X').
+      StringRef DestTypeString = Lexer::getSourceText(
+          CharSourceRange::getTokenRange(
+              MatchedCast->getLParenLoc().getLocWithOffset(1),
+              MatchedCast->getRParenLoc().getLocWithOffset(-1)),
+          *Result.SourceManager, Result.Context->getLangOpts());
+
+      auto diag_builder = diag(
+          MatchedCast->getLocStart(),
+          "do not use C-style cast to downcast from a base to a derived class; "
+          "use dynamic_cast instead");
+
+      const Expr *SubExpr =
+          MatchedCast->getSubExprAsWritten()->IgnoreImpCasts();
+      std::string CastText = ("dynamic_cast<" + DestTypeString + ">").str();
+      if (!isa<ParenExpr>(SubExpr)) {
+        CastText.push_back('(');
+        diag_builder << FixItHint::CreateInsertion(
+            Lexer::getLocForEndOfToken(SubExpr->getLocEnd(), 0,
+                                       *Result.SourceManager,
+                                       Result.Context->getLangOpts()),
+            ")");
+      }
+      auto ParenRange = CharSourceRange::getTokenRange(
+          MatchedCast->getLParenLoc(), MatchedCast->getRParenLoc());
+      diag_builder << FixItHint::CreateReplacement(ParenRange, CastText);
+    } else {
+      diag(
+          MatchedCast->getLocStart(),
+          "do not use C-style cast to downcast from a base to a derived class");
+    }
+    return;
+  }
+
+  if (MatchedCast->getCastKind() == CK_NoOp &&
+      needsConstCast(SourceType, MatchedCast->getType())) {
+    diag(MatchedCast->getLocStart(),
+         "do not use C-style cast to cast away constness");
+  }
+}
+
+} // namespace tidy
+} // namespace clang
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeCstyleCastCheck.h b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeCstyleCastCheck.h
new file mode 100644
index 00000000000..f85be87d93b
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeCstyleCastCheck.h
@@ -0,0 +1,34 @@
+//===--- ProTypeCstyleCastCheck.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_CSTYLE_CAST_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CPPCOREGUIDELINES_PRO_TYPE_CSTYLE_CAST_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+
+/// This check flags all use of C-style casts that perform a static_cast
+/// downcast, const_cast, or reinterpret_cast.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines-pro-type-cstyle-cast.html
+class ProTypeCstyleCastCheck : public ClangTidyCheck {
+public:
+  ProTypeCstyleCastCheck(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_CSTYLE_CAST_H