move the process_finder CLI code to its own library

Summary:
Enable pyre-strict type checking for `process_finder.py`, and split it into
its own library.

Reviewed By: genevievehelsel

Differential Revision: D20178483

fbshipit-source-id: e6c62ca5d84c7b7e599ae00fb51df6f7e4c55a65

eden/cli/doctor/test/lib/testcase.py

@@ -11,11 +11,10 @@ from typing import Tuple
 import eden.cli.doctor as doctor
 import eden.dirstate
 from eden.cli.config import EdenCheckout
+from eden.cli.test.lib.fake_process_finder import FakeProcessFinder
 from eden.cli.test.lib.output import TestOutput
 from eden.test_support.temporary_directory import TemporaryDirectoryMixin
 
-from .fake_process_finder import FakeProcessFinder
-
 
 class DoctorTestBase(unittest.TestCase, TemporaryDirectoryMixin):
     def create_fixer(self, dry_run: bool) -> Tuple[doctor.ProblemFixer, TestOutput]:

eden/cli/process_finder.py

@@ -4,6 +4,8 @@
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2.
 
+# pyre-strict
+
 import abc
 import logging
 import os
@@ -22,7 +24,7 @@ class ProcessInfo(NamedTuple):
     eden_dir: Optional[Path]
 
 
-log = logging.getLogger("eden.cli.process_finder")
+log: logging.Logger = logging.getLogger("eden.cli.process_finder")
 
 
 class ProcessFinder(abc.ABC):
@@ -160,7 +162,7 @@ class LinuxProcessFinder(ProcessFinder):
                     yield info
 
 
-def new():
+def new() -> ProcessFinder:
     if platform.system() == "Linux":
         return LinuxProcessFinder()
     return NopProcessFinder()