x/playground: web app runtime error with file/dir name conflicts in the txtar

[yaegashi]

What did you do?

Run the following in the Go Playground: https://play.golang.org/p/92soX8Gyrsn

package main

func main() {}
-- a --
-- a/b --

What did you expect to see?

It should tell there's a file/dir name conflict in the txtar.

What did you see instead?

Error communicating with remote server.
Program exited.

Addtional info

The playground web app emits either of the following runtime errors when there's a file/dir name conflict:

cmdFunc error: mkdir /tmp/sandbox253661173/a: not a directory

cmdFunc error: error creating temp file "/tmp/sandbox446449006/a": open /tmp/sandbox446449006/a: is a directory

[gopherbot]

Change https://golang.org/cl/297369 mentions this issue: playground: check file/dir name conflicts in txtar

[dmitshur]

CC @golang/release.