cmd/dist: make it possible to filter output of background commands
Many of the commands dist test executes are "background" commands run
by a work queue system. The work queue allows it to run commands in
parallel, but still serialize their output. Currently, the work queue
system assumes that exec.Cmd.Stdout and Stderr will be nil and that it
can take complete control over them.
We're about to inject output filters on many of these commands, so we
need a way to interpose on Stdout and Stderr. This CL rearranges
responsibilities in the work queue system to make that possible. Now,
the thing enqueuing the work item is responsible to constructing the
Cmd to write its output to work.out. There's only one place that
constructs work objects (there used to be many more), so that's
relatively easy, and sets us up to add filters.
For #37486.
Change-Id: I55ab71ddd456a12fdbf676bb49f698fc08a5689b
Reviewed-on: https://go-review.googlesource.com/c/go/+/494957
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>