Improve docs and add a test

Author: daniel-nichter

deep.go

@@ -61,10 +61,11 @@ const (
 	// pass it to Equal; if you do, it does nothing.
 	FLAG_NONE byte = iota
 
-	// FLAG_IGNORE_SLICE_ORDER causes Equal to ignore slice order and, instead,
-	// compare value counts. For example, []{1, 2} and []{2, 1} are equal
-	// because each value has the same count. But []{1, 2, 2} and []{1, 2}
-	// are not equal because the first slice has two occurrences of value 2.
+	// FLAG_IGNORE_SLICE_ORDER causes Equal to ignore slice order so that
+	// []int{1, 2} and []int{2, 1} are equal. Only slices of primitive scalars
+	// like numbers and strings are supported. Slices of complex types,
+	// like []T where T is a struct, are undefined because Equal does not
+	// recurse into the slice value when this flag is enabled.
 	FLAG_IGNORE_SLICE_ORDER
 )
 

deep_test.go

@@ -1561,3 +1561,23 @@ func TestSliceOrderString(t *testing.T) {
 		t.Errorf("got %s, expected '(unordered) slice[]=x: value count: 0 != 1'", diff[2])
 	}
 }
+
+func TestSliceOrderStruct(t *testing.T) {
+	// https://github.com/go-test/deep/issues/28
+	// This is NOT supported but Go is so wonderful that it just happens to work.
+	// But again: not supported. So if this test starts to fail or be a problem,
+	// it can and should be removed becuase the docs say it's not supported.
+	type T struct{ i int }
+	a := []T{
+		{i: 1},
+		{i: 2},
+	}
+	b := []T{
+		{i: 2},
+		{i: 1},
+	}
+	diff := deep.Equal(a, b, deep.FLAG_IGNORE_SLICE_ORDER)
+	if len(diff) != 0 {
+		t.Fatalf("expected 0 diff, got %d: %s", len(diff), diff)
+	}
+}