1 files changed, 125 insertions, 0 deletions
diff --git a/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp b/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp
new file mode 100644
index 00000000000..c5632a7301e
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+++ b/clang-tools-extra/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