Allow to mark files in a PR as viewed (#19007)

Users can now mark files in PRs as viewed, resulting in them not being shown again by default when they reopen the PR again.

models/migrations/migrations.go

@@ -385,6 +385,8 @@ var migrations = []Migration{
 	NewMigration("Add allow edits from maintainers to PullRequest table", addAllowMaintainerEdit),
 	// v214 -> v215
 	NewMigration("Add auto merge table", addAutoMergeTable),
+	// v215 -> v216
+	NewMigration("allow to view files in PRs", addReviewViewedFiles),
 }
 
 // GetCurrentDBVersion returns the current db version

models/migrations/v215.go

@@ -0,0 +1,25 @@
+// Copyright 2022 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 migrations
+
+import (
+	"code.gitea.io/gitea/models/pull"
+	"code.gitea.io/gitea/modules/timeutil"
+
+	"xorm.io/xorm"
+)
+
+func addReviewViewedFiles(x *xorm.Engine) error {
+	type ReviewState struct {
+		ID           int64                       `xorm:"pk autoincr"`
+		UserID       int64                       `xorm:"NOT NULL UNIQUE(pull_commit_user)"`
+		PullID       int64                       `xorm:"NOT NULL UNIQUE(pull_commit_user) DEFAULT 0"`
+		CommitSHA    string                      `xorm:"NOT NULL VARCHAR(40) UNIQUE(pull_commit_user)"`
+		UpdatedFiles map[string]pull.ViewedState `xorm:"NOT NULL LONGTEXT JSON"`
+		UpdatedUnix  timeutil.TimeStamp          `xorm:"updated"`
+	}
+
+	return x.Sync2(new(ReviewState))
+}

