Merge branch 'development' into releases/3.1.2

.github/workflows/release-pr.yml

@@ -37,7 +37,7 @@ jobs:
           private_key: ${{ secrets.DESKTOP_RELEASES_APP_PRIVATE_KEY }}
 
       - name: Create Release Pull Request
-        uses: peter-evans/create-pull-request@v4.1.1
+        uses: peter-evans/create-pull-request@v4.1.4
         if: |
           startsWith(github.ref, 'refs/heads/releases/') && !contains(github.ref, 'test')
         with:

README.md

@@ -41,8 +41,7 @@ The release notes for the latest beta versions are available [here](https://desk
 
 There are several community-supported package managers that can be used to
 install GitHub Desktop:
- - Windows users can install using [Chocolatey](https://chocolatey.org/) package manager:
-      `c:\> choco install github-desktop`
+ - Windows users can install using [winget](https://docs.microsoft.com/en-us/windows/package-manager/winget/) `c:/> winget install github-desktop` or [Chocolatey](https://chocolatey.org/) `c:\> choco install github-desktop`
  - macOS users can install using [Homebrew](https://brew.sh/) package manager:
       `$ brew install --cask github`
 
@@ -85,6 +84,10 @@ resources relevant to the project.
 
 If you're looking for something to work on, check out the [help wanted](https://github.com/desktop/desktop/issues?q=is%3Aissue+is%3Aopen+label%3A%22help%20wanted%22) label.
 
+## Building Desktop
+
+To get your development environment set up for building Desktop, see [setup.md](./docs/contributing/setup.md).
+
 ## More Resources
 
 See [desktop.github.com](https://desktop.github.com) for more product-oriented

app/src/lib/app-state.ts

@@ -170,6 +170,9 @@ export interface IAppState {
   /** The width of the files list in the stash view */
   readonly stashedFilesWidth: IConstrainedValue
 
+  /** The width of the files list in the pull request files changed view */
+  readonly pullRequestFilesListWidth: IConstrainedValue
+
   /**
    * Used to highlight access keys throughout the app when the
    * Alt key is pressed. Only applicable on non-macOS platforms.
@@ -194,6 +197,9 @@ export interface IAppState {
   /** Whether we should show a confirmation dialog */
   readonly askForConfirmationOnDiscardChangesPermanently: boolean
 
+  /** Should the app prompt the user to confirm a discard stash */
+  readonly askForConfirmationOnDiscardStash: boolean
+
   /** Should the app prompt the user to confirm a force push? */
   readonly askForConfirmationOnForcePush: boolean
 
@@ -230,6 +236,9 @@ export interface IAppState {
   /** Whether we should hide white space changes in history diff */
   readonly hideWhitespaceInHistoryDiff: boolean
 
+  /** Whether we should hide white space changes in the pull request diff */
+  readonly hideWhitespaceInPullRequestDiff: boolean
+
   /** Whether we should show side by side diffs */
   readonly showSideBySideDiff: boolean
 
@@ -965,4 +974,7 @@ export interface IPullRequestState {
    * diff between the latest commit and the earliest commits parent.
    */
   readonly commitSelection: ICommitSelection
+
+  /** The result of merging the pull request branch into the base branch */
+  readonly mergeStatus: MergeTreeResult | null
 }

app/src/lib/commit-url.ts

@@ -0,0 +1,24 @@
+import * as crypto from 'crypto'
+import { GitHubRepository } from '../models/github-repository'
+
+/** Method to create the url for viewing a commit on dotcom */
+export function createCommitURL(
+  gitHubRepository: GitHubRepository,
+  SHA: string,
+  filePath?: string
+): string | null {
+  const baseURL = gitHubRepository.htmlURL
+
+  if (baseURL === null) {
+    return null
+  }
+
+  if (filePath === undefined) {
+    return `${baseURL}/commit/${SHA}`
+  }
+
+  const fileHash = crypto.createHash('sha256').update(filePath).digest('hex')
+  const fileSuffix = '#diff-' + fileHash
+
+  return `${baseURL}/commit/${SHA}${fileSuffix}`
+}

app/src/lib/editors/linux.ts

@@ -62,6 +62,14 @@ const editors: ILinuxExternalEditor[] = [
     name: 'Lite XL',
     paths: ['/usr/bin/lite-xl'],
   },
+  {
+    name: 'Jetbrains PhpStorm',
+    paths: ['/snap/bin/phpstorm'],
+  },
+  {
+    name: 'Jetbrains WebStorm',
+    paths: ['/snap/bin/webstorm'],
+  },
 ]
 
 async function getAvailablePath(paths: string[]): Promise<string | null> {

app/src/lib/feature-flag.ts

@@ -110,5 +110,5 @@ export function enableSubmoduleDiff(): boolean {
 
 /** Should we enable starting pull requests? */
 export function enableStartingPullRequests(): boolean {
-  return enableDevelopmentFeatures()
+  return enableBetaFeatures()
 }

app/src/lib/git/diff.ts

@@ -254,7 +254,7 @@ export async function getBranchMergeBaseChangedFiles(
   baseBranchName: string,
   comparisonBranchName: string,
   latestComparisonBranchCommitRef: string
-): Promise<IChangesetData> {
+): Promise<IChangesetData | null> {
   const baseArgs = [
     'diff',
     '--merge-base',
@@ -268,22 +268,26 @@ export async function getBranchMergeBaseChangedFiles(
     '--',
   ]
 
-  const result = await git(
-    baseArgs,
-    repository.path,
-    'getBranchMergeBaseChangedFiles'
-  )
-
   const mergeBaseCommit = await getMergeBase(
     repository,
     baseBranchName,
     comparisonBranchName
   )
 
+  if (mergeBaseCommit === null) {
+    return null
+  }
+
+  const result = await git(
+    baseArgs,
+    repository.path,
+    'getBranchMergeBaseChangedFiles'
+  )
+
   return parseRawLogWithNumstat(
     result.combinedOutput,
     `${latestComparisonBranchCommitRef}`,
-    mergeBaseCommit ?? NullTreeSHA
+    mergeBaseCommit
   )
 }
 

app/src/lib/stores/app-store.ts

@@ -323,15 +323,20 @@ const commitSummaryWidthConfigKey: string = 'commit-summary-width'
 const defaultStashedFilesWidth: number = 250
 const stashedFilesWidthConfigKey: string = 'stashed-files-width'
 
+const defaultPullRequestFileListWidth: number = 250
+const pullRequestFileListConfigKey: string = 'pull-request-files-width'
+
 const askToMoveToApplicationsFolderDefault: boolean = true
 const confirmRepoRemovalDefault: boolean = true
 const confirmDiscardChangesDefault: boolean = true
 const confirmDiscardChangesPermanentlyDefault: boolean = true
+const confirmDiscardStashDefault: boolean = true
 const askForConfirmationOnForcePushDefault = true
 const confirmUndoCommitDefault: boolean = true
 const askToMoveToApplicationsFolderKey: string = 'askToMoveToApplicationsFolder'
 const confirmRepoRemovalKey: string = 'confirmRepoRemoval'
 const confirmDiscardChangesKey: string = 'confirmDiscardChanges'
+const confirmDiscardStashKey: string = 'confirmDiscardStash'
 const confirmDiscardChangesPermanentlyKey: string =
   'confirmDiscardChangesPermanentlyKey'
 const confirmForcePushKey: string = 'confirmForcePush'
@@ -348,6 +353,9 @@ const hideWhitespaceInChangesDiffDefault = false
 const hideWhitespaceInChangesDiffKey = 'hide-whitespace-in-changes-diff'
 const hideWhitespaceInHistoryDiffDefault = false
 const hideWhitespaceInHistoryDiffKey = 'hide-whitespace-in-diff'
+const hideWhitespaceInPullRequestDiffDefault = false
+const hideWhitespaceInPullRequestDiffKey =
+  'hide-whitespace-in-pull-request-diff'
 
