feat(04-02): select CLDR and Laravel plural forms with PHP parameters

- Use go-i18n only to pick a category label, then substitute :name/:Name/:NAME - Treat YAML maps as plurals when all keys are locale CLDR categories - Parse pipe strings with {n} and [a,b]/[a,*] conditions at catalog load Co-authored-by: Cursor <cursoragent@cursor.com>
2026-09-18 13:51:15 +02:00
parent f824e55c81
commit 6d8786a2af
7 changed files with 500 additions and 11 deletions
--- a/examples/hello/plugins/base/lang/en/lang.yaml
+++ b/examples/hello/plugins/base/lang/en/lang.yaml
@@ -1,3 +1,8 @@
 greeting: Hello
 labels:
  pluginName: Hello plugin
+albums:
+  one: ":count album"
+  other: ":count albums"
+items: "{0} No items|{1} One item|[2,*] :count items"
+helloName: "hi :name :Name :NAME"
--- a/examples/hello/plugins/base/lang/pl/lang.yaml
+++ b/examples/hello/plugins/base/lang/pl/lang.yaml
@@ -1,3 +1,10 @@
 greeting: Cześć
 labels:
  pluginName: Wtyczka Hello
+albums:
+  one: ":count album"
+  few: ":count albumy"
+  many: ":count albumów"
+  other: ":count albumu"
+posts: ":count wpis|:count wpisy|:count wpisów|:count wpisu"
+helloName: "cześć :name :Name :NAME"
--- a/go.mod
+++ b/go.mod
@@ -1,7 +1,6 @@
 module git.golem15.com/golem15/summercms

 go 1.27.0
-toolchain go1.27.0

 require (
 	github.com/fsnotify/fsnotify v1.10.1
@@ -14,10 +13,12 @@ require (
 	github.com/knadh/koanf/providers/env/v2 v2.0.1
 	github.com/knadh/koanf/providers/file v1.2.1
 	github.com/knadh/koanf/v2 v2.3.6
+	github.com/nicksnyder/go-i18n/v2 v2.6.1
 	github.com/spf13/cobra v1.10.2
 	github.com/testcontainers/testcontainers-go v0.44.0
 	github.com/testcontainers/testcontainers-go/modules/postgres v0.44.0
 	golang.org/x/term v0.46.0
+	golang.org/x/text v0.40.0
 	gorm.io/driver/postgres v1.6.3
 	gorm.io/gorm v1.31.2
 )
@@ -86,6 +87,5 @@ require (
 	golang.org/x/crypto v0.54.0 // indirect
 	golang.org/x/sync v0.22.0 // indirect
 	golang.org/x/sys v0.48.0 // indirect
-	golang.org/x/text v0.40.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
--- a/go.sum
+++ b/go.sum
@@ -4,6 +4,8 @@ github.com/AdaLogics/go-fuzz-headers v0.0.0-20240806141605-e8a1dd7889d6 h1:He8af
 github.com/AdaLogics/go-fuzz-headers v0.0.0-20240806141605-e8a1dd7889d6/go.mod h1:8o94RPi1/7XTJvwPpRSzSUedZrtlirdB3r9Z20bi2f8=
 github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c h1:udKWzYgxTojEKWjV8V+WSxDXJ4NFATAsZjh8iIbsQIg=
 github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c/go.mod h1:xomTg63KZ2rFqZQzSB4Vz2SUXa1BpHTVz9L5PTmPC4E=
+github.com/BurntSushi/toml v1.6.0 h1:dRaEfpa2VI55EwlIW72hMRHdWouJeRF7TPYhI+AUQjk=
+github.com/BurntSushi/toml v1.6.0/go.mod h1:ukJfTF/6rtPPRCnwkur4qwRxa8vTRFBF0uk2lLoLwho=
 github.com/Microsoft/go-winio v0.6.2 h1:F2VQgta7ecxGYO8k3ZZz3RS8fVIXVxONVUPlNERoyfY=
 github.com/Microsoft/go-winio v0.6.2/go.mod h1:yd8OoFMLzJbo9gZq8j5qaps8bJ9aShtEA8Ipt1oGCvU=
 github.com/cenkalti/backoff/v4 v4.3.0 h1:MyRJ/UdXutAwSAT+s3wNd7MfTIcy71VQueUuFK343L8=
@@ -122,6 +124,8 @@ github.com/moby/sys/userns v0.1.0 h1:tVLXkFOxVu9A64/yh59slHVv9ahO9UIev4JZusOLG/g
 github.com/moby/sys/userns v0.1.0/go.mod h1:IHUYgu/kao6N8YZlp9Cf444ySSvCmDlmzUcYfDHOl28=
 github.com/moby/term v0.5.2 h1:6qk3FJAFDs6i/q3W/pQ97SX192qKfZgGjCQqfCJkgzQ=
 github.com/moby/term v0.5.2/go.mod h1:d3djjFCrjnB+fl8NJux+EJzu0msscUP+f8it8hPkFLc=
+github.com/nicksnyder/go-i18n/v2 v2.6.1 h1:JDEJraFsQE17Dut9HFDHzCoAWGEQJom5s0TRd17NIEQ=
+github.com/nicksnyder/go-i18n/v2 v2.6.1/go.mod h1:Vee0/9RD3Quc/NmwEjzzD7VTZ+Ir7QbXocrkhOzmUKA=
 github.com/opencontainers/go-digest v1.0.0 h1:apOUWs51W5PlhuyGyz9FCeeBIOUDA/6nW8Oi/yOhh5U=
 github.com/opencontainers/go-digest v1.0.0/go.mod h1:0JzlMkj0TRzQZfJkVvzbP0HBR3IKzErnv2BNG4W4MAM=
 github.com/opencontainers/image-spec v1.1.1 h1:y0fUlFfIZhPF1W537XOLg0/fcx6zcHCJwooC2xJA040=
--- a/phrasebook/loader.go
+++ b/phrasebook/loader.go
@@ -4,7 +4,9 @@ import (
 	"fmt"
 	"io/fs"
 	"path"
+	"regexp"
 	"sort"
+	"strconv"
 	"strings"
 	"unicode"

