Clean up run_command

This cleans up run_command to separate Windows and non-Windows argument
prep. It still needs to be verified on Windows.

One other change is to the structure of E970. E970 assumed that if a
command was not found we would always have the command name, but that is
not true on Windows if the input command is a string, which we can't
split reliably.

spacy/errors.py

@@ -812,7 +812,7 @@ class Errors(metaclass=ErrorsWithCodes):
             "assign it a name, e.g. `@Language.component('your_name')`. You can "
             "then run `nlp.replace_pipe('{name}', 'your_name')`.")
     E969 = ("Expected string values for field '{field}', but received {types} instead. ")
-    E970 = ("Can not execute command '{str_command}'. Do you have '{tool}' installed?")
+    E970 = ("Can not execute command '{str_command}'.{msg}")
     E971 = ("Found incompatible lengths in `Doc.from_array`: {array_length} for the "
             "array and {doc_length} for the Doc itself.")
     E972 = ("`Example.__init__` got None for '{arg}'. Requires Doc.")

spacy/util.py

@@ -954,23 +954,36 @@ def run_command(
         when you want to run the command more like a function.
     RETURNS (Optional[CompletedProcess]): The process object.
     """
-    if isinstance(command, str):
+
-        # On Windows, it's possible for the split here to be different from what
+    # The actual command to execute
-        # will actually be used for execution, but it will *usually* be correct,
+    cmd_to_run = None
-        # and is only used in debugging output if a command failed.
+    # these are used for debugging
-        cmd_list = shlex.split(command, posix=True)
+    cmd_str = None
-        cmd_str = command
+    tool = None
+
+    if is_windows:
+        # On Windows we can pass a list or string. In this case we'll just pass
+        # what we're given.
+        cmd_to_run = command
+        if isinstance(command, str):
+            cmd_str = command
+        else:  # list
+            # TODO list2cmdline is an intentionally undocumented internal Python
+            # function, check if we want to use this.
+            cmd_str = subprocess.list2cmdline(command)
+            tool = command[0]
     else:
-        cmd_list = command
+        # on Posix systems we should pass a list of strings
-        # As above, this will usually but not always be correct on Windows, but
+        if isinstance(command, str):
-        # is only used for debugging purposes.
+            cmd_str = command
-        if hasattr(shlex, "join"):
+            cmd_to_run = shlex.split(command, posix=True)
-            cmd_str = shlex.join(command)  # type: ignore
+            tool = cmd_to_run[0]
-        else:
+        else:  # list
-            # shlex.join is more correct, but is only available in 3.8+
+            cmd_to_run = command
-            cmd_str = " ".join(command)
+            tool = command[0]
+            # This is the same as shlex.join, added in Py 3.8
+            cmd_str = " ".join(shlex.quote(arg) for arg in command)
     try:
-        cmd_to_run = command if is_windows else cmd_list
         ret = subprocess.run(
             cmd_to_run,
             env=os.environ.copy(),
@@ -983,9 +996,17 @@ def run_command(
     except FileNotFoundError:
         # Indicates the *command* wasn't found, it's an error before the command
         # is run.
+
+        if tool is None:
+            # On Windows we may be unable to get the executable name.
+            tool_check = ""
+        else:
+            tool_check = f" Do you have {tool} installed?"
+
         raise FileNotFoundError(
-            Errors.E970.format(str_command=cmd_str, tool=cmd_list[0])
+            Errors.E970.format(str_command=cmd_str, msg=tool_check)
         ) from None
+
     if ret.returncode != 0 and capture:
         message = f"Error running command:\n\n{cmd_str}\n\n"
         message += f"Subprocess exited with status {ret.returncode}"