Improve template system and panic recovery (#24461)

Partially for #24457

Major changes:

1. The old `signedUserNameStringPointerKey` is quite hacky, use
`ctx.Data[SignedUser]` instead
2. Move duplicate code from `Contexter` to `CommonTemplateContextData`
3. Remove incorrect copying&pasting code `ctx.Data["Err_Password"] =
true` in API handlers
4. Use one unique `RenderPanicErrorPage` for panic error page rendering
5. Move `stripSlashesMiddleware` to be the first middleware
6. Install global panic recovery handler, it works for both `install`
and `web`
7. Make `500.tmpl` only depend minimal template functions/variables,
avoid triggering new panics

Screenshot:

<details>

![image](https://user-images.githubusercontent.com/2114189/235444895-cecbabb8-e7dc-4360-a31c-b982d11946a7.png)

</details>

11 files changed, 104 insertions, 110 deletions

diff --git a/modules/context/access_log.go b/modules/context/access_log.go
index 64d204733b..b6468d139b 100644
--- a/modules/context/access_log.go
+++ b/modules/context/access_log.go
@@ -5,7 +5,6 @@ package context
 
 import (
 	"bytes"
-	"context"
 	"fmt"
 	"net"
 	"net/http"
@@ -13,8 +12,10 @@ import (
 	"text/template"
 	"time"
 
+	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/web/middleware"
 )
 
 type routerLoggerOptions struct {
@@ -26,8 +27,6 @@ type routerLoggerOptions struct {
 	RequestID      *string
 }
 
-var signedUserNameStringPointerKey interface{} = "signedUserNameStringPointerKey"
-
 const keyOfRequestIDInTemplate = ".RequestID"
 
 // According to:
@@ -60,8 +59,6 @@ func AccessLogger() func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
 			start := time.Now()
-			identity := "-"
-			r := req.WithContext(context.WithValue(req.Context(), signedUserNameStringPointerKey, &identity))
 
 			var requestID string
 			if needRequestID {
@@ -73,9 +70,14 @@ func AccessLogger() func(http.Handler) http.Handler {
 				reqHost = req.RemoteAddr
 			}
 
-			next.ServeHTTP(w, r)
+			next.ServeHTTP(w, req)
 			rw := w.(ResponseWriter)
 
+			identity := "-"
+			data := middleware.GetContextData(req.Context())
+			if signedUser, ok := data[middleware.ContextDataKeySignedUser].(*user_model.User); ok {
+				identity = signedUser.Name
+			}
 			buf := bytes.NewBuffer([]byte{})
 			err = logTemplate.Execute(buf, routerLoggerOptions{
 				req:            req,
diff --git a/modules/context/api.go b/modules/context/api.go
index ae245ec1cb..e263dcbe8d 100644
--- a/modules/context/api.go
+++ b/modules/context/api.go
@@ -222,7 +222,7 @@ func APIContexter() func(http.Handler) http.Handler {
 			ctx := APIContext{
 				Context: &Context{
 					Resp:   NewResponse(w),
-					Data:   map[string]interface{}{},
+					Data:   middleware.GetContextData(req.Context()),
 					Locale: locale,
 					Cache:  cache.GetCache(),
 					Repo: &Repository{
@@ -250,17 +250,6 @@ func APIContexter() func(http.Handler) http.Handler {
 			ctx.Data["Context"] = &ctx
 
 			next.ServeHTTP(ctx.Resp, ctx.Req)
-
-			// Handle adding signedUserName to the context for the AccessLogger
-			usernameInterface := ctx.Data["SignedUserName"]
-			identityPtrInterface := ctx.Req.Context().Value(signedUserNameStringPointerKey)
-			if usernameInterface != nil && identityPtrInterface != nil {
-				username := usernameInterface.(string)
-				identityPtr := identityPtrInterface.(*string)
-				if identityPtr != nil && username != "" {
-					*identityPtr = username
-				}
-			}
 		})
 	}
 }
diff --git a/modules/context/context.go b/modules/context/context.go
index cd7fcebe55..d73a26e5b6 100644
--- a/modules/context/context.go
+++ b/modules/context/context.go
@@ -55,7 +55,7 @@ type Render interface {
 type Context struct {
 	Resp     ResponseWriter
 	Req      *http.Request
-	Data     map[string]interface{} // data used by MVC templates
+	Data     middleware.ContextData // data used by MVC templates
 	PageData map[string]interface{} // data used by JavaScript modules in one page, it's `window.config.pageData`
 	Render   Render
 	translation.Locale
@@ -97,7 +97,7 @@ func (ctx *Context) TrHTMLEscapeArgs(msg string, args ...string) string {
 }
 