 const commitSpellcheckEnabledDefault = true
 const commitSpellcheckEnabledKey = 'commit-spellcheck-enabled'
@@ -424,6 +432,7 @@ export class AppStore extends TypedBaseStore<IAppState> {
   private sidebarWidth = constrain(defaultSidebarWidth)
   private commitSummaryWidth = constrain(defaultCommitSummaryWidth)
   private stashedFilesWidth = constrain(defaultStashedFilesWidth)
+  private pullRequestFileListWidth = constrain(defaultPullRequestFileListWidth)
 
   private windowState: WindowState | null = null
   private windowZoomFactor: number = 1
@@ -437,6 +446,7 @@ export class AppStore extends TypedBaseStore<IAppState> {
   private confirmDiscardChanges: boolean = confirmDiscardChangesDefault
   private confirmDiscardChangesPermanently: boolean =
     confirmDiscardChangesPermanentlyDefault
+  private confirmDiscardStash: boolean = confirmDiscardStashDefault
   private askForConfirmationOnForcePush = askForConfirmationOnForcePushDefault
   private confirmUndoCommit: boolean = confirmUndoCommitDefault
   private imageDiffType: ImageDiffType = imageDiffTypeDefault
@@ -444,6 +454,8 @@ export class AppStore extends TypedBaseStore<IAppState> {
     hideWhitespaceInChangesDiffDefault
   private hideWhitespaceInHistoryDiff: boolean =
     hideWhitespaceInHistoryDiffDefault
+  private hideWhitespaceInPullRequestDiff: boolean =
+    hideWhitespaceInPullRequestDiffDefault
   /** Whether or not the spellchecker is enabled for commit summary and description */
   private commitSpellcheckEnabled: boolean = commitSpellcheckEnabledDefault
   private showSideBySideDiff: boolean = ShowSideBySideDiffDefault
@@ -901,6 +913,7 @@ export class AppStore extends TypedBaseStore<IAppState> {
       sidebarWidth: this.sidebarWidth,
       commitSummaryWidth: this.commitSummaryWidth,
       stashedFilesWidth: this.stashedFilesWidth,
+      pullRequestFilesListWidth: this.pullRequestFileListWidth,
       appMenuState: this.appMenu ? this.appMenu.openMenus : [],
       highlightAccessKeys: this.highlightAccessKeys,
       isUpdateAvailableBannerVisible: this.isUpdateAvailableBannerVisible,
@@ -913,6 +926,7 @@ export class AppStore extends TypedBaseStore<IAppState> {
       askForConfirmationOnDiscardChanges: this.confirmDiscardChanges,
       askForConfirmationOnDiscardChangesPermanently:
         this.confirmDiscardChangesPermanently,
+      askForConfirmationOnDiscardStash: this.confirmDiscardStash,
       askForConfirmationOnForcePush: this.askForConfirmationOnForcePush,
       askForConfirmationOnUndoCommit: this.confirmUndoCommit,
       uncommittedChangesStrategy: this.uncommittedChangesStrategy,
@@ -920,6 +934,7 @@ export class AppStore extends TypedBaseStore<IAppState> {
       imageDiffType: this.imageDiffType,
       hideWhitespaceInChangesDiff: this.hideWhitespaceInChangesDiff,
       hideWhitespaceInHistoryDiff: this.hideWhitespaceInHistoryDiff,
+      hideWhitespaceInPullRequestDiff: this.hideWhitespaceInPullRequestDiff,
       showSideBySideDiff: this.showSideBySideDiff,
       selectedShell: this.selectedShell,
       repositoryFilterText: this.repositoryFilterText,
@@ -1426,17 +1441,11 @@ export class AppStore extends TypedBaseStore<IAppState> {
     }
 
     if (tip.kind === TipState.Valid && aheadBehind.behind > 0) {
-      const mergeTreePromise = promiseWithMinimumTimeout(
-        () => determineMergeability(repository, tip.branch, action.branch),
-        500
+      this.currentMergeTreePromise = this.setupMergabilityPromise(
+        repository,
+        tip.branch,
+        action.branch
       )
-        .catch(err => {
-          log.warn(
-            `Error occurred while trying to merge ${tip.branch.name} (${tip.branch.tip.sha}) and ${action.branch.name} (${action.branch.tip.sha})`,
-            err
-          )
-          return null
-        })
         .then(mergeStatus => {
           this.repositoryStateCache.updateCompareState(repository, () => ({
             mergeStatus,
@@ -1444,16 +1453,9 @@ export class AppStore extends TypedBaseStore<IAppState> {
 
           this.emitUpdate()
         })
-
-      const cleanup = () => {
-        this.currentMergeTreePromise = null
-      }
-
-      // TODO: when we have Promise.prototype.finally available we
-      //       should use that here to make this intent clearer
-      mergeTreePromise.then(cleanup, cleanup)
-
-      this.currentMergeTreePromise = mergeTreePromise
+        .finally(() => {
+          this.currentMergeTreePromise = null
+        })
 
       return this.currentMergeTreePromise
     } else {
@@ -1465,6 +1467,23 @@ export class AppStore extends TypedBaseStore<IAppState> {
     }
   }
 
+  private setupMergabilityPromise(
+    repository: Repository,
+    baseBranch: Branch,
+    compareBranch: Branch
+  ) {
+    return promiseWithMinimumTimeout(
+      () => determineMergeability(repository, baseBranch, compareBranch),
+      500
+    ).catch(err => {
+      log.warn(
+        `Error occurred while trying to merge ${baseBranch.name} (${baseBranch.tip.sha}) and ${compareBranch.name} (${compareBranch.tip.sha})`,
+        err
+      )
+      return null
+    })
+  }
+
   /** This shouldn't be called directly. See `Dispatcher`. */
   public _updateCompareForm<K extends keyof ICompareFormUpdate>(
     repository: Repository,
@@ -1951,8 +1970,13 @@ export class AppStore extends TypedBaseStore<IAppState> {
     this.stashedFilesWidth = constrain(
       getNumber(stashedFilesWidthConfigKey, defaultStashedFilesWidth)
     )
+    this.pullRequestFileListWidth = constrain(
+      getNumber(pullRequestFileListConfigKey, defaultPullRequestFileListWidth)
+    )
 
     this.updateResizableConstraints()
+    // TODO: Initiliaze here for now... maybe move to dialog mounting
+    this.updatePullRequestResizableConstraints()
 
     this.askToMoveToApplicationsFolderSetting = getBoolean(
       askToMoveToApplicationsFolderKey,
@@ -1974,6 +1998,11 @@ export class AppStore extends TypedBaseStore<IAppState> {
       confirmDiscardChangesPermanentlyDefault
     )
 
+    this.confirmDiscardStash = getBoolean(
+      confirmDiscardStashKey,
+      confirmDiscardStashDefault
+    )
+
     this.askForConfirmationOnForcePush = getBoolean(
       confirmForcePushKey,
       askForConfirmationOnForcePushDefault
@@ -2011,6 +2040,10 @@ export class AppStore extends TypedBaseStore<IAppState> {
       hideWhitespaceInHistoryDiffKey,
       false
     )
+    this.hideWhitespaceInPullRequestDiff = getBoolean(
+      hideWhitespaceInPullRequestDiffKey,
+      false
+    )
     this.commitSpellcheckEnabled = getBoolean(
       commitSpellcheckEnabledKey,
       commitSpellcheckEnabledDefault
@@ -2077,6 +2110,41 @@ export class AppStore extends TypedBaseStore<IAppState> {
     this.stashedFilesWidth = constrain(this.stashedFilesWidth, 100, filesMax)
   }
 
