From 3b8a8793f2b610c4c00058398bdcec2e6e35ef3a Mon Sep 17 00:00:00 2001
From: Jaye Doepke <jdoepke@mintel.com>
Date: Tue, 9 Jan 2024 14:17:01 -0600
Subject: [PATCH] Preserve field order when updating kustomization.yaml file

This commit causes argocd-image-updater to preserve the order of fields
in the kustomization.yaml file when updating the image(s). Doing so will
minimize git diffs in the case that other tools also edit the
kustomization.yaml file.

Fixes #502
---
 pkg/argocd/git.go      | 34 ++++++++++++++++++--
 pkg/argocd/git_test.go | 72 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 104 insertions(+), 2 deletions(-)

diff --git a/pkg/argocd/git.go b/pkg/argocd/git.go
index 76af3910..e48d8491 100644
--- a/pkg/argocd/git.go
+++ b/pkg/argocd/git.go
@@ -12,6 +12,7 @@ import (
 
 	"sigs.k8s.io/kustomize/api/konfig"
 	"sigs.k8s.io/kustomize/api/types"
+	"sigs.k8s.io/kustomize/kyaml/order"
 	kyaml "sigs.k8s.io/kustomize/kyaml/yaml"
 
 	"github.com/argoproj-labs/argocd-image-updater/pkg/image"
@@ -314,14 +315,43 @@ func writeKustomization(app *v1alpha1.Application, wbc *WriteBackConfig, gitC gi
 	if err != nil {
 		return err, false
 	}
-	err = kyaml.UpdateFile(filterFunc, kustFile)
-	if err != nil {
+
+	if err = updateKustomizeFile(filterFunc, kustFile); err != nil {
 		return err, false
 	}
 
 	return nil, false
 }
 
+// updateKustomizeFile reads the kustomization file at path, applies the filter to it, and writes the result back
+// to the file. This is the same behavior as kyaml.UpdateFile, but it preserves the original order
+// of YAML fields to minimize git diffs.
+func updateKustomizeFile(filter kyaml.Filter, path string) error {
+	// Read the yaml
+	y, err := kyaml.ReadFile(path)
+	if err != nil {
+		return err
+	}
+
+	// Update the yaml
+	yCpy := y.Copy()
+	if err := yCpy.PipeE(filter); err != nil {
+		return err
+	}
+
+	// Preserve the original order of fields
+	if err := order.SyncOrder(y, yCpy); err != nil {
+		return err
+	}
+
+	// Write the yaml
+	if err := kyaml.WriteFile(yCpy, path); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func imagesFilter(images v1alpha1.KustomizeImages) (kyaml.Filter, error) {
 	var overrides []kyaml.Filter
 	for _, img := range images {
diff --git a/pkg/argocd/git_test.go b/pkg/argocd/git_test.go
index 69f7027f..4070ae8a 100644
--- a/pkg/argocd/git_test.go
+++ b/pkg/argocd/git_test.go
@@ -1,6 +1,7 @@
 package argocd
 
 import (
+	"os"
 	"testing"
 	"text/template"
 	"time"
@@ -215,3 +216,74 @@ images:
 		})
 	}
 }
+
+func Test_updateKustomizeFile(t *testing.T) {
+	makeTmpKustomization := func(t *testing.T, content []byte) string {
+		f, err := os.CreateTemp("", "kustomization-*.yaml")
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, err = f.Write(content)
+		if err != nil {
+			t.Fatal(err)
+		}
+		f.Close()
+		t.Cleanup(func() {
+			os.Remove(f.Name())
+		})
+		return f.Name()
+	}
+
+	filter, err := imagesFilter(v1alpha1.KustomizeImages{"foo@sha23456"})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tests := []struct {
+		name        string
+		content     []byte
+		wantContent []byte
+		filter      kyaml.Filter
+		wantErr     bool
+	}{
+		{
+			name: "sorted",
+			content: []byte(`images:
+- digest: sha12345
+  name: foo
+`),
+			wantContent: []byte(`images:
+- digest: sha23456
+  name: foo
+`),
+			filter: filter,
+		},
+		{
+			name: "not-sorted",
+			content: []byte(`images:
+- name: foo
+  digest: sha12345
+`),
+			wantContent: []byte(`images:
+- name: foo
+  digest: sha23456
+`),
+			filter: filter,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			path := makeTmpKustomization(t, tt.content)
+			err := updateKustomizeFile(tt.filter, path)
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				got, err := os.ReadFile(path)
+				if err != nil {
+					t.Fatal(err)
+				}
+				assert.Equal(t, string(tt.wantContent), string(got))
+			}
+		})
+	}
+}