models/pull/review_state.go

@@ -0,0 +1,139 @@
+// Copyright 2022 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 pull
+
+import (
+	"context"
+	"fmt"
+
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/timeutil"
+)
+
+// ViewedState stores for a file in which state it is currently viewed
+type ViewedState uint8
+
+const (
+	Unviewed   ViewedState = iota
+	HasChanged             // cannot be set from the UI/ API, only internally
+	Viewed
+)
+
+func (viewedState ViewedState) String() string {
+	switch viewedState {
+	case Unviewed:
+		return "unviewed"
+	case HasChanged:
+		return "has-changed"
+	case Viewed:
+		return "viewed"
+	default:
+		return fmt.Sprintf("unknown(value=%d)", viewedState)
+	}
+}
+
+// ReviewState stores for a user-PR-commit combination which files the user has already viewed
+type ReviewState struct {
+	ID           int64                  `xorm:"pk autoincr"`
+	UserID       int64                  `xorm:"NOT NULL UNIQUE(pull_commit_user)"`
+	PullID       int64                  `xorm:"NOT NULL UNIQUE(pull_commit_user) DEFAULT 0"`   // Which PR was the review on?
+	CommitSHA    string                 `xorm:"NOT NULL VARCHAR(40) UNIQUE(pull_commit_user)"` // Which commit was the head commit for the review?
+	UpdatedFiles map[string]ViewedState `xorm:"NOT NULL LONGTEXT JSON"`                        // Stores for each of the changed files of a PR whether they have been viewed, changed since last viewed, or not viewed
+	UpdatedUnix  timeutil.TimeStamp     `xorm:"updated"`                                       // Is an accurate indicator of the order of commits as we do not expect it to be possible to make reviews on previous commits
+}
+
+func init() {
+	db.RegisterModel(new(ReviewState))
+}
+
+// GetReviewState returns the ReviewState with all given values prefilled, whether or not it exists in the database.
+// If the review didn't exist before in the database, it won't afterwards either.
+// The returned boolean shows whether the review exists in the database
+func GetReviewState(ctx context.Context, userID, pullID int64, commitSHA string) (*ReviewState, bool, error) {
+	review := &ReviewState{UserID: userID, PullID: pullID, CommitSHA: commitSHA}
+	has, err := db.GetEngine(ctx).Get(review)
+	return review, has, err
+}
+
+// UpdateReviewState updates the given review inside the database, regardless of whether it existed before or not
+// The given map of files with their viewed state will be merged with the previous review, if present
+func UpdateReviewState(ctx context.Context, userID, pullID int64, commitSHA string, updatedFiles map[string]ViewedState) error {
+	log.Trace("Updating review for user %d, repo %d, commit %s with the updated files %v.", userID, pullID, commitSHA, updatedFiles)
+
+	review, exists, err := GetReviewState(ctx, userID, pullID, commitSHA)
+	if err != nil {
+		return err
+	}
+
+	if exists {
+		review.UpdatedFiles = mergeFiles(review.UpdatedFiles, updatedFiles)
+	} else if previousReview, err := getNewestReviewStateApartFrom(ctx, userID, pullID, commitSHA); err != nil {
+		return err
+
+		// Overwrite the viewed files of the previous review if present
+	} else if previousReview != nil {
+		review.UpdatedFiles = mergeFiles(previousReview.UpdatedFiles, updatedFiles)
+	} else {
+		review.UpdatedFiles = updatedFiles
+	}
+
+	// Insert or Update review
+	engine := db.GetEngine(ctx)
+	if !exists {
+		log.Trace("Inserting new review for user %d, repo %d, commit %s with the updated files %v.", userID, pullID, commitSHA, review.UpdatedFiles)
+		_, err := engine.Insert(review)
+		return err
+	}
+	log.Trace("Updating already existing review with ID %d (user %d, repo %d, commit %s) with the updated files %v.", review.ID, userID, pullID, commitSHA, review.UpdatedFiles)
+	_, err = engine.ID(review.ID).Update(&ReviewState{UpdatedFiles: review.UpdatedFiles})
+	return err
+}
+
+// mergeFiles merges the given maps of files with their viewing state into one map.
+// Values from oldFiles will be overridden with values from newFiles
+func mergeFiles(oldFiles, newFiles map[string]ViewedState) map[string]ViewedState {
+	if oldFiles == nil {
+		return newFiles
+	} else if newFiles == nil {
+		return oldFiles
+	}
+
+	for file, viewed := range newFiles {
+		oldFiles[file] = viewed
+	}
+	return oldFiles
+}
+
+// GetNewestReviewState gets the newest review of the current user in the current PR.
+// The returned PR Review will be nil if the user has not yet reviewed this PR.
+func GetNewestReviewState(ctx context.Context, userID, pullID int64) (*ReviewState, error) {
+	var review ReviewState
+	has, err := db.GetEngine(ctx).Where("user_id = ?", userID).And("pull_id = ?", pullID).OrderBy("updated_unix DESC").Get(&review)
+	if err != nil || !has {
+		return nil, err
+	}
+	return &review, err
+}
+
+// getNewestReviewStateApartFrom is like GetNewestReview, except that the second newest review will be returned if the newest review points at the given commit.
+// The returned PR Review will be nil if the user has not yet reviewed this PR.
+func getNewestReviewStateApartFrom(ctx context.Context, userID, pullID int64, commitSHA string) (*ReviewState, error) {
+	var reviews []ReviewState
+	err := db.GetEngine(ctx).Where("user_id = ?", userID).And("pull_id = ?", pullID).OrderBy("updated_unix DESC").Limit(2).Find(&reviews)
+	// It would also be possible to use ".And("commit_sha != ?", commitSHA)" instead of the error handling below
+	// However, benchmarks show drastically improved performance by not doing that
+
+	// Error cases in which no review should be returned
+	if err != nil || len(reviews) == 0 || (len(reviews) == 1 && reviews[0].CommitSHA == commitSHA) {
+		return nil, err
+
+		// The first review points at the commit to exclude, hence skip to the second review
+	} else if len(reviews) >= 2 && reviews[0].CommitSHA == commitSHA {
+		return &reviews[1], nil
+	}
+
+	// As we have no error cases left, the result must be the first element in the list
+	return &reviews[0], nil
+}

modules/git/repo_compare.go

@@ -286,6 +286,15 @@ func (repo *Repository) GetPatch(base, head string, w io.Writer) error {
 	return err
 }
 
