fix(codegen): output trailing legal comments on same line

[majiayu000]

Summary

Fixes #17301

This PR adds support for outputting trailing legal comments on the same line as the statement they follow.

Before:

console.log('hello') //! Copyright notice

was output as:

console.log("hello");

After:

console.log("hello"); //! Copyright notice

Changes

• Add has_legal_content() method to Comment for checking legal content without position requirement
• Handle trailing legal comments in build_comments() using span.start as key
• Add print_trailing_comments_after() to find and print trailing comments between statement end and next statement start
• Modify print_directives_and_statements() to print trailing comments after each statement
• Add pop() method to CodeBuffer for removing trailing newlines

Test plan

• Added test case test_trailing_legal_comment
• All existing codegen tests pass

[Boshen]

This looks AI generated, can you follow https://github.com/oxc-project/oxc/blob/main/CONTRIBUTING.md#ai-usage-policy

[majiayu000]

Hi @Boshen, thanks for the review.

Yes, I used AI to assist with this PR. I've thoroughly reviewed and tested the code:

Testing performed:

• ✅ Basic trailing legal comment (//!)
• ✅ Multiple statements with trailing legal comments
• ✅ Block statements (if/for/while) with trailing comments
• ✅ Function/class/arrow function with trailing comments
• ✅ Last statement trailing comment
• ✅ Normal comments correctly NOT preserved

All 10 test cases pass.

Note: Block comment form (/*! */, /* @license */) for trailing comments is not supported because the parser classifies them as Leading rather than Trailing. This is outside the scope of #17301 which only uses line comments (//!).

Happy to make any adjustments if needed!