feat: colorize field managers in blame output (#44)

Each unique field manager gets a distinct, deterministic ANSI color
based on an FNV hash of its name, making it easier to visually
distinguish managers when there are many. Adds a --color flag
(auto|always|never, default auto) that auto-detects TTY.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: knight42

README.md

@@ -58,5 +58,6 @@ cat deployment.yaml | kubectl blame
 | flag               | default    | description                                                              |
 |--------------------|------------|--------------------------------------------------------------------------|
 | `--time`           | `relative` | Time format. One of: `full`, `relative`, `none`.                         |
+| `--color`          | `auto`     | Color output. One of: `auto`, `always`, `never`.                         |
 | `--filename`, `-f` |            | Filename identifying the resource to get from a server.                  |
 | `--input`, `-i`    | `auto`     | Read object from the given file. When set to `auto`, automatically read from stdin if piped. Use `-` to force reading from stdin. |

cmd/blame.go

@@ -6,6 +6,7 @@ import (
 	"os"
 
 	"github.com/spf13/cobra"
+	"golang.org/x/term"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/util/yaml"
@@ -16,6 +17,7 @@ import (
 
 type Options struct {
 	timeFormat   string
+	colorMode    string
 	inputFile    string
 	fileNameOpts resource.FilenameOptions
 
@@ -78,6 +80,7 @@ func NewCmdBlame() *cobra.Command {
 	flags := cmd.Flags()
 	f.AddFlags(flags)
 	flags.StringVar(&o.timeFormat, "time", TimeFormatRelative, "Time format. One of: full|relative|none.")
+	flags.StringVar(&o.colorMode, "color", "auto", "Color output. One of: auto|always|never.")
 	flags.StringSliceVarP(&o.fileNameOpts.Filenames, "filename", "f", o.fileNameOpts.Filenames, "Filename identifying the resource to get from a server.")
 	flags.StringVarP(&o.inputFile, "input", "i", "auto", "Read object from the given file. When set to 'auto', automatically read from stdin if piped. Use '-' to force reading from stdin.")
 	return cmd
@@ -174,9 +177,24 @@ func (o *Options) visitClusterObjects(visit func(object metav1.Object) error) er
 	})
 }
 
+func (o *Options) resolveColorEnabled() bool {
+	switch o.colorMode {
+	case "always":
+		return true
+	case "never":
+		return false
+	default: // "auto"
+		if f, ok := o.out.(*os.File); ok {
+			return term.IsTerminal(int(f.Fd()))
+		}
+		return false
+	}
+}
+
 func (o *Options) Run() error {
+	colorizer := NewColorizer(o.resolveColorEnabled())
 	enc := newEncoder(o.out, func(obj metav1.Object) ([]byte, error) {
-		return MarshalMetaObject(obj, o.timeFormat)
+		return MarshalMetaObject(obj, o.timeFormat, colorizer)
 	})
 
 	if o.inputFile == "auto" {

cmd/color.go

@@ -0,0 +1,49 @@
+package cmd
+
+import (
+	"hash/fnv"
+
+	"github.com/fatih/color"
+)
+
+var colorPalette = []color.Attribute{
+	color.FgRed,
+	color.FgGreen,
+	color.FgYellow,
+	color.FgBlue,
+	color.FgMagenta,
+	color.FgCyan,
+	color.FgHiRed,
+	color.FgHiGreen,
+	color.FgHiYellow,
+	color.FgHiBlue,
+	color.FgHiMagenta,
+	color.FgHiCyan,
+}
+
+type Colorizer struct {
+	enabled bool
+	cache   map[string]*color.Color
+}
+
+func NewColorizer(enabled bool) *Colorizer {
+	return &Colorizer{
+		enabled: enabled,
+		cache:   make(map[string]*color.Color),
+	}
+}
+
+func (c *Colorizer) Sprint(managerName, s string) string {
+	if c == nil || !c.enabled {
+		return s
+	}
+	clr, ok := c.cache[managerName]
+	if !ok {
+		h := fnv.New32a()
+		h.Write([]byte(managerName))
+		idx := int(h.Sum32()) % len(colorPalette)
+		clr = color.New(colorPalette[idx])
+		c.cache[managerName] = clr
+	}
+	return clr.Sprint(s)
+}

