[clang] bcab8ac - [clang] return type not correctly deduced for discarded lambdas (#153921)

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Author: Oliver Hunt
Date: 2025-08-18T02:07:27-07:00
New Revision: bcab8ac126c0b4c439caa3104d66d33d0f70f86f

URL: https://github.com/llvm/llvm-project/commit/bcab8ac126c0b4c439caa3104d66d33d0f70f86f
DIFF: https://github.com/llvm/llvm-project/commit/bcab8ac126c0b4c439caa3104d66d33d0f70f86f.diff

LOG: [clang] return type not correctly deduced for discarded lambdas (#153921)

The early return for lamda expressions with deduced return types in
Sema::ActOnCapScopeReturnStmt meant that we were not actually perform
the required return type deduction for such lambdas when in a discarded
context.

This PR removes that early return allowing the existing return type
deduction steps to be performed.

Fixes #153884

Fix developed by, and

Co-authored-by: Corentin Jabot <corentinjabot at gmail.com>

Added: 
    

Modified: 
    clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
    clang/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index f02a295220efb..6b423ce06523a 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -5669,7 +5669,7 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
   };
   Function->setDeclarationNameLoc(NameLocPointsToPattern());
 
-  EnterExpressionEvaluationContext EvalContext(
+  EnterExpressionEvaluationContextForFunction EvalContext(
       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
 
   Qualifiers ThisTypeQuals;

diff  --git a/clang/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp b/clang/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp
index abb42447d3e0b..05830de9891fe 100644
--- a/clang/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp
+++ b/clang/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp
@@ -239,5 +239,21 @@ void f2() {
 
 }
 
+namespace GH153884 {
+  bool f1() {
+    auto f = [](auto) { return true; };
+    if constexpr (0)
+      return f(1);
+    return false;
+  }
+  bool f2() {
+    auto f = [](auto x) { if (x) return 1.5; else return "wat"; };
+    // expected-error at -1 {{'auto' in return type deduced as 'const char *' here but deduced as 'double' in earlier return statement}}
+    if constexpr (0)
+      return f(1);
+    // expected-note at -1 {{in instantiation of function template specialization 'GH153884::f2()}}
+    return false;
+  }
+}
 
 #endif