x/playground: play.golang.org hangs on a simple program with unreachable code

[marat-rkh]

I run this simple program on play.golang.org:

package main

func main() {
	return
	_ = "unreachable"
}

After I press "Run", the output window at the bottom of the page says "Waiting for remote server..." and nothing happens. If I run this program locally, it terminates instantly.

[pjebs]

I can verify this.

[bradfitz]

/cc @andybons @dmitshur @broady

[dmitshur]

It looks like a bug in the frontend script:

It seems to happen whenever there's vet output (in this case, a warning about unreachable code) and nothing is written to stdout.

[dmitshur]

The failing code is:

if (dataVet.Errors) {
	// inject errors from the vet as the first event in the output
	data.Events.unshift({Message: 'Go vet exited.\n\n', Kind: 'system', Delay: 0});
	data.Events.unshift({Message: dataVet.Errors, Kind: 'stderr', Delay: 0});
}

It fails when data.Events is null rather than an array.

[andybons]

@ysmolsky

[ysmolski]

I will take a look.

[ysmolski]

@andybons
I do remember fixing this long time ago. It seems that playground uses old version of godoc:

# Repo golang.org/x/tools at 48418e5 (2018-05-08)
ENV REV=48418e5732e1b1e2a10207c8007a5f959e422f20
RUN go get -d golang.org/x/tools/go/ast/astutil `#and 3 other pkgs` &&\
    (cd /go/src/golang.org/x/tools && (git cat-file -t $REV 2>/dev/null || git fetch -q origin $REV) && git reset --hard $REV)

And this was fixed on May 25th: https://go-review.googlesource.com/c/tools/+/113875

[gopherbot]

Change https://golang.org/cl/140017 mentions this issue: playground: use latest godoc with fixed playground.js

[bradfitz]

Reopening until this is deployed.

[dmitshur]

Redeployed play.golang.org, confirmed the issue is resolved:

(Source: https://play.golang.org/p/egwBhqHiRnk.)