When getting started with the JVM, it's not obvious how/when to create your intial lockfile

[stuhood]

To create a lockfile for the JVM, you need to run ./pants generate-lockfiles. But if you haven't done that, and have redefined the lockfile location, you will get a unmatched globs warning instead:

10:14:46.00 [ERROR] 1 Exception encountered:

  Exception: Unmatched glob from The resolve `jvm-default` from `[jvm].resolves`: "lib/3rdparty/jvm/default.lock"

Do the file(s) exist? If so, check if the file(s) are in your `.gitignore` or the global `pants_ignore` option, which may result in Pants not being able to see the file(s) even though they exist on disk. Refer to https://www.pantsbuild.org/v2.14/docs/troubleshooting#pants-cannot-find-a-file-in-your-project.

Rather than an unmatched glob, we should instead detect the missing file at a higher level, and explain how to create the lockfile. It looks like we already attempt to do that (in some cases):

pants/src/python/pants/jvm/resolve/coursier_fetch.py

Lines 761 to 767 in c1514b7

	lockfile_snapshot = await Get(Snapshot, PathGlobs([lockfile_req.read_lockfile_dest]))
	if not lockfile_snapshot.files:
	raise ValueError(
	f"No lockfile found at {lockfile_req.read_lockfile_dest}, which is configured "
	f"by the option {lockfile_req.lockfile_option_name}."
	f"Run {regen_command} to generate it."
	)

... but apparently not in others.

[rbuckland]

The reproducible scenario is where the lock file exists, but it is empty.

❯ cat pants.toml 
[GLOBAL]
pants_version = "2.14.0"

backend_packages = [
  "pants.backend.python",
  "pants.backend.docker",
  "pants.backend.shell",
  'pants.backend.python.lint.black',
  'pants.backend.python.lint.isort',

  # antlr compiler
  "pants.backend.experimental.java",
]

[python]
# This will become the default in Pants 2.15.
tailor_pex_binary_targets = false

[jvm]
jdk = "temurin:1.17"

[jvm.resolves]
jvm-default = "lib/3rdparty/jvm/default.lock"

❯ echo > lib/3rdparty/jvm/default.lock 

❯ ./pants run  path/to-something/with/jar/dependency 
10:26:46.04 [ERROR] 1 Exception encountered:

  KeyError: 'entries'

[rbuckland]

the other scenario is where the lockfile does not exist, as per the original issue description.
my "activities" were

• define the repo standard, non-pants default location in pants.toml - lib/3rdparty/jvm/default.lock
• mkdir -p ib/3rdparty/jvm
• run pants and it errored that the file did not exist (see issue description)
• "ok, create an empty file maybe" :-) echo > lib/3rdparty/jvm/default.lock
• resulted in even worse error

[stuhood]

• run pants and it errored that the file did not exist (see issue description)

Which command did you run, in particular?

[rbuckland]

@stuhood - these steps - #17521 (comment)