refactor: replace sort package usage with slices/cmp

Modernise pre-1.21 sorting idioms: sort.Strings/Ints/Slice become
slices.Sort/SortFunc, Names() collapses to slices.Sorted(maps.Keys),
and the sort-then-take-first pattern in the lexer registry becomes
slices.MinFunc, which is O(n) and deterministically breaks priority
ties by registration order.

The exported Lexers/PrioritisedLexers sort.Interface method sets are
retained for external users; PrioritisedLexers.Less now delegates to
the new compareLexersByPriority comparator so the ordering logic has
a single source of truth.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: alecthomas

formatters/api.go

@@ -3,7 +3,8 @@ package formatters
 import (
 	"io"
 	"iter"
-	"sort"
+	"maps"
+	"slices"
 
 	"github.com/alecthomas/chroma/v3"
 	"github.com/alecthomas/chroma/v3/formatters/html"
@@ -32,12 +33,7 @@ var registry = map[string]chroma.Formatter{}
 
 // Names of registered formatters.
 func Names() []string {
-	out := []string{}
-	for name := range registry {
-		out = append(out, name)
-	}
-	sort.Strings(out)
-	return out
+	return slices.Sorted(maps.Keys(registry))
 }
 
 // Get formatter by name.

formatters/html/html.go

@@ -1,12 +1,13 @@
 package html
 
 import (
+	"cmp"
 	"fmt"
 	"html"
 	"io"
 	"iter"
+	"maps"
 	"slices"
-	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -127,7 +128,7 @@ func WithLinkableLineNumbers(b bool, prefix string) Option {
 func HighlightLines(ranges [][2]int) Option {
 	return func(f *Formatter) {
 		f.highlightRanges = ranges
-		sort.Sort(f.highlightRanges)
+		f.highlightRanges.sort()
 	}
 }
 
@@ -138,7 +139,7 @@ func WithLinePrompts(prompt string, ranges [][2]int) Option {
 	return func(f *Formatter) {
 		f.linePrompt = prompt
 		f.linePromptRanges = ranges
-		sort.Sort(f.linePromptRanges)
+		f.linePromptRanges.sort()
 	}
 }
 
@@ -238,9 +239,9 @@ type Formatter struct {
 
 type lineRanges [][2]int
 
-func (r lineRanges) Len() int           { return len(r) }
-func (r lineRanges) Swap(i, j int)      { r[i], r[j] = r[j], r[i] }
-func (r lineRanges) Less(i, j int) bool { return r[i][0] < r[j][0] }
+func (r lineRanges) sort() {
+	slices.SortFunc(r, func(a, b [2]int) int { return cmp.Compare(a[0], b[0]) })
+}
 
 func (r lineRanges) match(rangeIndex, line int) (bool, int) {
 	for rangeIndex < len(r) && line > r[rangeIndex][1] {
@@ -525,13 +526,7 @@ func (f *Formatter) WriteCSS(w io.Writer, style *chroma.Style) error {
 			}
 		}
 	}
-	tts := []int{}
-	for tt := range css {
-		tts = append(tts, int(tt))
-	}
-	sort.Ints(tts)
-	for _, ti := range tts {
-		tt := chroma.TokenType(ti)
+	for _, tt := range slices.Sorted(maps.Keys(css)) {
 		switch tt {
 		case chroma.Background, chroma.PreWrapper:
 			continue

lexer.go

@@ -1,6 +1,7 @@
 package chroma
 
 import (
+	"cmp"
 	"fmt"
 	"iter"
 	"strings"
@@ -160,15 +161,21 @@ type PrioritisedLexers []Lexer
 func (l PrioritisedLexers) Len() int      { return len(l) }
 func (l PrioritisedLexers) Swap(i, j int) { l[i], l[j] = l[j], l[i] }
 func (l PrioritisedLexers) Less(i, j int) bool {
-	ip := l[i].Config().Priority
-	if ip == 0 {
-		ip = 1
+	return compareLexersByPriority(l[i], l[j]) < 0
+}
+
+// compareLexersByPriority orders lexers by descending priority, treating an
+// unset priority as 1.
+func compareLexersByPriority(a, b Lexer) int {
+	ap := a.Config().Priority
+	if ap == 0 {
+		ap = 1
 	}
-	jp := l[j].Config().Priority
-	if jp == 0 {
-		jp = 1
+	bp := b.Config().Priority
+	if bp == 0 {
+		bp = 1
 	}
-	return ip > jp
+	return cmp.Compare(bp, ap)
 }
 
