[clang-tidy] Adding Fuchsia checker for multiple inheritance

Adds a check to the Fuchsia module to warn when a class
inherits from multiple classes that are not pure virtual.

See https://fuchsia.googlesource.com/zircon/+/master/docs/cxx.md
for reference.

Differential Revision: https://reviews.llvm.org/D40580

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@323011 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 177 insertions, 0 deletions

diff --git a/clang-tidy/fuchsia/CMakeLists.txt b/clang-tidy/fuchsia/CMakeLists.txt
index 25da1394..0dfc04ee 100644
--- a/clang-tidy/fuchsia/CMakeLists.txt
+++ b/clang-tidy/fuchsia/CMakeLists.txt
@@ -3,6 +3,7 @@ set(LLVM_LINK_COMPONENTS support)
 add_clang_library(clangTidyFuchsiaModule
   DefaultArgumentsCheck.cpp
   FuchsiaTidyModule.cpp
+  MultipleInheritanceCheck.cpp
   OverloadedOperatorCheck.cpp
   StaticallyConstructedObjectsCheck.cpp
   TrailingReturnCheck.cpp
diff --git a/clang-tidy/fuchsia/FuchsiaTidyModule.cpp b/clang-tidy/fuchsia/FuchsiaTidyModule.cpp
index 0eed7407..59c63893 100644
--- a/clang-tidy/fuchsia/FuchsiaTidyModule.cpp
+++ b/clang-tidy/fuchsia/FuchsiaTidyModule.cpp
@@ -11,6 +11,7 @@
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
 #include "DefaultArgumentsCheck.h"
+#include "MultipleInheritanceCheck.h"
 #include "OverloadedOperatorCheck.h"
 #include "StaticallyConstructedObjectsCheck.h"
 #include "TrailingReturnCheck.h"
@@ -28,6 +29,8 @@ public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.registerCheck<DefaultArgumentsCheck>(
         "fuchsia-default-arguments");
+    CheckFactories.registerCheck<MultipleInheritanceCheck>(
+        "fuchsia-multiple-inheritance");
     CheckFactories.registerCheck<OverloadedOperatorCheck>(
         "fuchsia-overloaded-operator");
     CheckFactories.registerCheck<StaticallyConstructedObjectsCheck>(
diff --git a/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp b/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp
new file mode 100644
index 00000000..c5632a73
--- /dev/null
+++ b/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp
@@ -0,0 +1,125 @@
+//===--- MultipleInheritanceCheck.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 "MultipleInheritanceCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang;
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace fuchsia {
+  
+AST_MATCHER(CXXRecordDecl, hasBases) {
+  if (Node.hasDefinition())
+    return Node.getNumBases() > 0;
+  return false;
+}
+
+// Adds a node (by name) to the interface map, if it was not present in the map
+// previously.
+void MultipleInheritanceCheck::addNodeToInterfaceMap(const CXXRecordDecl *Node,
+                                                     bool isInterface) {
+  StringRef Name = Node->getIdentifier()->getName();
+  InterfaceMap.insert(std::make_pair(Name, isInterface));
+}
+
+// Returns "true" if the boolean "isInterface" has been set to the
+// interface status of the current Node. Return "false" if the
+// interface status for the current node is not yet known.
+bool MultipleInheritanceCheck::getInterfaceStatus(const CXXRecordDecl *Node,
+                                                  bool &isInterface) const {
+  StringRef Name = Node->getIdentifier()->getName();
+  llvm::StringMapConstIterator<bool> Pair = InterfaceMap.find(Name);
+  if (Pair == InterfaceMap.end())
+    return false;
+  isInterface = Pair->second;
+  return true;
+}
+
+bool MultipleInheritanceCheck::isCurrentClassInterface(
+    const CXXRecordDecl *Node) const {
+  // Interfaces should have no fields.
+  if (!Node->field_empty()) return false;
+
+  // Interfaces should have exclusively pure methods.
+  return llvm::none_of(Node->methods(), [](const CXXMethodDecl *M) {
+    return M->isUserProvided() && !M->isPure() && !M->isStatic();
+  });
+}
+
+bool MultipleInheritanceCheck::isInterface(const CXXRecordDecl *Node) {
