Port TypeScript PR #62789: Fix "never nullish" diagnostic missing expressions wrapped in parentheses

[Copilot]

The "never nullish" diagnostic (TS2869/TS2881) was not reported when the left operand of ?? was wrapped in parentheses because checkNullishCoalesceOperandRight checked node.parent directly without traversing through outer expressions.

const x: { y: string | undefined } | undefined = undefined as any;

const foo = x?.y ?? `oops` ?? "";      // Error reported ✓
const bar = (x?.y ?? `oops`) ?? "";    // Error NOT reported (bug)

Changes

• Remove checkNullishCoalesceOperandRight function and its call
• Modify getSyntacticNullishnessSemantics to recurse on the right operand for ??, ??=, =, and , operators instead of returning PredicateSemanticsSometimes

This allows semantic analysis to properly evaluate through ?? chains regardless of parenthesization.

Ports microsoft/TypeScript#62789

Original prompt

Port microsoft/TypeScript#62789

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[Copilot]

Pull request overview

This PR ports TypeScript PR #62789, which fixes a bug where the "never nullish" diagnostic (TS2869/TS2881) was not reported when the left operand of ?? was wrapped in parentheses. The fix removes a separate right operand check function and instead modifies the semantic analysis to properly recurse through nullish coalescing chains.

Changes:

• Removed checkNullishCoalesceOperandRight function which incorrectly checked parent nodes without traversing outer expressions
• Modified getSyntacticNullishnessSemantics to recurse on right operands for ??, ??=, =, and , operators
• Updated test baselines showing improved error reporting with more specific diagnostic codes

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/checker/checker.go	Removed checkNullishCoalesceOperandRight function and modified getSyntacticNullishnessSemantics to recurse on right operands for certain operators
testdata/baselines/reference/submodule/compiler/predicateSemantics.errors.txt	Updated baseline showing improved error diagnostics with proper TS2869 codes instead of TS2881
testdata/baselines/reference/submodule/compiler/predicateSemantics.errors.txt.diff	Diff showing baseline changes with better error locations and codes