+// GetFilesChangedBetween returns a list of all files that have been changed between the given commits
+func (repo *Repository) GetFilesChangedBetween(base, head string) ([]string, error) {
+	stdout, _, err := NewCommand(repo.Ctx, "diff", "--name-only", base+".."+head).RunStdString(&RunOpts{Dir: repo.Path})
+	if err != nil {
+		return nil, err
+	}
+	return strings.Split(stdout, "\n"), err
+}
+
 // GetDiffFromMergeBase generates and return patch data from merge base to head
 func (repo *Repository) GetDiffFromMergeBase(base, head string, w io.Writer) error {
 	stderr := new(bytes.Buffer)

options/locale/locale_en-US.ini

@@ -1493,6 +1493,9 @@ pulls.allow_edits_from_maintainers = Allow edits from maintainers
 pulls.allow_edits_from_maintainers_desc = Users with write access to the base branch can also push to this branch
 pulls.allow_edits_from_maintainers_err = Updating failed
 pulls.compare_changes_desc = Select the branch to merge into and the branch to pull from.
+pulls.has_viewed_file = Viewed
+pulls.has_changed_since_last_review = Changed since your last review
+pulls.viewed_files_label = %[1]d / %[2]d files viewed
 pulls.compare_base = merge into
 pulls.compare_compare = pull from
 pulls.switch_comparison_type = Switch comparison type

routers/web/repo/pull.go

@@ -685,22 +685,35 @@ func ViewPullFiles(ctx *context.Context) {
 	if fileOnly && (len(files) == 2 || len(files) == 1) {
 		maxLines, maxFiles = -1, -1
 	}
+	diffOptions := &gitdiff.DiffOptions{
+		BeforeCommitID:     startCommitID,
+		AfterCommitID:      endCommitID,
+		SkipTo:             ctx.FormString("skip-to"),
+		MaxLines:           maxLines,
+		MaxLineCharacters:  setting.Git.MaxGitDiffLineCharacters,
+		MaxFiles:           maxFiles,
+		WhitespaceBehavior: gitdiff.GetWhitespaceFlag(ctx.Data["WhitespaceBehavior"].(string)),
+	}
 
-	diff, err := gitdiff.GetDiff(gitRepo,
-		&gitdiff.DiffOptions{
-			BeforeCommitID:     startCommitID,
-			AfterCommitID:      endCommitID,
-			SkipTo:             ctx.FormString("skip-to"),
-			MaxLines:           maxLines,
-			MaxLineCharacters:  setting.Git.MaxGitDiffLineCharacters,
-			MaxFiles:           maxFiles,
-			WhitespaceBehavior: gitdiff.GetWhitespaceFlag(ctx.Data["WhitespaceBehavior"].(string)),
-		}, ctx.FormStrings("files")...)
+	var methodWithError string
+	var diff *gitdiff.Diff
+	if !ctx.IsSigned {
+		diff, err = gitdiff.GetDiff(gitRepo, diffOptions, files...)
+		methodWithError = "GetDiff"
+	} else {
+		diff, err = gitdiff.SyncAndGetUserSpecificDiff(ctx, ctx.Doer.ID, pull, gitRepo, diffOptions, files...)
+		methodWithError = "SyncAndGetUserSpecificDiff"
+	}
 	if err != nil {
-		ctx.ServerError("GetDiffRangeWithWhitespaceBehavior", err)
+		ctx.ServerError(methodWithError, err)
 		return
 	}
 
+	ctx.PageData["prReview"] = map[string]interface{}{
+		"numberOfFiles":       diff.NumFiles,
+		"numberOfViewedFiles": diff.NumViewedFiles,
+	}
+
 	if err = diff.LoadComments(ctx, issue, ctx.Doer); err != nil {
 		ctx.ServerError("LoadComments", err)
 		return

routers/web/repo/pull_review.go

@@ -9,8 +9,10 @@ import (
 	"net/http"
 
 	"code.gitea.io/gitea/models"
+	pull_model "code.gitea.io/gitea/models/pull"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/json"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/web"
@@ -242,3 +244,47 @@ func DismissReview(ctx *context.Context) {
 
