No longer crash when PWD is removed

news/delcwd.rst

@@ -0,0 +1,18 @@
+**Added:**
+
+* Xonsh will issue a warning message when the current working
+  directory has been remove out from under it and not replaced
+  prior to running the next command.
+
+**Changed:** None
+
+**Deprecated:** None
+
+**Removed:** None
+
+**Fixed:**
+
+* Xonsh will no longer crash is the current working directory is
+  removed out from it.
+
+**Security:** None

xonsh/base_shell.py

@@ -375,8 +375,26 @@ class BaseShell(object):
     def _fix_cwd(self):
         """Check if the cwd changed out from under us."""
         env = builtins.__xonsh_env__
+        try:
             cwd = os.getcwd()
-        if 'PWD' not in env:
+        except (FileNotFoundError, OSError):
+            cwd = None
+        if cwd is None:
+            # directory has been deleted out from under us, most likely
+            pwd = env.get('PWD', None)
+            if pwd is None:
+                # we have no idea where we are
+                env['PWD'] = '<invalid directory>'
+            elif os.path.isdir(pwd):
+                # unclear why os.getcwd() failed. do nothing.
+                pass
+            else:
+                # OK PWD is really gone.
+                msg = '{UNDERLINE_INTENSE_WHITE}{BACKGROUND_INTENSE_BLACK}'
+                msg += "xonsh: working directory does not exist: " + pwd
+                msg += '{NO_COLOR}'
+                self.print_color(msg, file=sys.stderr)
+        elif 'PWD' not in env:
             # $PWD is missing from env, recreate it
             env['PWD'] = cwd
         elif os.path.realpath(cwd) != os.path.realpath(env['PWD']):

xonsh/prompt/vc.py

@@ -54,8 +54,10 @@ def get_git_branch():
 
 
 def _get_hg_root(q):
-    _curpwd = os.getcwd()
+    _curpwd = builtins.__xonsh_env__['PWD']
     while True:
+        if not os.path.isdir(_curpwd):
+            return False
         if any([b.name == '.hg' for b in os.scandir(_curpwd)]):
             q.put(_curpwd)
             break

xonsh/pyghooks.py

@@ -34,7 +34,10 @@ load_module_in_background('pkg_resources', debug='XONSH_DEBUG',
 
 
 def _command_is_valid(cmd):
+    try:
         cmd_abspath = os.path.abspath(os.path.expanduser(cmd))
+    except (FileNotFoundError, OSError):
+        return False
     return cmd in builtins.__xonsh_commands_cache__ or \
         (os.path.isfile(cmd_abspath) and os.access(cmd_abspath, os.X_OK))