cmd cache: check possibilities when checking if alias overrides (#4996)

* cmd cache: check possibilities when checking if alias overrides

This fixes an issue on Windows where an alias could not override a
command without specifying the path extension.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

news/fix-windows-alias-override.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* fixed using aliases to override commands without the file extension on Windows
+
+**Security:**
+
+* <news item>

xonsh/commands_cache.py

@@ -145,11 +145,18 @@ class CommandsCache(cabc.Mapping):
 
             # aliases override cmds
             for cmd in self.aliases:
-                key = cmd.upper() if ON_WINDOWS else cmd
-                if key in all_cmds:
+                # Get the possible names the alias could be overriding,
+                # and check if any are in all_cmds.
+                possibilities = self.get_possible_names(cmd)
+                override_key = next(
+                    (possible for possible in possibilities if possible in all_cmds),
+                    None,
+                )
+                if override_key:
                     # (path, False) -> has same named alias
-                    all_cmds[key] = (all_cmds[key][0], False)
+                    all_cmds[override_key] = (all_cmds[override_key][0], False)
                 else:
+                    key = cmd.upper() if ON_WINDOWS else cmd
                     # True -> pure alias
                     all_cmds[key] = (cmd, True)
             self._cmds_cache = all_cmds