 	ctx.Redirect(fmt.Sprintf("%s/pulls/%d#%s", ctx.Repo.RepoLink, comm.Issue.Index, comm.HashTag()))
 }
+
+// viewedFilesUpdate Struct to parse the body of a request to update the reviewed files of a PR
+// If you want to implement an API to update the review, simply move this struct into modules.
+type viewedFilesUpdate struct {
+	Files         map[string]bool `json:"files"`
+	HeadCommitSHA string          `json:"headCommitSHA"`
+}
+
+func UpdateViewedFiles(ctx *context.Context) {
+	// Find corresponding PR
+	issue := checkPullInfo(ctx)
+	if ctx.Written() {
+		return
+	}
+	pull := issue.PullRequest
+
+	var data *viewedFilesUpdate
+	err := json.NewDecoder(ctx.Req.Body).Decode(&data)
+	if err != nil {
+		log.Warn("Attempted to update a review but could not parse request body: %v", err)
+		ctx.Resp.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	// Expect the review to have been now if no head commit was supplied
+	if data.HeadCommitSHA == "" {
+		data.HeadCommitSHA = pull.HeadCommitID
+	}
+
+	updatedFiles := make(map[string]pull_model.ViewedState, len(data.Files))
+	for file, viewed := range data.Files {
+
+		// Only unviewed and viewed are possible, has-changed can not be set from the outside
+		state := pull_model.Unviewed
+		if viewed {
+			state = pull_model.Viewed
+		}
+		updatedFiles[file] = state
+	}
+
+	if err := pull_model.UpdateReviewState(ctx, ctx.Doer.ID, pull.ID, data.HeadCommitSHA, updatedFiles); err != nil {
+		ctx.ServerError("UpdateReview", err)
+	}
+}

routers/web/web.go

@@ -849,6 +849,7 @@ func RegisterRoutes(m *web.Route) {
 				m.Post("/deadline", bindIgnErr(structs.EditDeadlineOption{}), repo.UpdateIssueDeadline)
 				m.Post("/watch", repo.IssueWatch)
 				m.Post("/ref", repo.UpdateIssueRef)
+				m.Post("/viewed-files", repo.UpdateViewedFiles)
 				m.Group("/dependency", func() {
 					m.Post("/add", repo.AddDependency)
 					m.Post("/delete", repo.RemoveDependency)

services/gitdiff/gitdiff.go

@@ -22,6 +22,7 @@ import (
 
 	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/models/db"
+	pull_model "code.gitea.io/gitea/models/pull"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/analyze"
 	"code.gitea.io/gitea/modules/charset"
@@ -602,25 +603,27 @@ func (diffSection *DiffSection) GetComputedInlineDiffFor(diffLine *DiffLine) Dif
 
 // DiffFile represents a file diff.
 type DiffFile struct {
-	Name                    string
-	OldName                 string
-	Index                   int
-	Addition, Deletion      int
-	Type                    DiffFileType
-	IsCreated               bool
-	IsDeleted               bool
-	IsBin                   bool
-	IsLFSFile               bool
-	IsRenamed               bool
-	IsAmbiguous             bool
-	IsSubmodule             bool
-	Sections                []*DiffSection
-	IsIncomplete            bool
-	IsIncompleteLineTooLong bool
-	IsProtected             bool
-	IsGenerated             bool
-	IsVendored              bool
-	Language                string
+	Name                      string
+	OldName                   string
+	Index                     int
+	Addition, Deletion        int
+	Type                      DiffFileType
+	IsCreated                 bool
+	IsDeleted                 bool
+	IsBin                     bool
+	IsLFSFile                 bool
+	IsRenamed                 bool
+	IsAmbiguous               bool
+	IsSubmodule               bool
+	Sections                  []*DiffSection
+	IsIncomplete              bool
+	IsIncompleteLineTooLong   bool
+	IsProtected               bool
+	IsGenerated               bool
+	IsVendored                bool
+	IsViewed                  bool // User specific
+	HasChangedSinceLastReview bool // User specific
+	Language                  string
 }
 
 // GetType returns type of diff file.
@@ -663,6 +666,18 @@ func (diffFile *DiffFile) GetTailSection(gitRepo *git.Repository, leftCommitID,
 	return tailSection
 }
 
+// GetDiffFileName returns the name of the diff file, or its old name in case it was deleted
+func (diffFile *DiffFile) GetDiffFileName() string {
+	if diffFile.Name == "" {
+		return diffFile.OldName
+	}
+	return diffFile.Name
+}
+
+func (diffFile *DiffFile) ShouldBeHidden() bool {
+	return diffFile.IsGenerated || diffFile.IsViewed
+}
+
 func getCommitFileLineCount(commit *git.Commit, filePath string) int {
 	blob, err := commit.GetBlobByPath(filePath)
 	if err != nil {
@@ -677,10 +692,12 @@ func getCommitFileLineCount(commit *git.Commit, filePath string) int {
 
