Read the class base after the callable-base case in super calls (#1281)

docs/content/limitations/runtime-type-checks.mdx

@@ -3,3 +3,5 @@ Casts from values whose type is only known at runtime validate the value. For ex
 Casts between program classes are checked too: casting an instance to a class it does not extend throws a `TypeError`, where Node.js reads the members structurally. `SC6004` reports calls that pass such an instance to a function that casts it.
 
 A Promise converted from `unknown` to a typed result validates its fulfilled value. A mismatch rejects with a `TypeError`. Rejection reasons and reference equality are preserved across conversions.
+
+A non-null assertion (`value!`) checks the value when it extracts an object, array or other non-nullable member from a union. If the value holds `null` or `undefined`, the assertion throws a `TypeError`, even when the result is never used; Node.js continues until a property of the value is read.

docs/src/generated/node-v24-compatibility-meta.json

@@ -2,6 +2,6 @@
   "schemaVersion": 3,
   "nodeVersion": "24.22.0",
   "nodeCommit": "f14cd3aa7bf9ca8df2cc5b8bb14beb0f335b1d93",
-  "artifactVersion": "56f660f5e2eb7391a048",
+  "artifactVersion": "cade1b8e6e0c5c42fcc9",
   "rowCount": 3880
 }

docs/src/generated/node-v24-compatibility.json

@@ -569,9 +569,9 @@
       "apiEntries": 120,
       "static": {
         "supported": 0,
-        "partial": 50,
+        "partial": 51,
         "refused": 0,
-        "not-implemented": 70,
+        "not-implemented": 69,
         "by-design": 0,
         "unreviewed": 0,
         "not-applicable": 0
@@ -57593,9 +57593,9 @@
       "anchor": "",
       "nodeStability": null,
       "static": {
-        "status": "not-implemented",
+        "status": "partial",
-        "detail": "No static compiler lowering is registered for this API yet.",
+        "detail": "Implemented for the call shapes accepted by the compiler lowering.",
-        "verification": "registry-gap"
+        "verification": "test-backed"
       }
     },
     {

internal/compatibility/generated/node-v24-backlog.json

@@ -7,8 +7,8 @@
     "tierItemCount": 3456,
     "tiers": {
       "static": {
-        "audit-partial": 1142,
+        "audit-partial": 1143,
-        "verify-gap": 2187,
+        "verify-gap": 2186,
         "replace-refusal": 40,
         "classify": 2,
         "implement": 85
@@ -57507,12 +57507,15 @@
       "priority": "normal",
       "tiers": {
         "static": {
-          "status": "not-implemented",
+          "status": "partial",
-          "action": "verify-gap",
+          "action": "audit-partial",
-          "verification": "registry-gap",
+          "verification": "test-backed",
-          "confidence": "low",
+          "confidence": "high",
-          "source": "compiler-unmatched:process",
+          "source": "surface-manifest:node-builtin.process.execArgv",
-          "tests": []
+          "tests": [
+            "tests/corpus/990-process-basics.ts",
+            "tests/corpus/2314-process-introspection.ts"
+          ]
         }
       }
     },

internal/compatibility/generated/node-v24-internal.json

@@ -596,9 +596,9 @@
       "apiEntries": 120,
       "static": {
         "supported": 0,
-        "partial": 50,
+        "partial": 51,
         "refused": 0,
-        "not-implemented": 70,
+        "not-implemented": 69,
         "by-design": 0,
         "unreviewed": 0,
         "not-applicable": 0
@@ -80949,8 +80949,12 @@
       "anchor": "",
       "nodeStability": null,
       "static": {
-        "status": "not-implemented",
+        "status": "partial",
-        "evidence": "compiler-unmatched:process"
+        "evidence": "surface-manifest:node-builtin.process.execArgv",
+        "tests": [
+          "tests/corpus/990-process-basics.ts",
+          "tests/corpus/2314-process-introspection.ts"
+        ]
       },
       "anchorSource": "chapter"
     },

