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cmd/gofmt: rewrite might eat comments when given statement #6099

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DanielMorsing opened this issue Aug 10, 2013 · 9 comments
Closed

cmd/gofmt: rewrite might eat comments when given statement #6099

DanielMorsing opened this issue Aug 10, 2013 · 9 comments
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@DanielMorsing
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@DanielMorsing DanielMorsing commented Aug 10, 2013

run "gofmt -r 'x := s.foo[y] -> x := s.foo.Get(y)'" on the following file.

package main

type s struct {
    // my precious comment
    foo bool
}

func (*s) weird() bool {
    return false
}

The comment will be deleted and the return declaration will be put in parens. Like so:

package main

type s struct {
    foo bool
}

func (*s) weird() (bool) {
    return false
}

This happened on a much larger program and I had to spend some time restoring all the
comments that were eaten.
@dominikh
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@dominikh dominikh commented Aug 10, 2013

Comment 2:

2-3 Two things at play here.
1) https://golang.org/cl/6294076/ added removal of comments to gofmt -r. It
only keeps comments for which a node exists in the new AST
2) 'x := s.foo[y] -> x := s.foo.Get(y)' seems to get interpreted as 'x -> x', replacing
every identifier/expression with itself
3) Due to the way equality is checked (map lookup with ast.Node's as keys), the
replacements aren't equal to the old nodes, causing all attached comments to be lost.
@dominikh
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@dominikh dominikh commented Aug 10, 2013

Comment 3:

Considering 2), it would probably already go a long way to refuse patterns that don't
get fully consumed during parsing, since that means they don't express what the user
thought they did.
@rsc
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@rsc rsc commented Sep 10, 2013

Comment 4:

Labels changed: removed go1.2maybe.

@griesemer
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@griesemer griesemer commented Oct 10, 2013

Comment 5:

Owner changed to @griesemer.

@rsc
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@rsc rsc commented Nov 27, 2013

Comment 6:

Labels changed: added go1.3maybe.

@rsc
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@rsc rsc commented Dec 4, 2013

Comment 7:

Labels changed: added release-none, removed go1.3maybe.

@rsc
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@rsc rsc commented Dec 4, 2013

Comment 8:

Labels changed: added repo-main.

@griesemer
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@griesemer griesemer commented Feb 26, 2014

Comment 9:

This is partly addressed with https://golang.org/cl/68920044 :
gofmt -r 'x := s.foo[y] -> x := s.foo.Get(y)'
now complains that the expression pattern is incorrect. Thanks to dominik.honnef for
analyzing the case.
@griesemer
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@griesemer griesemer commented Feb 26, 2014

Comment 10:

The before mentioned CL fixes the confusion (per dominik.honnef's suggestion.
Closing this in favor of the more specific issue #7417.

Status changed to Fixed.

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