+  /**
+   * Calculate the constraints of the resizable pane in the pull request dialog
+   * whenever the window dimensions change.
+   */
+  private updatePullRequestResizableConstraints() {
+    // TODO: Get width of PR dialog -> determine if we will have default width
+    // for pr dialog. The goal is for it expand to fill some percent of
+    // available window so it will change on window resize. We may have some max
+    // value and min value of where to derive a default is we cannot obtain the
+    // width for some reason (like initialization nad no pr dialog is open)
+    // Thoughts -> ß
+    // 1. Use dialog id to grab dialog if exists, else use default
+    // 2. Pass dialog width up when and call this contrainst on dialog mounting
+    //    to initialize and subscribe to window resize inside dialog to be able
+    //    to pass up dialog width on window resize.
+
+    // Get the width of the dialog
+    const available = 850
+    const dialogPadding = 20
+
+    // This is a pretty silly width for a diff but it will fit ~9 chars per line
+    // in unified mode after subtracting the width of the unified gutter and ~4
+    // chars per side in split diff mode. No one would want to use it this way
+    // but it doesn't break the layout and it allows users to temporarily
+    // maximize the width of the file list to see long path names.
+    const diffPaneMinWidth = 150
+    const filesListMax = available - dialogPadding - diffPaneMinWidth
+
+    this.pullRequestFileListWidth = constrain(
+      this.pullRequestFileListWidth,
+      100,
+      filesListMax
+    )
+  }
+
   private updateSelectedExternalEditor(
     selectedEditor: string | null
   ): Promise<void> {
@@ -5193,6 +5261,15 @@ export class AppStore extends TypedBaseStore<IAppState> {
     return Promise.resolve()
   }
 
+  public _setConfirmDiscardStashSetting(value: boolean): Promise<void> {
+    this.confirmDiscardStash = value
+
+    setBoolean(confirmDiscardStashKey, value)
+    this.emitUpdate()
+
+    return Promise.resolve()
+  }
+
   public _setConfirmForcePushSetting(value: boolean): Promise<void> {
     this.askForConfirmationOnForcePush = value
     setBoolean(confirmForcePushKey, value)
@@ -5279,6 +5356,19 @@ export class AppStore extends TypedBaseStore<IAppState> {
     }
   }
 
+  public _setHideWhitespaceInPullRequestDiff(
+    hideWhitespaceInDiff: boolean,
+    repository: Repository,
+    file: CommittedFileChange | null
+  ) {
+    setBoolean(hideWhitespaceInPullRequestDiffKey, hideWhitespaceInDiff)
+    this.hideWhitespaceInPullRequestDiff = hideWhitespaceInDiff
+
+    if (file !== null) {
+      this._changePullRequestFileSelection(repository, file)
+    }
+  }
+
   public _setShowSideBySideDiff(showSideBySideDiff: boolean) {
     if (showSideBySideDiff !== this.showSideBySideDiff) {
       setShowSideBySideDiff(showSideBySideDiff)
@@ -7146,27 +7236,36 @@ export class AppStore extends TypedBaseStore<IAppState> {
     if (defaultBranch === null || tip.kind !== TipState.Valid) {
       return
     }
-
     const currentBranch = tip.branch
+    this._initializePullRequestPreview(repository, defaultBranch, currentBranch)
+  }
+
+  private async _initializePullRequestPreview(
+    repository: Repository,
+    baseBranch: Branch,
+    currentBranch: Branch
+  ) {
+    const { branchesState, localCommitSHAs } =
+      this.repositoryStateCache.get(repository)
     const gitStore = this.gitStoreCache.get(repository)
 
     const pullRequestCommits = await gitStore.getCommitsBetweenBranches(
-      defaultBranch,
+      baseBranch,
       currentBranch
     )
 
-    const commitSHAs = pullRequestCommits.map(c => c.sha)
+    const commitsBetweenBranches = pullRequestCommits.map(c => c.sha)
 
     // A user may compare two branches with no changes between them.
     const emptyChangeSet = { files: [], linesAdded: 0, linesDeleted: 0 }
     const changesetData =
-      commitSHAs.length > 0
+      commitsBetweenBranches.length > 0
         ? await gitStore.performFailableOperation(() =>
             getBranchMergeBaseChangedFiles(
               repository,
-              defaultBranch.name,
+              baseBranch.name,
               currentBranch.name,
-              commitSHAs[0]
+              commitsBetweenBranches[0]
             )
           )
         : emptyChangeSet
@@ -7175,25 +7274,64 @@ export class AppStore extends TypedBaseStore<IAppState> {
       return
     }
 
+    const hasMergeBase = changesetData !== null
+    // We don't care how many commits exist on the unrelated history that
+    // can't be merged.
+    const commitSHAs = hasMergeBase ? commitsBetweenBranches : []
+
     this.repositoryStateCache.initializePullRequestState(repository, {
-      baseBranch: defaultBranch,
+      baseBranch,
       commitSHAs,
       commitSelection: {
         shas: commitSHAs,
         shasInDiff: commitSHAs,
         isContiguous: true,
-        changesetData,
+        changesetData: changesetData ?? emptyChangeSet,
         file: null,
         diff: null,
       },
+      mergeStatus:
+        commitSHAs.length > 0 || !hasMergeBase
+          ? {
+              kind: hasMergeBase
+                ? ComputedAction.Loading
+                : ComputedAction.Invalid,
+            }
+          : null,
     })
 
-    if (changesetData.files.length > 0) {
+    this.emitUpdate()
+
+    if (commitSHAs.length > 0) {
+      this.setupPRMergeTreePromise(repository, baseBranch, currentBranch)
+    }
+
+    if (changesetData !== null && changesetData.files.length > 0) {
       await this._changePullRequestFileSelection(
         repository,
         changesetData.files[0]
       )
     }
+
+    const { allBranches, recentBranches, defaultBranch } = branchesState
+    const { imageDiffType, selectedExternalEditor, showSideBySideDiff } =
+      this.getState()
+
+    this._showPopup({
+      type: PopupType.StartPullRequest,
+      allBranches,
+      currentBranch,
+      defaultBranch,
+      imageDiffType,
+      recentBranches,
+      repository,
+      externalEditorLabel: selectedExternalEditor ?? undefined,
+      nonLocalCommitSHA:
+        commitSHAs.length > 0 && !localCommitSHAs.includes(commitSHAs[0])
+          ? commitSHAs[0]
+          : null,
+      showSideBySideDiff,
+    })
   }
 
   public async _changePullRequestFileSelection(
@@ -7223,6 +7361,7 @@ export class AppStore extends TypedBaseStore<IAppState> {
         diff: null,
       })
     )
+
     this.emitUpdate()
 
     if (commitSHAs.length === 0) {
@@ -7240,7 +7379,7 @@ export class AppStore extends TypedBaseStore<IAppState> {
             file,
             baseBranch.name,
             currentBranch.name,
-            this.hideWhitespaceInHistoryDiff,
+            this.hideWhitespaceInPullRequestDiff,
             commitSHAs[0]
           )
         )) ?? null
@@ -7263,6 +7402,66 @@ export class AppStore extends TypedBaseStore<IAppState> {
 
     this.emitUpdate()
   }
+
+  public _setPullRequestFileListWidth(width: number): Promise<void> {
+    this.pullRequestFileListWidth = {
+      ...this.pullRequestFileListWidth,
+      value: width,
+    }
+    setNumber(pullRequestFileListConfigKey, width)
+    this.updatePullRequestResizableConstraints()
+    this.emitUpdate()
+
+    return Promise.resolve()
+  }
+
+  public _resetPullRequestFileListWidth(): Promise<void> {
+    this.pullRequestFileListWidth = {
+      ...this.pullRequestFileListWidth,
+      value: defaultPullRequestFileListWidth,
+    }
+    localStorage.removeItem(pullRequestFileListConfigKey)
+    this.updatePullRequestResizableConstraints()
+    this.emitUpdate()
+
+    return Promise.resolve()
+  }
+
+  public _updatePullRequestBaseBranch(
+    repository: Repository,
+    baseBranch: Branch
+  ) {
+    const { branchesState, pullRequestState } =
+      this.repositoryStateCache.get(repository)
+    const { tip } = branchesState
+
+    if (tip.kind !== TipState.Valid) {
+      return
+    }
+
+    if (pullRequestState === null) {
+      // This would mean the user submitted PR after requesting base branch
+      // update.
+      return
+    }
+
+    this._initializePullRequestPreview(repository, baseBranch, tip.branch)
+  }
+
+  private setupPRMergeTreePromise(
+    repository: Repository,
+    baseBranch: Branch,
+    compareBranch: Branch
+  ) {
+    this.setupMergabilityPromise(repository, baseBranch, compareBranch).then(
+      (mergeStatus: MergeTreeResult | null) => {
+        this.repositoryStateCache.updatePullRequestState(repository, () => ({
+          mergeStatus,
+        }))
+        this.emitUpdate()
+      }
+    )
+  }
 }
 
