Bug 1047267 - Add a memoize decorator to the mozbuild module. r=gps

python/mozbuild/mozbuild/test/test_util.py

@@ -20,6 +20,7 @@ from mozunit import (
 from mozbuild.util import (
     FileAvoidWrite,
     hash_file,
+    memoize,
     resolve_target_to_make,
     MozbuildDeletionError,
     HierarchicalStringList,
@@ -429,5 +430,27 @@ class TestHierarchicalStringListWithFlagsFactory(unittest.TestCase):
             l.x['y'].baz = False
 
 
+class TestMemoize(unittest.TestCase):
+    def test_memoize(self):
+        self._count = 0
+        @memoize
+        def wrapped(a, b):
+            self._count += 1
+            return a + b
+
+        self.assertEqual(wrapped(1, 1), 2)
+        self.assertEqual(self._count, 1)
+        self.assertEqual(wrapped(1, 1), 2)
+        self.assertEqual(self._count, 1)
+        self.assertEqual(wrapped(2, 1), 3)
+        self.assertEqual(self._count, 2)
+        self.assertEqual(wrapped(1, 2), 3)
+        self.assertEqual(self._count, 3)
+        self.assertEqual(wrapped(1, 2), 3)
+        self.assertEqual(self._count, 3)
+        self.assertEqual(wrapped(1, 1), 2)
+        self.assertEqual(self._count, 3)
+
+
 if __name__ == '__main__':
     main()

python/mozbuild/mozbuild/util.py

@@ -20,6 +20,7 @@ from collections import (
     defaultdict,
     OrderedDict,
 )
+from functools import wraps
 from StringIO import StringIO
 
 
@@ -706,3 +707,14 @@ class OrderedDefaultDict(OrderedDict):
         except KeyError:
             value = self[key] = self._default_factory()
             return value
+
+
+def memoize(func):
+    cache = {}
+
+    @wraps(func)
+    def wrapper(*args):
+        if args not in cache:
+            cache[args] = func(*args)
+        return cache[args]
+    return wrapper