fix: Support elementSummaries for inlined union members

[LekoArts]

Hello!

I've noticed a bug for a use case like this:

/**
 * @inline
 */
type TestReturn =
    /**
     * An apple a day keeps the doctor away.
     */
    | { kind: 'apple', isHealthy: true }
    /**
     * A donut a day keeps the doctor not away.
     */
    | { kind: 'sweets', isHealthy: false }

/**
 * Returns a random value
 */
export function test(): TestReturn {
    return Math.random() > 0.5
        ? { kind: 'apple', isHealthy: true }
        : { kind: 'sweets', isHealthy: false };
}

The type.types inside the signature doesn't receive the elementSummaries for the union type. I'm adding a failing test in this PR first to showcase the problem and show that it fails.

I'll spend some time to see if I can find the fix in this (so far unfamiliar) codebase. If not, I'll let you know 👍

[LekoArts]

Mh, I do wonder, is the current behavior intentional because it's not possible?

Reading

typedoc/src/lib/models/types.ts

Lines 1381 to 1387 in 4bf00b5

	/**
	* If present, there should be as many items in this array as there are items in the {@link types} array.
	*
	* This member is only valid on unions which are on {@link DeclarationReflection.type | DeclarationReflection.type} with a
	* {@link ReflectionKind} `kind` of `TypeAlias`. Specifying it on any other union is undefined behavior.
	*/
	elementSummaries?: CommentDisplayPart[][];

I'm wondering if what I want can even be achieved.

I can workaround this limitation by using a custom blockTag:

/**
 * Returns a random value
 *
 * @unionReturnHeadings
 * ["An apple a day keeps the doctor away.", "A donut a day keeps the doctor not away."]
 */
export function test(): TestReturn {
    return Math.random() > 0.5
        ? { kind: 'apple', isHealthy: true }
        : { kind: 'sweets', isHealthy: false };
}

[Gerrit0]

Yeah, this is intentional. Supporting comments on union elements only makes sense if TypeDoc is converting based on the type node rather than the actual type. This only happens in a few select cases, and only actually needs to happen for type aliases, so it is only valid to include it there.

TypeDoc doesn't support rendering the union comments anywhere except type alias types and I didn't want people expecting it to work in other locations, which is why that comment says what it does.

[LekoArts]

Ok, thanks for enlightening me. Then I'll close it :)