Erase the half-built ts.If when an optional call fails

tslang/lib/TypeScript/MLIRGenAccessCall.cpp

@@ -1427,8 +1427,14 @@ namespace mlirgen
 
             auto result = mlirGenCallExpression(location, innerFuncRef, typeArguments, operands, genContext);
             // a failed call (e.g. too few arguments) must fail the expression, not leave an
-            // empty branch behind - for a void callee that silently dropped the call
-            EXIT_IF_FAILED(result)
+            // empty branch behind - for a void callee that silently dropped the call. Nor may the
+            // half-built if stay in the IR for a caller that carries on (as in conditionalValue)
+            if (mlir::failed(result))
+            {
+                builder.setInsertionPoint(ifOp);
+                ifOp.erase();
+                return mlir::failure();
+            }
             auto value = V(result);
             if (value)
             {

tslang/test/tester/CMakeLists.txt

@@ -2215,7 +2215,8 @@ set(call_arity_cases
     "closure|Expected 2 arguments, but got 1\\."
     "declared|Expected 2 arguments, but got 1\\."
     "varargs|Expected at least 1 arguments, but got 0\\."
-    "optional_call|Expected 2 arguments, but got 1\\.")
+    "optional_call|Expected 2 arguments, but got 1\\."
+    "optional_call_value|Expected 2 arguments, but got 1\\.")
 foreach(call_arity_case ${call_arity_cases})
     string(FIND "${call_arity_case}" "|" call_arity_sep)
     string(SUBSTRING "${call_arity_case}" 0 ${call_arity_sep} call_arity_name)

tslang/test/tester/call-arity/optional_call_value.ts

@@ -0,0 +1,8 @@
+// An optional call whose result is used, inside a larger expression, at module level: the
+// failed call must take its half-built `if` with it, not leave it in the global's initializer.
+let f: ((a: number, b: number) => number) | undefined = (a: number, b: number) => a + b;
+const r = `${f?.(1) ?? 0}`;
+
+function main() {
+    print(r);
+}