cmd/go: leave $GOPATH/pkg/mod directories writable (removable)

[jasonkeene]

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

$ go version
go version go1.11rc1 linux/amd64

Does this issue reproduce with the latest release?

yeap

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

$ uname -a
Linux theia 4.15.0-32-generic #35-Ubuntu SMP Fri Aug 10 17:58:07 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/pivotal/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/pivotal/workspace/mod-experiment/go"
GOPROXY=""
GORACE=""
GOROOT="/home/pivotal/sdk/go1.11rc1"
GOTMPDIR=""
GOTOOLDIR="/home/pivotal/sdk/go1.11rc1/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/pivotal/workspace/mod-experiment/mod/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=/tmp/go-build771004922=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I tried to do rm -r $GOPATH/pkg/mod to reset my modules cache. It failed with a permissions error. Write permission bit is not set. Even rm -rf does not work.

Steps to reproduce:

$ mkdir ~/workspace/mod-experiment
$ cd ~/workspace/mod-experiment
$ export GOPATH=$PWD/go
$ mkdir go mod
$ cd mod
$ go mod init foo
go: creating new go.mod: module foo
$ go get rsc.io/quote
go: finding rsc.io/quote v1.5.2
go: finding rsc.io/sampler v1.3.0
go: finding golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c
go: downloading rsc.io/quote v1.5.2
go: downloading rsc.io/sampler v1.3.0
go: downloading golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c
$ rm -rf $GOPATH/pkg/mod
rm: cannot remove '/home/pivotal/workspace/mod-experiment/go/pkg/mod/golang.org/x/text@v0.0.0-20170915032832-14c0d48ead0c/AUTHORS': Permission denied
...
rm: cannot remove '/home/pivotal/workspace/mod-experiment/go/pkg/mod/rsc.io/sampler@v1.3.0/hello_test.go': Permission denied
$ chmod -R +w $GOPATH/pkg
$ rm -rf $GOPATH/pkg/mod

What did you expect to see?

The $GOPATH/pkg/mod dir should be deleted.

What did you see instead?

It wasn't.

[bradfitz]

https://tip.golang.org/cmd/go/#hdr-Remove_object_files_and_cached_files

$ go clean -modcache

[jasonkeene]

Interesting, I wasn't aware of that command. I think most folks are more familiar with rm -r though. Especially when deleting the entire $GOPATH it seems silly to require users to remember to do go clean -modcache and most likely forget that command and just do sudo rm -r $GOPATH.

[FiloSottile]

Read-only modules are useful to add friction to local modifications which cause "works on my machine" issues (which I'm often guilty of in Python for example).

However, we'd probably get most of the benefit by just marking the files read-only, and not the folders, such that modifying files still fails but removing them succeeds.

$ mkdir dir
$ touch dir/file
$ chmod 400 dir/file
$ rm -rf dir

vs

$ mkdir dir
$ touch dir/file
$ chmod -R 500 dir
$ rm -rf dir
rm: dir/file: Permission denied
rm: dir: Directory not empty

[wfernandes]

So if my understanding is correct, everything should be acceptable if we had the directories within the mod folder have write permissions but the files with read only permissions.

[jasonkeene]

This would work for me.

[agnivade]

Paging @rsc for a decision on this. Other folks are stumbling on this too.

What do you think of @FiloSottile's suggestion ?

[rsc]

I am still concerned that "write a temp file and mv it into the target file" will succeed at the system call level unless the directory is marked read-only (that's definitely true).

It may be that all the popular editors that use this trick are also smart enough to check the writability of the target file themselves.

I am also very surprised that rm -r is somehow too dumb to do the right thing.

But fine, we can leave the directories writable to make up for rm -r's inadequacy.