Fix Element.matches strict narrowing

[cjc0013]

Fixes microsoft/TypeScript#63497.

This follows the direction discussed in that issue: matches() should only act as a type guard when the selected tag's element type is a strict subtype of the current receiver type. For tags that map back to the same receiver type, it should still be accepted but return boolean, so the false branch does not narrow the receiver to never.

Summary

• restrict Element.matches() type-predicate overloads to strict subtype matches
• keep tag-name boolean overloads for same-type matches
• regenerate DOM baselines
• add a compile-only regression fixture for the reported false-branch never behavior

Validation

• npm run generate
• npm test
• focused local TypeScript probe: the current baseline produced Property 'id' does not exist on type 'never'; the patched baseline compiles cleanly

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @saschanaz - if they write a comment saying "LGTM" then it will be merged.

[cjc0013]

@microsoft-github-policy-service agree

[saschanaz]

This is hard to parse, can you use something like ElementMap and ElementType than T and U? And also with parentheses.

It also kinda works weird, keyof ElementMatchesMap<HTMLElementTagNameMap, HTMLDivElement> is somehow "object" | "col" | "colgroup" | "embed" | "hr" | "iframe" | "img" | "input" | "legend" | "table" | "tbody" | "td" | "tfoot" | "th" | "thead" | "tr" ? It should be "div", right?

[cjc0013]

Thanks, that makes sense. I updated the helper to make the strict-narrowing intent explicit with clearer names and a parenthesized mapped-type condition.

I also changed the narrowing map so same-type matches and structurally unrelated matches fall back to boolean. That covers the HTMLDivElement case you pointed out, so HTMLDivElement.matches("div") stays boolean and HTMLDivElement.matches("object") no longer gets a bogus type-guard path.

I added fixture coverage for the original false-branch regression, HTMLElement narrowing to HTMLDivElement, HTMLDivElement.matches("div") staying boolean, and HTMLDivElement.matches("object") not narrowing to HTMLObjectElement.