diff: prettify premature diff log

Signed-off-by: Hidde Beydals <hello@hidde.co>

go.mod

@@ -14,6 +14,7 @@ require (
 	github.com/fluxcd/pkg/ssa v0.24.1
 	github.com/fluxcd/source-controller/api v0.35.1
 	github.com/go-logr/logr v1.2.3
+	github.com/google/go-cmp v0.5.9
 	github.com/hashicorp/go-retryablehttp v0.7.2
 	github.com/onsi/gomega v1.26.0
 	github.com/spf13/pflag v1.0.5
@@ -80,7 +81,6 @@ require (
 	github.com/golang/protobuf v1.5.2 // indirect
 	github.com/google/btree v1.1.2 // indirect
 	github.com/google/gnostic v0.6.9 // indirect
-	github.com/google/go-cmp v0.5.9 // indirect
 	github.com/google/gofuzz v1.2.0 // indirect
 	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510 // indirect
 	github.com/google/uuid v1.3.0 // indirect

internal/cmp/simple_unstructured.go

@@ -0,0 +1,110 @@
+/*
+Copyright 2023 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmp
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+// SimpleUnstructuredReporter is a simple reporter for Unstructured objects
+// that only records differences detected during comparison, in a diff-like
+// format.
+type SimpleUnstructuredReporter struct {
+	path  cmp.Path
+	diffs []string
+}
+
+// Report writes a diff entry if rs is not equal. In the format of:
+//
+//	spec.replicas
+//	-3
+//	+1
+//
+//	spec.template.spec.containers.[0].command.[6]
+//	---deleted=true
+//
+//	spec.template.spec.containers.[0].env.[?->1]:
+//	+map[name:ADDED]
+func (r *SimpleUnstructuredReporter) Report(rs cmp.Result) {
+	if !rs.Equal() {
+		vx, vy := r.path.Last().Values()
+		isNonEmptyX := isValidAndNonEmpty(vx)
+		isNonEmptyY := isValidAndNonEmpty(vy)
+
+		if !isNonEmptyX && !isNonEmptyY {
+			// Skip empty values.
+			return
+		}
+
+		var sb strings.Builder
+		sb.WriteString(pathToString(r.path))
+		sb.WriteString("\n")
+		if isNonEmptyX {
+			sb.WriteString(fmt.Sprintf("-%v", vx))
+			sb.WriteString("\n")
+		}
+		if isNonEmptyY {
+			sb.WriteString(fmt.Sprintf("+%v", vy))
+			sb.WriteString("\n")
+		}
+		r.diffs = append(r.diffs, sb.String())
+	}
+}
+
+// String returns the diff entries joined together with newline, trimmed from
+// spaces.
+func (r *SimpleUnstructuredReporter) String() string {
+	return strings.TrimSpace(strings.Join(r.diffs, "\n"))
+}
+
+func (r *SimpleUnstructuredReporter) PushStep(ps cmp.PathStep) {
+	r.path = append(r.path, ps)
+}
+
+func (r *SimpleUnstructuredReporter) PopStep() {
+	r.path = r.path[:len(r.path)-1]
+}
+
+func isValidAndNonEmpty(v reflect.Value) bool {
+	if !v.IsValid() {
+		return false
+	}
+	switch v.Kind() {
+	case reflect.Interface:
+		return isValidAndNonEmpty(v.Elem())
+	case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String:
+		return v.Len() > 0
+	}
+	return true
+}
+
+func pathToString(path cmp.Path) (p string) {
+	for _, step := range path {
+		switch t := step.(type) {
+		case cmp.MapIndex:
+			p += fmt.Sprintf(".%v", t.Key())
+		case cmp.SliceIndex:
+			p += fmt.Sprintf("%v", t.String())
+		}
+	}
+	p = strings.TrimPrefix(p, ".")
+	return
+}