@@ -20,9 +22,30 @@ type Catalog struct {
 }

 type entry struct {
-	text string
+	text    string
+	plurals map[string]string
+	pipes   []pipePart
 }

+type pipePart struct {
+	exact *float64
+	lo    *float64
+	hi    *float64
+	text  string
+	cat   string
+}
+
+var cldrNames = map[string]struct{}{
+	"zero":  {},
+	"one":   {},
+	"two":   {},
+	"few":   {},
+	"many":  {},
+	"other": {},
+}
+
+var cldrOrder = []string{"zero", "one", "two", "few", "many", "other"}
+
 // NewCatalog returns an empty translation catalog.
 func NewCatalog() *Catalog {
 	return &Catalog{
@@ -105,11 +128,14 @@ func (c *Catalog) loadFile(pluginID, file, locale, group string, raw []byte) err
 func flatten(c *Catalog, pluginID, file, locale, prefix string, v any) error {
 	switch val := v.(type) {
 	case string:
-		return c.put(pluginID, file, locale, prefix, val)
+		return c.putString(pluginID, file, locale, prefix, val)
 	case map[string]any:
 		if len(val) == 0 {
 			return nil
 		}
+		if isPluralMap(val) {
+			return c.putPluralMap(pluginID, file, locale, prefix, val)
+		}
 		keys := make([]string, 0, len(val))
 		for k := range val {
 			keys = append(keys, k)
@@ -135,7 +161,58 @@ func flatten(c *Catalog, pluginID, file, locale, prefix string, v any) error {
 	}
 }

-func (c *Catalog) put(pluginID, file, locale, key, text string) error {
+func isPluralMap(m map[string]any) bool {
+	if len(m) == 0 {
+		return false
+	}
+	for k := range m {
+		if _, ok := cldrNames[k]; !ok {
+			return false
+		}
+	}
+	return true
+}
+
+func (c *Catalog) putString(pluginID, file, locale, key, text string) error {
+	e := entry{text: text}
+	if strings.Contains(text, "|") {
+		parts, err := parsePipe(text, locale)
+		if err != nil {
+			return catalogErrorf(pluginID, file, key, "%s", err.Error())
+		}
+		e.pipes = parts
+	}
+	return c.put(pluginID, file, locale, key, e)
+}
+
+func (c *Catalog) putPluralMap(pluginID, file, locale, key string, raw map[string]any) error {
+	if _, ok := raw["other"]; !ok {
+		return catalogErrorf(pluginID, file, key, "plural map requires other")
+	}
+	allowed, err := cldrCategorySet(locale)
+	if err != nil {
+		return catalogErrorf(pluginID, file, key, "%s", err.Error())
+	}
+	plurals := make(map[string]string, len(raw))
+	keys := make([]string, 0, len(raw))
+	for k := range raw {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, k := range keys {
+		if _, ok := allowed[k]; !ok {
+			return catalogErrorf(pluginID, file, key, "invalid plural category %q for locale %s", k, locale)
+		}
+		s, ok := raw[k].(string)
+		if !ok {
+			return catalogErrorf(pluginID, file, joinKey(key, k), "non-string leaf (%T)", raw[k])
+		}
+		plurals[k] = s
+	}
+	return c.put(pluginID, file, locale, key, entry{plurals: plurals})
+}
+
+func (c *Catalog) put(pluginID, file, locale, key string, e entry) error {
 	if key == "" || strings.HasSuffix(key, "::") || strings.HasSuffix(key, ".") {
 		return catalogErrorf(pluginID, file, key, "empty key")
 	}
@@ -147,7 +224,7 @@ func (c *Catalog) put(pluginID, file, locale, key, text string) error {
 	if _, exists := byKey[key]; exists {
 		return catalogErrorf(pluginID, file, key, "duplicate key")
 	}
-	byKey[key] = entry{text: text}
+	byKey[key] = e
 	return nil
 }

