x/vgo: vgo install of submodule modifies root go.mod

[myitcv]

Please answer these questions before submitting your issue. Thanks!

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

go version go1.10.1 linux/amd64 vgo:2018-02-20.1

Specifically vgo is as of 5db81b5cd6ab5ee1dd1b1b0ee0843f194ab7b908

Does this issue reproduce with the latest release?

Yes.

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/myitcv/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/myitcv/.mountpoints/x"
GORACE=""
GOROOT="/home/myitcv/gos"
GOTMPDIR=""
GOTOOLDIR="/home/myitcv/gos/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build749051986=/tmp/go-build -gno-record-gcc-switches"
VGOMODROOT=""

What did you do?

Edit: edited original issue to make it not depend on myitcv.io/... packages.

cd `mktemp -d`
echo 'module "rubbish.com"' > go.mod

# make blah submodule
mkdir blah
cd blah

echo 'module "rubbish.com/blah"' > go.mod

# create skeleton implementation that depends on external code
cat <<EOD > blah.go
package blah

import _ "rsc.io/pdf"
EOD

vgo build

which gives the expected output:

vgo: resolving import "rsc.io/pdf"
vgo: finding rsc.io/pdf (latest)
vgo: adding rsc.io/pdf v0.0.0-20180112171046-225057252246
vgo: finding rsc.io/pdf v0.0.0-20180112171046-225057252246
vgo: downloading rsc.io/pdf v0.0.0-20180112171046-225057252246

We can also vgo list as expected:

vgo list -f "{{printf \"%#v\"  .Module}}" .
vgo list -f "{{printf \"%#v\"  .Module}}" rubbish.com/blah

gives the expected:

modinfo.ModulePublic{Top:true, Path:"rubbish.com/blah", Version:""}
modinfo.ModulePublic{Top:true, Path:"rubbish.com/blah", Version:""}

But then if we move to the parent (?) module and vgo list:

cd ..
vgo list .

we get the possibly-to-be expected:

vgo: import "rubbish.com" [/tmp/tmp.Q8I5ISBSzQ]: no Go source files

(although I think you could argue that a module doesn't need to contain source files, it can just contain other modules?)

But then if we:

vgo list ./...

we get:

vgo: resolving import "rsc.io/pdf"
vgo: finding rsc.io/pdf (latest)
vgo: adding rsc.io/pdf v0.0.0-20180112171046-225057252246
rubbish.com/blah

The last line is fine, but the resolving of "rsc.io/pdf" is unexpected because that requirement only exists for the submodule (we are currently in top module directory).

The "rubbish.com" go.mod file has also been modified:

$ cat go.mod
module "rubbish.com"

require "rsc.io/pdf" v0.0.0-20180112171046-225057252246

which is unexpected.

What did you expect to see?

• The root go.mod file to be untouched
• No resolving required when doing vgo list ./... at the top module level

What did you see instead?

Per above.

[myitcv]

Updated this issue description to include a standalone example.

[rsc]

This is a dup of #24605 - ... has to avoid walking into directories containing go.mod files.