Fix changing directories between drives on Windows

invoke/context.py

@@ -1,4 +1,5 @@
 import os
+import platform
 import re
 from contextlib import contextmanager
 from itertools import cycle
@@ -248,7 +249,16 @@ def _prefix_commands(self, command):
         prefixes = list(self.command_prefixes)
         current_directory = self.cwd
         if current_directory:
-            prefixes.insert(0, "cd {}".format(current_directory))
+            cd_command = "cd"
+            if platform.system() == "Windows":
+                # On Windows when switching between different drives like C:\
+                # or E:\ the /d flag must be specified.
+                # To avoid the command failing when a drive must be changed we
+                # always add the flag. It would be too convoluted and
+                # complicated to add it only in case the drive changes, also
+                # the flag has no ill side effects.
+                cd_command += " /d"
+            prefixes.insert(0, "{} {}".format(cd_command, current_directory))
 
         return " && ".join(prefixes + [command])
 

tests/context.py

@@ -1,5 +1,6 @@
 import os
 import pickle
+import platform
 import re
 import sys
 
@@ -225,6 +226,20 @@ def __str__(self):
             cmd = "cd foo && whoami"
             assert runner.run.call_args[0][0] == cmd
 
+        @patch(local_path)
+        def cd_on_windows_must_append_flag(self, Local):
+            if platform.system() != "Windows":
+                skip()
+
+            runner = Local.return_value
+            c = Context()
+            with c.cd("foo"):
+                c.run("whoami")
+
+            cmd = "cd /d foo && whoami"
+            assert runner.run.called, "run() never called runner.run()!"
+            assert runner.run.call_args[0][0] == cmd
+
     class prefix:
         def setup(self):
             self.escaped_prompt = re.escape(Config().sudo.prompt)