[clang-tidy] add check cppcoreguidelines-pro-type-static-cast-downcast

Summary:
This check flags all usages of static_cast, where a base class is casted
to a derived class.
In those cases, a fixit is provided to convert the cast to a
dynamic_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.

This rule is part of the "Type safety" profile of the C++ Core
Guidelines, see
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#-type2-dont-use-static_cast-downcasts-use-dynamic_cast-instead

Depends on D13313

Reviewers: alexfh, sbenza, bkramer, aaron.ballman

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D13368

llvm-svn: 250098

4 files changed, 89 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt b/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
index 5a83b3fef08..d35b9a56f94 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
@@ -4,6 +4,7 @@ add_clang_library(clangTidyCppCoreGuidelinesModule
   CppCoreGuidelinesTidyModule.cpp
   ProTypeConstCastCheck.cpp
   ProTypeReinterpretCastCheck.cpp
+  ProTypeStaticCastDowncastCheck.cpp
 
   LINK_LIBS
   clangAST
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
index 130eabe29f1..358bd6ec8fd 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
@@ -12,6 +12,7 @@
 #include "../ClangTidyModuleRegistry.h"
 #include "ProTypeConstCastCheck.h"
 #include "ProTypeReinterpretCastCheck.h"
+#include "ProTypeStaticCastDowncastCheck.h"
 
 namespace clang {
 namespace tidy {
@@ -25,6 +26,8 @@ public:
         "cppcoreguidelines-pro-type-const-cast");
     CheckFactories.registerCheck<ProTypeReinterpretCastCheck>(
         "cppcoreguidelines-pro-type-reinterpret-cast");
+    CheckFactories.registerCheck<ProTypeStaticCastDowncastCheck>(
+        "cppcoreguidelines-pro-type-static-cast-downcast");
   }
 };
 
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeStaticCastDowncastCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeStaticCastDowncastCheck.cpp
new file mode 100644
index 00000000000..0033e4ed9d3
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeStaticCastDowncastCheck.cpp
@@ -0,0 +1,52 @@
+//===--- ProTypeStaticCastDowncastCheck.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 "ProTypeStaticCastDowncastCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+
+void ProTypeStaticCastDowncastCheck::registerMatchers(MatchFinder *Finder) {
+  if (!getLangOpts().CPlusPlus)
+    return;
+
+  Finder->addMatcher(
+      cxxStaticCastExpr(unless(isInTemplateInstantiation())).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();
+  if (!SourceDecl) // The cast is from object to reference
+    SourceDecl = SourceType->getAsCXXRecordDecl();
+  if (!SourceDecl)
+    return;
+
+  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");
+}
+
+} // namespace tidy
+} // namespace clang
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeStaticCastDowncastCheck.h b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeStaticCastDowncastCheck.h
new file mode 100644
index 00000000000..02de48ae957
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeStaticCastDowncastCheck.h
@@ -0,0 +1,33 @@
+//===--- ProTypeStaticCastDowncastCheck.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_STATIC_CAST_DOWNCAST_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CPPCOREGUIDELINES_PRO_TYPE_STATIC_CAST_DOWNCAST_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+
+/// Checks for usages of static_cast, where a base class is downcasted to a derived class.
+///
+/// For the user-facing documentation see:
+/// 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) {}
+  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_STATIC_CAST_DOWNCAST_H