Fix using transform variable shadowing in for-of loops

[Copilot]

The using declaration transform was throwing "redeclaration of const" errors when the for-of loop body contained variables that shadowed the using variable name.

Problem:

class Foo {}
for (using foo of []) {
  const foo = new Foo(); // Error: redeclaration of const foo
}

The transformed output would generate:

for (const foo_1 of []) {
    try {
        const foo = __addDisposableResource(env_1, foo_1, false);
        const foo = new Foo(); // ❌ Duplicate declaration
    }
    // ...
}

Solution:
This PR implements variable renaming for shadowing variables in using for-of loops, similar to how ES5 for-of transforms handle variable conflicts. The fix:

1. Detects variables in the loop body that shadow the using variable name
2. Renames them with unique identifiers (e.g., foo → foo_2)
3. Updates all references to use the renamed variables

After the fix:

for (const foo_1 of []) {
    try {
        const foo = __addDisposableResource(env_1, foo_1, false);
        const foo_2 = new Foo(); // ✅ Renamed to avoid conflict
    }
    // ...
}

Features:

• Works with all variable declaration types (const, let, var)
• Handles nested scopes and multiple shadowing variables
• Preserves legitimate scoping errors (e.g., var vs block-scoped conflicts)
• Only affects using for-of loops, regular for-of loops unchanged

Fixes #61714.

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[RyanCavanaugh]

Run hereby format to fix your line endings

Add importHelpers: true to your testcase so the emit is tidier

[Copilot]

Run hereby format to fix your line endings

Add importHelpers: true to your testcase so the emit is tidier

Fixed line endings by adding missing newline at end of file. Added importHelpers: true directive and restructured test with multi-file format for cleaner organization. Commit 2738f69.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• plugins.dprint.dev
  • Triggering command: /home/REDACTED/work/TypeScript/TypeScript/node_modules/dprint/dprint fmt (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

[weswigham]

@copilot I'd prefer a different approach. Instead of renaming anything, inject an extra block scope between the moved and downleveled using declaration and the actual loop body. So the output should look like

for (const foo_1 of []) {
    try {
        const foo = __addDisposableResource(env_1, foo_1, false);
        {
            const foo = new Foo();
        }
    }
    // ...
}

instead.

[Copilot]

@copilot I'd prefer a different approach. Instead of renaming anything, inject an extra block scope between the moved and downleveled using declaration and the actual loop body. So the output should...

Implemented the block scoping approach as suggested. Instead of renaming variables, the transformation now wraps the loop body in an additional block scope to handle shadowing naturally. The output now matches your specification exactly. Commit 8f3df02.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• plugins.dprint.dev
  • Triggering command: /home/REDACTED/work/TypeScript/TypeScript/node_modules/dprint/dprint fmt (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

[weswigham]

If the existing block is empty, we shouldn't bother adding a new, empty block.

[Copilot]

Fixed in commit 0b3bf33. The implementation now checks if the loop body is empty and skips adding the extra wrapping block in those cases. Empty using for-of loops no longer generate redundant empty blocks.

[weswigham]

Delete this comment.

[Copilot]

Deleted the comment in commit 0b3bf33. The obsolete comment about collecting variable declarations has been removed from esnext.ts.

[weswigham]

Also don't change the line endings that are already in the edited code.

[weswigham]

We should consider a block with just an empty statement the same as an empty block and avoid emitting the new block.

[Copilot]

Fixed in commit 957cf79. The implementation now considers blocks containing only empty statements as effectively empty and avoids generating the extra wrapping block in those cases.

[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• plugins.dprint.dev
  • Triggering command: /home/REDACTED/work/TypeScript/TypeScript/node_modules/dprint/dprint fmt (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list