cmd/color_test.go

@@ -0,0 +1,57 @@
+package cmd
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestColorizer_Determinism(t *testing.T) {
+	c := NewColorizer(true)
+	first := c.Sprint("manager-a", "some text")
+	second := c.Sprint("manager-a", "some text")
+	if first != second {
+		t.Errorf("expected deterministic output, got %q and %q", first, second)
+	}
+}
+
+func TestColorizer_DifferentManagers(t *testing.T) {
+	c := NewColorizer(true)
+	a := c.Sprint("manager-a", "text")
+	b := c.Sprint("manager-b", "text")
+	// Different managers should (with high probability) produce different colored output.
+	// Both should contain the original text.
+	if !strings.Contains(a, "text") {
+		t.Errorf("expected output to contain original text, got %q", a)
+	}
+	if !strings.Contains(b, "text") {
+		t.Errorf("expected output to contain original text, got %q", b)
+	}
+}
+
+func TestColorizer_Disabled(t *testing.T) {
+	c := NewColorizer(false)
+	got := c.Sprint("manager-a", "plain text")
+	if got != "plain text" {
+		t.Errorf("expected unmodified string when disabled, got %q", got)
+	}
+}
+
+func TestColorizer_Nil(t *testing.T) {
+	var c *Colorizer
+	got := c.Sprint("manager-a", "plain text")
+	if got != "plain text" {
+		t.Errorf("expected unmodified string for nil colorizer, got %q", got)
+	}
+}
+
+func TestGetInfoOr_NilColorizer(t *testing.T) {
+	node := &Node{
+		Managers: []ManagerInfo{
+			{Manager: "mgr", Operation: "Apply"},
+		},
+	}
+	got := getInfoOr(node, "default", nil)
+	if got != "mgr Apply " {
+		t.Errorf("unexpected result: %q", got)
+	}
+}

cmd/marshal.go

@@ -35,6 +35,7 @@ type Marshaller struct {
 
 	now        time.Time
 	timeFormat string
+	colorizer  *Colorizer
 }
 
 type ManagerInfo struct {
@@ -176,10 +177,11 @@ func (m *Marshaller) buildTree(managedFields []metav1.ManagedFieldsEntry, mgrMax
 	return root, nil
 }
 
-func MarshalMetaObject(obj metav1.Object, timeFmt string) ([]byte, error) {
+func MarshalMetaObject(obj metav1.Object, timeFmt string, colorizer *Colorizer) ([]byte, error) {
 	m := Marshaller{
 		now:        time.Now(),
 		timeFormat: timeFmt,
+		colorizer:  colorizer,
 	}
 	return m.marshalMetaObject(obj)
 }
@@ -262,10 +264,10 @@ func (m *Marshaller) marshalMapWithCtx(ctx Context, o map[string]interface{}, w
 		} else {
 			ok := child != nil
 			if ok {
-				info := getInfoOr(child, m.emptyInfo)
+				info := getInfoOr(child, m.emptyInfo, m.colorizer)
 				writeString(w, info)
 			} else {
-				info := getInfoOr(root, m.emptyInfo)
+				info := getInfoOr(root, m.emptyInfo, m.colorizer)
 				writeString(w, info)
 			}
 			writeIndent(w, ctx.Level)
@@ -323,7 +325,7 @@ func (m *Marshaller) marshalListWithCtx(ctx Context, o []interface{}, w io.Write
 	}
 
 	root := ctx.Node
-	prefix := getInfoOr(root, m.emptyInfo)
+	prefix := getInfoOr(root, m.emptyInfo, m.colorizer)
 	for i, val := range o {
 		switch actual := val.(type) {
 		case map[string]interface{}:
@@ -334,11 +336,11 @@ func (m *Marshaller) marshalListWithCtx(ctx Context, o []interface{}, w io.Write
 					break
 				}
 			}
-			mapPrefix := getInfoOr(child, m.emptyInfo)
+			mapPrefix := getInfoOr(child, m.emptyInfo, m.colorizer)
 			if len(actual) > 0 {
 				firstKey := firstSortedMapKey(actual)
 				if fc := child.Fields[firstKey]; fc != nil {
-					mapPrefix = getInfoOr(fc, m.emptyInfo)
+					mapPrefix = getInfoOr(fc, m.emptyInfo, m.colorizer)
 				}
 			}
 			writeString(w, mapPrefix)
@@ -364,7 +366,7 @@ func (m *Marshaller) marshalListWithCtx(ctx Context, o []interface{}, w io.Write
 		if root.Values != nil {
 			s := value.ToString(value.NewValueInterface(val))
 			if v, ok := root.Values[s]; ok {
-				valPrefix = getInfoOr(v.Node, m.emptyInfo)
+				valPrefix = getInfoOr(v.Node, m.emptyInfo, m.colorizer)
 			}
 		}
 		writeString(w, valPrefix)

cmd/marshal_test.go

@@ -232,7 +232,7 @@ m1 (Update 2020-11-23 16:52:45 +0000) /
 m2 (Update 2020-11-23 16:52:45 +0000)   serviceAccountName: foo
                                       status: {}
 `
-	data, err := MarshalMetaObject(pod, TimeFormatFull)
+	data, err := MarshalMetaObject(pod, TimeFormatFull, nil)
 	r.NoError(err)
 	if diff := cmp.Diff(expected, string(data)); len(diff) > 0 {
 		t.Errorf("unexpected diff (-want +got): %s", diff)

cmd/util.go

@@ -15,15 +15,19 @@ import (
 	"sigs.k8s.io/yaml"
 )
 
