Start using template context function (#26254)

Before:

* `{{.locale.Tr ...}}`
* `{{$.locale.Tr ...}}`
* `{{$.root.locale.Tr ...}}`
* `{{template "sub" .}}`
* `{{template "sub" (dict "locale" $.locale)}}`
* `{{template "sub" (dict "root" $)}}`
* .....

With context function: only need to `{{ctx.Locale.Tr ...}}`

The "ctx" could be considered as a super-global variable for all
templates including sub-templates.


To avoid potential risks (any bug in the template context function
package), this PR only starts using "ctx" in "head.tmpl" and
"footer.tmpl" and it has a "DataRaceCheck". If there is anything wrong,
the code can be fixed or reverted easily.

modules/context/context.go

@@ -5,6 +5,7 @@
 package context
 
 import (
+	"context"
 	"html"
 	"html/template"
 	"io"
@@ -31,14 +32,16 @@ import (
 
 // Render represents a template render
 type Render interface {
-	TemplateLookup(tmpl string) (templates.TemplateExecutor, error)
-	HTML(w io.Writer, status int, name string, data any) error
+	TemplateLookup(tmpl string, templateCtx context.Context) (templates.TemplateExecutor, error)
+	HTML(w io.Writer, status int, name string, data any, templateCtx context.Context) error
 }
 
 // Context represents context of a request.
 type Context struct {
 	*Base
 
+	TemplateContext TemplateContext
+
 	Render   Render
 	PageData map[string]any // data used by JavaScript modules in one page, it's `window.config.pageData`
 
@@ -60,6 +63,8 @@ type Context struct {
 	Package *Package
 }
 
+type TemplateContext map[string]any
+
 func init() {
 	web.RegisterResponseStatusProvider[*Context](func(req *http.Request) web_types.ResponseStatusProvider {
 		return req.Context().Value(WebContextKey).(*Context)
@@ -133,8 +138,12 @@ func Contexter() func(next http.Handler) http.Handler {
 			}
 			defer baseCleanUp()
 
+			// TODO: "install.go" also shares the same logic, which should be refactored to a general function
+			ctx.TemplateContext = NewTemplateContext(ctx)
+			ctx.TemplateContext["Locale"] = ctx.Locale
+
 			ctx.Data.MergeFrom(middleware.CommonTemplateContextData())
-			ctx.Data["Context"] = &ctx
+			ctx.Data["Context"] = ctx // TODO: use "ctx" in template and remove this
 			ctx.Data["CurrentURL"] = setting.AppSubURL + req.URL.RequestURI()
 			ctx.Data["Link"] = ctx.Link
 			ctx.Data["locale"] = ctx.Locale