Track whether a repo is pinned or unpinned by explicit attr

Doing this by performing string interpretation on the repo name is a bit
brittle. And it works less well under Bzlmod where the unpinned repo
name is going to look something like
`rules_jvm_external~~maven~unpinned_maven`.

After this change, the lockfile pinning script, `@maven//:pin` will use the local
machine's Coursier cache (`~/Library/Caches/Coursier` on MacOS) even under
Bzlmod. A populated cache makes version resolutions substantially faster to obtain.

private/extensions/maven.bzl

@@ -412,6 +412,7 @@ def _maven_impl(mctx):
  # created from the maven_install.json file in the coursier_fetch
  # invocation after this.
  name = "unpinned_" + name if repo.get("lock_file") else name,
+ pinned_repo_name = name if repo.get("lock_file") else None,
  user_provided_name = name,
  repositories = repo.get("repositories"),
  artifacts = artifacts_json,

private/rules/coursier.bzl

@@ -138,7 +138,7 @@ def _is_directory(repository_ctx, path):
  return repository_ctx.which("test") and repository_ctx.execute(["test", "-d", path]).return_code == 0
 
 def _is_unpinned(repository_ctx):
- return repository_ctx.attr.name.startswith("unpinned_")
+ return repository_ctx.attr.pinned_repo_name != ""
 
 def _shell_quote(s):
  # Lifted from
@@ -1240,7 +1240,7 @@ def _coursier_fetch_impl(repository_ctx):
  # This repository rule can be either in the pinned or unpinned state, depending on when
  # the user invokes artifact pinning. Normalize the repository name here.
  if _is_unpinned(repository_ctx):
- repository_name = repository_ctx.name[len("unpinned_"):]
+ repository_name = repository_ctx.attr.pinned_repo_name
  outdated_build_file_content = ""
  else:
  repository_name = repository_ctx.name
@@ -1442,6 +1442,10 @@ coursier_fetch = repository_rule(
  ),
  "ignore_empty_files": attr.bool(default = False, doc = "Treat jars that are empty as if they were not found."),
  "additional_coursier_options": attr.string_list(doc = "Additional options that will be passed to coursier."),
+ "pinned_repo_name": attr.string(
+ doc = "Name of the corresponding pinned repo for this repo. Presence implies that this is an unpinned repo.",
+ mandatory = False,
+ ),
  },
  environ = [
  "JAVA_HOME",

private/rules/maven_install.bzl

@@ -123,6 +123,7 @@ def maven_install(
  # created from the maven_install.json file in the coursier_fetch
  # invocation after this.
  name = name if maven_install_json == None else "unpinned_" + name,
+ pinned_coursier_fetch = None if maven_install_json == None else name,
  repositories = repositories_json_strings,
  artifacts = artifacts_json_strings,
  fail_on_missing_checksum = fail_on_missing_checksum,