From 7f1df9d0b31413e59846cc955d2a955d3f361e2a Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Wed, 30 Apr 2025 14:17:45 -0700
Subject: Initial support for immutable lambda expressions. (#6914)

* Initial support for immutable lambda expressions.

* More diagnostics, and langauge server fix.

* Language server fix.

* Fix bug identified in review.

* Add expected result.

* Update expected result.
---
 source/slang/slang-check-stmt.cpp | 41 +++++++++++++++++++++++++++------------
 1 file changed, 29 insertions(+), 12 deletions(-)

(limited to 'source/slang/slang-check-stmt.cpp')

diff --git a/source/slang/slang-check-stmt.cpp b/source/slang/slang-check-stmt.cpp
index 9525f71c9..0e5ed92aa 100644
--- a/source/slang/slang-check-stmt.cpp
+++ b/source/slang/slang-check-stmt.cpp
@@ -547,9 +547,19 @@ void SemanticsStmtVisitor::visitDiscardStmt(DiscardStmt*)
 void SemanticsStmtVisitor::visitReturnStmt(ReturnStmt* stmt)
 {
     auto function = getParentFunc();
+    Type* returnType = nullptr;
+    Type* expectedReturnType = nullptr;
+    if (m_parentLambdaDecl)
+    {
+        expectedReturnType = m_parentLambdaDecl->funcDecl->returnType.type;
+    }
+    else if (function)
+    {
+        expectedReturnType = function->returnType.type;
+    }
     if (!stmt->expression)
     {
-        if (function && !function->returnType.equals(m_astBuilder->getVoidType()) &&
+        if (expectedReturnType && !expectedReturnType->equals(m_astBuilder->getVoidType()) &&
             !as<ConstructorDecl>(function))
         {
             getSink()->diagnose(stmt, Diagnostics::returnNeedsExpression);
@@ -558,24 +568,31 @@ void SemanticsStmtVisitor::visitReturnStmt(ReturnStmt* stmt)
     else
     {
         stmt->expression = CheckTerm(stmt->expression);
+        returnType = stmt->expression->type.type;
         if (!stmt->expression->type->equals(m_astBuilder->getErrorType()))
         {
-            if (function)
+            if (!m_parentLambdaExpr && expectedReturnType)
             {
                 stmt->expression =
-                    coerce(CoercionSite::Return, function->returnType.Ptr(), stmt->expression);
-            }
-            else
-            {
-                // TODO(tfoley): this case currently gets triggered for member functions,
-                // which aren't being checked consistently (because of the whole symbol
-                // table idea getting in the way).
-
-                //							getSink()->diagnose(stmt,
-                // Diagnostics::unimplemented, "case for return stmt");
+                    coerce(CoercionSite::Return, expectedReturnType, stmt->expression);
             }
         }
     }
+    if (m_parentLambdaDecl)
+    {
+        if (!returnType)
+            returnType = m_astBuilder->getVoidType();
+        if (!m_parentLambdaDecl->funcDecl->returnType.type)
+            m_parentLambdaDecl->funcDecl->returnType.type = returnType;
+        if (!m_parentLambdaDecl->funcDecl->returnType.type->equals(returnType))
+        {
+            getSink()->diagnose(
+                stmt,
+                Diagnostics::returnTypeMismatchInsideLambda,
+                returnType,
+                m_parentLambdaDecl->funcDecl->returnType.type);
+        }
+    }
 
     if (FindOuterStmt<DeferStmt>())
     {
-- 
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