 // Diff represents a difference between two git trees.
 type Diff struct {
-	Start, End                             string
-	NumFiles, TotalAddition, TotalDeletion int
-	Files                                  []*DiffFile
-	IsIncomplete                           bool
+	Start, End                   string
+	NumFiles                     int
+	TotalAddition, TotalDeletion int
+	Files                        []*DiffFile
+	IsIncomplete                 bool
+	NumViewedFiles               int // user-specific
 }
 
 // LoadComments loads comments into each line
@@ -1497,6 +1514,70 @@ func GetDiff(gitRepo *git.Repository, opts *DiffOptions, files ...string) (*Diff
 	return diff, nil
 }
 
+// SyncAndGetUserSpecificDiff is like GetDiff, except that user specific data such as which files the given user has already viewed on the given PR will also be set
+// Additionally, the database asynchronously is updated if files have changed since the last review
+func SyncAndGetUserSpecificDiff(ctx context.Context, userID int64, pull *models.PullRequest, gitRepo *git.Repository, opts *DiffOptions, files ...string) (*Diff, error) {
+	diff, err := GetDiff(gitRepo, opts, files...)
+	if err != nil {
+		return nil, err
+	}
+	review, err := pull_model.GetNewestReviewState(ctx, userID, pull.ID)
+	if err != nil || review == nil || review.UpdatedFiles == nil {
+		return diff, err
+	}
+
+	latestCommit := opts.AfterCommitID
+	if latestCommit == "" {
+		latestCommit = pull.HeadBranch // opts.AfterCommitID is preferred because it handles PRs from forks correctly and the branch name doesn't
+	}
+
+	changedFiles, err := gitRepo.GetFilesChangedBetween(review.CommitSHA, latestCommit)
+	if err != nil {
+		return diff, err
+	}
+
+	filesChangedSinceLastDiff := make(map[string]pull_model.ViewedState)
+outer:
+	for _, diffFile := range diff.Files {
+		fileViewedState := review.UpdatedFiles[diffFile.GetDiffFileName()]
+
+		// Check whether it was previously detected that the file has changed since the last review
+		if fileViewedState == pull_model.HasChanged {
+			diffFile.HasChangedSinceLastReview = true
+			continue
+		}
+
+		filename := diffFile.GetDiffFileName()
+
+		// Check explicitly whether the file has changed since the last review
+		for _, changedFile := range changedFiles {
+			diffFile.HasChangedSinceLastReview = filename == changedFile
+			if diffFile.HasChangedSinceLastReview {
+				filesChangedSinceLastDiff[filename] = pull_model.HasChanged
+				continue outer // We don't want to check if the file is viewed here as that would fold the file, which is in this case unwanted
+			}
+		}
+		// Check whether the file has already been viewed
+		if fileViewedState == pull_model.Viewed {
+			diffFile.IsViewed = true
+			diff.NumViewedFiles++
+		}
+	}
+
+	// Explicitly store files that have changed in the database, if any is present at all.
+	// This has the benefit that the "Has Changed" attribute will be present as long as the user does not explicitly mark this file as viewed, so it will even survive a page reload after marking another file as viewed.
+	// On the other hand, this means that even if a commit reverting an unseen change is committed, the file will still be seen as changed.
+	if len(filesChangedSinceLastDiff) > 0 {
+		err := pull_model.UpdateReviewState(ctx, review.UserID, review.PullID, review.CommitSHA, filesChangedSinceLastDiff)
+		if err != nil {
+			log.Warn("Could not update review for user %d, pull %d, commit %s and the changed files %v: %v", review.UserID, review.PullID, review.CommitSHA, filesChangedSinceLastDiff, err)
+			return nil, err
+		}
+	}
+
+	return diff, err
+}
+
 // CommentAsDiff returns c.Patch as *Diff
 func CommentAsDiff(c *models.Comment) (*Diff, error) {
 	diff, err := ParsePatch(setting.Git.MaxGitDiffLines,