+  // Short circuit the lookup if we have analyzed this record before.
+  bool PreviousIsInterfaceResult;
+  if (getInterfaceStatus(Node, PreviousIsInterfaceResult))
+    return PreviousIsInterfaceResult;
+
+  // To be an interface, all base classes must be interfaces as well.
+  for (const auto &I : Node->bases()) {
+    if (I.isVirtual()) continue;  
+    const auto *Ty = I.getType()->getAs<RecordType>();
+    assert(Ty && "RecordType of base class is unknown");
+    const RecordDecl *D = Ty->getDecl()->getDefinition();
+    if (!D) continue;
+    const auto *Base = cast<CXXRecordDecl>(D);
+    if (!isInterface(Base)) {
+      addNodeToInterfaceMap(Node, false);
+      return false;
+    }
+  }
+
+  bool CurrentClassIsInterface = isCurrentClassInterface(Node);
+  addNodeToInterfaceMap(Node, CurrentClassIsInterface);
+  return CurrentClassIsInterface;
+}
+
+void MultipleInheritanceCheck::registerMatchers(MatchFinder *Finder) {
+  // Requires C++.
+  if (!getLangOpts().CPlusPlus)
+    return;
+
+  // Match declarations which have bases.
+  Finder->addMatcher(cxxRecordDecl(hasBases()).bind("decl"), this);
+}
+
+void MultipleInheritanceCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *D = Result.Nodes.getNodeAs<CXXRecordDecl>("decl")) {
+    // Check against map to see if if the class inherits from multiple
+    // concrete classes
+    unsigned NumConcrete = 0;
+    for (const auto &I : D->bases()) {
+      if (I.isVirtual()) continue;
+      const auto *Ty = I.getType()->getAs<RecordType>();
+      assert(Ty && "RecordType of base class is unknown");
+      const auto *Base = cast<CXXRecordDecl>(Ty->getDecl()->getDefinition());
+      if (!isInterface(Base)) NumConcrete++;
+    }
+    
+    // Check virtual bases to see if there is more than one concrete 
+    // non-virtual base.
+    for (const auto &V : D->vbases()) {
+      const auto *Ty = V.getType()->getAs<RecordType>();
+      assert(Ty && "RecordType of base class is unknown");
+      const auto *Base = cast<CXXRecordDecl>(Ty->getDecl()->getDefinition());
+      if (!isInterface(Base)) NumConcrete++;
+    }
+
+    if (NumConcrete > 1) {
+      diag(D->getLocStart(),
+           "inheriting mulitple classes that aren't "
+           "pure virtual is discouraged");
+    }
+  }
+}
+
+}  // namespace fuchsia
+}  // namespace tidy
+}  // namespace clang
diff --git a/clang-tidy/fuchsia/MultipleInheritanceCheck.h b/clang-tidy/fuchsia/MultipleInheritanceCheck.h
new file mode 100644
index 00000000..6250e3ec
--- /dev/null
+++ b/clang-tidy/fuchsia/MultipleInheritanceCheck.h
@@ -0,0 +1,48 @@
+//===--- MultipleInheritanceCheck.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_FUCHSIA_MULTIPLE_INHERITANCE_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_FUCHSIA_MULTIPLE_INHERITANCE_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace fuchsia {
+
+/// Mulitple implementation inheritance is discouraged.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/fuchsia-multiple-inheritance.html
+class MultipleInheritanceCheck : public ClangTidyCheck {
+public:
+  MultipleInheritanceCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+
+  void onEndOfTranslationUnit() override { InterfaceMap.clear(); }
+
+private:
+  void addNodeToInterfaceMap(const CXXRecordDecl *Node, bool isInterface);
+  bool getInterfaceStatus(const CXXRecordDecl *Node, bool &isInterface) const;
+  bool isCurrentClassInterface(const CXXRecordDecl *Node) const;
+  bool isInterface(const CXXRecordDecl *Node);
+
+  // Contains the identity of each named CXXRecord as an interface.  This is
+  // used to memoize lookup speeds and improve performance from O(N^2) to O(N),
+  // where N is the number of classes.
+  llvm::StringMap<bool> InterfaceMap;
+};
+
+} // namespace fuchsia
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_FUCHSIA_MULTIPLE_INHERITANCE_H