 /**

app/src/main-process/menu/build-default-menu.ts

@@ -640,7 +640,7 @@ function emit(name: MenuEvent): ClickHandler {
 }
 
 /** The zoom steps that we support, these factors must sorted */
-const ZoomInFactors = [1, 1.1, 1.25, 1.5, 1.75, 2]
+const ZoomInFactors = [0.67, 0.75, 0.8, 0.9, 1, 1.1, 1.25, 1.5, 1.75, 2]
 const ZoomOutFactors = ZoomInFactors.slice().reverse()
 
 /**

app/src/models/popup.ts

@@ -14,7 +14,7 @@ import { Commit, CommitOneLine, ICommitContext } from './commit'
 import { IStashEntry } from './stash-entry'
 import { Account } from '../models/account'
 import { Progress } from './progress'
-import { ITextDiff, DiffSelection } from './diff'
+import { ITextDiff, DiffSelection, ImageDiffType } from './diff'
 import { RepositorySettingsTab } from '../ui/repository-settings/repository-settings'
 import { ICommitMessage } from './commit-message'
 import { IAuthor } from './author'
@@ -362,4 +362,13 @@ export type Popup =
     }
   | {
       type: PopupType.StartPullRequest
+      allBranches: ReadonlyArray<Branch>
+      currentBranch: Branch
+      defaultBranch: Branch | null
+      externalEditorLabel?: string
+      imageDiffType: ImageDiffType
+      recentBranches: ReadonlyArray<Branch>
+      repository: Repository
+      nonLocalCommitSHA: string | null
+      showSideBySideDiff: boolean
     }

app/src/ui/app.tsx

@@ -1,5 +1,4 @@
 import * as React from 'react'
-import * as crypto from 'crypto'
 import { TransitionGroup, CSSTransition } from 'react-transition-group'
 import {
   IAppState,
@@ -158,6 +157,8 @@ import { SSHUserPassword } from './ssh/ssh-user-password'
 import { showContextualMenu } from '../lib/menu-item'
 import { UnreachableCommitsDialog } from './history/unreachable-commits-dialog'
 import { OpenPullRequestDialog } from './open-pull-request/open-pull-request-dialog'
+import { sendNonFatalException } from '../lib/helpers/non-fatal-exception'
+import { createCommitURL } from '../lib/commit-url'
 
 const MinuteInMilliseconds = 1000 * 60
 const HourInMilliseconds = MinuteInMilliseconds * 60
@@ -1481,6 +1482,7 @@ export class App extends React.Component<IAppProps, IAppState> {
             confirmDiscardChangesPermanently={
               this.state.askForConfirmationOnDiscardChangesPermanently
             }
+            confirmDiscardStash={this.state.askForConfirmationOnDiscardStash}
             confirmForcePush={this.state.askForConfirmationOnForcePush}
             confirmUndoCommit={this.state.askForConfirmationOnUndoCommit}
             uncommittedChangesStrategy={this.state.uncommittedChangesStrategy}
@@ -1849,6 +1851,9 @@ export class App extends React.Component<IAppProps, IAppState> {
           <ConfirmDiscardStashDialog
             key="confirm-discard-stash-dialog"
             dispatcher={this.props.dispatcher}
+            askForConfirmationOnDiscardStash={
+              this.state.askForConfirmationOnDiscardStash
+            }
             repository={repository}
             stash={stash}
             onDismissed={onPopupDismissedFn}
@@ -2243,25 +2248,35 @@ export class App extends React.Component<IAppProps, IAppState> {
         )
       }
       case PopupType.StartPullRequest: {
-        const { selectedState } = this.state
-        if (
-          selectedState == null ||
-          selectedState.type !== SelectionType.Repository
-        ) {
+        // Intentionally chose to get the current pull request state  on
+        // rerender because state variables such as file selection change
+        // via the dispatcher.
+        const pullRequestState = this.getPullRequestState()
+        if (pullRequestState === null) {
+          // This shouldn't happen..
+          sendNonFatalException(
+            'FailedToStartPullRequest',
+            new Error(
+              'Failed to start pull request because pull request state was null'
+            )
+          )
           return null
         }
 
-        const { state: repoState, repository } = selectedState
-        const { pullRequestState, branchesState } = repoState
-        if (
-          pullRequestState === null ||
-          branchesState.tip.kind !== TipState.Valid
-        ) {
-          return null
-        }
-        const { allBranches, recentBranches, defaultBranch, tip } =
-          branchesState
-        const currentBranch = tip.branch
+        const { pullRequestFilesListWidth, hideWhitespaceInPullRequestDiff } =
+          this.state
+
+        const {
+          allBranches,
+          currentBranch,
+          defaultBranch,
+          imageDiffType,
+          externalEditorLabel,
+          nonLocalCommitSHA,
+          recentBranches,
+          repository,
+          showSideBySideDiff,
+        } = popup
 
         return (
           <OpenPullRequestDialog
@@ -2270,9 +2285,15 @@ export class App extends React.Component<IAppProps, IAppState> {
             currentBranch={currentBranch}
             defaultBranch={defaultBranch}
             dispatcher={this.props.dispatcher}
+            fileListWidth={pullRequestFilesListWidth}
+            hideWhitespaceInDiff={hideWhitespaceInPullRequestDiff}
+            imageDiffType={imageDiffType}
+            nonLocalCommitSHA={nonLocalCommitSHA}
             pullRequestState={pullRequestState}
             recentBranches={recentBranches}
             repository={repository}
+            externalEditorLabel={externalEditorLabel}
+            showSideBySideDiff={showSideBySideDiff}
             onDismissed={onPopupDismissedFn}
           />
         )
@@ -2282,6 +2303,18 @@ export class App extends React.Component<IAppProps, IAppState> {
     }
   }
 
+  private getPullRequestState() {
+    const { selectedState } = this.state
+    if (
+      selectedState == null ||
+      selectedState.type !== SelectionType.Repository
+    ) {
+      return null
+    }
+
+    return selectedState.state.pullRequestState
+  }
+
   private getWarnForcePushDialogOnBegin(
     onBegin: () => void,
     onPopupDismissedFn: () => void
@@ -2955,6 +2988,9 @@ export class App extends React.Component<IAppProps, IAppState> {
           askForConfirmationOnDiscardChanges={
             state.askForConfirmationOnDiscardChanges
           }
+          askForConfirmationOnDiscardStash={
+            state.askForConfirmationOnDiscardStash
+          }
           accounts={state.accounts}
           externalEditorLabel={externalEditorLabel}
           resolvedExternalEditor={state.resolvedExternalEditor}
@@ -3049,22 +3085,17 @@ export class App extends React.Component<IAppProps, IAppState> {
       return
     }
 
-    const baseURL = repository.gitHubRepository.htmlURL
+    const commitURL = createCommitURL(
+      repository.gitHubRepository,
+      SHA,
+      filePath
+    )
 
-    let fileSuffix = ''
-    if (filePath != null) {
-      const fileHash = crypto
-        .createHash('sha256')
-        .update(filePath)
-        .digest('hex')
-      fileSuffix = '#diff-' + fileHash
+    if (commitURL === null) {
+      return
     }
 
-    if (baseURL) {
-      this.props.dispatcher.openInBrowser(
-        `${baseURL}/commit/${SHA}${fileSuffix}`
-      )
-    }
+    this.props.dispatcher.openInBrowser(commitURL)
   }
 
   private onBranchDeleted = (repository: Repository) => {

app/src/ui/branches/branch-select.tsx

@@ -1,19 +1,12 @@
 import * as React from 'react'
 import { IMatches } from '../../lib/fuzzy-find'
 import { Branch } from '../../models/branch'
-import { Button } from '../lib/button'
 import { ClickSource } from '../lib/list'
-import { Popover } from '../lib/popover'
-import { Ref } from '../lib/ref'
-import { Octicon } from '../octicons'
-import * as OcticonSymbol from '../octicons/octicons.generated'
+import { PopoverDropdown } from '../lib/popover-dropdown'
 import { BranchList } from './branch-list'
 import { renderDefaultBranch } from './branch-renderer'
 import { IBranchListItem } from './group-branches'
 
