x/build/cmd/coordinator: detect temp dir leaks

[bradfitz]

The build infrastructure could explicitly set $TMPDIR (or %TMP% on Windows) to an empty directory and at the end of a successful build check that the directory is still empty. If not, it could fail.

Or we could do it in cmd/dist test, perhaps optionally.

/cc @ianlancetaylor @alexbrainman

[alexbrainman]

SGTM

Non Windows users might struggle if they do not know that you cannot delete running executable on Windows, you cannot delete opened file on Windows, you cannot remove directory if it is current directory on Windows and similar.

Alex

[bradfitz]

The first part of this is done. https://go-review.googlesource.com/c/144637 in Oct 2018 set $TMPDIR to $WORKDIR/tmp.

Now we need to make the coordinator do the $WORKDIR/tmp scan at the end of a successful build.

This bug is about modifying the coordinator to do that. Bug #30500 is about fixing the resulting problems. We'll probably need a way to make the trybot behavior opt-in for a bit while we clean up the tree.

/cc @bsiegert