[Copilot]

Fixes #65170

Analysis

Erasing as or satisfies can expose an unparenthesized unary or await expression as the left operand of **, producing invalid JavaScript.

Fix

• Parser: Extend the existing erasure-precedence guard to reject these forms regardless of erasableSyntaxOnly. Preserve explicitly parenthesized operands and update expressions.
• Coverage: Exercise every unary operator, await, mixed assertion chains, and legal boundaries with erasableSyntaxOnly enabled and disabled.

-x as number ** 2;   // Error
(-x) as number ** 2; // OK

Copilot Checklist

I successfully ran the applicable command at the end of my session, and it completed without error:

• npx hereby validate
• npx hereby validate --api (for TypeScript API changes)

• Fixes Erasing as or satisfies can expose an invalid left operand of ** #65170

[Ryan Cavanaugh (RyanCavanaugh)]

Copilot ; expected is an unsatisfactory error message here, we should be issuing the same error for -n as any ** 2 as if you had written -n ** 2

[Copilot]

Copilot ; expected is an unsatisfactory error message here, we should be issuing the same error for -n as any ** 2 as if you had written -n ** 2

Addressed in b64beb2. Bare and assertion-wrapped operands now share the TS17006 reporter, including the operator name and original operand span; type assertions use TS17007. Added matching bare-form controls and recovery coverage. npx hereby validate passed.

[Copilot]

🟢 Approval recommended

No active review issues were identified for the change extending exponentiation operand checks through TypeScript assertions.

No open issues 🎉

What changed in this PR

Addresses #65170 by extending the native TypeScript parser’s exponentiation checks to reject unary and await operands hidden by as or satisfies, regardless of erasableSyntaxOnly.

Changes:

• Detects invalid left operands across assertion chains and reuses a shared diagnostic helper.
• Preserves valid parenthesized operands, update expressions, and unary right operands.
• Adds regression coverage and diagnostic baselines for both erasableSyntaxOnly settings.

File	Description
tsc/​testdata/​tests/​cases/​compiler/​exponentiationWithErasedUnaryExpression.ts	Covers invalid assertion-wrapped operands and valid boundaries.
tsc/​testdata/​baselines/​reference/​compiler/​exponentiationWithErasedUnaryExpression(erasablesyntaxonly=true).errors.txt	Records expected diagnostics with erasure-only syntax enabled.
tsc/​testdata/​baselines/​reference/​compiler/​exponentiationWithErasedUnaryExpression(erasablesyntaxonly=false).errors.txt	Records expected diagnostics with erasure-only syntax disabled.
tsc/​internal/​parser/​parser.go	Extends operand validation and extracts shared diagnostic reporting.

_{Review effort: Balanced}