[Clang][Sema] Make lambda in non-dependent context generate same analysis-based warnings as function[ template]

clang/docs/ReleaseNotes.rst

@@ -312,6 +312,9 @@ Improvements to Clang's diagnostics
   properly being rejected when used at compile-time. It was not implemented
   and caused assertion failures before (#GH158471).
 
+- Some reachability-analysis-based warnings in lambda expression which is in
+  non-templated context are emitted same as in function[ template].
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Sema/Sema.h

@@ -1166,7 +1166,7 @@ class Sema final : public SemaBase {
   /// getCurFunctionOrMethodDecl - Return the Decl for the current ObjC method
   /// or C function we're in, otherwise return null.  If we're currently
   /// in a 'block', this returns the containing context.
-  NamedDecl *getCurFunctionOrMethodDecl() const;
+  NamedDecl *getCurFunctionOrMethodDecl(bool AllowLambda = false) const;
 
   /// Warn if we're implicitly casting from a _Nullable pointer type to a
   /// _Nonnull one.

clang/lib/Sema/Sema.cpp

@@ -1656,8 +1656,8 @@ ObjCMethodDecl *Sema::getCurMethodDecl() {
   return dyn_cast<ObjCMethodDecl>(DC);
 }
 
-NamedDecl *Sema::getCurFunctionOrMethodDecl() const {
-  DeclContext *DC = getFunctionLevelDeclContext();
+NamedDecl *Sema::getCurFunctionOrMethodDecl(bool AllowLambda) const {
+  DeclContext *DC = getFunctionLevelDeclContext(AllowLambda);
   if (isa<ObjCMethodDecl>(DC) || isa<FunctionDecl>(DC))
     return cast<NamedDecl>(DC);
   return nullptr;

clang/lib/Sema/SemaExpr.cpp

@@ -20542,7 +20542,7 @@ void Sema::MarkDeclarationsReferencedInExpr(Expr *E,
 ///        namespace { auto *p = new double[3][false ? (1, 2) : 3]; }
 bool Sema::DiagIfReachable(SourceLocation Loc, ArrayRef<const Stmt *> Stmts,
                            const PartialDiagnostic &PD) {
-  if (!Stmts.empty() && getCurFunctionOrMethodDecl()) {
+  if (!Stmts.empty() && getCurFunctionOrMethodDecl(/*AllowLambda=*/true)) {
     if (!FunctionScopes.empty())
       FunctionScopes.back()->PossiblyUnreachableDiags.push_back(
           sema::PossiblyUnreachableDiag(PD, Loc, Stmts));

clang/lib/Sema/SemaLambda.cpp

@@ -1972,6 +1972,10 @@ ExprResult Sema::ActOnLambdaExpr(SourceLocation StartLoc, Stmt *Body) {
   if (LSI.CallOperator->hasAttr<SYCLKernelEntryPointAttr>())
     SYCL().CheckSYCLEntryPointFunctionDecl(LSI.CallOperator);
 
+  // TODO: Find out if passing LSI.CallOperator->getDescribedFunctionTemplate()
+  //       is better when it is a generic lambda. Are there any behaviour
+  //       changes? `FunctionTemplateDecl` is always passed when handling simple
+  //       function templates.
   ActOnFinishFunctionBody(LSI.CallOperator, Body, /*IsInstantiation=*/false,
                           /*RetainFunctionScopeInfo=*/true);
 
@@ -2149,24 +2153,28 @@ ExprResult Sema::BuildLambdaExpr(SourceLocation StartLoc,
   CleanupInfo LambdaCleanup = LSI->Cleanup;
   bool ContainsUnexpandedParameterPack = LSI->ContainsUnexpandedParameterPack;
   bool IsGenericLambda = Class->isGenericLambda();
+  sema::AnalysisBasedWarnings::Policy WP =
+      AnalysisWarnings.getPolicyInEffectAt(EndLoc);
 
   CallOperator->setLexicalDeclContext(Class);
-  Decl *TemplateOrNonTemplateCallOperatorDecl =
-      CallOperator->getDescribedFunctionTemplate()
-          ? CallOperator->getDescribedFunctionTemplate()
-          : cast<Decl>(CallOperator);
+  Decl *TemplateOrNonTemplateCallOperatorDecl = CallOperator;
+  sema::AnalysisBasedWarnings::Policy *ActivePolicy = &WP;
+  if (IsGenericLambda) {
+    TemplateOrNonTemplateCallOperatorDecl =
+        CallOperator->getDescribedFunctionTemplate();
+    ActivePolicy = nullptr;
+  }
 
   // FIXME: Is this really the best choice? Keeping the lexical decl context
   // set as CurContext seems more faithful to the source.
   TemplateOrNonTemplateCallOperatorDecl->setLexicalDeclContext(Class);
 
   PopExpressionEvaluationContext();
 
-  sema::AnalysisBasedWarnings::Policy WP =
-      AnalysisWarnings.getPolicyInEffectAt(EndLoc);
   // We cannot release LSI until we finish computing captures, which
   // requires the scope to be popped.
-  Sema::PoppedFunctionScopePtr _ = PopFunctionScopeInfo(&WP, LSI->CallOperator);
+  Sema::PoppedFunctionScopePtr _ =
+      PopFunctionScopeInfo(ActivePolicy, TemplateOrNonTemplateCallOperatorDecl);
 
   // True if the current capture has a used capture or default before it.
   bool CurHasPreviousCapture = CaptureDefault != LCD_None;

clang/test/SemaCXX/warn-unused-value.cpp

@@ -178,3 +178,41 @@ auto b() {
 }
 } // namespace test6
 #endif
+
+#if __cplusplus >= 201402L
+// ensure lambda in non-dependent context generate same diagnostics as function[ template]
+namespace lambda_in_non_dependent_context {
+void f1() {
+  0, 0; // expected-warning {{left operand of comma operator has no effect}}
+  return;
+  0, 0;
+}
+template <typename T> void f2(T) {
+  0, 0; // expected-warning {{left operand of comma operator has no effect}}
+  return;
+  0, 0; // expected-warning {{left operand of comma operator has no effect}}
+}
+auto L1 = [] {
+  0, 0; // expected-warning {{left operand of comma operator has no effect}}
+  return;
+  0, 0;
+};
+auto L2 = [](auto) {
+  0, 0; // expected-warning {{left operand of comma operator has no effect}}
+  return;
+  0, 0; // expected-warning {{left operand of comma operator has no effect}}
+};
+void f() {
+  auto L1 = [] {
+    0, 0; // expected-warning {{left operand of comma operator has no effect}}
+    return;
+    0, 0;
+  };
+  auto L2 = [](auto) {
+    0, 0; // expected-warning {{left operand of comma operator has no effect}}
+    return;
+    0, 0; // expected-warning {{left operand of comma operator has no effect}}
+  };
+}
+}
+#endif