python · emmatyping · Jan 8, 2019 · Jan 6, 2019 · Jan 7, 2019 · Jan 7, 2019
diff --git a/mypy/dmypy.py b/mypy/dmypy.py
@@ -1,7 +1,5 @@
 """Client for mypy daemon mode.
 
-Highly experimental!  Only supports UNIX-like systems.
-
 This manages a daemon process which keeps useful state in memory
 rather than having to read it back from disk on each run.
 """

diff --git a/mypy/dmypy_server.py b/mypy/dmypy_server.py
@@ -1,12 +1,12 @@
 """Server for mypy daemon mode.
 
-Only supports UNIX-like systems.
-
 This implements a daemon process which keeps useful state in memory
 to enable fine-grained incremental reprocessing of changes.
 """
 
+import argparse
 import base64
+import io
 import json
 import os
 import pickle
@@ -29,6 +29,7 @@
 from mypy.modulefinder import BuildSource, compute_search_paths
 from mypy.options import Options
 from mypy.typestate import reset_global_state
+from mypy.util import redirect_stderr, redirect_stdout
 from mypy.version import __version__
 
 
@@ -270,11 +271,19 @@ def cmd_stop(self) -> Dict[str, object]:
     def cmd_run(self, version: str, args: Sequence[str]) -> Dict[str, object]:
         """Check a list of files, triggering a restart if needed."""
         try:
-            sources, options = mypy.main.process_options(
-                ['-i'] + list(args),
-                require_targets=True,
-                server_options=True,
-                fscache=self.fscache)
+            # Process options can exit on improper arguments, so we need to catch that and
+            # capture stderr so the client can report it
+            stderr = io.StringIO()
+            stdout = io.StringIO()
+            with redirect_stderr(stderr):
+                with redirect_stdout(stdout):
+                    sources, options = mypy.main.process_options(
+                        ['-i'] + list(args),
+                        require_targets=True,
+                        server_options=True,
+                        fscache=self.fscache,
+                        program='mypy-daemon',
+                        header=argparse.SUPPRESS)
             # Signal that we need to restart if the options have changed
             if self.options_snapshot != options.snapshot():
                 return {'restart': 'configuration changed'}
@@ -288,6 +297,8 @@ def cmd_run(self, version: str, args: Sequence[str]) -> Dict[str, object]:
                     return {'restart': 'plugins changed'}
         except InvalidSourceList as err:
             return {'out': '', 'err': str(err), 'status': 2}
+        except SystemExit as e:
+            return {'out': stdout.getvalue(), 'err': stderr.getvalue(), 'status': e.code}
         return self.check(sources)
 
     def cmd_check(self, files: Sequence[str]) -> Dict[str, object]:

diff --git a/mypy/main.py b/mypy/main.py
@@ -297,15 +297,17 @@ def process_options(args: List[str],
                     require_targets: bool = True,
                     server_options: bool = False,
                     fscache: Optional[FileSystemCache] = None,
+                    program: str = 'mypy',
+                    header: str = HEADER,
                     ) -> Tuple[List[BuildSource], Options]:
     """Parse command line arguments.
 
     If a FileSystemCache is passed in, and package_root options are given,
     call fscache.set_package_root() to set the cache's package root.
     """
 
-    parser = argparse.ArgumentParser(prog='mypy',
-                                     usage=HEADER,
+    parser = argparse.ArgumentParser(prog=program,
+                                     usage=header,
                                      description=DESCRIPTION,
                                      epilog=FOOTER,
                                      fromfile_prefix_chars='@',

diff --git a/mypy/util.py b/mypy/util.py
@@ -1,10 +1,12 @@
 """Utility functions with no non-trivial dependencies."""
+import contextlib
 import os
 import pathlib
 import re
 import subprocess
 import sys
-from typing import TypeVar, List, Tuple, Optional, Dict, Sequence
+from types import TracebackType
+from typing import TypeVar, List, Tuple, Optional, Dict, Sequence, TextIO
 
 MYPY = False
 if MYPY:
@@ -255,3 +257,50 @@ def hard_exit(status: int = 0) -> None:
     sys.stdout.flush()
     sys.stderr.flush()
     os._exit(status)
+
+
+# The following is a backport of stream redirect utilities from Lib/contextlib.py
+# We need this for 3.4 support. They can be removed in March 2019!
+
+
+class _RedirectStream:
+
+    _stream = None  # type: str
+
+    def __init__(self, new_target: TextIO) -> None:
+        self._new_target = new_target
+        # We use a list of old targets to make this CM re-entrant
+        self._old_targets = []  # type: List[TextIO]
+
+    def __enter__(self) -> TextIO:
+        self._old_targets.append(getattr(sys, self._stream))
+        setattr(sys, self._stream, self._new_target)
+        return self._new_target
+
+    def __exit__(self,
+                 exc_ty: 'Optional[Type[BaseException]]' = None,
+                 exc_val: Optional[BaseException] = None,
+                 exc_tb: Optional[TracebackType] = None,
+                 ) -> bool:
+        setattr(sys, self._stream, self._old_targets.pop())
+        return False
+
+
+class redirect_stdout(_RedirectStream):
+    """Context manager for temporarily redirecting stdout to another file.
+        # How to send help() to stderr
+        with redirect_stdout(sys.stderr):
+            help(dir)
+        # How to write help() to a file
+        with open('help.txt', 'w') as f:
+            with redirect_stdout(f):
+                help(pow)
+    """
+
+    _stream = "stdout"
+
+
+class redirect_stderr(_RedirectStream):
+    """Context manager for temporarily redirecting stderr to another file."""
+
+    _stream = "stderr"
diff --git a/test-data/unit/daemon.test b/test-data/unit/daemon.test
@@ -122,3 +122,11 @@ Daemon stopped
 import bar
 [file bar.py]
 pass
+
+[case testDaemonRunNoTarget]
+$ dmypy run -- --follow-imports=error
+Daemon started
+mypy-daemon: error: Missing target module, package, files, or command.
+== Return code: 2
+$ dmypy stop
+Daemon stopped