🐛 Bug: Crash in `isPropertyReadonlyInType` on argument to readonly type parameter (?)

[JoshuaKGoldberg]

Bug Report Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Expected

Calling isPropertyReadonlyInType({ abc: 42 }, "abc") in the following code block should not crash:

declare const fooFactory: <T>(x: readonly T[]) => (f: (x: T) => void) => void;

fooFactory([{ abc: 42 }])((x) => { });

Actual

typescript-eslint/typescript-eslint#11289:

TypeError: Cannot read properties of undefined (reading 'checkFlags')
Occurred while linting /Users/josh/repos/typescript-eslint/packages/eslint-plugin/tests/fixtures/file.ts:4
Rule: "@rule-tester/prefer-readonly-parameter-types"
 ❯ isTransientSymbolLinksFlagSet ../../node_modules/ts-api-utils/lib/index.cjs:143:26
 ❯ isInConstContext ../../node_modules/ts-api-utils/lib/index.cjs:994:16
 ❯ ../../node_modules/ts-api-utils/lib/index.cjs:1088:464
 ❯ symbolHasReadonlyDeclaration ../../node_modules/ts-api-utils/lib/index.cjs:1087:145
 ❯ ../../node_modules/ts-api-utils/lib/index.cjs:1172:5
 ❯ isReadonlyPropertyIntersection ../../node_modules/ts-api-utils/lib/index.cjs:1154:23
 ❯ Object.isPropertyReadonlyInType ../../node_modules/ts-api-utils/lib/index.cjs:1059:41
 ❯ isTypeReadonlyObject ../type-utils/dist/isTypeReadonly.js:138:25

Additional Info

The specific crash is in:

ts-api-utils/src/flags.ts

Lines 96 to 101 in 7935007

	export function isTransientSymbolLinksFlagSet(
	links: ts.TransientSymbolLinks,
	flag: ts.CheckFlags,
	): boolean {
	return isFlagSet(links.checkFlags, flag);
	}

...but the root is that undefined is getting used instead of a value, somewhere in the stack.

💖

[brianh-vista]

I'm running into this failure (with a different reproduction case). The issue seems to be that some objects have undefined explicitly in properties, instead of the properties being missing. Could this be addressed by having a more defensive check in https://github.com/JoshuaKGoldberg/ts-api-utils/blob/main/src/nodes/utilities.ts#L82:

Instead of:

				if (propertySymbol === undefined || !("links" in propertySymbol)) {

We could have:

				if (propertySymbol === undefined || !("links" in propertySymbol) || propertySymbol.links === undefined) {

I don't know if we'd want to modify other similar checks to be more defensive.

[kirkwaiblinger]

@brianh-vista That sounds quite plausible but probably just needs an experiment/test in order to know for sure. Many properties in the TS API are computed on demand, so there could always be same arcane getter shenanigans going on.

[brianh-vista]

I used pnpm patch to patch this in my reproduction case, and it solved the issue.

But I admit that I'm not familiar enough with all of the code around this to know that this is the best way to fix it.