Fix JSX indentation in JavaScript output

[Copilot]

• Explore the codebase and understand the issue
• Examine existing tsx test (jsxUnicodeEscapeSequence.tsx)
• Create test case based on the issue (jsxNestedIndentation.tsx)
• Reproduce the bug and confirm TypeScript's expected output
• Accept initial test baselines (shows bug: all on one line)
• Fix the bug in printer.go by uncommenting EFStartOnNewLine handling
• Re-run tests and accept new baselines (4488 → 37 .diff files!)
• Run full test suite to ensure no regressions
• Verify linting and formatting pass
• Fix regression in commentsOnJSXExpressionsArePreserved test
  • Fixed inJsxChild flag state management for nested transforms
  • Fixed children newline logic to check count after filtering
  • All tests now pass with 3 more .diff files removed

Original prompt

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This section details on the original issue you should resolve

<issue_title>Indentation removed in JavaScript output for JSX (minor)</issue_title>
<issue_description>## Steps to reproduce

import * as React from 'react'
declare function Child(props: { children?: React.ReactNode }): React.ReactNode;
function Test() {
    return <Child>
        <Child>
            <Child></Child>
        </Child>
    </Child>
}

Behavior with [email protected]

The output preserves the newlines and indentation of the tags:

function Test() {
    return React.createElement(Child, null,
        React.createElement(Child, null,
            React.createElement(Child, null)));
}

Behavior with tsgo

The output collapses everything on a single line:

function Test() {
    return React.createElement(Child, null, React.createElement(Child, null, React.createElement(Child, null)));
}

</issue_description>

<agent_instructions>Examine an existing tsx test first. Then create a test based on the issue and accept its baselines. Then fix the bug.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes #1791

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[jakebailey]

I think this is good?

[Copilot]

Pull Request Overview

This PR fixes JSX indentation in JavaScript output to match TypeScript's behavior. The issue was that nested JSX elements were being collapsed to a single line instead of preserving proper indentation and newlines.

• Fixed JSX indentation by enabling the EFStartOnNewLine flag handling in the printer
• Improved state management for JSX child transformations to prevent context corruption
• Updated newline logic to check children count after filtering out null children

Reviewed Changes

Copilot reviewed 91 out of 91 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
testdata/tests/cases/compiler/jsxNestedIndentation.tsx	New test case to verify JSX nested indentation behavior
testdata/tests/cases/compiler/jsxNestedIndentation.js	Expected JavaScript output with proper indentation
internal/transformers/jsxtransforms/jsx.go	Fixed JSX child state management and newline logic for proper indentation
internal/printer/printer.go	Enabled EFStartOnNewLine flag handling to support multiline JSX output
Various baseline files	Updated test baselines showing the fix applied across many JSX tests