-func getInfoOr(n *Node, defVal string) string {
+func getInfoOr(n *Node, defVal string, colorizer *Colorizer) string {
 	for n != nil {
 		if len(n.Managers) > 0 {
 			var buf strings.Builder
 			for i, info := range n.Managers {
 				if i > 0 {
 					buf.WriteString("/\n")
 				}
-				buf.WriteString(info.String())
+				s := info.String()
+				if colorizer != nil {
+					s = colorizer.Sprint(strings.TrimSpace(info.Manager), s)
+				}
+				buf.WriteString(s)
 			}
 			return buf.String()
 		}

go.mod

@@ -5,9 +5,11 @@ go 1.24.0
 toolchain go1.24.1
 
 require (
+	github.com/fatih/color v1.18.0
 	github.com/google/go-cmp v0.7.0
 	github.com/spf13/cobra v1.9.1
 	github.com/stretchr/testify v1.10.0
+	golang.org/x/term v0.32.0
 	k8s.io/api v0.33.2
 	k8s.io/apimachinery v0.33.2
 	k8s.io/cli-runtime v0.33.2
@@ -38,6 +40,8 @@ require (
 	github.com/json-iterator/go v1.1.12 // indirect
 	github.com/liggitt/tabwriter v0.0.0-20181228230101-89fcab3d43de // indirect
 	github.com/mailru/easyjson v0.7.7 // indirect
+	github.com/mattn/go-colorable v0.1.13 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/moby/term v0.5.0 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
@@ -55,7 +59,6 @@ require (
 	golang.org/x/oauth2 v0.27.0 // indirect
 	golang.org/x/sync v0.14.0 // indirect
 	golang.org/x/sys v0.33.0 // indirect
-	golang.org/x/term v0.32.0 // indirect
 	golang.org/x/text v0.25.0 // indirect
 	golang.org/x/time v0.9.0 // indirect
 	google.golang.org/protobuf v1.36.5 // indirect

go.sum

@@ -11,6 +11,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/emicklei/go-restful/v3 v3.11.0 h1:rAQeMHw1c7zTmncogyy8VvRZwtkmkZ4FxERmMY4rD+g=
 github.com/emicklei/go-restful/v3 v3.11.0/go.mod h1:6n3XBCmQQb25CM2LCACGz8ukIrRry+4bhvbpWn3mrbc=
+github.com/fatih/color v1.18.0 h1:S8gINlzdQ840/4pfAwic/ZE0djQEH3wM94VfqLTZcOM=
+github.com/fatih/color v1.18.0/go.mod h1:4FelSpRwEGDpQ12mAdzqdOukCy4u8WUtOY6lkT/6HfU=
 github.com/fxamacker/cbor/v2 v2.7.0 h1:iM5WgngdRBanHcxugY4JySA0nk1wZorNOpTgCMedv5E=
 github.com/fxamacker/cbor/v2 v2.7.0/go.mod h1:pxXPTn3joSm21Gbwsv0w9OSA2y1HFR9qXEeXQVeNoDQ=
 github.com/go-errors/errors v1.4.2 h1:J6MZopCL4uSllY1OfXM374weqZFFItUbrImctkmUxIA=
@@ -64,6 +66,11 @@ github.com/liggitt/tabwriter v0.0.0-20181228230101-89fcab3d43de h1:9TO3cAIGXtEhn
 github.com/liggitt/tabwriter v0.0.0-20181228230101-89fcab3d43de/go.mod h1:zAbeS9B/r2mtpb6U+EI2rYA5OAXxsYw6wTamcNW+zcE=
 github.com/mailru/easyjson v0.7.7 h1:UGYAvKxe3sBsEDzO8ZeWOSlIQfWFlxbzLZe7hwFURr0=
 github.com/mailru/easyjson v0.7.7/go.mod h1:xzfreul335JAWq5oZzymOObrkdz5UnU4kGfJJLY9Nlc=
+github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxecdEvA=
+github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
+github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=
+github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
+github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/moby/term v0.5.0 h1:xt8Q1nalod/v7BqbG21f8mQPqH+xAaC9C3N3wfWbVP0=
 github.com/moby/term v0.5.0/go.mod h1:8FzsFHVUBGZdbDsJw/ot+X+d5HLUbvklYLJ9uGfcI3Y=
 github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
@@ -140,6 +147,8 @@ golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210616094352-59db8d763f22/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.33.0 h1:q3i8TbbEz+JRD9ywIRlyRAQbM0qF7hu24q3teo2hbuw=
 golang.org/x/sys v0.33.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
 golang.org/x/term v0.32.0 h1:DR4lr0TjUs3epypdhTOkMmuF5CDFJ/8pOnbzMZPQ7bg=