[clang] [Clang] SemaFunctionEffects: Fix bug where lambdas produced by template expansion weren't verified. (PR #116505)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Doug Wyatt (dougsonos)

<details>
<summary>Changes</summary>

Lambdas are added to the list of Decls to verify using `Sema::maybeAddDeclWithEffects()`. Up until now this call was in  `ActOnLambdaExpr`, which happens in the context of a template but not in the context of template expansion.

Template expansion calls `BuildLambdaExpr`, so move the call to `Sema::maybeAddDeclWithEffects()` there.

Fixing this created a not-previously-seen situation where the custom "In template expansion here" diagnostic didn't have a valid location. This breaks tests because there's a note with no location. For now I've just skipped emitting the diagnostic but maybe there's a better solution.

---
Full diff: https://github.com/llvm/llvm-project/pull/116505.diff


3 Files Affected:

- (modified) clang/lib/Sema/SemaFunctionEffects.cpp (+2-1) 
- (modified) clang/lib/Sema/SemaLambda.cpp (+1-2) 
- (modified) clang/test/Sema/attr-nonblocking-constraints.cpp (+17) 


``````````diff
diff --git a/clang/lib/Sema/SemaFunctionEffects.cpp b/clang/lib/Sema/SemaFunctionEffects.cpp
index 4b5ddb74b1262f..6fe4d2353a2282 100644
--- a/clang/lib/Sema/SemaFunctionEffects.cpp
+++ b/clang/lib/Sema/SemaFunctionEffects.cpp
@@ -807,7 +807,8 @@ class Analyzer {
 
     auto MaybeAddTemplateNote = [&](const Decl *D) {
       if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
-        while (FD != nullptr && FD->isTemplateInstantiation()) {
+        while (FD != nullptr && FD->isTemplateInstantiation() &&
+               FD->getPointOfInstantiation().isValid()) {
           S.Diag(FD->getPointOfInstantiation(),
                  diag::note_func_effect_from_template);
           FD = FD->getTemplateInstantiationPattern();
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index e7afa0f4c81fc4..a67c0b2b367d1a 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -1950,8 +1950,6 @@ ExprResult Sema::ActOnLambdaExpr(SourceLocation StartLoc, Stmt *Body) {
   LambdaScopeInfo LSI = *cast<LambdaScopeInfo>(FunctionScopes.back());
   ActOnFinishFunctionBody(LSI.CallOperator, Body);
 
-  maybeAddDeclWithEffects(LSI.CallOperator);
-
   return BuildLambdaExpr(StartLoc, Body->getEndLoc(), &LSI);
 }
 
@@ -2284,6 +2282,7 @@ ExprResult Sema::BuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
     case ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed:
       break;
     }
+    maybeAddDeclWithEffects(LSI->CallOperator);
   }
 
   return MaybeBindToTemporary(Lambda);
diff --git a/clang/test/Sema/attr-nonblocking-constraints.cpp b/clang/test/Sema/attr-nonblocking-constraints.cpp
index cc9108c0a4fbd6..87cbcc9713859f 100644
--- a/clang/test/Sema/attr-nonblocking-constraints.cpp
+++ b/clang/test/Sema/attr-nonblocking-constraints.cpp
@@ -144,6 +144,23 @@ void nb9() [[clang::nonblocking]]
 		expected-note {{in template expansion here}}
 }
 
+// Make sure we verify lambdas produced from template expansions.
+struct HasTemplatedLambda {
+	void (*fptr)() [[clang::nonblocking]];
+
+	template <typename C>
+	HasTemplatedLambda(const C&)
+		: fptr{ []() [[clang::nonblocking]] {
+			auto* y = new int; // expected-warning {{lambda with 'nonblocking' attribute must not allocate or deallocate memory}}
+		} }
+	{}
+};
+
+void nb9a()
+{
+	HasTemplatedLambda bad(42);
+}
+
 void nb10(
 	void (*fp1)(), // expected-note {{function pointer cannot be inferred 'nonblocking'}}
 	void (*fp2)() [[clang::nonblocking]]

``````````

</details>


https://github.com/llvm/llvm-project/pull/116505