Add render cache for SVG icons (#36863)

Cache the final rendered `template.HTML` output for SVG icons that use
non-default size or class parameters using `sync.Map`.

Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/svg/svg.go

@@ -8,13 +8,32 @@ import (
 	"html/template"
 	"path"
 	"strings"
+	"sync"
 
 	gitea_html "code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/public"
 )
 
-var svgIcons map[string]string
+type svgIconItem struct {
+	html    string
+	mocking bool
+}
+
+type svgCacheKey struct {
+	icon  string
+	size  int
+	class string
+}
+
+var (
+	svgIcons map[string]svgIconItem
+
+	svgCacheMu    sync.Mutex
+	svgCache      sync.Map
+	svgCacheCount int
+	svgCacheLimit = 10000
+)
 
 const defaultSize = 16
 
@@ -26,7 +45,7 @@ func Init() error {
 		return err
 	}
 
-	svgIcons = make(map[string]string, len(files))
+	svgIcons = make(map[string]svgIconItem, len(files))
 	for _, file := range files {
 		if path.Ext(file) != ".svg" {
 			continue
@@ -35,7 +54,7 @@ func Init() error {
 		if err != nil {
 			log.Error("Failed to read SVG file %s: %v", file, err)
 		} else {
-			svgIcons[file[:len(file)-4]] = string(Normalize(bs, defaultSize))
+			svgIcons[file[:len(file)-4]] = svgIconItem{html: string(Normalize(bs, defaultSize))}
 		}
 	}
 	return nil
@@ -43,10 +62,13 @@ func Init() error {
 
 func MockIcon(icon string) func() {
 	if svgIcons == nil {
-		svgIcons = make(map[string]string)
+		svgIcons = make(map[string]svgIconItem)
 	}
 	orig, exist := svgIcons[icon]
-	svgIcons[icon] = fmt.Sprintf(`<svg class="svg %s" width="%d" height="%d"></svg>`, icon, defaultSize, defaultSize)
+	svgIcons[icon] = svgIconItem{
+		html:    fmt.Sprintf(`<svg class="svg %s" width="%d" height="%d"></svg>`, icon, defaultSize, defaultSize),
+		mocking: true,
+	}
 	return func() {
 		if exist {
 			svgIcons[icon] = orig
@@ -58,11 +80,28 @@ func MockIcon(icon string) func() {
 
 // RenderHTML renders icons - arguments icon name (string), size (int), class (string)
 func RenderHTML(icon string, others ...any) template.HTML {
+	result, _ := renderHTML(icon, others...)
+	return result
+}
+
+func renderHTML(icon string, others ...any) (_ template.HTML, usingCache bool) {
 	if icon == "" {
-		return ""
+		return "", false
 	}
 	size, class := gitea_html.ParseSizeAndClass(defaultSize, "", others...)
-	if svgStr, ok := svgIcons[icon]; ok {
+	if svgItem, ok := svgIcons[icon]; ok {
+		svgStr := svgItem.html
+		// fast path for default size and no classes
+		if size == defaultSize && class == "" {
+			return template.HTML(svgStr), false
+		}
+
+		cacheKey := svgCacheKey{icon, size, class}
+		cachedHTML, cached := svgCache.Load(cacheKey)
+		if cached && !svgItem.mocking {
+			return cachedHTML.(template.HTML), true
+		}
+
 		// the code is somewhat hacky, but it just works, because the SVG contents are all normalized
 		if size != defaultSize {
 			svgStr = strings.Replace(svgStr, fmt.Sprintf(`width="%d"`, defaultSize), fmt.Sprintf(`width="%d"`, size), 1)
@@ -71,8 +110,24 @@ func RenderHTML(icon string, others ...any) template.HTML {
 		if class != "" {
 			svgStr = strings.Replace(svgStr, `class="`, fmt.Sprintf(`class="%s `, class), 1)
 		}
-		return template.HTML(svgStr)
+		result := template.HTML(svgStr)
+
+		if !svgItem.mocking {
+			// no need to double-check, the rendering is fast enough and the cache is just an optimization
+			svgCacheMu.Lock()
+			if svgCacheCount >= svgCacheLimit {
+				svgCache.Clear()
+				svgCacheCount = 0
 			}
+			svgCacheCount++
+			svgCache.Store(cacheKey, result)
+			svgCacheMu.Unlock()
+		}
+
+		return result, false
+	}
+
 	// during test (or something wrong happens), there is no SVG loaded, so use a dummy span to tell that the icon is missing
-	return template.HTML(fmt.Sprintf("<span>%s(%d/%s)</span>", template.HTMLEscapeString(icon), size, template.HTMLEscapeString(class)))
+	dummy := template.HTML(fmt.Sprintf("<span>%s(%d/%s)</span>", template.HTMLEscapeString(icon), size, template.HTMLEscapeString(class)))
+	return dummy, false
 }

modules/svg/svg_test.go

@@ -0,0 +1,54 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package svg
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/modules/test"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRenderHTMLCache(t *testing.T) {
+	const svgRealContent = "RealContent"
+	svgIcons = map[string]svgIconItem{
+		"test": {html: `<svg class="svg test" width="16" height="16">` + svgRealContent + `</svg>`},
+	}
+
+	// default params: no cache entry
+	_, usingCache := renderHTML("test")
+	assert.False(t, usingCache)
+	_, usingCache = renderHTML("test")
+	assert.False(t, usingCache)
+
+	// non-default params: cached
+	_, usingCache = renderHTML("test", 24)
+	assert.False(t, usingCache)
+	_, usingCache = renderHTML("test", 24)
+	assert.True(t, usingCache)
+
+	// mocked svg shouldn't be cached
+	revertMock := MockIcon("test")
+	mockedHTML, usingCache := renderHTML("test", 24)
+	assert.False(t, usingCache)
+	assert.NotContains(t, mockedHTML, svgRealContent)
+	revertMock()
+	realHTML, usingCache := renderHTML("test", 24)
+	assert.True(t, usingCache)
+	assert.Contains(t, realHTML, svgRealContent)
+
+	t.Run("CacheWithLimit", func(t *testing.T) {
+		assert.NotZero(t, svgCacheCount)
+		const testLimit = 3
+		defer test.MockVariableValue(&svgCacheLimit, testLimit)()
+		for i := range 10 {
+			_, usingCache = renderHTML("test", 100+i)
+			assert.False(t, usingCache)
+			_, usingCache = renderHTML("test", 100+i)
+			assert.True(t, usingCache)
+			assert.LessOrEqual(t, svgCacheCount, testLimit)
+		}
+	})
+}