fix: handle synthetic comments in commentBefore function

[go-wyvern]

fix: #2747

[gemini-code-assist]

Code Review

This pull request modifies the commentBefore function in printer/printer.go to correctly handle synthetic comments attached via CommentedStmts when their offset matches the statement's first token offset. It also adds a corresponding unit test TestCommentedNodesInEventHandler in printer/printer_test.go to verify this behavior. No review comments were provided, so there is no additional feedback.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.20%. Comparing base (a7e45c7) to head (cee9464).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2745      +/-   ##
==========================================
+ Coverage   94.09%   94.20%   +0.10%     
==========================================
  Files          32       32              
  Lines       10074    10074              
==========================================
+ Hits         9479     9490      +11     
+ Misses        425      419       -6     
+ Partials      170      165       -5     

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[fennoai]

Overview

This PR fixes a bug where synthetic comments attached to statements via CommentedStmts were not being printed before their associated statement. The root cause: the original commentBefore check used strict < comparison, so a synthetic comment with Slash set to exactly the statement's first-token offset (offset equal, not less-than) was silently dropped.

Code Change Analysis

printer/printer.go:167–171 — commentBefore

The two changes to the return expression are both necessary:

1. < → <= — correct fix for the core bug: a synthetic comment whose Pos() equals the statement's offset is now treated as a leading comment.
2. Added p.commentOffset != infinity guard — critical correctness requirement. Without it, the new <= would fire when p.flush is called at EOF with Offset: infinity and p.commentOffset is also infinity (no more comments). The old < happened to be safe there; the new <= is not.

The combination is correct. The comment in the code explains the <= change but omits mention of why the != infinity guard is needed — a reader might think it is defensive boilerplate when it is load-bearing.

Suggestion: Expand the inline comment to document the infinity guard:

// For synthetic comments attached via CommentedStmts, the comment offset may
// be exactly the same as the statement's first token offset. Treat it as a
// leading comment to preserve expected placement.
// The != infinity guard is required because flush() calls this with
// Offset: infinity; without it, <= would falsely match when no comments remain.
return p.commentOffset != infinity && p.commentOffset <= next.Offset && (!p.impliedSemi || !p.commentNewline)

printer/nodes.go:1417–1424 — stmt (unchanged, context only)

The injection point where setComment is called before the switch. setComment only fires when p.useNodeComments is true — the PR relies on this path being active, which it is when CommentedNodes is used. This looks correct.

Test Coverage

TestCommentedNodesInEventHandler correctly reproduces the bug scenario:

• Parses a .gox file with an onStart => event handler (the exact construct that triggered the issue).
• Sets Slash: eventStmt.Pos() to co-locate the synthetic comment with the statement (the key precondition).
• Asserts the comment text immediately precedes onStart => in the output.

Minor observations:

• The test uses strings.Contains rather than an exact match, which is appropriate since the full file has surrounding content.
• ShadowEntry access is guarded with nil checks before use — good defensive test setup.
• The test does not cover the infinity edge case directly. This is acceptable: the guard is already exercised implicitly by every test that calls Fprint to completion (all of which invoke the final flush at EOF).
• Existing TestCommentedNodes subtests continue to cover the strict < cases, providing regression coverage.

Summary

The fix is correct, minimal, and well-targeted. The new test covers the bug scenario precisely. The only actionable suggestion is to document why the != infinity guard is load-bearing in the inline comment, so a future reader does not mistake it for optional boilerplate and remove it.

[xushiwei]

please create an issue before creating a PR.

[go-wyvern]

please create an issue before creating a PR.

created: #2747