perf: cache suggested commands (#4497)

Calls to `suggest_commands` would result in repeated calls to
the Levenshtein distance routine, which whilst optimally
implemented is still expensive. The change proposes to cache the
result instead.

news/perf-cache-suggested-commands.rst

@@ -0,0 +1,23 @@
+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* Suggested commands are cached for better performance.
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>

xonsh/procs/specs.py

@@ -488,9 +488,9 @@ class SubprocSpec:
                     )
             e = "xonsh: subprocess mode: command not found: {0}".format(cmd0)
             env = XSH.env
-            sug = xt.suggest_commands(cmd0, env, XSH.aliases)
+            sug = xt.suggest_commands(cmd0, env)
             if len(sug.strip()) > 0:
-                e += "\n" + xt.suggest_commands(cmd0, env, XSH.aliases)
+                e += "\n" + xt.suggest_commands(cmd0, env)
             raise xt.XonshError(e)
         return p
 

xonsh/tools.py

@@ -884,7 +884,8 @@ def command_not_found(cmd, env):
     return rtn
 
 
-def suggest_commands(cmd, env, aliases):
+@functools.lru_cache()
+def suggest_commands(cmd, env):
     """Suggests alternative commands given an environment and aliases."""
     if not env.get("SUGGEST_COMMANDS"):
         return ""