 // GetData returns the data
-func (ctx *Context) GetData() map[string]interface{} {
+func (ctx *Context) GetData() middleware.ContextData {
 	return ctx.Data
 }
 
@@ -219,6 +219,7 @@ const tplStatus500 base.TplName = "status/500"
 // HTML calls Context.HTML and renders the template to HTTP response
 func (ctx *Context) HTML(status int, name base.TplName) {
 	log.Debug("Template: %s", name)
+
 	tmplStartTime := time.Now()
 	if !setting.IsProd {
 		ctx.Data["TemplateName"] = name
@@ -226,13 +227,19 @@ func (ctx *Context) HTML(status int, name base.TplName) {
 	ctx.Data["TemplateLoadTimes"] = func() string {
 		return strconv.FormatInt(time.Since(tmplStartTime).Nanoseconds()/1e6, 10) + "ms"
 	}
-	if err := ctx.Render.HTML(ctx.Resp, status, string(name), templates.BaseVars().Merge(ctx.Data)); err != nil {
-		if status == http.StatusInternalServerError && name == tplStatus500 {
-			ctx.PlainText(http.StatusInternalServerError, "Unable to find HTML templates, the template system is not initialized, or Gitea can't find your template files.")
-			return
-		}
+
+	err := ctx.Render.HTML(ctx.Resp, status, string(name), ctx.Data)
+	if err == nil {
+		return
+	}
+
+	// if rendering fails, show error page
+	if name != tplStatus500 {
 		err = fmt.Errorf("failed to render template: %s, error: %s", name, templates.HandleTemplateRenderingError(err))
-		ctx.ServerError("Render failed", err)
+		ctx.ServerError("Render failed", err) // show the 500 error page
+	} else {
+		ctx.PlainText(http.StatusInternalServerError, "Unable to render status/500 page, the template system is broken, or Gitea can't find your template files.")
+		return
 	}
 }
 
@@ -676,7 +683,7 @@ func getCsrfOpts() CsrfOptions {
 }
 
 // Contexter initializes a classic context for a request.
-func Contexter(ctx context.Context) func(next http.Handler) http.Handler {
+func Contexter() func(next http.Handler) http.Handler {
 	rnd := templates.HTMLRenderer()
 	csrfOpts := getCsrfOpts()
 	if !setting.IsProd {
@@ -684,34 +691,30 @@ func Contexter(ctx context.Context) func(next http.Handler) http.Handler {
 	}
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
-			locale := middleware.Locale(resp, req)
-			startTime := time.Now()
-			link := setting.AppSubURL + strings.TrimSuffix(req.URL.EscapedPath(), "/")
-
 			ctx := Context{
 				Resp:    NewResponse(resp),
 				Cache:   mc.GetCache(),
-				Locale:  locale,
-				Link:    link,
+				Locale:  middleware.Locale(resp, req),
+				Link:    setting.AppSubURL + strings.TrimSuffix(req.URL.EscapedPath(), "/"),
 				Render:  rnd,
 				Session: session.GetSession(req),
 				Repo: &Repository{
 					PullRequest: &PullRequest{},
 				},
-				Org: &Organization{},
-				Data: map[string]interface{}{
-					"CurrentURL":    setting.AppSubURL + req.URL.RequestURI(),
-					"PageStartTime": startTime,
-					"Link":          link,
-					"RunModeIsProd": setting.IsProd,
-				},
+				Org:  &Organization{},
+				Data: middleware.GetContextData(req.Context()),
 			}
 			defer ctx.Close()
 