-const defaultDropdownListHeight = 300
-const maxDropdownListHeight = 500
-
 interface IBranchSelectProps {
   /** The initially selected branch. */
   readonly branch: Branch
@@ -43,10 +36,8 @@ interface IBranchSelectProps {
 }
 
 interface IBranchSelectState {
-  readonly showBranchDropdown: boolean
   readonly selectedBranch: Branch | null
   readonly filterText: string
-  readonly dropdownListHeight: number
 }
 
 /**
@@ -56,67 +47,25 @@ export class BranchSelect extends React.Component<
   IBranchSelectProps,
   IBranchSelectState
 > {
-  private invokeButtonRef: HTMLButtonElement | null = null
+  private popoverRef = React.createRef<PopoverDropdown>()
 
   public constructor(props: IBranchSelectProps) {
     super(props)
 
     this.state = {
-      showBranchDropdown: false,
       selectedBranch: props.branch,
       filterText: '',
-      dropdownListHeight: defaultDropdownListHeight,
     }
   }
 
-  public componentDidMount() {
-    this.calculateDropdownListHeight()
-  }
-
-  public componentDidUpdate() {
-    this.calculateDropdownListHeight()
-  }
-
-  private calculateDropdownListHeight = () => {
-    if (this.invokeButtonRef === null) {
-      return
-    }
-
-    const windowHeight = window.innerHeight
-    const bottomOfButton = this.invokeButtonRef.getBoundingClientRect().bottom
-    const listHeaderHeight = 75
-    const calcMaxHeight = Math.round(
-      windowHeight - bottomOfButton - listHeaderHeight
-    )
-
-    const dropdownListHeight =
-      calcMaxHeight > maxDropdownListHeight
-        ? maxDropdownListHeight
-        : calcMaxHeight
-    if (dropdownListHeight !== this.state.dropdownListHeight) {
-      this.setState({ dropdownListHeight })
-    }
-  }
-
-  private onInvokeButtonRef = (buttonRef: HTMLButtonElement | null) => {
-    this.invokeButtonRef = buttonRef
-  }
-
-  private toggleBranchDropdown = () => {
-    this.setState({ showBranchDropdown: !this.state.showBranchDropdown })
-  }
-
-  private closeBranchDropdown = () => {
-    this.setState({ showBranchDropdown: false })
-  }
-
   private renderBranch = (item: IBranchListItem, matches: IMatches) => {
     return renderDefaultBranch(item, matches, this.props.currentBranch)
   }
 
   private onItemClick = (branch: Branch, source: ClickSource) => {
     source.event.preventDefault()
-    this.setState({ showBranchDropdown: false, selectedBranch: branch })
+    this.popoverRef.current?.closePopover()
+    this.setState({ selectedBranch: branch })
     this.props.onChange?.(branch)
   }
 
@@ -124,67 +73,32 @@ export class BranchSelect extends React.Component<
     this.setState({ filterText })
   }
 
-  public renderBranchDropdown() {
-    if (!this.state.showBranchDropdown) {
-      return
-    }
-
+  public render() {
     const { currentBranch, defaultBranch, recentBranches, allBranches } =
       this.props
 
-    const { filterText, selectedBranch, dropdownListHeight } = this.state
+    const { filterText, selectedBranch } = this.state
 
     return (
-      <Popover
-        className="branch-select-dropdown"
-        onClickOutside={this.closeBranchDropdown}
+      <PopoverDropdown
+        contentTitle="Choose a base branch"
+        buttonContent={selectedBranch?.name ?? ''}
+        label="base:"
+        ref={this.popoverRef}
       >
-        <div className="branch-select-dropdown-header">
-          Choose a base branch
-          <button
-            className="close"
-            onClick={this.closeBranchDropdown}
-            aria-label="close"
-          >
-            <Octicon symbol={OcticonSymbol.x} />
-          </button>
-        </div>
-        <div
-          className="branch-select-dropdown-list"
-          style={{ height: `${dropdownListHeight}px` }}
-        >
-          <BranchList
-            allBranches={allBranches}
-            currentBranch={currentBranch}
-            defaultBranch={defaultBranch}
-            recentBranches={recentBranches}
-            filterText={filterText}
-            onFilterTextChanged={this.onFilterTextChanged}
-            selectedBranch={selectedBranch}
-            canCreateNewBranch={false}
-            renderBranch={this.renderBranch}
-            onItemClick={this.onItemClick}
-          />
-        </div>
-      </Popover>
-    )
-  }
-
-  public render() {
-    return (
-      <div className="branch-select-component">
-        <Button
-          onClick={this.toggleBranchDropdown}
-          onButtonRef={this.onInvokeButtonRef}
-        >
-          <Ref>
-            <span className="base-label">base:</span>
-            {this.state.selectedBranch?.name}
-            <Octicon symbol={OcticonSymbol.triangleDown} />
-          </Ref>
-        </Button>
-        {this.renderBranchDropdown()}
-      </div>
+        <BranchList
+          allBranches={allBranches}
+          currentBranch={currentBranch}
+          defaultBranch={defaultBranch}
+          recentBranches={recentBranches}
+          filterText={filterText}
+          onFilterTextChanged={this.onFilterTextChanged}
+          selectedBranch={selectedBranch}
+          canCreateNewBranch={false}
+          renderBranch={this.renderBranch}
+          onItemClick={this.onItemClick}
+        />
+      </PopoverDropdown>
     )
   }
 }

app/src/ui/changes/changed-file-details.tsx

@@ -6,7 +6,6 @@ import { Octicon, iconForStatus } from '../octicons'
 import * as OcticonSymbol from '../octicons/octicons.generated'
 import { mapStatus } from '../../lib/status'
 import { DiffOptions } from '../diff/diff-options'
-import { RepositorySectionTab } from '../../lib/app-state'
 
 interface IChangedFileDetailsProps {
   readonly path: string
@@ -61,7 +60,7 @@ export class ChangedFileDetails extends React.Component<
 
     return (
       <DiffOptions
-        sourceTab={RepositorySectionTab.Changes}
+        isInteractiveDiff={true}
         onHideWhitespaceChangesChanged={
           this.props.onHideWhitespaceInDiffChanged
         }

app/src/ui/changes/commit-message.tsx

@@ -351,7 +351,7 @@ export class CommitMessage extends React.Component<
     if (
       isShortcutKey &&
       event.key === 'Enter' &&
-      this.canCommit() &&
+      (this.canCommit() || this.canAmend()) &&
       this.canExcecuteCommitShortcut()
     ) {
       this.createCommit()

app/src/ui/clone-repository/clone-repository.tsx

@@ -3,6 +3,7 @@ import * as React from 'react'
 import { Dispatcher } from '../dispatcher'
 import { getDefaultDir, setDefaultDir } from '../lib/default-dir'
 import { Account } from '../../models/account'
+import { FoldoutType } from '../../lib/app-state'
 import {
   IRepositoryIdentifier,
   parseRepositoryIdentifier,
@@ -728,6 +729,7 @@ export class CloneRepository extends React.Component<
 
     const { url, defaultBranch } = cloneInfo
 
+    this.props.dispatcher.closeFoldout(FoldoutType.Repository)
     try {
       this.cloneImpl(url.trim(), path, defaultBranch)
     } catch (e) {

app/src/ui/diff/diff-options.tsx

@@ -4,14 +4,13 @@ import { Octicon } from '../octicons'
 import * as OcticonSymbol from '../octicons/octicons.generated'
 import { RadioButton } from '../lib/radio-button'
 import { Popover, PopoverCaretPosition } from '../lib/popover'
-import { RepositorySectionTab } from '../../lib/app-state'
 
 interface IDiffOptionsProps {
-  readonly sourceTab: RepositorySectionTab
+  readonly isInteractiveDiff: boolean
   readonly hideWhitespaceChanges: boolean
   readonly onHideWhitespaceChangesChanged: (
     hideWhitespaceChanges: boolean
-  ) => Promise<void>
+  ) => void
 
   readonly showSideBySideDiff: boolean
   readonly onShowSideBySideDiffChanged: (showSideBySideDiff: boolean) => void
@@ -144,7 +143,7 @@ export class DiffOptions extends React.Component<
             __DARWIN__ ? 'Hide Whitespace Changes' : 'Hide whitespace changes'
           }
         />
-        {this.props.sourceTab === RepositorySectionTab.Changes && (
+        {this.props.isInteractiveDiff && (
           <p className="secondary-text">
             Interacting with individual lines or hunks will be disabled while
             hiding whitespace.

