added diff

diff.go

@@ -0,0 +1,44 @@
+package carapace
+
+import (
+	"github.com/rsteube/carapace/internal/common"
+	"github.com/rsteube/carapace/pkg/style"
+)
+
+// Diff compares values of two actions.
+// It overrides the style to hightlight changes.
+//
+//	red:   only present in original
+//	dim:   present in both
+//	green: only present in new
+func Diff(original, new Action) Action {
+	return ActionCallback(func(c Context) Action {
+		invokedBatch := Batch(
+			original,
+			new,
+		).Invoke(c)
+
+		merged := make(map[string]common.RawValue)
+		for _, v := range invokedBatch[0].action.rawValues {
+			v.Style = style.Red
+			merged[v.Value] = v
+		}
+
+		for _, v := range invokedBatch[1].action.rawValues {
+			if _, ok := merged[v.Value]; ok {
+				v.Style = style.Dim
+				merged[v.Value] = v
+			} else {
+				v.Style = style.Green
+				merged[v.Value] = v
+			}
+		}
+
+		mergedBatch := invokedBatch.Merge()
+		mergedBatch.action.rawValues = make(common.RawValues, 0)
+		for _, v := range merged {
+			mergedBatch.action.rawValues = append(mergedBatch.action.rawValues, v)
+		}
+		return mergedBatch.ToA()
+	})
+}

diff_test.go

@@ -0,0 +1,27 @@
+package carapace
+
+import (
+	"testing"
+
+	"github.com/rsteube/carapace/pkg/style"
+)
+
+func TestDiff(t *testing.T) {
+	original := ActionValues(
+		"removed",
+		"same",
+	)
+	new := ActionValues(
+		"same",
+		"added",
+	)
+
+	assertEqual(t,
+		Diff(original, new).Invoke(NewContext()),
+		ActionStyledValues(
+			"removed", style.Red,
+			"same", style.Dim,
+			"added", style.Green,
+		).Invoke(NewContext()),
+	)
+}