Clean up template locale usage (#27856)

After many refactoring PRs for the "locale" and "template context
function", now the ".locale" is not needed for web templates any more.

This PR does a clean up for:

1. Remove `ctx.Data["locale"]` for web context.
2. Use `ctx.Locale` in `500.tmpl`, for consistency.
3. Add a test check for `500 page` locale usage.
4. Remove the `Str2html` and `DotEscape` from mail template context
data, they are copy&paste errors introduced by #19169 and #16200 . These
functions are template functions (provided by the common renderer), but
not template data variables.
5. Make email `SendAsync` function mockable (I was planning to add more
tests but it would make this PR much too complex, so the tests could be
done in another PR)

2 files changed, 8 insertions, 8 deletions

diff --git a/routers/common/errpage.go b/routers/common/errpage.go
index 9c8ccc3388..923421a29c 100644
--- a/routers/common/errpage.go
+++ b/routers/common/errpage.go
@@ -9,6 +9,7 @@ import (
 
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/httpcache"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
@@ -35,20 +36,18 @@ func RenderPanicErrorPage(w http.ResponseWriter, req *http.Request, err any) {
 	httpcache.SetCacheControlInHeader(w.Header(), 0, "no-transform")
 	w.Header().Set(`X-Frame-Options`, setting.CORSConfig.XFrameOptions)
 
-	data := middleware.GetContextData(req.Context())
-	if data["locale"] == nil {
-		data = middleware.CommonTemplateContextData()
-		data["locale"] = middleware.Locale(w, req)
-	}
+	tmplCtx := context.TemplateContext{}
+	tmplCtx["Locale"] = middleware.Locale(w, req)
+	ctxData := middleware.GetContextData(req.Context())
 
 	// This recovery handler could be called without Gitea's web context, so we shouldn't touch that context too much.
 	// Otherwise, the 500-page may cause new panics, eg: cache.GetContextWithData, it makes the developer&users couldn't find the original panic.
-	user, _ := data[middleware.ContextDataKeySignedUser].(*user_model.User)
+	user, _ := ctxData[middleware.ContextDataKeySignedUser].(*user_model.User)
 	if !setting.IsProd || (user != nil && user.IsAdmin) {
-		data["ErrorMsg"] = "PANIC: " + combinedErr
+		ctxData["ErrorMsg"] = "PANIC: " + combinedErr
 	}
 
-	err = templates.HTMLRenderer().HTML(w, http.StatusInternalServerError, string(tplStatus500), data, nil)
+	err = templates.HTMLRenderer().HTML(w, http.StatusInternalServerError, string(tplStatus500), ctxData, tmplCtx)
 	if err != nil {
 		log.Error("Error occurs again when rendering error page: %v", err)
 		w.WriteHeader(http.StatusInternalServerError)
diff --git a/routers/common/errpage_test.go b/routers/common/errpage_test.go
index 58a633b2a4..4fd63ba49e 100644
--- a/routers/common/errpage_test.go
+++ b/routers/common/errpage_test.go
@@ -26,6 +26,7 @@ func TestRenderPanicErrorPage(t *testing.T) {
 	respContent := w.Body.String()
 	assert.Contains(t, respContent, `class="page-content status-page-500"`)
 	assert.Contains(t, respContent, `</html>`)
+	assert.Contains(t, respContent, `lang="en-US"`) // make sure the locale work
 
 	// the 500 page doesn't have normal pages footer, it makes it easier to distinguish a normal page and a failed page.
 	// especially when a sub-template causes page error, the HTTP response code is still 200,