app/src/ui/dispatcher/dispatcher.ts

@@ -2122,6 +2122,19 @@ export class Dispatcher {
     )
   }
 
+  /** Change the hide whitespace in pull request diff setting */
+  public onHideWhitespaceInPullRequestDiffChanged(
+    hideWhitespaceInDiff: boolean,
+    repository: Repository,
+    file: CommittedFileChange | null = null
+  ) {
+    this.appStore._setHideWhitespaceInPullRequestDiff(
+      hideWhitespaceInDiff,
+      repository,
+      file
+    )
+  }
+
   /** Change the side by side diff setting */
   public onShowSideBySideDiffChanged(showSideBySideDiff: boolean) {
     return this.appStore._setShowSideBySideDiff(showSideBySideDiff)
@@ -2338,6 +2351,10 @@ export class Dispatcher {
     await this.appStore._loadStatus(repository)
   }
 
+  public setConfirmDiscardStashSetting(value: boolean) {
+    return this.appStore._setConfirmDiscardStashSetting(value)
+  }
+
   public setConfirmForcePushSetting(value: boolean) {
     return this.appStore._setConfirmForcePushSetting(value)
   }
@@ -3963,9 +3980,33 @@ export class Dispatcher {
 
   public startPullRequest(repository: Repository) {
     this.appStore._startPullRequest(repository)
+  }
 
-    this.showPopup({
-      type: PopupType.StartPullRequest,
-    })
+  /**
+   * Change the selected changed file of the current pull request state.
+   */
+  public changePullRequestFileSelection(
+    repository: Repository,
+    file: CommittedFileChange
+  ): Promise<void> {
+    return this.appStore._changePullRequestFileSelection(repository, file)
+  }
+
+  /**
+   * Set the width of the file list column in the pull request files changed
+   */
+  public setPullRequestFileListWidth(width: number): Promise<void> {
+    return this.appStore._setPullRequestFileListWidth(width)
+  }
+
+  /**
+   * Reset the width of the file list column in the pull request files changed
+   */
+  public resetPullRequestFileListWidth(): Promise<void> {
+    return this.appStore._resetPullRequestFileListWidth()
+  }
+
+  public updatePullRequestBaseBranch(repository: Repository, branch: Branch) {
+    this.appStore._updatePullRequestBaseBranch(repository, branch)
   }
 }

app/src/ui/history/commit-summary.tsx

@@ -12,7 +12,6 @@ import { CommitAttribution } from '../lib/commit-attribution'
 import { Tokenizer, TokenResult } from '../../lib/text-token-parser'
 import { wrapRichTextCommitMessage } from '../../lib/wrap-rich-text-commit-message'
 import { DiffOptions } from '../diff/diff-options'
-import { RepositorySectionTab } from '../../lib/app-state'
 import { IChangesetData } from '../../lib/git'
 import { TooltippedContent } from '../lib/tooltipped-content'
 import { AppFileStatusKind } from '../../models/status'
@@ -505,7 +504,7 @@ export class CommitSummary extends React.Component<
               title="Diff Options"
             >
               <DiffOptions
-                sourceTab={RepositorySectionTab.History}
+                isInteractiveDiff={false}
                 hideWhitespaceChanges={this.props.hideWhitespaceInDiff}
                 onHideWhitespaceChangesChanged={
                   this.props.onHideWhitespaceInDiffChanged

app/src/ui/lib/popover-dropdown.tsx

@@ -0,0 +1,133 @@
+import * as React from 'react'
+import { Button } from './button'
+import { Popover, PopoverCaretPosition } from './popover'
+import { Octicon } from '../octicons'
+import * as OcticonSymbol from '../octicons/octicons.generated'
+import classNames from 'classnames'
+
+const defaultPopoverContentHeight = 300
+const maxPopoverContentHeight = 500
+
+interface IPopoverDropdownProps {
+  readonly className?: string
+  readonly contentTitle: string
+  readonly buttonContent: JSX.Element | string
+  readonly label: string
+}
+
+interface IPopoverDropdownState {
+  readonly showPopover: boolean
+  readonly popoverContentHeight: number
+}
+
+/**
+ * A dropdown component for displaying a dropdown button that opens
+ * a popover to display contents relative to the button content.
+ */
+export class PopoverDropdown extends React.Component<
+  IPopoverDropdownProps,
+  IPopoverDropdownState
+> {
+  private invokeButtonRef: HTMLButtonElement | null = null
+
+  public constructor(props: IPopoverDropdownProps) {
+    super(props)
+
+    this.state = {
+      showPopover: false,
+      popoverContentHeight: defaultPopoverContentHeight,
+    }
+  }
+
+  public componentDidMount() {
+    this.calculateDropdownListHeight()
+  }
+
+  public componentDidUpdate() {
+    this.calculateDropdownListHeight()
+  }
+
+  private calculateDropdownListHeight = () => {
+    if (this.invokeButtonRef === null) {
+      return
+    }
+
+    const windowHeight = window.innerHeight
+    const bottomOfButton = this.invokeButtonRef.getBoundingClientRect().bottom
+    const listHeaderHeight = 75
+    const calcMaxHeight = Math.round(
+      windowHeight - bottomOfButton - listHeaderHeight
+    )
+
+    const popoverContentHeight =
+      calcMaxHeight > maxPopoverContentHeight
+        ? maxPopoverContentHeight
+        : calcMaxHeight
+    if (popoverContentHeight !== this.state.popoverContentHeight) {
+      this.setState({ popoverContentHeight })
+    }
+  }
+
+  private onInvokeButtonRef = (buttonRef: HTMLButtonElement | null) => {
+    this.invokeButtonRef = buttonRef
+  }
+
+  private togglePopover = () => {
+    this.setState({ showPopover: !this.state.showPopover })
+  }
+
+  public closePopover = () => {
+    this.setState({ showPopover: false })
+  }
+
+  private renderPopover() {
+    if (!this.state.showPopover) {
+      return
+    }
+
+    const { contentTitle } = this.props
+    const { popoverContentHeight } = this.state
+    const contentStyle = { height: `${popoverContentHeight}px` }
+
+    return (
+      <Popover
+        className="popover-dropdown-popover"
+        caretPosition={PopoverCaretPosition.TopLeft}
+        onClickOutside={this.closePopover}
+      >
+        <div className="popover-dropdown-header">
+          {contentTitle}
+          <button
+            className="close"
+            onClick={this.closePopover}
+            aria-label="close"
+          >
+            <Octicon symbol={OcticonSymbol.x} />
+          </button>
+        </div>
+        <div className="popover-dropdown-content" style={contentStyle}>
+          {this.props.children}
+        </div>
+      </Popover>
+    )
+  }
+
+  public render() {
+    const { className, buttonContent, label } = this.props
+    const cn = classNames('popover-dropdown-component', className)
+
+    return (
+      <div className={cn}>
+        <Button
+          onClick={this.togglePopover}
+          onButtonRef={this.onInvokeButtonRef}
+        >
+          <span className="popover-dropdown-button-label">{label}</span>
+          <span className="button-content">{buttonContent}</span>
+          <Octicon symbol={OcticonSymbol.triangleDown} />
+        </Button>
+        {this.renderPopover()}
+      </div>
+    )
+  }
+}

app/src/ui/lib/tooltip.tsx

@@ -299,7 +299,13 @@ export class Tooltip<T extends TooltipTarget> extends React.Component<
     }
   }
 
