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Pants

i'm wondering if an exception is being raised in the code you're calling.

maybe drop a `try: except:` around the entire rule body and see if it is even running

is there a good way to log the contents of the exception / can i re-raise it?

oh, another thing to check: is compiler_inst precisely an instance of `Compiler`? `SingletonRule(Compiler, compiler_inst)`

"is there a good way to log the contents of the exception / can i re-raise it?" &lt;- just printing to stdout

so Compiler is a mixin so that might be problem numero uno

`SingletonRule` should definitely validate that.

i read that somewhere but didn't think it applied to me (for no reason)

(i mean, subclass all you want. but we do exact type matches for almost everything)

but yes: `SingletonRule` should blow up immediately there.

i'm not familiar with what an exact type match means

`type(x) is Compiler` as opposed to `isinstance(x, Compiler)`

if x is an instance of a subclass of `Compiler`, `type(x)` is the subclass

i'm unblocked now it's not clear to me why the exact match is necessary but i haven't checked that code yet

the next thing i saw in there is that Snapshots captured from the working copy are all implicitly relative to the root of the working copy

yep, i knew i was going to run into that at exactly the point i was able to get the engine to run my rules

so the idea of absolute paths and relativizing doesn't make sense / isn't necessary

`ValueError: At least one request failed: [Throw(exc=Exception(u'Failed to parse PathGlobs: Failed to parse PathGlobs for include(["/private/var/folders/j2/x6ckkbrn08g8536d6_n3_ywm0000gn/T/tmpMkhtBs_BUILD_ROOT/hello.cpp"]), exclude([]): Absolute paths not supported: "/private/var/folders/j2/x6ckkbrn08g8536d6_n3_ywm0000gn/T/tmpMkhtBs_BUILD_ROOT/hello.cpp"',))]. Visualized as /var/folders/j2/x6ckkbrn08g8536d6_n3_ywm0000gn/T/tmpQnrY04.dot`

as an example of executing a process though:

```@rule(JVMImports, [Select(Snapshot)])
def extract_imports(snapshot):
  # TODO
  cmd = tuple(['/Users/stuhood/src/pants/extractimports'] + [f.path for f in snapshot.files])
  result = yield Get(ExecuteProcessResult,
                     ExecuteProcessRequest(cmd, [], snapshot.fingerprint, snapshot.digest_length))
  if result.exit_code:
    raise Exception('Import extraction `{}` failed ({}):\n{}'.format(
      ' '.join(cmd), result.exit_code, result.stderr))

  def packages():
    matched = set()
    for p in result.stdout.splitlines():
      match = _PACKAGE_RE.match(p.strip())
      if match:
        yield JVMPackageName(match.group(1))

  yield JVMImports(set(packages()))```