golang/go

go/ast: trailing func comments mishandled in CommentMap

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#22,371 opened on Oct 20, 2017

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Description

Working example: https://play.golang.org/p/TlsDxVbGow

Prints: g: "trailing comment in f\n"

Seems like the correct output should either be nothing (if it is associated with _ = x), or f: "trailing comment in f\n".

What's currently happening is that the "_ = x" in func f is the most recent "important" node when we encounter the comment. Since the comment isn't on the line immediately following "_ = x", it doesn't get associated with it. We don't look further up the "important nodes" stack to notice that it's within the bounds of f. Instead, we just give up and associate it with g.

/cc @griesemer

Contributor guide

Research direction
Investigate the CommentMap implementation in go/ast; focus on how trailing comments are associated with the nearest enclosing function. Trace the logic that assigns comments to nodes and identify why the comment in func f is incorrectly linked to g.
Tech stack
go
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Go
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30