+  private updateMouseRect = (event: MouseEvent) => {
+    this.mouseRect = new DOMRect(event.clientX - 10, event.clientY - 10, 20, 20)
+  }
+
   private onTargetMouseEnter = (event: MouseEvent) => {
+    this.updateMouseRect(event)
+
     this.mouseOverTarget = true
     this.cancelHideTooltip()
     if (!this.state.show) {
@@ -308,7 +314,7 @@ export class Tooltip<T extends TooltipTarget> extends React.Component<
   }
 
   private onTargetMouseMove = (event: MouseEvent) => {
-    this.mouseRect = new DOMRect(event.clientX - 10, event.clientY - 10, 20, 20)
+    this.updateMouseRect(event)
   }
 
   private onTargetMouseDown = (event: MouseEvent) => {

app/src/ui/multi-commit-operation/base-multi-commit-operation.tsx

@@ -93,6 +93,8 @@ export abstract class BaseMultiCommitOperation extends React.Component<IMultiCom
         {targetBranch !== null ? <strong>{targetBranch.name}</strong> : null}
       </>
     )
+
+    this.props.dispatcher.closePopup(PopupType.MultiCommitOperation)
     return dispatcher.onConflictsFoundBanner(
       repository,
       operationDescription,

app/src/ui/open-pull-request/open-pull-request-dialog.tsx

@@ -1,10 +1,18 @@
 import * as React from 'react'
-import { IPullRequestState } from '../../lib/app-state'
+import { IConstrainedValue, IPullRequestState } from '../../lib/app-state'
+import { getDotComAPIEndpoint } from '../../lib/api'
 import { Branch } from '../../models/branch'
+import { ImageDiffType } from '../../models/diff'
 import { Repository } from '../../models/repository'
 import { DialogFooter, OkCancelButtonGroup, Dialog } from '../dialog'
 import { Dispatcher } from '../dispatcher'
+import { Ref } from '../lib/ref'
+import { Octicon } from '../octicons'
+import * as OcticonSymbol from '../octicons/octicons.generated'
 import { OpenPullRequestDialogHeader } from './open-pull-request-header'
+import { PullRequestFilesChanged } from './pull-request-files-changed'
+import { PullRequestMergeStatus } from './pull-request-merge-status'
+import { ComputedAction } from '../../models/computed-action'
 
 interface IOpenPullRequestDialogProps {
   readonly repository: Repository
@@ -35,6 +43,25 @@ interface IOpenPullRequestDialogProps {
    */
   readonly recentBranches: ReadonlyArray<Branch>
 
+  /** Whether we should display side by side diffs. */
+  readonly showSideBySideDiff: boolean
+
+  /** Whether we should hide whitespace in diff. */
+  readonly hideWhitespaceInDiff: boolean
+
+  /** The type of image diff to display. */
+  readonly imageDiffType: ImageDiffType
+
+  /** Label for selected external editor */
+  readonly externalEditorLabel?: string
+
+  /** Width to use for the files list pane in the files changed view */
+  readonly fileListWidth: IConstrainedValue
+
+  /** If the latest commit of the pull request is not local, this will contain
+   * it's SHA  */
+  readonly nonLocalCommitSHA: string | null
+
   /** Called to dismiss the dialog */
   readonly onDismissed: () => void
 }
@@ -47,6 +74,11 @@ export class OpenPullRequestDialog extends React.Component<IOpenPullRequestDialo
     this.props.dispatcher.recordCreatePullRequest()
   }
 
+  private onBranchChange = (branch: Branch) => {
+    const { repository } = this.props
+    this.props.dispatcher.updatePullRequestBaseBranch(repository, branch)
+  }
+
   private renderHeader() {
     const {
       currentBranch,
@@ -64,22 +96,107 @@ export class OpenPullRequestDialog extends React.Component<IOpenPullRequestDialo
         allBranches={allBranches}
         recentBranches={recentBranches}
         commitCount={commitSHAs?.length ?? 0}
+        onBranchChange={this.onBranchChange}
         onDismissed={this.props.onDismissed}
       />
     )
   }
 
   private renderContent() {
-    return <div>Content</div>
+    return (
+      <div className="open-pull-request-content">
+        {this.renderNoChanges()}
+        {this.renderFilesChanged()}
+      </div>
+    )
+  }
+
+  private renderFilesChanged() {
+    const {
+      dispatcher,
+      externalEditorLabel,
+      hideWhitespaceInDiff,
+      imageDiffType,
+      pullRequestState,
+      repository,
+      fileListWidth,
+      nonLocalCommitSHA,
+    } = this.props
+    const { commitSelection } = pullRequestState
+    const { diff, file, changesetData, shas } = commitSelection
+    const { files } = changesetData
+
+    if (shas.length === 0) {
+      return
+    }
+
+    return (
+      <PullRequestFilesChanged
+        diff={diff}
+        dispatcher={dispatcher}
+        externalEditorLabel={externalEditorLabel}
+        fileListWidth={fileListWidth}
+        files={files}
+        hideWhitespaceInDiff={hideWhitespaceInDiff}
+        imageDiffType={imageDiffType}
+        nonLocalCommitSHA={nonLocalCommitSHA}
+        selectedFile={file}
+        showSideBySideDiff={this.props.showSideBySideDiff}
+        repository={repository}
+      />
+    )
+  }
+
+  private renderNoChanges() {
+    const { pullRequestState, currentBranch } = this.props
+    const { commitSelection, baseBranch, mergeStatus } = pullRequestState
+    const { shas } = commitSelection
+
+    if (shas.length !== 0) {
+      return
+    }
+    const hasMergeBase = mergeStatus?.kind !== ComputedAction.Invalid
+    const message = hasMergeBase ? (
+      <>
+        <Ref>{baseBranch.name}</Ref> is up to date with all commits from{' '}
+        <Ref>{currentBranch.name}</Ref>.
+      </>
+    ) : (
+      <>
+        <Ref>{baseBranch.name}</Ref> and <Ref>{currentBranch.name}</Ref> are
+        entirely different commit histories.
+      </>
+    )
+    return (
+      <div className="open-pull-request-no-changes">
+        <div>
+          <Octicon symbol={OcticonSymbol.gitPullRequest} />
+          <h3>There are no changes.</h3>
+          {message}
+        </div>
+      </div>
+    )
   }
 
   private renderFooter() {
+    const { mergeStatus, commitSHAs } = this.props.pullRequestState
+    const gitHubRepository = this.props.repository.gitHubRepository
+    const isEnterprise =
+      gitHubRepository && gitHubRepository.endpoint !== getDotComAPIEndpoint()
+    const buttonTitle = `Create pull request on GitHub${
+      isEnterprise ? ' Enterprise' : ''
+    }.`
+
     return (
       <DialogFooter>
+        <PullRequestMergeStatus mergeStatus={mergeStatus} />
         <OkCancelButtonGroup
-          okButtonText="Create Pull Request"
-          okButtonTitle="Create pull request on GitHub."
+          okButtonText={
+            __DARWIN__ ? 'Create Pull Request' : 'Create pull request'
+          }
+          okButtonTitle={buttonTitle}
           cancelButtonText="Cancel"
+          okButtonDisabled={commitSHAs === null || commitSHAs.length === 0}
         />
       </DialogFooter>
     )
@@ -93,8 +210,7 @@ export class OpenPullRequestDialog extends React.Component<IOpenPullRequestDialo
         onDismissed={this.props.onDismissed}
       >
         {this.renderHeader()}
-        <div className="content">{this.renderContent()}</div>
-
+        {this.renderContent()}
         {this.renderFooter()}
       </Dialog>
     )

app/src/ui/open-pull-request/open-pull-request-header.tsx

@@ -30,6 +30,9 @@ interface IOpenPullRequestDialogHeaderProps {
   /** The count of commits of the pull request */
   readonly commitCount: number
 
