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cmd/go: build constraint of 'ignore' is special for modules? #29598

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myitcv opened this issue Jan 7, 2019 · 1 comment

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@myitcv
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@myitcv myitcv commented Jan 7, 2019

What version of Go are you using (go version)?

> go version
[stdout]
go version go1.12beta1 linux/amd64

Does this issue reproduce with the latest release?

Yes; testing with the beta ahead of the 1.12 release.

What operating system and processor architecture are you using (go env)?

go env Output
> go env
[stdout]
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/myitcv/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="$WORK/gopath"
GOPROXY="http://127.0.0.1:40043/mod"
GORACE=""
GOROOT="/home/myitcv/gos"
GOTMPDIR=""
GOTOOLDIR="/home/myitcv/gos/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="$WORK/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/tmp/go-build168896432=/tmp/go-build -gno-record-gcc-switches"

What did you do?

# no build constraint
go list
go mod tidy
grep 'fruit.com v1.0.0' go.mod

# build constraint of other
cp mod.go.other mod.go
go mod tidy
grep 'fruit.com v1.0.0' go.mod

# build constraint of ignore
cp mod.go.ignore mod.go
go mod tidy
grep 'fruit.com v1.0.0' go.mod


-- go.mod --
module mod

-- mod.go --
package mod

import _ "fruit.com/fruit"

-- mod.go.ignore --
// +build ignore

package mod

import _ "fruit.com/fruit"

-- mod.go.other --
// +build other

package mod

import _ "fruit.com/fruit"

using the following module definition:

# mod/fruit.com_v1.0.0.txt 
-- .mod --
module fruit.com

-- .info --
{"Version":"v1.0.0","Time":"2018-10-22T18:45:39Z"}

-- go.mod --
module fruit.com

-- fruit/fruit.go --
package fruit

What did you expect to see?

A passing test.

What did you see instead?

--- FAIL: TestScripts (0.04s)
    --- FAIL: TestScripts/script (0.23s)
        testscript.go:193:
            # no build constraint (0.107s)
            # build constraint of other (0.021s)
            # build constraint of ignore (0.032s)
            > cp mod.go.ignore mod.go
            > go mod tidy
            > grep 'fruit.com v1.0.0' go.mod
            [go.mod]
            module mod

            go 1.12

            FAIL: testdata/script.txt:17: no match for `fruit.com v1.0.0` found in go.mod

I wasn't aware that the ignore build constraint was special but judging from the above it appears to be.

ignore is described as being conventional, but not that it carries any special semantics.

The cmd/go docs also don't appear to make mention of this special case.

Assuming this is the intended behaviour, I think it would be worth updating the docs to call this out. I just spent a good few mins trying to track down a go mod tidy bug that in fact turned out to be an instance of a file with a // +build ignore constraint.

cc @bcmills

FYI @mvdan @rogpeppe

@gopherbot

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@gopherbot gopherbot commented Mar 13, 2019

Change https://golang.org/cl/167159 mentions this issue: all: add go.mod

gopherbot pushed a commit to golang/talks that referenced this issue Mar 13, 2019
Commands run:
	sed -i 's;// +build OMIT;// +build ignore,OMIT;' $(grep -l OMIT -r)
	go mod init
	go mod edit -go=1.11
	go mod tidy
	go list -m all
	go test ./...

Updates golang/go#30228
Updates golang/go#29598

Change-Id: I3d0a4787c1158572bed8dd3785ff02e16d1cc1f3
Reviewed-on: https://go-review.googlesource.com/c/talks/+/167159
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
@andybons andybons modified the milestones: Go1.13, Go1.14 Jul 8, 2019
@rsc rsc modified the milestones: Go1.14, Backlog Oct 9, 2019
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