+			ctx.Data.MergeFrom(middleware.CommonTemplateContextData())
+			ctx.Data["Context"] = &ctx
+			ctx.Data["CurrentURL"] = setting.AppSubURL + req.URL.RequestURI()
+			ctx.Data["Link"] = ctx.Link
+			ctx.Data["locale"] = ctx.Locale
+
 			// PageData is passed by reference, and it will be rendered to `window.config.pageData` in `head.tmpl` for JavaScript modules
-			ctx.PageData = map[string]interface{}{}
+			ctx.PageData = map[string]any{}
 			ctx.Data["PageData"] = ctx.PageData
-			ctx.Data["Context"] = &ctx
 
 			ctx.Req = WithContext(req, &ctx)
 			ctx.Csrf = PrepareCSRFProtector(csrfOpts, &ctx)
@@ -755,16 +758,6 @@ func Contexter(ctx context.Context) func(next http.Handler) http.Handler {
 			ctx.Data["CsrfTokenHtml"] = template.HTML(`<input type="hidden" name="_csrf" value="` + ctx.Data["CsrfToken"].(string) + `">`)
 
 			// FIXME: do we really always need these setting? There should be someway to have to avoid having to always set these
-			ctx.Data["IsLandingPageHome"] = setting.LandingPageURL == setting.LandingPageHome
-			ctx.Data["IsLandingPageExplore"] = setting.LandingPageURL == setting.LandingPageExplore
-			ctx.Data["IsLandingPageOrganizations"] = setting.LandingPageURL == setting.LandingPageOrganizations
-
-			ctx.Data["ShowRegistrationButton"] = setting.Service.ShowRegistrationButton
-			ctx.Data["ShowMilestonesDashboardPage"] = setting.Service.ShowMilestonesDashboardPage
-			ctx.Data["ShowFooterVersion"] = setting.Other.ShowFooterVersion
-
-			ctx.Data["EnableSwagger"] = setting.API.EnableSwagger
-			ctx.Data["EnableOpenIDSignIn"] = setting.Service.EnableOpenIDSignIn
 			ctx.Data["DisableMigrations"] = setting.Repository.DisableMigrations
 			ctx.Data["DisableStars"] = setting.Repository.DisableStars
 			ctx.Data["EnableActions"] = setting.Actions.Enabled
@@ -777,21 +770,9 @@ func Contexter(ctx context.Context) func(next http.Handler) http.Handler {
 			ctx.Data["UnitProjectsGlobalDisabled"] = unit.TypeProjects.UnitGlobalDisabled()
 			ctx.Data["UnitActionsGlobalDisabled"] = unit.TypeActions.UnitGlobalDisabled()
 
-			ctx.Data["locale"] = locale
 			ctx.Data["AllLangs"] = translation.AllLangs()
 
 			next.ServeHTTP(ctx.Resp, ctx.Req)
-
-			// Handle adding signedUserName to the context for the AccessLogger
-			usernameInterface := ctx.Data["SignedUserName"]
-			identityPtrInterface := ctx.Req.Context().Value(signedUserNameStringPointerKey)
-			if usernameInterface != nil && identityPtrInterface != nil {
-				username := usernameInterface.(string)
-				identityPtr := identityPtrInterface.(*string)
-				if identityPtr != nil && username != "" {
-					*identityPtr = username
-				}
-			}
 		})
 	}
 }
diff --git a/modules/context/package.go b/modules/context/package.go
index 6c418b3164..fe5bdac19d 100644
--- a/modules/context/package.go
+++ b/modules/context/package.go
@@ -16,6 +16,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/templates"
+	"code.gitea.io/gitea/modules/web/middleware"
 )
 
