gh-125355: Rewrite parse_intermixed_args() in argparse (GH-125356)

* The parser no longer changes temporarily during parsing.
* Default values are not processed twice.
* Required mutually exclusive groups containing positional arguments are
  now supported.
* The missing arguments report now includes the names of all required
  optional and positional arguments.
* Unknown options can be intermixed with positional arguments in
  parse_known_intermixed_args().

1 files changed, 34 insertions, 65 deletions

diff --git a/Lib/argparse.py b/Lib/argparse.py
index 49271a1..024622b 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1924,6 +1924,9 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         return args
 
     def parse_known_args(self, args=None, namespace=None):
+        return self._parse_known_args2(args, namespace, intermixed=False)
+
+    def _parse_known_args2(self, args, namespace, intermixed):
         if args is None:
             # args default to the system args
             args = _sys.argv[1:]
@@ -1950,18 +1953,18 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         # parse the arguments and exit if there are any errors
         if self.exit_on_error:
             try:
-                namespace, args = self._parse_known_args(args, namespace)
+                namespace, args = self._parse_known_args(args, namespace, intermixed)
             except ArgumentError as err:
                 self.error(str(err))
         else:
-            namespace, args = self._parse_known_args(args, namespace)
+            namespace, args = self._parse_known_args(args, namespace, intermixed)
 
         if hasattr(namespace, _UNRECOGNIZED_ARGS_ATTR):
             args.extend(getattr(namespace, _UNRECOGNIZED_ARGS_ATTR))
             delattr(namespace, _UNRECOGNIZED_ARGS_ATTR)
         return namespace, args
 
-    def _parse_known_args(self, arg_strings, namespace):
+    def _parse_known_args(self, arg_strings, namespace, intermixed):
         # replace arg strings that are file references
         if self.fromfile_prefix_chars is not None:
             arg_strings = self._read_args_from_files(arg_strings)
@@ -2052,6 +2055,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
                 # if we found no optional action, skip it
                 if action is None:
                     extras.append(arg_strings[start_index])
+                    extras_pattern.append('O')
                     return start_index + 1
 
                 # if there is an explicit argument, try to match the
@@ -2087,6 +2091,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
                                 sep = ''
                         else:
                             extras.append(char + explicit_arg)
+                            extras_pattern.append('O')
                             stop = start_index + 1
                             break
                     # if the action expect exactly one argument, we've
@@ -2165,6 +2170,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         # consume Positionals and Optionals alternately, until we have
         # passed the last option string
         extras = []
+        extras_pattern = []
         start_index = 0
         if option_string_indices:
             max_option_string_index = max(option_string_indices)
@@ -2178,7 +2184,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
                 if next_option_string_index in option_string_indices:
                     break
                 next_option_string_index += 1
-            if start_index != next_option_string_index:
+            if not intermixed and start_index != next_option_string_index:
                 positionals_end_index = consume_positionals(start_index)
 
                 # only try to parse the next optional if we didn't consume
@@ -2194,16 +2200,35 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
             if start_index not in option_string_indices:
                 strings = arg_strings[start_index:next_option_string_index]
                 extras.extend(strings)
+                extras_pattern.extend(arg_strings_pattern[start_index:next_option_string_index])
                 start_index = next_option_string_index
 
             # consume the next optional and any arguments for it
             start_index = consume_optional(start_index)
 
-        # consume any positionals following the last Optional
-        stop_index = consume_positionals(start_index)
+        if not intermixed:
+            # consume any positionals following the last Optional
+            stop_index = consume_positionals(start_index)
 
-        # if we didn't consume all the argument strings, there were extras
-        extras.extend(arg_strings[stop_index:])
+            # if we didn't consume all the argument strings, there were extras
+            extras.extend(arg_strings[stop_index:])
+        else:
+            extras.extend(arg_strings[start_index:])
+            extras_pattern.extend(arg_strings_pattern[start_index:])
+            extras_pattern = ''.join(extras_pattern)
+            assert len(extras_pattern) == len(extras)
+            # consume all positionals
+            arg_strings = [s for s, c in zip(extras, extras_pattern) if c != 'O']
+            arg_strings_pattern = extras_pattern.replace('O', '')
+            stop_index = consume_positionals(0)
+            # leave unknown optionals and non-consumed positionals in extras
+            for i, c in enumerate(extras_pattern):
+                if not stop_index:
+                    break
+                if c != 'O':
+                    stop_index -= 1
+                    extras[i] = None
+            extras = [s for s in extras if s is not None]
 
         # make sure all required actions were present and also convert
         # action defaults which were not given as arguments
@@ -2469,10 +2494,6 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         # are then parsed.  If the parser definition is incompatible with the
         # intermixed assumptions (e.g. use of REMAINDER, subparsers) a
         # TypeError is raised.
-        #
-        # positionals are 'deactivated' by setting nargs and default to
-        # SUPPRESS.  This blocks the addition of that positional to the
-        # namespace
 
         positionals = self._get_positional_actions()
         a = [action for action in positionals
@@ -2481,59 +2502,7 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
             raise TypeError('parse_intermixed_args: positional arg'
                             ' with nargs=%s'%a[0].nargs)
 
-        if [action.dest for group in self._mutually_exclusive_groups
-            for action in group._group_actions if action in positionals]:
-            raise TypeError('parse_intermixed_args: positional in'
-                            ' mutuallyExclusiveGroup')
-
-        try:
-            save_usage = self.usage
-            try:
-                if self.usage is None:
-                    # capture the full usage for use in error messages
-                    self.usage = self.format_usage()[7:]
-                for action in positionals:
-                    # deactivate positionals
-                    action.save_nargs = action.nargs
-                    # action.nargs = 0
-                    action.nargs = SUPPRESS
-                    action.save_default = action.default
-                    action.default = SUPPRESS
-                namespace, remaining_args = self.parse_known_args(args,
-                                                                  namespace)
-                for action in positionals:
-                    # remove the empty positional values from namespace
-                    if (hasattr(namespace, action.dest)
-                            and getattr(namespace, action.dest)==[]):
-                        from warnings import warn
-                        warn('Do not expect %s in %s' % (action.dest, namespace))
-                        delattr(namespace, action.dest)
-            finally:
-                # restore nargs and usage before exiting
-                for action in positionals:
-                    action.nargs = action.save_nargs
-                    action.default = action.save_default
-            optionals = self._get_optional_actions()
-            try:
-                # parse positionals.  optionals aren't normally required, but
-                # they could be, so make sure they aren't.
-                for action in optionals:
-                    action.save_required = action.required
-                    action.required = False
-                for group in self._mutually_exclusive_groups:
-                    group.save_required = group.required
-                    group.required = False
-                namespace, extras = self.parse_known_args(remaining_args,
-                                                          namespace)
-            finally:
-                # restore parser values before exiting
-                for action in optionals:
-                    action.required = action.save_required
-                for group in self._mutually_exclusive_groups:
-                    group.required = group.save_required
-        finally:
-            self.usage = save_usage
-        return namespace, extras
+        return self._parse_known_args2(args, namespace, intermixed=True)
 
     # ========================
     # Value conversion methods