4 files changed, 60 insertions, 1 deletions
diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index d2f338e65..425548518 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -3229,6 +3229,40 @@ Expr* SemanticsExprVisitor::visitInvokeExpr(InvokeExpr* expr)
     if (auto newExpr = convertToLogicOperatorExpr(expr))
         return newExpr;
 
+    // Check for comma operator usage and emit warning if not in for-loop side effect context
+    // Skip warning in Slang 2026+ mode where parentheses create tuples
+    if (!isSlang2026OrLater(this))
+    {
+        bool exprIsInfixExpr = false;
+        InfixExpr* infixExpr = nullptr;
+        if (auto candidateInfixExpr = as<InfixExpr>(expr))
+        {
+            exprIsInfixExpr = true;
+            infixExpr = candidateInfixExpr;
+        }
+
+        bool functionExprIsVarExpr = false;
+        VarExpr* varExpr = nullptr;
+        if (exprIsInfixExpr)
+        {
+            if (auto candidateVarExpr = as<VarExpr>(infixExpr->functionExpr))
+            {
+                functionExprIsVarExpr = true;
+                varExpr = candidateVarExpr;
+            }
+        }
+
+        if (functionExprIsVarExpr && varExpr->name && varExpr->name->text == ",")
+        {
+            // Allow comma operators in for-loop side effects and expand expressions without
+            // warning
+            if (!getInForLoopSideEffect() && !m_parentExpandExpr)
+            {
+                getSink()->diagnose(infixExpr, Diagnostics::commaOperatorUsedInExpression);
+            }
+        }
+    }
+
     expr->functionExpr = CheckTerm(expr->functionExpr);
 
     if (auto baseType = as<DeclRefType>(expr->functionExpr->type))
diff --git a/source/slang/slang-check-impl.h b/source/slang/slang-check-impl.h
index 2675ecee0..48b06eb9f 100644
--- a/source/slang/slang-check-impl.h
+++ b/source/slang/slang-check-impl.h
@@ -1069,6 +1069,18 @@ public:
         return result;
     }
 
+    // Setup the flag to indicate we're in a for-loop side effect context where comma operators are
+    // allowed
+    SemanticsContext withInForLoopSideEffect()
+    {
+        SemanticsContext result(*this);
+        result.m_inForLoopSideEffect = true;
+        return result;
+    }
+
+    bool getInForLoopSideEffect() { return m_inForLoopSideEffect; }
+
+
     TryClauseType getEnclosingTryClauseType() { return m_enclosingTryClauseType; }
 
     SemanticsContext withEnclosingTryClauseType(TryClauseType tryClauseType)
@@ -1202,6 +1214,11 @@ protected:
     // 3. the logic expression is in an array size declaration.
     bool m_shouldShortCircuitLogicExpr = true;
 
+    // Flag to track when we're in a for-loop side effect expression where comma operators are
+    // allowed
+    bool m_inForLoopSideEffect = false;
+
+
     ExpandExpr* m_parentExpandExpr = nullptr;
 
     OrderedHashSet<Type*>* m_capturedTypePacks = nullptr;
diff --git a/source/slang/slang-check-stmt.cpp b/source/slang/slang-check-stmt.cpp
index bf8ddc94e..8c9e24d48 100644
--- a/source/slang/slang-check-stmt.cpp
+++ b/source/slang/slang-check-stmt.cpp
@@ -281,7 +281,10 @@ void SemanticsStmtVisitor::visitForStmt(ForStmt* stmt)
     }
     if (stmt->sideEffectExpression)
     {
-        stmt->sideEffectExpression = CheckExpr(stmt->sideEffectExpression);
+        // Use special context for for-loop side effect to allow comma operators without warning
+        SemanticsContext sideEffectContext = withInForLoopSideEffect();
+        SemanticsExprVisitor subExprVisitor(sideEffectContext);
+        stmt->sideEffectExpression = subExprVisitor.CheckExpr(stmt->sideEffectExpression);
     }
     subContext.checkStmt(stmt->statement);
 
diff --git a/source/slang/slang-diagnostic-defs.h b/source/slang/slang-diagnostic-defs.h
index e9c8acfe3..284cb634c 100644
--- a/source/slang/slang-diagnostic-defs.h
+++ b/source/slang/slang-diagnostic-defs.h
@@ -2512,6 +2512,11 @@ DIAGNOSTIC(
     Warning,
     methodNeverMutates,
     "method marked `[mutable]` but never modifies `this`")
+DIAGNOSTIC(
+    41024,
+    Warning,
+    commaOperatorUsedInExpression,
+    "comma operator used in expression (may be unintended)")
 
 DIAGNOSTIC(
     41024,