make @llnl.util.lang.memoized support kwargs (#21722)

* make memoized() support kwargs

* add testing for @memoized

lib/spack/llnl/util/lang.py

@@ -13,9 +13,10 @@
 import sys
 from datetime import datetime, timedelta
 
+import six
 from six import string_types
 
-from llnl.util.compat import Hashable, MutableMapping, zip_longest
+from llnl.util.compat import MutableMapping, zip_longest
 
 # Ignore emacs backups when listing modules
 ignore_modules = [r'^\.#', '~$']
@@ -165,6 +166,19 @@ def union_dicts(*dicts):
     return result
 
 
+# Used as a sentinel that disambiguates tuples passed in *args from coincidentally
+# matching tuples formed from kwargs item pairs.
+_kwargs_separator = (object(),)
+
+
+def stable_args(*args, **kwargs):
+    """A key factory that performs a stable sort of the parameters."""
+    key = args
+    if kwargs:
+        key += _kwargs_separator + tuple(sorted(kwargs.items()))
+    return key
+
+
 def memoized(func):
     """Decorator that caches the results of a function, storing them in
     an attribute of that function.
@@ -172,15 +186,23 @@ def memoized(func):
     func.cache = {}
 
     @functools.wraps(func)
-    def _memoized_function(*args):
-        if not isinstance(args, Hashable):
-            # Not hashable, so just call the function.
-            return func(*args)
+    def _memoized_function(*args, **kwargs):
+        key = stable_args(*args, **kwargs)
 
-        if args not in func.cache:
-            func.cache[args] = func(*args)
-
-        return func.cache[args]
+        try:
+            return func.cache[key]
+        except KeyError:
+            ret = func(*args, **kwargs)
+            func.cache[key] = ret
+            return ret
+        except TypeError as e:
+            # TypeError is raised when indexing into a dict if the key is unhashable.
+            raise six.raise_from(
+                UnhashableArguments(
+                    "args + kwargs '{}' was not hashable for function '{}'"
+                    .format(key, func.__name__),
+                ),
+                e)
 
     return _memoized_function
 
@@ -930,3 +952,7 @@ def nullcontext(*args, **kwargs):
     TODO: replace with contextlib.nullcontext() if we ever require python 3.7.
     """
     yield
+
+
+class UnhashableArguments(TypeError):
+    """Raise when an @memoized function receives unhashable arg or kwarg values."""