Allow enum keys accessed with bracket notation as computed properties

[tt-a1i]

Summary

This PR fixes #25083 where enum keys accessed with bracket notation (e.g., Type['3x14']) were not recognized as valid computed property names in type literals, even when they resolved to literal types.

The problem

enum Type {
  Foo = 'foo',
  '3x14' = '3x14'  // Non-identifier enum key
}

type TypeMap = {
  [Type.Foo]: any;        // ✅ Works
  [Type['3x14']]: any;    // ❌ Error: TS1170 - but should work!
}

The error occurred because isLateBindableAST only recognized EntityNameExpression (Identifier or PropertyAccessExpression) but not ElementAccessExpression with literal keys.

The fix

Introduced isLateBindableAccessExpression, a helper function that recursively validates access expressions:

• Identifiers
• PropertyAccessExpression where the name is an Identifier (not PrivateIdentifier) and the base is valid
• ElementAccessExpression where the argument is a string/numeric literal (after skipping parentheses) and the base is valid
• Parenthesized expressions are skipped via skipParentheses

This supports:

• Pure property access: obj.a.b.c
• Pure element access: obj['a']['b']['c']
• Mixed chains: obj.a['b'].c['d']
• Parenthesized expressions: (obj.a)['b']
• Parenthesized keys: obj[('a')]

Also updated checkGrammarForInvalidDynamicName to use the new helper (it handles skipParentheses internally now).

Testing

Added test case enumKeysAsComputedPropertiesWithBracketNotation.ts covering:

• Enum keys with bracket notation (Type['3x14'])
• Bracket notation with identifier keys (Type['Foo'])
• Nested element access (obj['a']['b'])
• Mixed chains (obj['a'].b, obj.a['b'])
• Complex mixed chains (deep.a['b'].c['d'])
• Parenthesized expressions ((obj.a).b, (obj['a']).b)
• Parenthesized keys (obj[('a')], deep[('a')][('b')].c['d'])

Baseline changes

enumKeysAsComputedPropertiesWithBracketNotation.*

• New test file baselines for the fix

isolatedDeclarationLazySymbols.errors.txt

• Removed false positive error for Direction['Up'] in [Direction['Up']]: number
• This was previously incorrectly flagged as TS1170 because Direction['Up'] wasn't recognized as a valid late-bindable name
• Now correctly allows this pattern since it resolves to a literal type "UP"

isolatedDeclarationLazySymbols.types

• The type for [Direction['Up']] now correctly resolves to "UP" instead of showing error
• This reflects the fix allowing element access on enums to be used as computed property names

All 99,161 tests pass.

[tt-a1i]

@microsoft-github-policy-service agree

[typescript-bot]

With 6.0 out as the final release vehicle for this codebase, we're closing all PRs that don't fit the merge criteria for post-6.0 patches. If you think this was a mistake and this PR fits the post-6.0 patch criteria, please post to the 6.0 iteration issue with details (specifically, which PR and which patch criteria it satisfies).

Next steps for PRs:

• For crash bugfixes or language service improvements, PRs are currently accepted at the typescript-go repo
• Changes to type system behavior should wait until after 7.0, at which point mainline TypeScript development will resume in this repository with the Go codebase
• Library file updates (lib.d.ts etc) continue to live in this repo or the DOM Generator repo as appropriate