cmd/cue: tool failure is hard to debug

[rogpeppe]

What version of CUE are you using (cue version)?

$ cue version
cue version v0.0.0-20231004170206-6c71b2c90d63

go version devel go1.21-af8f94e3c5 Tue Jul 11 21:30:51 2023 +0000
      -buildmode exe
       -compiler gc
  DefaultGODEBUG panicnil=1
     CGO_ENABLED 1
          GOARCH amd64
            GOOS linux
         GOAMD64 v1
             vcs git
    vcs.revision 6c71b2c90d63846f2983deb07102253298a568c0
        vcs.time 2023-10-04T17:02:06Z
    vcs.modified false

Does this issue reproduce with the latest stable release?

Yes

What did you do?

! exec cue cmd foo
stdout 'foo'
stdout 'bar'

-- cue.mod/module.cue --
module: "example.com"

-- foo_tool.cue --
package foo
import "tool/file"

command: foo: bar: file.Create & {
	filename: "/something/non-existent"
	contents: "x"
}

What did you expect to see?

A passing test: the failure should at least mention the path to the task that failed.

What did you see instead?

> ! exec cue cmd foo
[stderr]
task failed: open /something/non-existent: no such file or directory
[exit status 1]
> stdout 'foo'
FAIL: /tmp/testscript573993553/x.txtar/script.txtar:2: no match for `foo` found in stdout
error running /tmp/x.txtar in /tmp/testscript573993553/x.txtar

The error message does not mention which task has failed, making it quite hard to determine where the error has arisen, particularly when there are many hundreds of tasks.

[rogpeppe]

Another possibility would be that passing the -v flag to cue cmd might print information about commands being run, but it doesn't change the output at all.