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cmd/cgo: leading whitespace in generated files is noncanonical #9019

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adonovan opened this issue Oct 29, 2014 · 3 comments

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@adonovan
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commented Oct 29, 2014

The output of cgo is not canonical according to gofmt, as it has an excessive number of
tabs preceding many source lines, notably the import paths (e.g. "fmt") inside
the import block, as the example below shows.  I suspect this is related to
printer.SourcePos mode and //line directives.

For what it's worth, I believe this behaviour is at least somewhat nondeterministic (it
caused my mapreduce consistency checks to fail), although I haven't succeeded in
reproducing that locally.

Deleting the blank line between the two imports hides the bug.

% go version
go version devel +6d6fbf7dee5b Mon Oct 20 11:10:03 2014 -0700 linux/amd64
% cat blurgh.go 
package blurgh

import (
        "blah"

        "foo"
)

import "C"

var _ foo.Foo
var _ blah.Blah
% go tool cgo blurgh.go 
% cat -t _obj/blurgh.cgo1.go 
// Created by cgo - DO NOT EDIT

//line /home/adonovan/test/blurgh.go:1
package blurgh
//line /home/adonovan/test/blurgh.go:4

//line /home/adonovan/test/blurgh.go:3
import (
^I^I^I^I^I"blah"
//line /home/adonovan/test/blurgh.go:7

//line /home/adonovan/test/blurgh.go:6
^I"foo"
)
//line /home/adonovan/test/blurgh.go:12

//line /home/adonovan/test/blurgh.go:11
var _ foo.Foo
var _ blah.Blah
@ianlancetaylor

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commented Oct 29, 2014

Comment 1:

Labels changed: added repo-main, release-go1.5.

@adonovan

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commented Oct 30, 2014

Comment 2:

(cgo's nondeterminism had a different cause.  I'll file a separate issue for that.)

@adonovan adonovan added new labels Oct 30, 2014

@bradfitz bradfitz modified the milestone: Go1.5 Dec 16, 2014

@rsc rsc removed the repo-main label Apr 14, 2015

@rsc

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commented Jun 8, 2015

Nondeterministic output is bad and should be fixed.

But non-gofmt'ed output is not a problem. People who care can run gofmt. (The build system doesn't care and doesn't expose these outputs.)

@rsc rsc closed this Jun 8, 2015

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