BLI: support == and != for Set

This makes it more convenient to check if two sets contain the same keys.

source/blender/blenlib/BLI_set.hh

@@ -646,6 +646,24 @@ class Set {
     return !Intersects(a, b);
   }
 
+  friend bool operator==(const Set &a, const Set &b)
+  {
+    if (a.size() != b.size()) {
+      return false;
+    }
+    for (const Key &key : a) {
+      if (!b.contains(key)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  friend bool operator!=(const Set &a, const Set &b)
+  {
+    return !(a == b);
+  }
+
  private:
   BLI_NOINLINE void realloc_and_reinsert(const int64_t min_usable_slots)
   {

source/blender/blenlib/tests/BLI_set_test.cc

@@ -600,6 +600,28 @@ TEST(set, RemoveUniquePtrWithRaw)
   EXPECT_TRUE(set.is_empty());
 }
 
+TEST(set, Equality)
+{
+  const Set<int> a = {1, 2, 3, 4, 5};
+  const Set<int> b = {5, 2, 3, 1, 4};
+  const Set<int> c = {1, 2, 3};
+  const Set<int> d = {1, 2, 3, 4, 5, 6};
+  const Set<int> e = {};
+  const Set<int> f = {10, 11, 12, 13, 14};
+
+  EXPECT_EQ(a, a);
+  EXPECT_EQ(a, b);
+  EXPECT_EQ(b, a);
+  EXPECT_NE(a, c);
+  EXPECT_NE(a, d);
+  EXPECT_NE(a, e);
+  EXPECT_NE(a, f);
+  EXPECT_NE(c, a);
+  EXPECT_NE(d, a);
+  EXPECT_NE(e, a);
+  EXPECT_NE(f, a);
+}
+
 /**
  * Set this to 1 to activate the benchmark. It is disabled by default, because it prints a lot.
  */