x/tools/cmd/present: support play snippets in module mode

[eliasnaur]

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

$ go version
go version devel +9325bec899 Wed Nov 13 11:59:24 2019 +0100 darwin/amd64

Does this issue reproduce with the latest release?

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

go env Output

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/elias/Library/Caches/go-build"
GOENV="/Users/elias/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/elias/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/elias/go-tip"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/elias/go-tip/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/elias/proj/gophercon-2019-talk/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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/_7/lnt35k555hl2bs7fjygkhgx00000gp/T/go-build183530635=/tmp/go-build -gno-record-gcc-switches -fno-common"
GOROOT/bin/go version: go version devel +9325bec899 Wed Nov 13 11:59:24 2019 +0100 darwin/amd64
GOROOT/bin/go tool compile -V: compile version devel +9325bec899 Wed Nov 13 11:59:24 2019 +0100
uname -v: Darwin Kernel Version 18.7.0: Sat Oct 12 00:02:19 PDT 2019; root:xnu-4903.278.12~1/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.14.6
BuildVersion:	18G1012
lldb --version: lldb-1100.0.28.19
Apple Swift version 5.1 (swiftlang-1100.0.270.13 clang-1100.0.33.7)

What did you do?

$ git clone https://github.com/eliasnaur/gophercon-2019-talk
$ cd gophercon-2019-talk
$ GO111MODULE=on present

Then, I opened http://127.0.0.1:3999/gophercon-2019.slide#7 in a browser and pressed "run".

What did you expect to see?

The program running locally.

What did you see instead?

compile1.go:7:5: cannot find module providing package gioui.org/app: working directory is not part of a module

Program exited: exit status 1

present used to work with GO111MODULE=on. I believe the fix for #32027 broke it.

[mvdan]

I assume you've considered running present inside a module, even if it's a temporary one?

[eliasnaur]

github.com/eliasnaur/gophercon-2019-talk is a module: https://github.com/eliasnaur/gophercon-2019-talk/blob/master/go.mod and I run present from there.

[mvdan]

Oh, my bad for missing that detail.

[dmitshur]

To clarify, since you're running GO111MODULE=on present without any flags, this issue is about the local play execution mode (rather than using play.golang.org), without using Native Client (which we'll need to remove or deal with otherwise soon, made #35675 for it). To make it more explicit:

GO111MODULE=on present -use_playground=false -nacl=false

From looking at it briefly, I suspect the problem is that the snippet is being built in a temporary directory:

https://github.com/golang/tools/blob/5a76f03bc7c327212912ed6b2a76a10d7f39b224/playground/socket/socket.go#L358

Which means it doesn't use the same module where present may be running in. We should figure out what behavior we want instead.

[jub0bs]

No progress on this? I'm trying to produce a slidedeck that showcase the new golang.org/x/exp/maps package, and this issue seems to be blocking me...

[mvdan]

@jub0bs I don't think anyone maintains the present package; see #27026 for instance. If there was any progress, you would be able to see it. But more realistically, I don't think there will be progress anytime soon unless someone steps up.