@@ -247,6 +324,87 @@ func anyMapToStringMap(v map[any]any) (map[string]any, error) {
 	return out, nil
 }

+var (
+	pipeExact = regexp.MustCompile(`^\{(-?\d+)\}\s*(.*)$`)
+	pipeRange = regexp.MustCompile(`^\[(-?\d+),(-?\d+|\*)\]\s*(.*)$`)
+)
+
+func parsePipe(text, locale string) ([]pipePart, error) {
+	raw := strings.Split(text, "|")
+	if len(raw) < 2 {
+		return nil, fmt.Errorf("malformed pipe")
+	}
+	cats, _, err := cldrCategories(locale)
+	if err != nil {
+		return nil, err
+	}
+	parts := make([]pipePart, 0, len(raw))
+	var forms []pipePart
+	for _, seg := range raw {
+		seg = strings.TrimSpace(seg)
+		if seg == "" {
+			return nil, fmt.Errorf("malformed pipe")
+		}
+		part, err := parsePipeSegment(seg)
+		if err != nil {
+			return nil, err
+		}
+		parts = append(parts, part)
+		if part.exact == nil && part.lo == nil {
+			forms = append(forms, part)
+		}
+	}
+	if len(forms) > 0 && len(forms) != len(cats) {
+		return nil, fmt.Errorf("incomplete pipe")
+	}
+	fi := 0
+	for i := range parts {
+		if parts[i].exact == nil && parts[i].lo == nil {
+			parts[i].cat = cats[fi]
+			fi++
+		}
+	}
+	return parts, nil
+}
+
+func parsePipeSegment(seg string) (pipePart, error) {
+	if strings.HasPrefix(seg, "{") {
+		m := pipeExact.FindStringSubmatch(seg)
+		if m == nil {
+			return pipePart{}, fmt.Errorf("malformed pipe")
+		}
+		n, err := strconv.ParseFloat(m[1], 64)
+		if err != nil {
+			return pipePart{}, fmt.Errorf("malformed pipe")
+		}
+		return pipePart{exact: &n, text: m[2]}, nil
+	}
+	if strings.HasPrefix(seg, "[") {
+		m := pipeRange.FindStringSubmatch(seg)
+		if m == nil {
+			return pipePart{}, fmt.Errorf("malformed pipe")
+		}
+		lo, err := strconv.ParseFloat(m[1], 64)
+		if err != nil {
+			return pipePart{}, fmt.Errorf("malformed pipe")
+		}
+		part := pipePart{lo: &lo, text: m[3]}
+		if m[2] == "*" {
+			return part, nil
+		}
+		hi, err := strconv.ParseFloat(m[2], 64)
+		if err != nil {
+			return pipePart{}, fmt.Errorf("malformed pipe")
+		}
+		if lo > hi {
+			return pipePart{}, fmt.Errorf("malformed pipe")
+		}
+		part.hi = &hi
+		return part, nil
+	}
+	return pipePart{text: seg}, nil
+}
+
 func catalogErrorf(pluginID, file, key, format string, args ...any) error {
 	msg := fmt.Sprintf(format, args...)
 	switch {
--- a/phrasebook/translator.go
+++ b/phrasebook/translator.go
@@ -3,13 +3,18 @@ package phrasebook
 import (
 	"context"
 	"fmt"
+	"strconv"
 	"strings"
+	"sync"
 	"unicode"
 	"unicode/utf8"

