1 files changed, 89 insertions, 0 deletions
diff --git a/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp b/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp
new file mode 100644
index 00000000000..53cc0825b7a
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/misc/UnconventionalAssignOperatorCheck.cpp
@@ -0,0 +1,89 @@
+//===--- UnconventionalUnconventionalAssignOperatorCheck.cpp - clang-tidy -----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "UnconventionalAssignOperatorCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace misc {
+
+void UnconventionalAssignOperatorCheck::registerMatchers(ast_matchers::MatchFinder *Finder) {
+  // Only register the matchers for C++; the functionality currently does not
+  // provide any benefit to other languages, despite being benign.
+  if (!getLangOpts().CPlusPlus)
+    return;
+
+  const auto HasGoodReturnType = cxxMethodDecl(returns(
+      lValueReferenceType(pointee(unless(isConstQualified()),
+                                  hasDeclaration(equalsBoundNode("class"))))));
+
+  const auto IsSelf = qualType(
+      anyOf(hasDeclaration(equalsBoundNode("class")),
+            referenceType(pointee(hasDeclaration(equalsBoundNode("class"))))));
+  const auto IsAssign =
+      cxxMethodDecl(unless(anyOf(isDeleted(), isPrivate(), isImplicit())),
+                    hasName("operator="), ofClass(recordDecl().bind("class")))
+          .bind("method");
+  const auto IsSelfAssign =
+      cxxMethodDecl(IsAssign, hasParameter(0, parmVarDecl(hasType(IsSelf))))
+          .bind("method");
+
+  Finder->addMatcher(
+      cxxMethodDecl(IsAssign, unless(HasGoodReturnType)).bind("ReturnType"),
+      this);
+
+  const auto BadSelf = referenceType(
+      anyOf(lValueReferenceType(pointee(unless(isConstQualified()))),
+            rValueReferenceType(pointee(isConstQualified()))));
+
+  Finder->addMatcher(
+      cxxMethodDecl(IsSelfAssign,
+                    hasParameter(0, parmVarDecl(hasType(BadSelf))))
+          .bind("ArgumentType"),
+      this);
+
+  Finder->addMatcher(
+      cxxMethodDecl(IsSelfAssign, anyOf(isConst(), isVirtual())).bind("cv"),
+      this);
+
+  const auto IsBadReturnStatement = returnStmt(unless(has(
+      unaryOperator(hasOperatorName("*"), hasUnaryOperand(cxxThisExpr())))));
+  const auto IsGoodAssign = cxxMethodDecl(IsAssign, HasGoodReturnType);
+
+  Finder->addMatcher(returnStmt(IsBadReturnStatement, forFunction(IsGoodAssign))
+                         .bind("returnStmt"),
+                     this);
+}
+
+void UnconventionalAssignOperatorCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *RetStmt = Result.Nodes.getNodeAs<ReturnStmt>("returnStmt")) {
+    diag(RetStmt->getLocStart(), "operator=() should always return '*this'");
+  } else {
+    static const char *const Messages[][2] = {
+        {"ReturnType", "operator=() should return '%0&'"},
+        {"ArgumentType", "operator=() should take '%0 const&', '%0&&' or '%0'"},
+        {"cv", "operator=() should not be marked '%1'"}};
+
+    const auto *Method = Result.Nodes.getNodeAs<CXXMethodDecl>("method");
+    for (const auto &Message : Messages) {
+      if (Result.Nodes.getNodeAs<Decl>(Message[0]))
+        diag(Method->getLocStart(), Message[1])
+            << Method->getParent()->getName()
+            << (Method->isConst() ? "const" : "virtual");
+    }
+  }
+}
+
+} // namespace misc
+} // namespace tidy
+} // namespace clang