Improve application diff

This changes the application diff to render a YAML diff with a number of
context lines instead of relying on the cmp library previously used
which would render a diff of Go objects.

go.mod

@@ -13,7 +13,6 @@ require (
 	github.com/cenkalti/backoff/v4 v4.2.1
 	github.com/go-test/deep v1.1.0
 	github.com/golang/mock v1.6.0
-	github.com/google/go-cmp v0.6.0
 	github.com/google/go-github/v62 v62.0.0
 	github.com/hashicorp/golang-lru/v2 v2.0.7
 	github.com/hexops/gotextdiff v1.0.3
@@ -26,6 +25,7 @@ require (
 	github.com/stretchr/testify v1.9.0
 	golang.org/x/exp v0.0.0-20240506185415-9bf2ced13842
 	golang.org/x/oauth2 v0.19.0
+	golang.org/x/tools v0.21.0
 	google.golang.org/grpc v1.63.2
 	gopkg.in/yaml.v2 v2.4.0
 	k8s.io/api v0.26.11
@@ -90,6 +90,7 @@ require (
 	github.com/google/btree v1.1.2 // indirect
 	github.com/google/gnostic v0.7.0 // indirect
 	github.com/google/gnostic-models v0.6.9-0.20230804172637-c7be7c783f49 // indirect
+	github.com/google/go-cmp v0.6.0 // indirect
 	github.com/google/go-github/v56 v56.0.0 // indirect
 	github.com/google/go-github/v60 v60.0.0 // indirect
 	github.com/google/go-querystring v1.1.0 // indirect
@@ -175,7 +176,6 @@ require (
 	golang.org/x/term v0.20.0 // indirect
 	golang.org/x/text v0.15.0 // indirect
 	golang.org/x/time v0.5.0 // indirect
-	golang.org/x/tools v0.21.0 // indirect
 	golang.org/x/xerrors v0.0.0-20220907171357-04be3eba64a2 // indirect
 	google.golang.org/genproto v0.0.0-20240401170217-c3f982113cda // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20240401170217-c3f982113cda // indirect

internal/pkg/argocd/argocd.go

@@ -24,11 +24,15 @@ import (
 	argodiff "github.com/argoproj/argo-cd/v2/util/argo/diff"
 	"github.com/argoproj/argo-cd/v2/util/argo/normalizers"
 	"github.com/argoproj/gitops-engine/pkg/sync/hook"
-	"github.com/google/go-cmp/cmp"
 	log "github.com/sirupsen/logrus"
+	"github.com/wayfair-incubator/telefonistka/internal/pkg/argocd/diff"
+	yaml2 "gopkg.in/yaml.v2"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 )
 
+// ctxLines is the number of context lines used in application diffs.
+const ctxLines = 10
+
 type argoCdClients struct {
 	app     application.ApplicationServiceClient
 	project projectpkg.ProjectServiceClient
@@ -145,10 +149,19 @@ func generateArgocdAppDiff(ctx context.Context, keepDiffData bool, app *argoappv
 	return foundDiffs, diffElements, nil
 }
 
-// Should return output that is compatible with github markdown diff highlighting format
+// diffLiveVsTargetObject returns the diff of live and target in a format that
+// is compatible with Github markdown diff highlighting.
 func diffLiveVsTargetObject(live, target *unstructured.Unstructured) (string, error) {
-	patch := cmp.Diff(live, target)
-	return patch, nil
+	a, err := yaml2.Marshal(live)
+	if err != nil {
+		return "", err
+	}
+	b, err := yaml2.Marshal(target)
+	if err != nil {
+		return "", err
+	}
+	patch := diff.Diff(ctxLines, "live", a, "target", b)
+	return string(patch), nil
 }
 
 func getEnv(key, fallback string) string {

internal/pkg/argocd/argocd_test.go

@@ -1,15 +1,99 @@
 package argocd
 
 import (
+	"bytes"
 	"context"
+	"os"
+	"strings"
 	"testing"
+	"text/template"
 
 	argoappv1 "github.com/argoproj/argo-cd/v2/pkg/apis/application/v1alpha1"
 	"github.com/golang/mock/gomock"
 	"github.com/wayfair-incubator/telefonistka/internal/pkg/mocks"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 )
 
+func readLiveTarget(t *testing.T) (live, target *unstructured.Unstructured, expected string) {
+	t.Helper()
+	live = readManifest(t, "testdata/"+t.Name()+".live")
+	target = readManifest(t, "testdata/"+t.Name()+".target")
+	expected = readFileString(t, "testdata/"+t.Name()+".want")
+	return live, target, expected
+}
+
+func readFileString(t *testing.T, path string) string {
+	b, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return string(b)
+}
+
+func readManifest(t *testing.T, path string) *unstructured.Unstructured {
+	t.Helper()
+
+	s := readFileString(t, path)
+	obj, err := argoappv1.UnmarshalToUnstructured(s)
+	if err != nil {
+		t.Fatalf("unmarshal %v: %v", path, err)
+	}
+	return obj
+}
+
+func TestDiffLiveVsTargetObject(t *testing.T) {
+	tests := []struct {
+		name string
+	}{
+		{"1"},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			live, target, want := readLiveTarget(t)
+			got, err := diffLiveVsTargetObject(live, target)
+			if err != nil {
+				t.Errorf("unexpected error: %v", err)
+			}
+
+			if got != want {
+				t.Errorf("got %q, want %q", got, want)
+			}
+		})
+	}
+}
+
+func TestRenderDiff(t *testing.T) {
+	live := readManifest(t, "testdata/TestRenderDiff.live")
+	target := readManifest(t, "testdata/TestRenderDiff.target")
+	want := readFileString(t, "testdata/TestRenderDiff.md")
+	data, err := diffLiveVsTargetObject(live, target)
+	if err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+
+	// backticks are tricky https://github.com/golang/go/issues/24475
+	r := strings.NewReplacer("¬", "`")
+	tmpl := r.Replace("¬¬¬diff\n{{.}}¬¬¬\n")
+
+	rendered := renderTemplate(t, tmpl, data)
+
+	if got, want := rendered.String(), want; got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+
+}
+
+func renderTemplate(t *testing.T, tpl string, data any) *bytes.Buffer {
+	buf := bytes.NewBuffer(nil)
+	tmpl := template.New("")
+	tmpl = template.Must(tmpl.Parse(tpl))
+	if err := tmpl.Execute(buf, data); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	return buf
+}
+
 func TestFindArgocdAppBySHA1Label(t *testing.T) {
 	// Here the filtering is done on the ArgoCD server side, so we are just testing the function returns a app
 	t.Parallel()

internal/pkg/argocd/diff/README.md

@@ -0,0 +1,5 @@
+This package has been pulled from the internal package
+https://github.com/golang/go/tree/master/src/internal/diff.
+
+Minor changes were done to allow a custom number of context lines, import a
+public `txtar` package and adhere to the local linter settings.