From fffcee35f9b2042d4edc5dccb3379972e03ffd84 Mon Sep 17 00:00:00 2001
From: John Ericson <Ericson2314@Yahoo.com>
Date: Sat, 1 Apr 2017 15:34:38 -0400
Subject: [PATCH] lib: Fix `matchAttrs`

---
 lib/attrsets.nix | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/lib/attrsets.nix b/lib/attrsets.nix
index f9e6b7495fc5..c686e1d20eb8 100644
--- a/lib/attrsets.nix
+++ b/lib/attrsets.nix
@@ -2,7 +2,7 @@
 
 let
   inherit (builtins) head tail length;
-  inherit (import ./trivial.nix) or;
+  inherit (import ./trivial.nix) and or;
   inherit (import ./default.nix) fold;
   inherit (import ./strings.nix) concatStringsSep;
   inherit (import ./lists.nix) concatMap concatLists all deepSeqList;
@@ -417,18 +417,15 @@ rec {
 
   /* Returns true if the pattern is contained in the set. False otherwise.
 
-     FIXME(zimbatm): this example doesn't work !!!
-
      Example:
-       sys = mkSystem { }
-       matchAttrs { cpu = { bits = 64; }; } sys
+       matchAttrs { cpu = {}; } { cpu = { bits = 64; }; }
        => true
    */
-  matchAttrs = pattern: attrs:
-    fold or false (attrValues (zipAttrsWithNames (attrNames pattern) (n: values:
+  matchAttrs = pattern: attrs: assert isAttrs pattern;
+    fold and true (attrValues (zipAttrsWithNames (attrNames pattern) (n: values:
       let pat = head values; val = head (tail values); in
       if length values == 1 then false
-      else if isAttrs pat then isAttrs val && matchAttrs head values
+      else if isAttrs pat then isAttrs val && matchAttrs pat val
       else pat == val
     ) [pattern attrs]));