Handle too long PR titles correctly (go-gitea#16517)

The CompareAndPullRequestPost handler for POST to /compare
incorrectly handles returning errors to the user. For a start
it does not set the necessary markers to switch SimpleMDE
but it also does not immediately return to the form.

This PR fixes this by setting the appropriate values, fixing
the templates and preventing the suggestion of a too long
title.

Fix go-gitea#16507

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/util/truncate.go

@@ -0,0 +1,35 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package util
+
+import "unicode/utf8"
+
+// SplitStringAtByteN splits a string at byte n accounting for rune boundaries. (Combining characters are not accounted for.)
+func SplitStringAtByteN(input string, n int) (left, right string) {
+	if len(input) <= n {
+		left = input
+		return
+	}
+
+	if !utf8.ValidString(input) {
+		left = input[:n-3] + "..."
+		right = "..." + input[n-3:]
+		return
+	}
+
+	// in UTF8 "…" is 3 bytes so doesn't really gain us anything...
+	end := 0
+	for end <= n-3 {
+		_, size := utf8.DecodeRuneInString(input[end:])
+		if end+size > n-3 {
+			break
+		}
+		end += size
+	}
+
+	left = input[:end] + "…"
+	right = "…" + input[end:]
+	return
+}

routers/web/repo/compare.go

@@ -24,6 +24,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/upload"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/services/gitdiff"
 )
 
@@ -567,6 +568,18 @@ func PrepareCompareDiff(
 	} else {
 		title = headBranch
 	}
+	if len(title) > 255 {
+		var trailer string
+		title, trailer = util.SplitStringAtByteN(title, 255)
+		if len(trailer) > 0 {
+			if ctx.Data["content"] != nil {
+				ctx.Data["content"] = fmt.Sprintf("%s\n\n%s", trailer, ctx.Data["content"])
+			} else {
+				ctx.Data["content"] = trailer + "\n"
+			}
+		}
+	}
+
 	ctx.Data["title"] = title
 	ctx.Data["Username"] = headUser.Name
 	ctx.Data["Reponame"] = headRepo.Name

routers/web/repo/pull.go

@@ -1001,10 +1001,14 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 	ctx.Data["Title"] = ctx.Tr("repo.pulls.compare_changes")
 	ctx.Data["PageIsComparePull"] = true
 	ctx.Data["IsDiffCompare"] = true
+	ctx.Data["IsRepoToolbarCommits"] = true
+	ctx.Data["RequireTribute"] = true
+	ctx.Data["RequireSimpleMDE"] = true
 	ctx.Data["RequireHighlightJS"] = true
 	ctx.Data["PullRequestWorkInProgressPrefixes"] = setting.Repository.PullRequest.WorkInProgressPrefixes
 	ctx.Data["IsAttachmentEnabled"] = setting.Attachment.Enabled
 	upload.AddUploadContext(ctx, "comment")
+	ctx.Data["HasIssuesOrPullsWritePermission"] = ctx.Repo.CanWrite(models.UnitTypePullRequests)
 
 	var (
 		repo        = ctx.Repo.Repository
@@ -1037,6 +1041,14 @@ func CompareAndPullRequestPost(ctx *context.Context) {
 			return
 		}
 
+		if len(form.Title) > 255 {
+			var trailer string
+			form.Title, trailer = util.SplitStringAtByteN(form.Title, 255)
+
+			form.Content = trailer + "\n\n" + form.Content
+		}
+		middleware.AssignForm(form, ctx.Data)
+
 		ctx.HTML(http.StatusOK, tplCompareDiff)
 		return
 	}

templates/repo/diff/compare.tmpl

@@ -176,10 +176,10 @@
 	{{if .IsNothingToCompare}}
 		{{if and $.IsSigned $.AllowEmptyPr (not .Repository.IsArchived) }}
 			<div class="ui segment">{{.i18n.Tr "repo.pulls.nothing_to_compare_and_allow_empty_pr"}}</div>
-			<div class="ui info message show-form-container">
+			<div class="ui info message show-form-container" {{if .Flash}}style="display: none"{{end}}>
 				<button class="ui button green show-form">{{.i18n.Tr "repo.pulls.new"}}</button>
 			</div>
-			<div class="pullrequest-form" style="display: none">
+			<div class="pullrequest-form" {{if not .Flash}}style="display: none"{{end}}>
 				{{template "repo/issue/new_form" .}}
 			</div>
 		{{else}}
@@ -192,7 +192,7 @@
 			</div>
 		{{else}}
 			{{if and $.IsSigned (not .Repository.IsArchived)}}
-				<div class="ui info message show-form-container">
+				<div class="ui info message show-form-container" {{if .Flash}}style="display: none"{{end}}>
 					<button class="ui button green show-form">{{.i18n.Tr "repo.pulls.new"}}</button>
 				</div>
 			{{else if .Repository.IsArchived}}
@@ -201,7 +201,7 @@
 				</div>
 			{{end}}
 			{{if $.IsSigned}}
-				<div class="pullrequest-form" style="display: none">
+				<div class="pullrequest-form" {{if not .Flash}}style="display: none"{{end}}>
 					{{template "repo/issue/new_form" .}}
 				</div>
 			{{end}}