fix(checker): emit precise error when labeled continue/break targets a non-enclosing label

[creazyfrog]

What this change intends to do

Fixes #30408

When a labeled continue or break references a label that exists in the same function but is not an ancestor of the jump statement, TypeScript incorrectly emits:

TS1107: Jump target cannot cross function boundary.

No function boundary is crossed — the label simply is not enclosing the jump. The misleading message causes developers to think they have a cross-function scoping problem when they actually have a non-enclosing label reference.

function foo() {
    for (let i = 0; i < 10; i++) {
        continue loopend; // ❌ TS1107 before fix — misleading
    }
    loopend:              // label exists in same function, just not enclosing
    console.log('done');
}

Fix

Adds a helper labelExistsInScope(scope, labelName) that walks the AST children of the enclosing function-like node looking for a matching LabeledStatement, without descending into nested function boundaries.

In checkGrammarBreakOrContinueStatement, when a function boundary is reached, the fix checks whether the named label exists anywhere in that function. If it does, it emits the accurate diagnostic instead of TS1107:

• TS1115 for continue — "A 'continue' statement can only jump to a label of an enclosing iteration statement."
• TS1116 for break — "A 'break' statement can only jump to a label of an enclosing statement."

TS1107 is preserved for the genuine case where the label is defined in an outer function (a real function-boundary violation).

Before / After

function foo() {
    for (let i = 0; i < 10; i++) {
        continue loopend;
        //       ~~~~~~~ Before: TS1107 "Jump target cannot cross function boundary"
        //               After:  TS1115 "A 'continue' statement can only jump to a label of an enclosing iteration statement"
    }
    loopend:
    console.log('done');
}

The genuine cross-function case still produces TS1107 correctly:

function outer() {
    myLabel:
    function inner() {
        continue myLabel; // TS1107 — still correctly reported
    }
}

File changed: src/compiler/checker.ts — 22 insertions, 0 deletions

Tests

This PR does not currently include a new compiler baseline test. A test in tests/cases/compiler/ covering:

• a same-function non-enclosing label (should produce TS1115/TS1116, not TS1107), and
• a genuine cross-function label (should still produce TS1107)

would be the right addition. I can add one if a maintainer confirms this approach before I invest the time, since baseline-accept changes require a full local build.

AI Assistance Disclosure

This PR was developed with the assistance of Claude Code (Anthropic), as required to be disclosed per the CONTRIBUTING.md guidelines.

[jakebailey]

Can you please tell me what tool you used to send this PR, and how you chose this issue to fix?

[creazyfrog]

Hi Jake, I used claude code to help me to generate the PR. Just going through the list of issues in github, I found the issue to give a try. Is it not as per the expectation?

…

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[jakebailey]

Please read CONTRIBUTING.md