[Copilot]

Fixes #65333

Analysis

Below ES2022, private logical assignments use arithmetic compound-assignment lowering: set(get() && value). This invokes the setter even when the assignment should short-circuit.

Fix

• Lowering: Emit get() && set(value)—likewise for || and ??—while preserving single receiver evaluation and expression results.
• Coverage: Add ES2015–ES2022 emit cases for instance/static accessors, wrapped targets, complex receivers, and non-writable members.

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 Downlevel this.#x &&= v / ||= / ??= on a private accessor always calls the setter #65333

[Copilot]

🟢 Approval recommended

No active review issues block approval of the private logical-assignment lowering change.

No open issues 🎉

What changed in this PR

Fixes #65333 by preserving short-circuit behavior when the native TypeScript compiler lowers private logical assignments below ES2022, preventing setter calls when no assignment should occur.

Changes:

• Emits conditional private writes for &&=, ||=, and ??=, preserving single receiver evaluation and expression results.
• Adds emit coverage for instance/static accessors, wrapped targets, complex receivers, and non-writable members.
• Updates baselines for downlevel output while retaining native ES2022 syntax.

File	Description
tsc/​testdata/​tests/​cases/​compiler/​privateAccessorLogicalAssignment.ts	Adds regression cases across four targets.
tsc/​testdata/​baselines/​reference/​conformance/​nullishCoalescingAssignmentVsPrivateFieldsJsEmit1.js	Updates expected conditional private-field writes.
tsc/​testdata/​baselines/​reference/​compiler/​privateAccessorLogicalAssignment(target=es2022).js	Records preserved native logical assignments.
tsc/​testdata/​baselines/​reference/​compiler/​privateAccessorLogicalAssignment(target=es2021).js	Records short-circuiting private helper calls.
tsc/​testdata/​baselines/​reference/​compiler/​privateAccessorLogicalAssignment(target=es2020).js	Records lowered assignments with native nullish coalescing.
tsc/​testdata/​baselines/​reference/​compiler/​privateAccessorLogicalAssignment(target=es2015).js	Records fully lowered assignments and nullish checks.
tsc/​internal/​transformers/​estransforms/​classfields.go	Separates logical-assignment lowering from arithmetic compound assignments.

_{Review effort: Balanced}