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

@@ -7861,7 +7861,6 @@ export function superCallStmt(
   args: IrExpr[],
   loc: SrcLoc,
 ): IrStmt {
-  const base = superBaseOf(info)!;
   const thisRef: IrExpr = {
     kind: "varRef",
     localId: thisLocal.id,
@@ -7906,6 +7905,8 @@ export function superCallStmt(
       },
       loc,
     };
+  // A callable base has no class info, so the base is read after that case.
+  const base = superBaseOf(info)!;
   if (base.builtinError) {
     // super(message) into the runtime-provided Error constructor: stamps
     // name/message on the (already-allocated) object. Receiver + message

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6020-class-extends-function-constructor.js.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6020-class-extends-function-constructor.js"
+ ],
+ "diags": []
+}

tests/corpus/6020-class-extends-function-constructor.js

@@ -0,0 +1,27 @@
+// Classes whose base is an ordinary function constructor, with a declared
+// constructor calling super and with the implicit derived constructor.
+function Shape(name, sides) {
+  this.name = name;
+  this.sides = sides;
+}
+Shape.prototype.describe = function () {
+  return `${this.name} with ${this.sides} sides`;
+};
+
+class Polygon extends Shape {
+  constructor(name, sides, length) {
+    super(name, sides);
+    this.length = length;
+  }
+  perimeter() {
+    return this.sides * this.length;
+  }
+}
+
+class Unnamed extends Shape {}
+
+const square = new Polygon("square", 4, 3);
+console.log(square.describe(), square.perimeter());
+console.log(square instanceof Polygon);
+const shape = new Unnamed("triangle", 3);
+console.log(shape.describe(), Object.keys(shape).join(","));

tests/harness/corpus-costs.json

@@ -1915,6 +1915,7 @@
     "600-closures-basic.ts": 2349,
     "601-closures-loops.ts": 1788,
     "602-closures-identity-recursion.ts": 2372,
+    "6020-class-extends-function-constructor.js": 4300,
     "603-closures-rc-stress.ts": 1832,
     "604-closures-for-of.ts": 2639,
     "605-closures-forward-capture-tdz.ts": 3277,
@@ -4611,6 +4612,7 @@
     "600-closures-basic.ts": 2534,
     "601-closures-loops.ts": 2297,
     "602-closures-identity-recursion.ts": 2427,
+    "6020-class-extends-function-constructor.js": 7500,
     "603-closures-rc-stress.ts": 2589,
     "604-closures-for-of.ts": 3514,
     "605-closures-forward-capture-tdz.ts": 4638,

tests/harness/dyncheck.test.ts

@@ -764,6 +764,38 @@ console.log("recovered");
     expect(r.stdout).toBe("TypeError true\narray: TypeError\nfunc: TypeError\nrecovered\n");
   });
 
+  test("a non-null assertion on a null object result throws at the assertion, even when the binding is never read", async () => {
+    // Node lets the null ride until a member read; the compiled program
+    // throws the stranded TypeError where `!` extracts the object.
+    const r = await compileAndRun(
+      "asserted-null-object-result",
+      `interface Info {
+  name: string;
+  base: Info | null;
+  callable: boolean;
+}
+function baseOf(info: Info): Info | null {
+  return info.base;
+}
+function describe(info: Info): string {
+  const base = baseOf(info)!;
+  if (info.callable) return info.name + ": callable base";
+  return info.name + " extends " + base.name;
+}
+const root: Info = { name: "Root", base: null, callable: false };
+console.log(describe({ name: "Child", base: root, callable: false }));
+try {
+  console.log("unreachable", describe({ name: "Wrapped", base: null, callable: true }));
+} catch (e) {
+  console.log((e as Error).name, (e as Error).message.includes("not representable in the target union"));
+}
+console.log("recovered");
+`,
+    );
+    expect(r.exitCode).toBe(0);
+    expect(r.stdout).toBe("Child extends Root\nTypeError true\nrecovered\n");
+  });
+
   test("a checker-approved function mismatch strands per piece: mismatched params compile at the flow, void results trap after the call", async () => {
     // funcCoerceAdapter's stranded dispositions. Param strand: an array
     // literal of arrows collapses to one element signature — the

tests/harness/native-frontend.ts

@@ -65,6 +65,7 @@ export const programs = [
   "nullish-long-chain.ts",
   "class-array-optional-return.ts",
   "contextual-array-union-write.ts",
+  "6020-class-extends-function-constructor.js",
 ];
 
 interface LowerRequest {