Refuse static member reads of MIMEType and MIMEParams in JavaScript

JavaScript sources hold node:util's MIMEType and MIMEParams as identity
tokens, so a read such as MIMEType.prototype or MIMEType.name answered
undefined where Node returns the class's member. Those reads now report
SC2020, as the TypeScript spelling does at compile time; in JavaScript
the refusal throws when the read runs.

The node24-mime-errors fixture reads MIMEType.prototype to take the
getters' descriptors, so its expected refusal is now SC2020.

packages/compiler/src/frontend/lowering/builtins/mime.ts

@@ -134,6 +134,17 @@ export function lowerMimeCall(lowerer: Lowerer, call: ts.CallExpression): IrExpr
   };
 }
 
+/** Reports SC2020 when `access` reads a static member of MIMEType or
+ * MIMEParams (`MIMEType.prototype`, `MIMEType.name`); null otherwise.
+ * JavaScript sources hold either class as an identity token, which has no
+ * members, so the read would answer undefined. MIMEType.parse calls lower
+ * in lowerMimeCall and never reach the member read. */
+export function fenceMimeStaticRead(lowerer: Lowerer, access: ts.PropertyAccessExpression): null {
+  const cls = mimeClassOf(lowerer, access.expression);
+  if (cls !== null) lowerer.noLowering(`util.${cls}.${access.name.text}`, access);
+  return null;
+}
+
 /** `v instanceof MIMEType` / `v instanceof MIMEParams`. */
 export function lowerMimeInstanceof(lowerer: Lowerer, expr: ts.BinaryExpression): IrExpr | null {
   const cls = mimeClassOf(lowerer, expr.right);

packages/compiler/src/frontend/lowering/expressions/property-access.ts

@@ -63,6 +63,7 @@ import {
 } from "../../../ir/ir.js";
 import { lowerNavigatorMember } from "../builtins/navigator.js";
 import { lowerX509PublicKey } from "../builtins/x509.js";
+import { fenceMimeStaticRead } from "../builtins/mime.js";
 import { NODE_COMPAT_VERSION } from "../builtins/process.js";
 import {
   inlineNamespaceRequireOf,
@@ -942,6 +943,7 @@ export function lowerPropertyAccessExpr(
     // prototype that no lowering above claimed keeps the SC2020 fence
     // rather than reading undefined through the field and dynamic reads.
     fenceBuiltinConstructorStaticRead(lowerer, expr) ??
+    fenceMimeStaticRead(lowerer, expr) ??
     lowerer.lowerFieldRead(expr);
   // A union-typed field read narrows like an identifier when the
   // checker has narrowed this use to one arm.

tests/harness/npm.test.ts

@@ -74,7 +74,7 @@ const KNOWN: Record<string, Known> = {
   "node24-file-url-conversion": { build: "SC1090" },
   "node24-fs-descriptors": { run: "SC2020" },
   "node24-mime": { run: "SC2020" },
-  "node24-mime-errors": { run: "SC1090" },
+  "node24-mime-errors": { run: "SC2020" },
   "node24-no-error-assertions": { run: "SC2020" },
   "node24-parseargs": { run: "SC1090" },
   "node24-promise-timers": { run: "SC2020" },