 // Package contains owner, access mode and optional the package descriptor
@@ -136,7 +137,7 @@ func PackageContexter(ctx gocontext.Context) func(next http.Handler) http.Handle
 		return http.HandlerFunc(func(resp http.ResponseWriter, req *http.Request) {
 			ctx := Context{
 				Resp:   NewResponse(resp),
-				Data:   map[string]interface{}{},
+				Data:   middleware.GetContextData(req.Context()),
 				Render: rnd,
 			}
 			defer ctx.Close()
diff --git a/modules/context/private.go b/modules/context/private.go
index 24f50fa471..f621dd6839 100644
--- a/modules/context/private.go
+++ b/modules/context/private.go
@@ -11,6 +11,7 @@ import (
 
 	"code.gitea.io/gitea/modules/graceful"
 	"code.gitea.io/gitea/modules/process"
+	"code.gitea.io/gitea/modules/web/middleware"
 )
 
 // PrivateContext represents a context for private routes
@@ -62,7 +63,7 @@ func PrivateContexter() func(http.Handler) http.Handler {
 			ctx := &PrivateContext{
 				Context: &Context{
 					Resp: NewResponse(w),
-					Data: map[string]interface{}{},
+					Data: middleware.GetContextData(req.Context()),
 				},
 			}
 			defer ctx.Close()
diff --git a/modules/templates/base.go b/modules/templates/base.go
index 4254a56976..ef28cc03f4 100644
--- a/modules/templates/base.go
+++ b/modules/templates/base.go
@@ -5,43 +5,12 @@ package templates
 
 import (
 	"strings"
-	"time"
 
 	"code.gitea.io/gitea/modules/assetfs"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/util"
 )
 
-// Vars represents variables to be render in golang templates
-type Vars map[string]interface{}
-
-// Merge merges another vars to the current, another Vars will override the current
-func (vars Vars) Merge(another map[string]interface{}) Vars {
-	for k, v := range another {
-		vars[k] = v
-	}
-	return vars
-}
-
-// BaseVars returns all basic vars
-func BaseVars() Vars {
-	startTime := time.Now()
-	return map[string]interface{}{
-		"IsLandingPageHome":          setting.LandingPageURL == setting.LandingPageHome,
-		"IsLandingPageExplore":       setting.LandingPageURL == setting.LandingPageExplore,
-		"IsLandingPageOrganizations": setting.LandingPageURL == setting.LandingPageOrganizations,
-
-		"ShowRegistrationButton":        setting.Service.ShowRegistrationButton,
-		"ShowMilestonesDashboardPage":   setting.Service.ShowMilestonesDashboardPage,
-		"ShowFooterVersion":             setting.Other.ShowFooterVersion,
-		"DisableDownloadSourceArchives": setting.Repository.DisableDownloadSourceArchives,
-
-		"EnableSwagger":      setting.API.EnableSwagger,
-		"EnableOpenIDSignIn": setting.Service.EnableOpenIDSignIn,
-		"PageStartTime":      startTime,
-	}
-}
-
 func AssetFS() *assetfs.LayeredFS {
 	return assetfs.Layered(CustomAssets(), BuiltinAssets())
 }
diff --git a/modules/test/context_tests.go b/modules/test/context_tests.go
index 4af7651250..35dd920bb9 100644
--- a/modules/test/context_tests.go
+++ b/modules/test/context_tests.go
@@ -30,7 +30,7 @@ func MockContext(t *testing.T, path string) *context.Context {
 	resp := &mockResponseWriter{}
 	ctx := context.Context{
 		Render: &mockRender{},
-		Data:   make(map[string]interface{}),
+		Data:   make(middleware.ContextData),
 		Flash: &middleware.Flash{
 			Values: make(url.Values),
 		},
diff --git a/modules/web/middleware/data.go b/modules/web/middleware/data.go
index 43189940ee..c1f0516d7d 100644
--- a/modules/web/middleware/data.go
+++ b/modules/web/middleware/data.go
@@ -3,7 +3,63 @@
 
