Improve error message for isort failure in IsortRun

[Eric-Arellano]

Problem

When ./pants fmt.isort fails, its failure message is difficult to parse, especially because it starts with the command, rather than human readable English introducing what happened. For example:

FAILURE: /Users/eric/.pyenv/shims/python3.6 /Users/eric/.cache/pants/python/CPython-3.6.8/d6bcba436bdefbc27a69dd880d6ee5716e004764/isort-c201e856817dc9ae802d18e3ec45a3bfa4c2ac11.pex --check-only src/python/pants/util/tarutil.py src/python/pants/util/retry.py src/python/pants/util/osutil.py src/python/pants/util/memo.py src/python/pants/util/process_handler.py src/python/pants/util/strutil.py src/python/pants/util/py2_compat.py src/python/pants/util/meta.py src/python/pants/util/xml_parser.py src/python/pants/util/objects.py src/python/pants/util/rwbuf.py src/python/pants/util/collections_abc_backport.py ... exited non-zero (1).

FAILURE

Solution

Invert the error message to be more readable.

Result

For example:

FAILURE: Exited with return code 1 while running `/Users/eric/.pyenv/shims/python3.6 /Users/eric/.cache/pants/python/CPython-3.6.8/d6bcba436bdefbc27a69dd880d6ee5716e004764/isort-c201e856817dc9ae802d18e3ec45a3bfa4c2ac11.pex --check-only src/python/pants/util/tarutil.py src/python/pants/util/retry.py src/python/pants/util/osutil.py src/python/pants/util/memo.py src/python/pants/util/process_handler.py src/python/pants/util/strutil.py src/python/pants/util/py2_compat.py src/python/pants/util/meta.py src/python/pants/util/xml_parser.py src/python/pants/util/objects.py src/python/pants/util/rwbuf.py src/python/pants/util/collections_abc_backport.py`.

FAILURE

[jsirois]

This shouldn't be a console task as things stand. I'm almost positive folks install it as a dependency of / directly in the compile goal for example. Any task not being run directly like that should never be a console task. I know this is vague but hopefully makes sense. If it helps, in v2 the console rule would be fmt, the implementations like isort would be plain rules returning result objects encapsulating the report of what they did. The fmt root console rule would print all the aggregate results it received from isort, gofmt, etc.

[jsirois]

Here's a rule for you, if the task is installed in a non-singleton goal in v1 it can't be a console task.

[Eric-Arellano]

Bummer, but good to know.

Is there any way to not swallow stdout and stderr when using ./pants --quiet in this case? That's really my main motivation. I'd love for build-support/bin/isort.sh to give better output. In the setup repo, I wrote a Python 3 script to do this, and Danny encouraged me to upstream those improvements to Pants itself.

Even if no, hope we can keep this change to make the TaskError a bit more readable: https://github.com/pantsbuild/pants/pull/7462/files#diff-71900004479b8668c33e31f7159d67ecR67.

[jsirois]

I'm pretty sure there is no canned way. The TaskError improvement stands on its own however.

[jsirois]

Oops. I disagree on the error message. You can actually directly run the prior message. You can't with yours.

[Eric-Arellano]

Bummer. Once we close out the blacklist and get Py3 on every CI shard, I'll copy my port of isort.sh to Python 3 over to here, which parses the output so that it's more readable for us.

--

Updated error message to keep the whole command. Think this is still an improvement, albeit much smaller scope than originally intended.

[jsirois]

To be clear, the existing message is structured:
<path to python actually used> <path to _loose_ isort PEX dir (not a directly executable PEX zip)> <args>