Bug 1384396 - Add a @depends_all utility function; r=nalexander

Often you only want to evaluate a function if all its dependencies
are true. Expressing this in a "when" can be difficult. So let's
add a convenience decorator for it.

The existing code for @depends_if() was refactored to take an
evaluation function as its first argument. This prevents some
duplicate code and turns @depends_if() and @depends_all() into
one-liners.

MozReview-Commit-ID: Jbugvf0lioM

--HG--
extra : rebase_source : 177741b80ac4fbfb547d6b36a6f5777fe514d91a
extra : source : 0c2bc12f4ebe44428385745266d2fd158e0c3382

build/moz.configure/util.configure

@@ -404,10 +404,11 @@ always = dependable(True)
 never = dependable(False)
 
 
-# Like @depends, but the decorated function is only called if one of the
+# Create a decorator that will only execute the body of a function
-# arguments it would be called with has a positive value (bool(value) is True)
+# if the passed function returns True when passed all positional
+# arguments.
 @template
-def depends_if(*args, **kwargs):
+def depends_tmpl(eval_args_fn, *args, **kwargs):
     if kwargs:
         assert len(kwargs) == 1
         when = kwargs['when']
@@ -416,11 +417,26 @@ def depends_if(*args, **kwargs):
     def decorator(func):
         @depends(*args, when=when)
         def wrapper(*args):
-            if any(arg for arg in args):
+            if eval_args_fn(args):
                 return func(*args)
         return wrapper
     return decorator
 
+
+# Like @depends, but the decorated function is only called if one of the
+# arguments it would be called with has a positive value (bool(value) is True)
+@template
+def depends_if(*args, **kwargs):
+    return depends_tmpl(any, *args, **kwargs)
+
+
+# Like @depends, but the decorated function is only called if all of the
+# arguments it would be called with have a positive value.
+@template
+def depends_all(*args, **kwargs):
+    return depends_tmpl(all, *args, **kwargs)
+
+
 # Hacks related to old-configure
 # ==============================