 package middleware
 
-// DataStore represents a data store
-type DataStore interface {
-	GetData() map[string]interface{}
+import (
+	"context"
+	"time"
+
+	"code.gitea.io/gitea/modules/setting"
+)
+
+// ContextDataStore represents a data store
+type ContextDataStore interface {
+	GetData() ContextData
+}
+
+type ContextData map[string]any
+
+func (ds ContextData) GetData() map[string]any {
+	return ds
+}
+
+func (ds ContextData) MergeFrom(other ContextData) ContextData {
+	for k, v := range other {
+		ds[k] = v
+	}
+	return ds
+}
+
+const ContextDataKeySignedUser = "SignedUser"
+
+type contextDataKeyType struct{}
+
+var contextDataKey contextDataKeyType
+
+func WithContextData(c context.Context) context.Context {
+	return context.WithValue(c, contextDataKey, make(ContextData, 10))
+}
+
+func GetContextData(c context.Context) ContextData {
+	if ds, ok := c.Value(contextDataKey).(ContextData); ok {
+		return ds
+	}
+	return nil
+}
+
+func CommonTemplateContextData() ContextData {
+	return ContextData{
+		"IsLandingPageHome":          setting.LandingPageURL == setting.LandingPageHome,
+		"IsLandingPageExplore":       setting.LandingPageURL == setting.LandingPageExplore,
+		"IsLandingPageOrganizations": setting.LandingPageURL == setting.LandingPageOrganizations,
+
+		"ShowRegistrationButton":        setting.Service.ShowRegistrationButton,
+		"ShowMilestonesDashboardPage":   setting.Service.ShowMilestonesDashboardPage,
+		"ShowFooterVersion":             setting.Other.ShowFooterVersion,
+		"DisableDownloadSourceArchives": setting.Repository.DisableDownloadSourceArchives,
+
+		"EnableSwagger":      setting.API.EnableSwagger,
+		"EnableOpenIDSignIn": setting.Service.EnableOpenIDSignIn,
+		"PageStartTime":      time.Now(),
+
+		"RunModeIsProd": setting.IsProd,
+	}
 }
diff --git a/modules/web/middleware/flash.go b/modules/web/middleware/flash.go
index f2d7cc692d..fa29ddeffc 100644
--- a/modules/web/middleware/flash.go
+++ b/modules/web/middleware/flash.go
@@ -18,7 +18,7 @@ var FlashNow bool
 
 // Flash represents a one time data transfer between two requests.
 type Flash struct {
-	DataStore
+	DataStore ContextDataStore
 	url.Values
 	ErrorMsg, WarningMsg, InfoMsg, SuccessMsg string
 }
@@ -34,7 +34,7 @@ func (f *Flash) set(name, msg string, current ...bool) {
 	}
 
 	if isShow {
-		f.GetData()["Flash"] = f
+		f.DataStore.GetData()["Flash"] = f
 	} else {
 		f.Set(name, msg)
 	}
diff --git a/modules/web/middleware/request.go b/modules/web/middleware/request.go
index 34add27214..0bb155df70 100644
--- a/modules/web/middleware/request.go
+++ b/modules/web/middleware/request.go
@@ -12,8 +12,3 @@ import (
 func IsAPIPath(req *http.Request) bool {
 	return strings.HasPrefix(req.URL.Path, "/api/")
 }
-
-// IsInternalPath returns true if the specified URL is an internal API path
-func IsInternalPath(req *http.Request) bool {
-	return strings.HasPrefix(req.URL.Path, "/api/internal/")
-}
diff --git a/modules/web/route.go b/modules/web/route.go
index 6fd60f4ca7..d801f1025c 100644
--- a/modules/web/route.go
+++ b/modules/web/route.go
@@ -25,12 +25,12 @@ func Bind[T any](_ T) any {
 }
 
 // SetForm set the form object
-func SetForm(data middleware.DataStore, obj interface{}) {
+func SetForm(data middleware.ContextDataStore, obj interface{}) {
 	data.GetData()["__form"] = obj
 }
 
 // GetForm returns the validate form information
-func GetForm(data middleware.DataStore) interface{} {
+func GetForm(data middleware.ContextDataStore) interface{} {
 	return data.GetData()["__form"]
 }