 	"git.golem15.com/golem15/summercms/backpack"
 	"git.golem15.com/golem15/summercms/pact"
 	"git.golem15.com/golem15/summercms/towel"
+	"github.com/nicksnyder/go-i18n/v2/i18n"
+	"github.com/nicksnyder/go-i18n/v2/i18n/template"
+	"golang.org/x/text/language"
 )

 const (
@@ -17,6 +22,26 @@ const (
 	defaultFallback = "en"
 )

+var (
+	bundleCache   sync.Map // locale -> *i18n.Bundle
+	categoryCache sync.Map // locale -> []string
+	identityParse = template.IdentityParser{}
+	pluralSamples = []any{
+		0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
+		20, 21, 22, 23, 24, 25, 100, 101, 102, 111, 1000, 1000000,
+		"0.0", "0.1", "0.5", "1.0", "1.1", "1.5", "2.0", "2.5", "10.0", "100.0",
+	}
+	categoryMessage = &i18n.Message{
+		ID:    "phrasebook.plural.category",
+		Zero:  "zero",
+		One:   "one",
+		Two:   "two",
+		Few:   "few",
+		Many:  "many",
+		Other: "other",
+	}
+)
+
 // Options configures an app-scoped translator.
 type Options struct {
 	Locale     string
@@ -101,19 +126,216 @@ func (t *Translator) GetIn(locale, key string, params map[string]string) string
 	if !ok {
 		return key
 	}
-	return interpolate(e.text, params)
+	text := e.text
+	if text == "" && e.plurals != nil {
+		text = e.plurals["other"]
+	}
+	return interpolate(text, params)
 }

-// Choice selects a translation for key. Plural selection is added in a later
-// task; a non-plural value is returned as Get would.
+// Choice selects a plural form for key using CLDR rules or Laravel pipe conditions.
 func (t *Translator) Choice(ctx context.Context, key string, count any, params map[string]string) string {
 	return t.ChoiceIn(t.localeFrom(ctx), key, count, params)
 }