 // Analyser determines how appropriate this lexer is for the given text.

regexp.go

@@ -1,6 +1,7 @@
 package chroma
 
 import (
+	"cmp"
 	"encoding/json"
 	"fmt"
 	"iter"
@@ -9,7 +10,6 @@ import (
 	"path/filepath"
 	"regexp"
 	"slices"
-	"sort"
 	"strings"
 	"sync"
 	"time"
@@ -27,8 +27,8 @@ type Rule struct {
 
 // Words creates a regex that matches any of the given literal words.
 func Words(prefix, suffix string, words ...string) string {
-	sort.Slice(words, func(i, j int) bool {
-		return len(words[j]) < len(words[i])
+	slices.SortFunc(words, func(a, b string) int {
+		return cmp.Compare(len(b), len(a))
 	})
 	for i, word := range words {
 		words[i] = regexp.QuoteMeta(word)

registry.go

@@ -2,7 +2,7 @@ package chroma
 
 import (
 	"path/filepath"
-	"sort"
+	"slices"
 	"strings"
 )
 
@@ -44,7 +44,7 @@ func (l *LexerRegistry) Names(withAliases bool) []string {
 			out = append(out, config.Aliases...)
 		}
 	}
-	sort.Strings(out)
+	slices.Sort(out)
 	return out
 }
 
@@ -62,7 +62,7 @@ func (l *LexerRegistry) Aliases(skipWithoutAliases bool) []string {
 		}
 		out = append(out, config.Aliases...)
 	}
-	sort.Strings(out)
+	slices.Sort(out)
 	return out
 }
 
@@ -93,8 +93,7 @@ func (l *LexerRegistry) Get(name string) Lexer {
 	if len(candidates) == 0 {
 		return nil
 	}
-	sort.Sort(candidates)
-	return candidates[0]
+	return slices.MinFunc(candidates, compareLexersByPriority)
 }
 
 // MatchMimeType attempts to find a lexer for the given MIME type.
@@ -108,8 +107,7 @@ func (l *LexerRegistry) MatchMimeType(mimeType string) Lexer {
 		}
 	}
 	if len(matched) != 0 {
-		sort.Sort(matched)
-		return matched[0]
+		return slices.MinFunc(matched, compareLexersByPriority)
 	}
 	return nil
 }
@@ -143,8 +141,7 @@ func (l *LexerRegistry) Match(filename string) Lexer {
 		}
 	}
 	if len(matched) > 0 {
-		sort.Sort(matched)
-		return matched[0]
+		return slices.MinFunc(matched, compareLexersByPriority)
 	}
 	matched = nil
 	// Next, try filename aliases.
@@ -170,8 +167,7 @@ func (l *LexerRegistry) Match(filename string) Lexer {
 		}
 	}
 	if len(matched) > 0 {
-		sort.Sort(matched)
-		return matched[0]
+		return slices.MinFunc(matched, compareLexersByPriority)
 	}
 	return nil
 }

styles/api.go

@@ -3,7 +3,8 @@ package styles
 import (
 	"embed"
 	"io/fs"
-	"sort"
+	"maps"
+	"slices"
 	"strings"
 
 	"github.com/alecthomas/chroma/v3"
@@ -47,12 +48,7 @@ func Register(style *chroma.Style) *chroma.Style {
 
 // Names of all available styles.
 func Names() []string {
-	out := []string{}
-	for name := range registry {
-		out = append(out, name)
-	}
-	sort.Strings(out)
-	return out
+	return slices.Sorted(maps.Keys(registry))
 }
 
 // Lookup a named style, returning false if not found.