Merge pull request #48 from RutledgePaulV/fix-map-diffing-under-variable-key-order

varying key order in maps should produce consistent diffs

Author: alysbrooks

.gitignore

@@ -20,3 +20,4 @@ resources/public/
 .store
 package-lock.json
 .cache
+*.iml

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ## Fixed
 
+Varying key order in maps should produce a consistent diff (#47)
+
 ## Changed
 
 # 2.9.202 (2023-06-09 / 35494a0)

src/lambdaisland/deep_diff2/diff_impl.cljc

@@ -1,5 +1,6 @@
 (ns lambdaisland.deep-diff2.diff-impl
   (:require [clojure.data :as data]
+            [clojure.set :as set]
             [lambdaisland.clj-diff.core :as seq-diff]))
 
 (declare diff diff-similar)
@@ -109,26 +110,22 @@
    (remove #(contains? exp %) act)))
 
 (defn diff-map [exp act]
-  (first
-   (let [exp-ks (keys exp)
-         act-ks (keys act)
-         [del ins] (del+ins exp-ks act-ks)]
-     (reduce
-      (fn [[m idx] k]
-        [(cond-> m
-           (contains? del idx)
-           (assoc (->Deletion k) (get exp k))
-
-           (not (contains? del idx))
-           (assoc k (diff (get exp k) (get act k)))
-
-           (contains? ins idx)
-           (into (map (juxt ->Insertion (partial get act))) (get ins idx)))
-         (inc idx)])
-      [(if (contains? ins -1)
-         (into {} (map (juxt ->Insertion (partial get act))) (get ins -1))
-         {}) 0]
-      exp-ks))))
+  (let [exp-ks (set (keys exp))
+        act-ks (set (keys act))]
+    (reduce
+      (fn [m k]
+        (case [(contains? exp-ks k) (contains? act-ks k)]
+          [true false]
+          (assoc m (->Deletion k) (get exp k))
+          [false true]
+          (assoc m (->Insertion k) (get act k))
+          [true true]
+          (assoc m k (diff (get exp k) (get act k)))
+          ; `[false false]` will never occur because `k` necessarily
+          ; originated from at least one of the two sets
+          ))
+      {}
+      (set/union exp-ks act-ks))))
 
 (defn primitive? [x]
   (or (number? x) (string? x) (boolean? x) (inst? x) (keyword? x) (symbol? x)))

test/lambdaisland/deep_diff2/diff_test.cljc

@@ -92,6 +92,15 @@
       (is (= {:a [1 (diff/->Deletion 2) 3]}
              (diff/diff {:a [1 2 3]} {:a [1 3]}))))
 
+    (testing "map key order doesn't impact diff result"
+      (is (= {:name (diff/->Mismatch "Alyysa P Hacker" "Alyssa P Hacker"), :age 40}
+
+             (diff/diff (array-map :name "Alyysa P Hacker" :age 40)
+                        (array-map :age 40 :name "Alyssa P Hacker"))
+
+             (diff/diff (array-map :age 40 :name "Alyysa P Hacker")
+                        (array-map :age 40 :name "Alyssa P Hacker")))))
+
     (testing "records"
       (is (= {:a (diff/->Mismatch 1 2)}
              (diff/diff (map->ARecord {:a 1}) (map->ARecord {:a 2}))))