Improve user experience for outdated comments (#29050)

Try to improve #28949

1. Make `ctx.Data["ShowOutdatedComments"] = true` by default: it brings
consistent user experience, and sometimes the "outdated (source
changed)" comments are still valuable.
2. Show a friendly message if the comment won't show, then the end users
won't fell that "the comment disappears" (it is the special case when
`ShowOutdatedComments = false`)

3 files changed, 84 insertions, 15 deletions

diff --git a/routers/web/repo/middlewares.go b/routers/web/repo/middlewares.go
index ee49649654..d70a53030e 100644
--- a/routers/web/repo/middlewares.go
+++ b/routers/web/repo/middlewares.go
@@ -98,23 +98,15 @@ func SetWhitespaceBehavior(ctx *context.Context) {
 // SetShowOutdatedComments set the show outdated comments option as context variable
 func SetShowOutdatedComments(ctx *context.Context) {
 	showOutdatedCommentsValue := ctx.FormString("show-outdated")
-	// var showOutdatedCommentsValue string
-
 	if showOutdatedCommentsValue != "true" && showOutdatedCommentsValue != "false" {
 		// invalid or no value for this form string -> use default or stored user setting
+		showOutdatedCommentsValue = "true"
 		if ctx.IsSigned {
-			showOutdatedCommentsValue, _ = user_model.GetUserSetting(ctx, ctx.Doer.ID, user_model.SettingsKeyShowOutdatedComments, "false")
-		} else {
-			// not logged in user -> use the default value
-			showOutdatedCommentsValue = "false"
+			showOutdatedCommentsValue, _ = user_model.GetUserSetting(ctx, ctx.Doer.ID, user_model.SettingsKeyShowOutdatedComments, showOutdatedCommentsValue)
 		}
-	} else {
+	} else if ctx.IsSigned {
 		// valid value -> update user setting if user is logged in
-		if ctx.IsSigned {
-			_ = user_model.SetUserSetting(ctx, ctx.Doer.ID, user_model.SettingsKeyShowOutdatedComments, showOutdatedCommentsValue)
-		}
+		_ = user_model.SetUserSetting(ctx, ctx.Doer.ID, user_model.SettingsKeyShowOutdatedComments, showOutdatedCommentsValue)
 	}
-
-	showOutdatedComments, _ := strconv.ParseBool(showOutdatedCommentsValue)
-	ctx.Data["ShowOutdatedComments"] = showOutdatedComments
+	ctx.Data["ShowOutdatedComments"], _ = strconv.ParseBool(showOutdatedCommentsValue)
 }
diff --git a/routers/web/repo/pull_review.go b/routers/web/repo/pull_review.go
index a6b3bd1c8d..b93460d169 100644
--- a/routers/web/repo/pull_review.go
+++ b/routers/web/repo/pull_review.go
@@ -22,6 +22,7 @@ import (
 
 const (
 	tplDiffConversation     base.TplName = "repo/diff/conversation"
+	tplConversationOutdated base.TplName = "repo/diff/conversation_outdated"
 	tplTimelineConversation base.TplName = "repo/issue/view_content/conversation"
 	tplNewComment           base.TplName = "repo/diff/new_comment"
 )
@@ -161,8 +162,8 @@ func renderConversation(ctx *context.Context, comment *issues_model.Comment, ori
 		return
 	}
 	if len(comments) == 0 {
-		// if the comments are empty (deleted, outdated, etc), it doesn't need to render anything, just return an empty body to replace "conversation-holder" on the page
-		ctx.Resp.WriteHeader(http.StatusOK)
+		// if the comments are empty (deleted, outdated, etc), it's better to tell the users that it is outdated
+		ctx.HTML(http.StatusOK, tplConversationOutdated)
 		return
 	}
 
diff --git a/routers/web/repo/pull_review_test.go b/routers/web/repo/pull_review_test.go
new file mode 100644
index 0000000000..65019af40b
--- /dev/null
+++ b/routers/web/repo/pull_review_test.go
@@ -0,0 +1,76 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repo
+
+import (
+	"net/http/httptest"
+	"testing"
+
+	"code.gitea.io/gitea/models/db"
+	issues_model "code.gitea.io/gitea/models/issues"
+	"code.gitea.io/gitea/models/unittest"
+	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/contexttest"
+	"code.gitea.io/gitea/modules/templates"
+	"code.gitea.io/gitea/services/pull"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRenderConversation(t *testing.T) {
+	unittest.PrepareTestEnv(t)
+
+	pr, _ := issues_model.GetPullRequestByID(db.DefaultContext, 2)
+	_ = pr.LoadIssue(db.DefaultContext)
+	_ = pr.Issue.LoadPoster(db.DefaultContext)
+	_ = pr.Issue.LoadRepo(db.DefaultContext)
+
+	run := func(name string, cb func(t *testing.T, ctx *context.Context, resp *httptest.ResponseRecorder)) {
+		t.Run(name, func(t *testing.T) {
+			ctx, resp := contexttest.MockContext(t, "/", contexttest.MockContextOption{Render: templates.HTMLRenderer()})
+			contexttest.LoadUser(t, ctx, pr.Issue.PosterID)
+			contexttest.LoadRepo(t, ctx, pr.BaseRepoID)
+			contexttest.LoadGitRepo(t, ctx)
+			defer ctx.Repo.GitRepo.Close()
+			cb(t, ctx, resp)
+		})
+	}
+
+	var preparedComment *issues_model.Comment
+	run("prepare", func(t *testing.T, ctx *context.Context, resp *httptest.ResponseRecorder) {
+		comment, err := pull.CreateCodeComment(ctx, pr.Issue.Poster, ctx.Repo.GitRepo, pr.Issue, 1, "content", "", false, 0, pr.HeadCommitID)
+		if !assert.NoError(t, err) {
+			return
+		}
+		comment.Invalidated = true
+		err = issues_model.UpdateCommentInvalidate(ctx, comment)
+		if !assert.NoError(t, err) {
+			return
+		}
+		preparedComment = comment
+	})
+	if !assert.NotNil(t, preparedComment) {
+		return
+	}
+	run("diff with outdated", func(t *testing.T, ctx *context.Context, resp *httptest.ResponseRecorder) {
+		ctx.Data["ShowOutdatedComments"] = true
+		renderConversation(ctx, preparedComment, "diff")
+		assert.Contains(t, resp.Body.String(), `<div class="content comment-container"`)
+	})
+	run("diff without outdated", func(t *testing.T, ctx *context.Context, resp *httptest.ResponseRecorder) {
+		ctx.Data["ShowOutdatedComments"] = false
+		renderConversation(ctx, preparedComment, "diff")
+		assert.Contains(t, resp.Body.String(), `conversation-not-existing`)
+	})
+	run("timeline with outdated", func(t *testing.T, ctx *context.Context, resp *httptest.ResponseRecorder) {
+		ctx.Data["ShowOutdatedComments"] = true
+		renderConversation(ctx, preparedComment, "timeline")
+		assert.Contains(t, resp.Body.String(), `<div id="code-comments-`)
+	})
+	run("timeline without outdated", func(t *testing.T, ctx *context.Context, resp *httptest.ResponseRecorder) {
+		ctx.Data["ShowOutdatedComments"] = false
+		renderConversation(ctx, preparedComment, "timeline")
+		assert.Contains(t, resp.Body.String(), `conversation-not-existing`)
+	})
+}