 // ChoiceIn is the explicit-locale form of Choice.
 func (t *Translator) ChoiceIn(locale, key string, count any, params map[string]string) string {
-	_ = count
-	return t.GetIn(locale, key, params)
+	if t == nil {
+		return key
+	}
+	e, ok := t.cat.lookup(locale, key)
+	if !ok {
+		return key
+	}
+	text := e.text
+	switch {
+	case len(e.pipes) > 0:
+		text = selectPipe(e.pipes, locale, count)
+	case e.plurals != nil:
+		text = selectMap(e.plurals, locale, count)
+	}
+	return interpolate(text, withCount(params, count))
+}
+
+func selectMap(plurals map[string]string, locale string, count any) string {
+	cat, err := cldrCategory(locale, count)
+	if err != nil {
+		return plurals["other"]
+	}
+	if s, ok := plurals[cat]; ok {
+		return s
+	}
+	return plurals["other"]
+}
+
+func selectPipe(parts []pipePart, locale string, count any) string {
+	if n, ok := asFloat(count); ok {
+		for _, p := range parts {
+			if p.exact != nil && n == *p.exact {
+				return p.text
+			}
+			if p.lo != nil && n >= *p.lo && (p.hi == nil || n <= *p.hi) {
+				return p.text
+			}
+		}
+	}
+	cat, err := cldrCategory(locale, count)
+	if err != nil {
+		cat = "other"
+	}
+	var other, last string
+	for _, p := range parts {
+		last = p.text
+		if p.cat == cat {
+			return p.text
+		}
+		if p.cat == "other" {
+			other = p.text
+		}
+	}
+	if other != "" {
+		return other
+	}
+	return last
+}
+
+func cldrCategory(locale string, count any) (string, error) {
+	if strings.TrimSpace(locale) == "" {
+		locale = defaultLocale
+	}
+	loc := i18n.NewLocalizer(bundleFor(locale), locale)
+	return loc.Localize(&i18n.LocalizeConfig{
+		DefaultMessage: categoryMessage,
+		PluralCount:    coercePluralCount(count),
+		TemplateParser: identityParse,
+	})
+}
+
+func bundleFor(locale string) *i18n.Bundle {
+	if v, ok := bundleCache.Load(locale); ok {
+		return v.(*i18n.Bundle)
+	}
+	tag, err := language.Parse(locale)
+	if err != nil {
+		tag = language.English
+	}
+	b := i18n.NewBundle(tag)
+	actual, _ := bundleCache.LoadOrStore(locale, b)
+	return actual.(*i18n.Bundle)
+}
+
+func coercePluralCount(count any) any {
+	switch count.(type) {
+	case float32, float64:
+		return formatCount(count)
+	default:
+		return count
+	}
+}
+
+func cldrCategories(locale string) ([]string, map[string]struct{}, error) {
+	if v, ok := categoryCache.Load(locale); ok {
+		ordered := v.([]string)
+		return ordered, setFrom(ordered), nil
+	}
+	seen := make(map[string]struct{})
+	for _, n := range pluralSamples {
+		cat, err := cldrCategory(locale, n)
+		if err != nil {
+			return nil, nil, err
+		}
+		seen[cat] = struct{}{}
+	}
+	seen["other"] = struct{}{}
+	ordered := make([]string, 0, len(cldrOrder))
+	for _, cat := range cldrOrder {
+		if _, ok := seen[cat]; ok {
+			ordered = append(ordered, cat)
+		}
+	}
+	categoryCache.Store(locale, ordered)
+	return ordered, seen, nil
+}
+
+func cldrCategorySet(locale string) (map[string]struct{}, error) {
+	_, set, err := cldrCategories(locale)
+	return set, err
+}
+
+func setFrom(vals []string) map[string]struct{} {
+	out := make(map[string]struct{}, len(vals))
+	for _, v := range vals {
+		out[v] = struct{}{}
+	}
+	return out
+}
+
+func withCount(params map[string]string, count any) map[string]string {
+	out := make(map[string]string, len(params)+1)
+	for k, v := range params {
+		out[k] = v
+	}
+	if _, ok := out["count"]; !ok {
+		out["count"] = formatCount(count)
+	}
+	return out
+}
+
+func formatCount(count any) string {
+	switch v := count.(type) {
+	case int:
+		return strconv.Itoa(v)
+	case int8:
+		return strconv.FormatInt(int64(v), 10)
+	case int16:
+		return strconv.FormatInt(int64(v), 10)
+	case int32:
+		return strconv.FormatInt(int64(v), 10)
+	case int64:
+		return strconv.FormatInt(v, 10)
+	case uint:
+		return strconv.FormatUint(uint64(v), 10)
+	case uint64:
+		return strconv.FormatUint(v, 10)
+	case float32:
+		return formatFloat(float64(v))
+	case float64:
+		return formatFloat(v)
+	default:
+		return fmt.Sprint(v)
+	}
+}
+
+func formatFloat(v float64) string {
+	if v == float64(int64(v)) {
+		return strconv.FormatInt(int64(v), 10)
+	}
+	return strconv.FormatFloat(v, 'f', -1, 64)
+}
+
+func asFloat(count any) (float64, bool) {
+	switch v := count.(type) {
+	case int:
+		return float64(v), true
+	case int8:
+		return float64(v), true
+	case int16:
+		return float64(v), true
+	case int32:
+		return float64(v), true
+	case int64:
+		return float64(v), true
+	case uint:
+		return float64(v), true
+	case uint64:
+		return float64(v), true
+	case float32:
+		return float64(v), true
+	case float64:
+		return v, true
+	default:
+		return 0, false
+	}
 }

