make XONSH_HISTORY_BACKEND support instance too

xonsh/environ.py

@@ -38,7 +38,7 @@ from xonsh.tools import (
     is_dynamic_cwd_width, to_dynamic_cwd_tuple, dynamic_cwd_tuple_to_str,
     is_logfile_opt, to_logfile_opt, logfile_opt_to_str, executables_in,
     is_nonstring_seq_of_strings, pathsep_to_upper_seq,
-    seq_to_upper_pathsep, print_color
+    seq_to_upper_pathsep, print_color, is_history_backend, to_itself,
 )
 import xonsh.prompt.base as prompt
 
@@ -176,7 +176,7 @@ def DEFAULT_ENSURERS():
     'XONSH_DEBUG': (always_false, to_debug, bool_or_int_to_str),
     'XONSH_ENCODING': (is_string, ensure_string, ensure_string),
     'XONSH_ENCODING_ERRORS': (is_string, ensure_string, ensure_string),
-    'XONSH_HISTORY_BACKEND': (is_string_or_callable, ensure_string, ensure_string),
+    'XONSH_HISTORY_BACKEND': (is_history_backend, to_itself, ensure_string),
     'XONSH_HISTORY_FILE': (is_string, ensure_string, ensure_string),
     'XONSH_HISTORY_SIZE': (is_history_tuple, to_history_tuple, history_tuple_to_str),
     'XONSH_LOGIN': (is_bool, to_bool, bool_to_str),
@@ -937,6 +937,7 @@ class Env(cabc.MutableMapping):
         if not ensurer.validate(val):
             val = ensurer.convert(val)
         # existing envvars can have any value including None
+
         old_value = self._d[key] if key in self._d else self._no_value
         self._d[key] = val
         if self.detypeable(val):

xonsh/history/main.py

@@ -9,6 +9,7 @@ import json
 import os
 import sys
 
+from xonsh.history.base import History
 from xonsh.history.dummy import DummyHistory
 from xonsh.history.json import JsonHistory
 from xonsh.history.sqlite import SqliteHistory
@@ -27,14 +28,16 @@ def construct_history(**kwargs):
     """Construct the history backend object."""
     env = builtins.__xonsh_env__
     backend = env.get('XONSH_HISTORY_BACKEND')
-    if inspect.isclass(backend):
+    if isinstance(backend, str) and backend in HISTORY_BACKENDS:
+        kls_history = HISTORY_BACKENDS[backend]
+    elif inspect.isclass(backend):
         kls_history = backend
-    elif backend not in HISTORY_BACKENDS:
+    elif isinstance(backend, History):
+        return backend
+    else:
         print('Unknown history backend: {}. Using JSON version'.format(
             backend), file=sys.stderr)
         kls_history = JsonHistory
-    else:
-        kls_history = HISTORY_BACKENDS[backend]
     return kls_history(**kwargs)
 
 

xonsh/tools.py

@@ -819,6 +819,11 @@ def is_string_or_callable(x):
     return is_string(x) or is_callable(x)
 
 
+def is_class(x):
+    """Tests if something is a class"""
+    return isinstance(x, type)
+
+
 def always_true(x):
     """Returns True"""
     return True
@@ -915,6 +920,11 @@ def to_bool(x):
         return bool(x)
 
 
+def to_itself(x):
+    """Do not do conversion, returns to itself."""
+    return x
+
+
 def bool_to_str(x):
     """Converts a bool to an empty string if False and the string '1' if
     True.
@@ -1240,6 +1250,11 @@ def is_history_tuple(x):
     return False
 
 
+def is_history_backend(x):
+    """Tests if something is a valid history backend."""
+    return is_string(x) or is_class(x) or isinstance(x, object)
+
+
 def is_dynamic_cwd_width(x):
     """ Determine if the input is a valid input for the DYNAMIC_CWD_WIDTH
     environement variable.