[clang-tidy] add check cppcoreguidelines-pro-type-union-access

Summary:
This check flags all access to members of unions. Passing unions as a
whole is not flagged.

Reading from a union member assumes that member was the last one
written, and writing to a union member assumes another member with a
nontrivial destructor had its destructor called. This is fragile because
it cannot generally be enforced to be safe in the language and so relies
on programmer discipline to get it right.

This rule is part of the "Type safety" profile of the C++ Core
Guidelines, see
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#-type7-avoid-accessing-members-of-raw-unions-prefer-variant-instead

Reviewers: alexfh, sbenza, bkramer, aaron.ballman

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D13784

llvm-svn: 250537

4 files changed, 72 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt b/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
index 791ec0394ef..cd81c4f6147 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
@@ -6,6 +6,7 @@ add_clang_library(clangTidyCppCoreGuidelinesModule
   ProTypeConstCastCheck.cpp
   ProTypeReinterpretCastCheck.cpp
   ProTypeStaticCastDowncastCheck.cpp
+  ProTypeUnionAccessCheck.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 0d239ff1b98..3d517902660 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
@@ -16,6 +16,7 @@
 #include "ProTypeConstCastCheck.h"
 #include "ProTypeReinterpretCastCheck.h"
 #include "ProTypeStaticCastDowncastCheck.h"
+#include "ProTypeUnionAccessCheck.h"
 
 namespace clang {
 namespace tidy {
@@ -35,6 +36,8 @@ public:
         "cppcoreguidelines-pro-type-reinterpret-cast");
     CheckFactories.registerCheck<ProTypeStaticCastDowncastCheck>(
         "cppcoreguidelines-pro-type-static-cast-downcast");
+    CheckFactories.registerCheck<ProTypeUnionAccessCheck>(
+        "cppcoreguidelines-pro-type-union-access");
     CheckFactories.registerCheck<misc::AssignOperatorSignatureCheck>(
         "cppcoreguidelines-c-copy-assignment-signature");
   }
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.cpp
new file mode 100644
index 00000000000..64f51369bd3
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.cpp
@@ -0,0 +1,33 @@
+//===--- ProTypeUnionAccessCheck.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 "ProTypeUnionAccessCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+
+void ProTypeUnionAccessCheck::registerMatchers(MatchFinder *Finder) {
+  if (!getLangOpts().CPlusPlus)
+    return;
+
+  Finder->addMatcher(memberExpr(hasObjectExpression(hasType(recordDecl(isUnion())))).bind("expr"), this);
+}
+
+void ProTypeUnionAccessCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *Matched = Result.Nodes.getNodeAs<MemberExpr>("expr");
+  diag(Matched->getMemberLoc(), "do not access members of unions; use (boost::)variant instead");
+}
+
+} // namespace tidy
+} // namespace clang
+
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.h b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.h
new file mode 100644
index 00000000000..67ce6165811
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/ProTypeUnionAccessCheck.h
@@ -0,0 +1,35 @@
+//===--- ProTypeUnionAccessCheck.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_UNION_ACCESS_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CPPCOREGUIDELINES_PRO_TYPE_UNION_ACCESS_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+
+/// This check flags all access to members of unions.
+/// Access to a union as a whole (e.g. passing to a function) is not flagged.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines-pro-type-union-access.html
+class ProTypeUnionAccessCheck : public ClangTidyCheck {
+public:
+  ProTypeUnionAccessCheck(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_UNION_ACCESS_H
+