templates/repo/diff/box.tmpl

@@ -18,6 +18,12 @@
 				{{svg "octicon-diff" 16 "mr-2"}}{{.i18n.Tr "repo.diff.stats_desc" .Diff.NumFiles .Diff.TotalAddition .Diff.TotalDeletion | Str2html}}
 			</div>
 			<div class="diff-detail-actions df ac">
+				{{if and .PageIsPullFiles $.SignedUserID (not .IsArchived)}}
+					<meter id="viewed-files-summary" value="{{.Diff.NumViewedFiles}}" max="{{.Diff.NumFiles}}"></meter>
+					<label for="viewed-files-summary" id="viewed-files-summary-label" data-text-changed-template="{{.i18n.Tr "repo.pulls.viewed_files_label"}}">
+						{{.i18n.Tr "repo.pulls.viewed_files_label" .Diff.NumViewedFiles .Diff.NumFiles}}
+					</label>
+				{{end}}
 				{{template "repo/diff/whitespace_dropdown" .}}
 				{{template "repo/diff/options_dropdown" .}}
 				{{if and .PageIsPullFiles $.SignedUserID (not .IsArchived)}}
@@ -58,11 +64,11 @@
 				{{$isCsv := (call $.IsCsvFile $file)}}
 				{{$showFileViewToggle := or $isImage (and (not $file.IsIncomplete) $isCsv)}}
 				{{$nameHash := Sha1 $file.Name}}
-				<div class="diff-file-box diff-box file-content {{TabSizeClass $.Editorconfig $file.Name}} mt-3" id="diff-{{$nameHash}}" data-old-filename="{{$file.OldName}}" data-new-filename="{{$file.Name}}" {{if $file.IsGenerated}}data-folded="true"{{end}}>
+				<div class="diff-file-box diff-box file-content {{TabSizeClass $.Editorconfig $file.Name}} mt-3" id="diff-{{$nameHash}}" data-old-filename="{{$file.OldName}}" data-new-filename="{{$file.Name}}" {{if $file.ShouldBeHidden}}data-folded="true"{{end}}>
 					<h4 class="diff-file-header sticky-2nd-row ui top attached normal header df ac sb">
 						<div class="df ac">
 							<a role="button" class="fold-file muted mr-2">
-								{{if $file.IsGenerated}}
+								{{if $file.ShouldBeHidden}}
 									{{svg "octicon-chevron-right" 18}}
 								{{else}}
 									{{svg "octicon-chevron-down" 18}}
@@ -106,9 +112,18 @@
 									<a class="ui basic tiny button" rel="nofollow" href="{{$.SourcePath}}/{{PathEscapeSegments .Name}}">{{$.i18n.Tr "repo.diff.view_file"}}</a>
 								{{end}}
 							{{end}}
+							{{if and $.IsSigned $.PageIsPullFiles (not $.IsArchived)}}
+								{{if $file.HasChangedSinceLastReview}}
+									<span class="changed-since-last-review unselectable">{{$.i18n.Tr "repo.pulls.has_changed_since_last_review"}}</span>
+								{{end}}
+								<div data-link="{{$.Issue.Link}}/viewed-files" data-headcommit="{{$.PullHeadCommitID}}" class="viewed-file-form unselectable{{if $file.IsViewed}} viewed-file-checked-form{{end}}">
+									<input type="checkbox" name="{{$file.GetDiffFileName}}" id="viewed-file-checkbox-{{$i}}" autocomplete="off" {{if $file.IsViewed}}checked{{end}}></input>
+									<label for="viewed-file-checkbox-{{$i}}">{{$.i18n.Tr "repo.pulls.has_viewed_file"}}</label>
+								</div>
+							{{end}}
 						</div>
 					</h4>
-					<div class="diff-file-body ui attached unstackable table segment">
+					<div class="diff-file-body ui attached unstackable table segment" {{if $file.IsViewed}}data-folded="true"{{end}}>
 						<div id="diff-source-{{$i}}" class="file-body file-code unicode-escaped code-diff{{if $.IsSplitStyle}} code-diff-split{{else}} code-diff-unified{{end}}{{if $showFileViewToggle}} hide{{end}}">
 							{{if or $file.IsIncomplete $file.IsBin}}
 								<div class="diff-file-body binary" style="padding: 5px 10px;">

