[clang] Don't warn if the capturing object is also temporary.

Author: hokein

clang/lib/Sema/SemaChecking.cpp

@@ -3248,9 +3248,13 @@ void Sema::checkLifetimeCaptureBy(FunctionDecl *FD, bool IsMemberFunction,
       checkCaptureByLifetime(*this, CE, Captured);
     }
   };
-  for (unsigned I = 0; I < FD->getNumParams(); ++I)
-    HandleCaptureByAttr(FD->getParamDecl(I)->getAttr<LifetimeCaptureByAttr>(),
-                        I + IsMemberFunction);
+  // Suppress the warning if the capturing object is also a temporary to reduce
+  // noise, e.g `vector<string_view>().push_back(std::string());`.
+  if (!isa_and_present<MaterializeTemporaryExpr>(ThisArg)) {
+    for (unsigned I = 0; I < FD->getNumParams(); ++I)
+      HandleCaptureByAttr(FD->getParamDecl(I)->getAttr<LifetimeCaptureByAttr>(),
+                          I + IsMemberFunction);
+  }
   // Check when the implicit object param is captured.
   if (IsMemberFunction) {
     TypeSourceInfo *TSI = FD->getTypeSourceInfo();

clang/test/Sema/warn-lifetime-analysis-capture-by.cpp

@@ -143,6 +143,17 @@ void use() {
 }
 } // namespace this_is_captured
 
+namespace ignore_temporary_class_object {
+struct S {
+  void add(const int& x [[clang::lifetime_capture_by(this)]]);
+};
+
+void test() {
+  S().add(1);
+  S{}.add(1);
+}
+} // namespace ignore_temporary_class_object
+
 // ****************************************************************************
 // Capture by Global and Unknown.
 // ****************************************************************************