fix: register chroma style once

don't register chroma style if it's already registered

this could cause a "concurrent map writes" fatal error when used in a
concurrent setting like a bubbletea wish app. use a package-wide mutex
to protect registering a new style.

ansi/codeblock.go

@@ -2,6 +2,7 @@ package ansi
 
 import (
 	"io"
+	"sync"
 
 	"github.com/alecthomas/chroma"
 	"github.com/alecthomas/chroma/quick"
@@ -9,6 +10,17 @@ import (
 	"github.com/muesli/reflow/indent"
 )
 
+const (
+	// The chroma style theme name used for rendering.
+	chromaStyleTheme = "charm"
+)
+
+var (
+	// mutex for synchronizing access to the chroma style registry.
+	// Related https://github.com/alecthomas/chroma/pull/650
+	mutex = sync.Mutex{}
+)
+
 // A CodeBlockElement is used to render code blocks.
 type CodeBlockElement struct {
 	Code     string
@@ -64,8 +76,12 @@ func (e *CodeBlockElement) Render(w io.Writer, ctx RenderContext) error {
 	theme := rules.Theme
 
 	if rules.Chroma != nil && ctx.options.ColorProfile > 1 {
-		theme = "charm"
-		styles.Register(chroma.MustNewStyle("charm",
+		theme = chromaStyleTheme
+		mutex.Lock()
+		// Don't register the style if it's already registered.
+		_, ok := styles.Registry[theme]
+		if !ok {
+			styles.Register(chroma.MustNewStyle(theme,
 				chroma.StyleEntries{
 					chroma.Text:                chromaStyle(rules.Chroma.Text),
 					chroma.Error:               chromaStyle(rules.Chroma.Error),
@@ -100,6 +116,8 @@ func (e *CodeBlockElement) Render(w io.Writer, ctx RenderContext) error {
 					chroma.Background:          chromaStyle(rules.Chroma.Background),
 				}))
 		}
+		mutex.Unlock()
+	}
 
 	iw := indent.NewWriterPipe(w, indentation+margin, func(wr io.Writer) {
 		renderText(w, ctx.options.ColorProfile, bs.Current().Style.StylePrimitive, " ")