fix(47508): noUncheckedIndexedAccess with enums Type narrowed

[navya9singh]

Fixes #47508

[typescript-bot]

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[navya9singh]

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

#47508

[RyanCavanaugh]

It looks like this also needs to check that the indexing enum type is the same as the indexed enum type, in other words this example should not have its behavior changed:

enum A {
  a, b, c
}
enum B {
  x, y, z
}
const p = A[B.x];

[ProKashif]

Suggested change

[ProKashif]

t variable name should be self-explaining

[navya9singh]

Made some changes, please have a look!

[RyanCavanaugh]

This is still duplicating the line that we started with.

Proposed code (I haven't tested this):

                    // When accessing an enum object with its own type,
                    // e.g. E[E.A] for enum E { A }, undefined shouldn't
                    // be included in the result type
                    if ((accessFlags & AccessFlags.IncludeUndefined) &&
                        !(objectType.symbol &&
                            objectType.symbol.flags & (SymbolFlags.RegularEnum | SymbolFlags.ConstEnum) &&
                            (indexType.symbol &&
                            indexType.flags & TypeFlags.EnumLiteral &&
                            getParentOfSymbol(indexType.symbol) === objectType.symbol))) {
                        return getUnionType([indexInfo.type, undefinedType]);
                    }
                    return indexInfo.type;