Fix Record array index property reads (#400) (#418)

* Fix Record array index property reads (#400)

- Narrow optional record receivers before keyed reads.
- Cover present and missing rows with differential tests.

* Record TypeScript 7 baseline for Record array fixture

- Add the new corpus program to the preflight and module order baseline.

* Stabilize HTTP timeout differential fixtures

- Release server responses after timeout callbacks.
- Bound missing callbacks with fallback responses.

packages/compiler/src/frontend/lowering/lower-exprs.ts

@@ -9316,7 +9316,24 @@ export function lowerBinary(lowerer: Lowerer, expr: ts.BinaryExpression): IrExpr
     // construction), typed as the index value armed with undefined under
     // noUncheckedIndexedAccess (mirroring lowerRecordKeyRead).
     if (target.container === "recordOvf") {
-      let t: IrType = target.fieldType;
+      let obj = target.obj;
+      if (obj.type.kind === "union" && ts.isPropertyAccessExpression(blame)) {
+        const present = lowerer.stripUndefinedArm(obj.type);
+        if (present.kind === "record") {
+          obj = lowerer.runtimeOptionalPropertyReceiver(
+            blame.expression,
+            obj,
+            present,
+            target.field,
+          ) ?? obj;
+        }
+      }
+      if (obj.type.kind !== "record") {
+        lowerer.unsupported("SC1090", blame, `reading '${target.field}' on a non-record receiver (narrow first)`);
+      }
+      const shape = lowerer.shapes.get(obj.type.shapeId);
+      if (!shape?.indexValue) lowerer.unsupported("SC1090", blame, `reading '${target.field}' on a record without an index signature`);
+      let t: IrType = shape.indexValue;
       if (lowerer.program.getCompilerOptions().noUncheckedIndexedAccess) {
         const armed = lowerer.withUndefinedArmOf(t);
         if (!armed) lowerer.badType(blame, lowerer.typeOf(blame));
@@ -9324,8 +9341,8 @@ export function lowerBinary(lowerer: Lowerer, expr: ts.BinaryExpression): IrExpr
       }
       return {
         kind: "recordKeyGet",
-        obj: target.obj,
-        shapeId: target.shapeId,
+        obj,
+        shapeId: obj.type.shapeId,
         key: { kind: "strLit", value: target.field, type: STRING, loc },
         overflowOnly: true,
         type: t,

packages/compiler/test/ts7/baselines/order-parity.json

@@ -7581,6 +7581,12 @@
    ],
    "diags": []
   },
+  "<repo>/tests/corpus/917-record-array-index-dot.ts": {
+   "order": [
+    "<repo>/tests/corpus/917-record-array-index-dot.ts"
+   ],
+   "diags": []
+  },
   "<repo>/tests/corpus/950-modules-basic/main.ts": {
    "order": [
     "<repo>/tests/corpus/950-modules-basic/util.ts",

tests/corpus/917-record-array-index-dot.ts

@@ -0,0 +1,20 @@
+type Row = Record<string, string | number | null>;
+
+function firstId(rows: Row[]): number {
+  return rows[0].id as number;
+}
+
+console.log(firstId([{ id: 1 }]));
+
+let evaluations = 0;
+function makeRows(): Row[] {
+  evaluations++;
+  return [{ id: evaluations }];
+}
+console.log(makeRows()[0].id, evaluations);
+
+try {
+  firstId([]);
+} catch (error) {
+  console.log(error instanceof TypeError, (error as Error).message);
+}