web_src/js/features/file-fold.js

@@ -0,0 +1,18 @@
+import {svg} from '../svg.js';
+
+
+// Hides the file if newFold is true, and shows it otherwise. The actual hiding is performed using CSS.
+//
+// The fold arrow is the icon displayed on the upper left of the file box, especially intended for components having the 'fold-file' class.
+// The file content box is the box that should be hidden or shown, especially intended for components having the 'file-content' class.
+//
+export function setFileFolding(fileContentBox, foldArrow, newFold) {
+  foldArrow.innerHTML = svg(`octicon-chevron-${newFold ? 'right' : 'down'}`, 18);
+  fileContentBox.setAttribute('data-folded', newFold);
+}
+
+// Like `setFileFolding`, except that it automatically inverts the current file folding state.
+export function invertFileFolding(fileContentBox, foldArrow) {
+  setFileFolding(fileContentBox, foldArrow, fileContentBox.getAttribute('data-folded') !== 'true');
+}
+

web_src/js/features/pull-view-file.js

@@ -0,0 +1,71 @@
+import {setFileFolding} from './file-fold.js';
+
+const {csrfToken, pageData} = window.config;
+const prReview = pageData.prReview || {};
+const viewedStyleClass = 'viewed-file-checked-form';
+const viewedCheckboxSelector = '.viewed-file-form'; // Selector under which all "Viewed" checkbox forms can be found
+
+
+// Refreshes the summary of viewed files if present
+// The data used will be window.config.pageData.prReview.numberOf{Viewed}Files
+function refreshViewedFilesSummary() {
+  const viewedFilesMeter = document.getElementById('viewed-files-summary');
+  viewedFilesMeter?.setAttribute('value', prReview.numberOfViewedFiles);
+  const summaryLabel = document.getElementById('viewed-files-summary-label');
+  if (summaryLabel) summaryLabel.innerHTML = summaryLabel.getAttribute('data-text-changed-template')
+    .replace('%[1]d', prReview.numberOfViewedFiles)
+    .replace('%[2]d', prReview.numberOfFiles);
+}
+
+// Explicitly recounts how many files the user has currently reviewed by counting the number of checked "viewed" checkboxes
+// Additionally, the viewed files summary will be updated if it exists
+export function countAndUpdateViewedFiles() {
+  // The number of files is constant, but the number of viewed files can change because files can be loaded dynamically
+  prReview.numberOfViewedFiles = document.querySelectorAll(`${viewedCheckboxSelector} > input[type=checkbox][checked]`).length;
+  refreshViewedFilesSummary();
+}
+
+// Initializes a listener for all children of the given html element
+// (for example 'document' in the most basic case)
+// to watch for changes of viewed-file checkboxes
+export function initViewedCheckboxListenerFor() {
+  for (const form of document.querySelectorAll(`${viewedCheckboxSelector}:not([data-has-viewed-checkbox-listener="true"])`)) {
+    // To prevent double addition of listeners
+    form.setAttribute('data-has-viewed-checkbox-listener', true);
+
+    // The checkbox consists of a div containing the real checkbox with its label and the CSRF token,
+    // hence the actual checkbox first has to be found
+    const checkbox = form.querySelector('input[type=checkbox]');
+    checkbox.addEventListener('change', function() {
+      // Mark the file as viewed visually - will especially change the background
+      if (this.checked) {
+        form.classList.add(viewedStyleClass);
+        prReview.numberOfViewedFiles++;
+      } else {
+        form.classList.remove(viewedStyleClass);
+        prReview.numberOfViewedFiles--;
+      }
+
+      // Update viewed-files summary and remove "has changed" label if present
+      refreshViewedFilesSummary();
+      const hasChangedLabel = form.parentNode.querySelector('.changed-since-last-review');
+      hasChangedLabel?.parentNode.removeChild(hasChangedLabel);
+
+      // Unfortunately, actual forms cause too many problems, hence another approach is needed
+      const files = {};
+      files[checkbox.getAttribute('name')] = this.checked;
+      const data = {files};
+      const headCommitSHA = form.getAttribute('data-headcommit');
+      if (headCommitSHA) data.headCommitSHA = headCommitSHA;
+      fetch(form.getAttribute('data-link'), {
+        method: 'POST',
+        headers: {'X-Csrf-Token': csrfToken},
+        body: JSON.stringify(data),
+      });
+
+      // Fold the file accordingly
+      const parentBox = form.closest('.diff-file-header');
+      setFileFolding(parentBox.closest('.file-content'), parentBox.querySelector('.fold-file'), this.checked);
+    });
+  }
+}

