1 files changed, 57 insertions, 0 deletions
diff --git a/build/clang-plugin/alpha/TempRefPtrChecker.cpp b/build/clang-plugin/alpha/TempRefPtrChecker.cpp
new file mode 100644
index 0000000000..0a4d078368
--- /dev/null
+++ b/build/clang-plugin/alpha/TempRefPtrChecker.cpp
@@ -0,0 +1,57 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "TempRefPtrChecker.h"
+#include "CustomMatchers.h"
+
+constexpr const char *kCallExpr = "call-expr";
+constexpr const char *kOperatorCallExpr = "operator-call";
+
+void TempRefPtrChecker::registerMatchers(MatchFinder *AstMatcher) {
+  AstMatcher->addMatcher(
+      cxxOperatorCallExpr(
+          hasOverloadedOperatorName("->"),
+          hasAnyArgument(implicitCastExpr(
+              hasSourceExpression(materializeTemporaryExpr(anyOf(
+                  hasDescendant(callExpr().bind(kCallExpr)), anything()))))),
+          callee(hasDeclContext(classTemplateSpecializationDecl(
+              isSmartPtrToRefCountedDecl(),
+              // ignore any calls on temporary RefPtr<MozPromise<T>>,
+              // since these typically need to be locally ref-counted,
+              // e.g. in Then chains where the promise might be resolved
+              // concurrently
+              unless(hasTemplateArgument(
+                  0, refersToType(hasDeclaration(
+                         cxxRecordDecl(hasName("mozilla::MozPromise"))))))))))
+          .bind(kOperatorCallExpr),
+      this);
+}
+
+void TempRefPtrChecker::check(const MatchFinder::MatchResult &Result) {
+  const auto *OCE =
+      Result.Nodes.getNodeAs<CXXOperatorCallExpr>(kOperatorCallExpr);
+
+  const auto *refPtrDecl =
+      dyn_cast<const CXXRecordDecl>(OCE->getCalleeDecl()->getDeclContext());
+
+  diag(OCE->getOperatorLoc(),
+       "performance issue: temporary %0 is only dereferenced here once which "
+       "involves short-lived AddRef/Release calls")
+      << refPtrDecl;
+
+  const auto *InnerCE = Result.Nodes.getNodeAs<CallExpr>(kCallExpr);
+  if (InnerCE) {
+    const auto functionName =
+        InnerCE->getCalleeDecl()->getAsFunction()->getQualifiedNameAsString();
+
+    if (functionName != "mozilla::MakeRefPtr") {
+      diag(
+          OCE->getOperatorLoc(),
+          "consider changing function %0 to return a raw reference instead (be "
+          "sure that the pointee is held alive by someone else though!)",
+          DiagnosticIDs::Note)
+          << functionName;
+    }
+  }
+}