Detour pydev_monkey.patch_args and construct the appropriate ptvsd command line.

ptvsd/multiproc.py

@@ -8,6 +8,7 @@ import atexit
 import itertools
 import os
 import random
+import re
 import socket
 
 try:
@@ -121,3 +122,100 @@ def init_subprocess(initial_pid, initial_request, parent_pid, parent_port, first
     ptvsd.wait_for_attach()
 
 
+def patch_args(args):
+    """
+    Patches a command line invoking Python such that it has the same meaning, but
+    the process runs under ptvsd. In general, this means that given something like:
+
+        python -R -Q warn -m app
+
+    the result should be:
+
+        python -R -Q warn -m ptvsd --host localhost --port 0 --multiprocess --wait -m app
+
+    Note that the first -m above is interpreted by Python, and the second by ptvsd.
+    """
+
+    args = list(args)
+    print(args)
+
+    # First, let's find the target of the invocation. This is one of:
+    #
+    #   filename.py
+    #   -m module_name
+    #   -c "code"
+    #   -
+    #
+    # This needs to take into account other switches that have values:
+    #
+    #   -Q -W -X --check-hash-based-pycs
+    #
+    # because in something like "-X -c", -c is a value, not a switch.
+    expect_value = False
+    for i, arg in enumerate(args):
+        # Skip Python binary.
+        if i == 0:
+            continue
+
+        if arg == '-':
+            # We do not support debugging while reading from stdin, so just let this
+            # process run without debugging.
+            return args
+
+        if expect_value:
+            expect_value = False
+            continue
+
+        if not arg.startswith('-') or arg in ('-c', '-m'):
+            break
+
+        if arg.startswith('--'):
+            expect_value = (arg == '--check-hash-based-pycs')
+            continue
+
+        # All short switches other than -c and -m can be combined together, including
+        # those with values. So, instead of -R -B -v -Q old, we might see -RBvQ old.
+        # Furthermore, the value itself can be concatenated with the switch, so rather
+        # than -Q old, we might have -Qold. When switches are combined, any switch that
+        # has a value "eats" the rest of the argument; for example, -RBQv is treated as
+        # -R -B -Qv, and not as -R -B -Q -v. So, we need to check whether one of 'Q',
+        # 'W' or 'X' was present somewhere in the arg, and whether there was anything
+        # following it in the arg. If it was there but nothing followed after it, then
+        # the switch is expecting a value.
+        split = re.split(r'[QWX]', arg, maxsplit=1)
+        expect_value = (len(split) > 1 and split[-1] != '')
+
+    else:
+        # Didn't find the target, so we don't know how to patch this command line; let
+        # it run without debugging.
+        return args
+
+    if not args[i].startswith('-'):
+        # If it was a filename, it can be a Python file, a directory, or a zip archive
+        # that is treated as if it were a directory. However, pydevd only supports the
+        # first scenario. Distinguishing between these can be tricky, and getting it
+        # wrong means that process fails to launch, so be conservative.
+        if not args[i].endswith('.py'):
+            print('!!!', args[i])
+            return args
+
+    # Now we need to inject the ptvsd invocation right before the target. The target
+    # itself can remain as is, because ptvsd is compatible with Python in that respect.
+    args[i:i] = [
+        '-m', 'ptvsd',
+        '--server-host', 'localhost',
+        '--port', '0',
+        '--multiprocess',
+        '--wait'
+    ]
+
+    print(args)
+    return args
+
+
+def patch_and_quote_args(args):
+    # On Windows, pydevd expects arguments to be quoted and escaped as necessary, such
+    # that simply concatenating them via ' ' produces a valid command line. This wraps
+    # patch_args and applies quoting (quote_args contains platform check), so that the
+    # implementation of patch_args can be kept simple.
+    return pydev_monkey.quote_args(patch_args(args))

ptvsd/pydevd_hooks.py

@@ -129,7 +129,7 @@ def install(pydevd_module, address,
     pydevd_comm.start_client = _start_client
 
     # This is invoked when a child process is spawned with multiproc debugging enabled.
-    pydev_monkey._get_python_c_args = get_python_c_args
+    pydev_monkey.patch_args = multiproc.patch_and_quote_args
 
     # Ensure that pydevd is using our functions.
     pydevd_module.start_server = _start_server

ptvsd/socket.py

@@ -76,6 +76,10 @@ def create_server(host, port, timeout=None):
         host = 'localhost'
     server = _new_sock()
     server.bind((host, port))
+
+    # _, listener_port = server.getsockname()
+    # print('Listening on', listener_port)
+
     if timeout is not None:
         server.settimeout(timeout)
     server.listen(1)