web_src/js/features/repo-code.js

@@ -1,5 +1,6 @@
 import $ from 'jquery';
 import {svg} from '../svg.js';
+import {invertFileFolding} from './file-fold.js';
 
 function changeHash(hash) {
   if (window.history.pushState) {
@@ -148,10 +149,7 @@ export function initRepoCodeView() {
     }).trigger('hashchange');
   }
   $(document).on('click', '.fold-file', ({currentTarget}) => {
-    const box = currentTarget.closest('.file-content');
-    const folded = box.getAttribute('data-folded') !== 'true';
-    currentTarget.innerHTML = svg(`octicon-chevron-${folded ? 'right' : 'down'}`, 18);
-    box.setAttribute('data-folded', String(folded));
+    invertFileFolding(currentTarget.closest('.file-content'), currentTarget);
   });
   $(document).on('click', '.blob-excerpt', async ({currentTarget}) => {
     const url = currentTarget.getAttribute('data-url');

web_src/js/features/repo-diff.js

@@ -2,6 +2,7 @@ import $ from 'jquery';
 import {initCompReactionSelector} from './comp/ReactionSelector.js';
 import {initRepoIssueContentHistory} from './repo-issue-content.js';
 import {validateTextareaNonEmpty} from './comp/EasyMDE.js';
+import {initViewedCheckboxListenerFor, countAndUpdateViewedFiles} from './pull-view-file.js';
 
 const {csrfToken} = window.config;
 
@@ -104,6 +105,13 @@ export function initRepoDiffConversationNav() {
   });
 }
 
+// Will be called when the show more (files) button has been pressed
+function onShowMoreFiles() {
+  initRepoIssueContentHistory();
+  initViewedCheckboxListenerFor();
+  countAndUpdateViewedFiles();
+}
+
 export function initRepoDiffShowMore() {
   $('#diff-files, #diff-file-boxes').on('click', '#diff-show-more-files, #diff-show-more-files-stats', (e) => {
     e.preventDefault();
@@ -125,7 +133,7 @@ export function initRepoDiffShowMore() {
       $('#diff-too-many-files-stats').remove();
       $('#diff-files').append($(resp).find('#diff-files li'));
       $('#diff-incomplete').replaceWith($(resp).find('#diff-file-boxes').children());
-      initRepoIssueContentHistory();
+      onShowMoreFiles();
     }).fail(() => {
       $('#diff-show-more-files, #diff-show-more-files-stats').removeClass('disabled');
     });
@@ -151,7 +159,7 @@ export function initRepoDiffShowMore() {
       }
 
       $target.parent().replaceWith($(resp).find('#diff-file-boxes .diff-file-body .file-body').children());
-      initRepoIssueContentHistory();
+      onShowMoreFiles();
     }).fail(() => {
       $target.removeClass('disabled');
     });

web_src/js/index.js

@@ -70,6 +70,7 @@ import {
   initRepoSettingsCollaboration,
   initRepoSettingSearchTeamBox,
 } from './features/repo-settings.js';
+import {initViewedCheckboxListenerFor} from './features/pull-view-file.js';
 import {initOrgTeamSearchRepoBox, initOrgTeamSettings} from './features/org-team.js';
 import {initUserAuthWebAuthn, initUserAuthWebAuthnRegister} from './features/user-auth-webauthn.js';
 import {initRepoRelease, initRepoReleaseEditor} from './features/repo-release.js';
@@ -178,6 +179,6 @@ $(document).ready(() => {
   initUserAuthWebAuthn();
   initUserAuthWebAuthnRegister();
   initUserSettings();
-
+  initViewedCheckboxListenerFor();
   checkAppUrl();
 });

web_src/less/_review.less

@@ -262,3 +262,21 @@ a.blob-excerpt:hover {
     scroll-margin-top: 130px;
   }
 }
+
+.changed-since-last-review {
+  margin: 0 5px;
+  padding: 0 3px;
+  border: 2px var(--color-primary-light-3) solid;
+  background-color: var(--color-primary-alpha-30);
+  border-radius: 7px;
+}
+
+.viewed-file-form {
+  margin: 0 3px;
+  padding: 0 3px;
+  border-radius: 3px;
+}
+
+.viewed-file-checked-form {
+  background-color: var(--color-primary-light-4);
+}