 func (t *Translator) localeFrom(ctx context.Context) string {
--- a/phrasebook/translator_test.go
+++ b/phrasebook/translator_test.go
@@ -96,3 +96,96 @@ func (p *langPlugin) Requires() []string           { return nil }
 func (p *langPlugin) Register(*backpack.App) error { return nil }
 func (p *langPlugin) Boot(*backpack.App) error     { return nil }
 func (p *langPlugin) LangFS() fs.FS                { return p.fsys }
+
+func TestPluralSmoke(t *testing.T) {
+	t.Parallel()
+
+	fsys := fstest.MapFS{
+		"lang/en/lang.yaml": {Data: []byte("" +
+			"albums:\n  one: \":count album\"\n  other: \":count albums\"\n" +
+			"items: \"{0} No items|{1} One item|[2,*] :count items\"\n" +
+			"helloName: \"hi :name :Name :NAME\"\n" +
+			"raw:\n  other: \"{{.Count}} bottles\"\n")},
+		"lang/pl/lang.yaml": {Data: []byte("" +
+			"albums:\n  one: \":count album\"\n  few: \":count albumy\"\n  many: \":count albumów\"\n  other: \":count albumu\"\n" +
+			"posts: \":count wpis|:count wpisy|:count wpisów|:count wpisu\"\n")},
+	}
+	cat := NewCatalog()
+	if err := cat.Load("golem15.hello", fsys); err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+	tr := NewTranslator(cat, Options{})
+
+	pl := map[any]string{1: "1 album", 2: "2 albumy", 5: "5 albumów", 22: "22 albumy", 0: "0 albumów", 1.5: "1.5 albumu"}
+	for n, want := range pl {
+		if got := tr.ChoiceIn("pl", "golem15.hello::lang.albums", n, nil); got != want {
+			t.Fatalf("pl albums %v = %q, want %q", n, got, want)
+		}
+	}
+	en := map[any]string{1: "1 album", 2: "2 albums", 0: "0 albums", 1.5: "1.5 albums"}
+	for n, want := range en {
+		if got := tr.ChoiceIn("en", "golem15.hello::lang.albums", n, nil); got != want {
+			t.Fatalf("en albums %v = %q, want %q", n, got, want)
+		}
+	}
+	if got := tr.ChoiceIn("pl", "golem15.hello::lang.posts", 1, nil); got != "1 wpis" {
+		t.Fatalf("pl posts 1 = %q", got)
+	}
+	if got := tr.ChoiceIn("pl", "golem15.hello::lang.posts", 2, nil); got != "2 wpisy" {
+		t.Fatalf("pl posts 2 = %q", got)
+	}
+	if got := tr.ChoiceIn("pl", "golem15.hello::lang.posts", 5, nil); got != "5 wpisów" {
+		t.Fatalf("pl posts 5 = %q", got)
+	}
+	if got := tr.ChoiceIn("pl", "golem15.hello::lang.posts", 22, nil); got != "22 wpisy" {
+		t.Fatalf("pl posts 22 = %q", got)
+	}
+	if got := tr.ChoiceIn("en", "golem15.hello::lang.items", 0, nil); got != "No items" {
+		t.Fatalf("items 0 = %q", got)
+	}
+	if got := tr.ChoiceIn("en", "golem15.hello::lang.items", 1, nil); got != "One item" {
+		t.Fatalf("items 1 = %q", got)
+	}
+	if got := tr.ChoiceIn("en", "golem15.hello::lang.items", 5, nil); got != "5 items" {
+		t.Fatalf("items 5 = %q", got)
+	}
+	if got := tr.ChoiceIn("en", "golem15.hello::lang.helloName", 1, map[string]string{"name": "alice"}); got != "hi alice Alice ALICE" {
+		t.Fatalf("params = %q", got)
+	}
+	if got := tr.ChoiceIn("en", "golem15.hello::lang.raw", 2, nil); got != "{{.Count}} bottles" {
+		t.Fatalf("go-i18n must not evaluate YAML as a template, got %q", got)
+	}
+
+	t.Run("invalid category for locale", func(t *testing.T) {
+		err := NewCatalog().Load("golem15.hello", fstest.MapFS{
+			"lang/en/lang.yaml": {Data: []byte("albums:\n  few: x\n  other: y\n")},
+		})
+		if err == nil || !strings.Contains(err.Error(), "invalid plural category") {
+			t.Fatalf("want invalid category, got %v", err)
+		}
+	})
+	t.Run("missing other", func(t *testing.T) {
+		err := NewCatalog().Load("golem15.hello", fstest.MapFS{
+			"lang/en/lang.yaml": {Data: []byte("albums:\n  one: x\n")},
+		})
+		if err == nil || !strings.Contains(err.Error(), "requires other") {
+			t.Fatalf("want missing other, got %v", err)
+		}
+	})
+	t.Run("malformed pipe", func(t *testing.T) {
+		err := NewCatalog().Load("golem15.hello", fstest.MapFS{
+			"lang/en/lang.yaml": {Data: []byte("items: \"{x} nope|{1} one\"\n")},
+		})
+		if err == nil || !strings.Contains(err.Error(), "malformed pipe") {
+			t.Fatalf("want malformed pipe, got %v", err)
+		}
+	})
+	t.Run("incomplete pipe", func(t *testing.T) {
+		err := NewCatalog().Load("golem15.hello", fstest.MapFS{
+			"lang/en/lang.yaml": {Data: []byte("items: \":count post|:count posts|:count extra\"\n")},
+		})
+		if err == nil || !strings.Contains(err.Error(), "incomplete pipe") {
+			t.Fatalf("want incomplete pipe, got %v", err)
+		}
+	})
+}