+  /** When the branch selection changes */
+  readonly onBranchChange: (branch: Branch) => void
+
   /**
    * Event triggered when the dialog is dismissed by the user in the
    * ways described in the dismissable prop.
@@ -54,6 +57,7 @@ export class OpenPullRequestDialogHeader extends React.Component<
       allBranches,
       recentBranches,
       commitCount,
+      onBranchChange,
       onDismissed,
     } = this.props
     const commits = `${commitCount} commit${commitCount > 1 ? 's' : ''}`
@@ -74,6 +78,7 @@ export class OpenPullRequestDialogHeader extends React.Component<
             currentBranch={currentBranch}
             allBranches={allBranches}
             recentBranches={recentBranches}
+            onChange={onBranchChange}
           />{' '}
           from <Ref>{currentBranch.name}</Ref>.
         </div>

app/src/ui/open-pull-request/pull-request-files-changed.tsx

@@ -0,0 +1,307 @@
+import * as React from 'react'
+import * as Path from 'path'
+import { IDiff, ImageDiffType } from '../../models/diff'
+import { Repository } from '../../models/repository'
+import { CommittedFileChange } from '../../models/status'
+import { SeamlessDiffSwitcher } from '../diff/seamless-diff-switcher'
+import { Dispatcher } from '../dispatcher'
+import { openFile } from '../lib/open-file'
+import { Resizable } from '../resizable'
+import { FileList } from '../history/file-list'
+import { IMenuItem, showContextualMenu } from '../../lib/menu-item'
+import { pathExists } from '../lib/path-exists'
+import {
+  CopyFilePathLabel,
+  CopyRelativeFilePathLabel,
+  DefaultEditorLabel,
+  isSafeFileExtension,
+  OpenWithDefaultProgramLabel,
+  RevealInFileManagerLabel,
+} from '../lib/context-menu'
+import { revealInFileManager } from '../../lib/app-shell'
+import { clipboard } from 'electron'
+import { IConstrainedValue } from '../../lib/app-state'
+import { clamp } from '../../lib/clamp'
+import { getDotComAPIEndpoint } from '../../lib/api'
+import { createCommitURL } from '../../lib/commit-url'
+import { DiffOptions } from '../diff/diff-options'
+
+interface IPullRequestFilesChangedProps {
+  readonly repository: Repository
+  readonly dispatcher: Dispatcher
+
+  /** The file whose diff should be displayed. */
+  readonly selectedFile: CommittedFileChange | null
+
+  /** The files changed in the pull request. */
+  readonly files: ReadonlyArray<CommittedFileChange>
+
+  /** The diff that should be rendered */
+  readonly diff: IDiff | null
+
+  /** The type of image diff to display. */
+  readonly imageDiffType: ImageDiffType
+
+  /** Whether we should display side by side diffs. */
+  readonly showSideBySideDiff: boolean
+
+  /** Whether we should hide whitespace in diff. */
+  readonly hideWhitespaceInDiff: boolean
+
+  /** Label for selected external editor */
+  readonly externalEditorLabel?: string
+
+  /** Width to use for the files list pane */
+  readonly fileListWidth: IConstrainedValue
+
+  /** If the latest commit of the pull request is not local, this will contain
+   * it's SHA  */
+  readonly nonLocalCommitSHA: string | null
+}
+
+interface IPullRequestFilesChangedState {
+  readonly showSideBySideDiff: boolean
+}
+
+/**
+ * A component for viewing the file changes for a pull request.
+ */
+export class PullRequestFilesChanged extends React.Component<
+  IPullRequestFilesChangedProps,
+  IPullRequestFilesChangedState
+> {
+  public constructor(props: IPullRequestFilesChangedProps) {
+    super(props)
+
+    this.state = { showSideBySideDiff: props.showSideBySideDiff }
+  }
+
+  private onOpenFile = (path: string) => {
+    const fullPath = Path.join(this.props.repository.path, path)
+    this.onOpenBinaryFile(fullPath)
+  }
+
+  /**
+   * Opens a binary file in an the system-assigned application for
+   * said file type.
+   */
+  private onOpenBinaryFile = (fullPath: string) => {
+    openFile(fullPath, this.props.dispatcher)
+  }
+
+  /** Called when the user changes the hide whitespace in diffs setting. */
+  private onHideWhitespaceInDiffChanged = (hideWhitespaceInDiff: boolean) => {
+    const { selectedFile } = this.props
+    return this.props.dispatcher.onHideWhitespaceInPullRequestDiffChanged(
+      hideWhitespaceInDiff,
+      this.props.repository,
+      selectedFile
+    )
+  }
+
+  private onShowSideBySideDiffChanged = (showSideBySideDiff: boolean) => {
+    this.setState({ showSideBySideDiff })
+  }
+
+  private onDiffOptionsOpened = () => {
+    this.props.dispatcher.recordDiffOptionsViewed()
+  }
+
+  /**
+   * Called when the user is viewing an image diff and requests
+   * to change the diff presentation mode.
+   */
+  private onChangeImageDiffType = (imageDiffType: ImageDiffType) => {
+    this.props.dispatcher.changeImageDiffType(imageDiffType)
+  }
+
+  private onFileListResize = (width: number) => {
+    this.props.dispatcher.setPullRequestFileListWidth(width)
+  }
+
+  private onFileListSizeReset = () => {
+    this.props.dispatcher.resetPullRequestFileListWidth()
+  }
+
+  private onViewOnGitHub = (file: CommittedFileChange) => {
+    const { nonLocalCommitSHA, repository, dispatcher } = this.props
+    const { gitHubRepository } = repository
+
+    if (gitHubRepository === null || nonLocalCommitSHA === null) {
+      return
+    }
+
+    const commitURL = createCommitURL(
+      gitHubRepository,
+      nonLocalCommitSHA,
+      file.path
+    )
+
+    if (commitURL === null) {
+      return
+    }
+
+    dispatcher.openInBrowser(commitURL)
+  }
+
+  private onFileContextMenu = async (
+    file: CommittedFileChange,
+    event: React.MouseEvent<HTMLDivElement>
+  ) => {
+    event.preventDefault()
+
+    const { repository } = this.props
+
+    const fullPath = Path.join(repository.path, file.path)
+    const fileExistsOnDisk = await pathExists(fullPath)
+    if (!fileExistsOnDisk) {
+      showContextualMenu([
+        {
+          label: __DARWIN__
+            ? 'File Does Not Exist on Disk'
+            : 'File does not exist on disk',
+          enabled: false,
+        },
+      ])
+      return
+    }
+
+    const { externalEditorLabel, dispatcher } = this.props
+
+    const extension = Path.extname(file.path)
+    const isSafeExtension = isSafeFileExtension(extension)
+    const openInExternalEditor =
+      externalEditorLabel !== undefined
+        ? `Open in ${externalEditorLabel}`
+        : DefaultEditorLabel
+
+    const items: IMenuItem[] = [
+      {
+        label: RevealInFileManagerLabel,
+        action: () => revealInFileManager(repository, file.path),
+        enabled: fileExistsOnDisk,
+      },
+      {
+        label: openInExternalEditor,
+        action: () => dispatcher.openInExternalEditor(fullPath),
+        enabled: fileExistsOnDisk,
+      },
+      {
+        label: OpenWithDefaultProgramLabel,
+        action: () => this.onOpenFile(file.path),
+        enabled: isSafeExtension && fileExistsOnDisk,
+      },
+      { type: 'separator' },
+      {
+        label: CopyFilePathLabel,
+        action: () => clipboard.writeText(fullPath),
+      },
+      {
+        label: CopyRelativeFilePathLabel,
+        action: () => clipboard.writeText(Path.normalize(file.path)),
+      },
+      { type: 'separator' },
+    ]
+
+    const { nonLocalCommitSHA } = this.props
+    const { gitHubRepository } = repository
+    const isEnterprise =
+      gitHubRepository && gitHubRepository.endpoint !== getDotComAPIEndpoint()
+
+    items.push({
+      label: `View on GitHub${isEnterprise ? ' Enterprise' : ''}`,
+      action: () => this.onViewOnGitHub(file),
+      enabled: nonLocalCommitSHA !== null && gitHubRepository !== null,
+    })
+
+    showContextualMenu(items)
+  }
+
+  private onFileSelected = (file: CommittedFileChange) => {
+    this.props.dispatcher.changePullRequestFileSelection(
+      this.props.repository,
+      file
+    )
+  }
+
+  private renderHeader() {
+    const { hideWhitespaceInDiff } = this.props
+    const { showSideBySideDiff } = this.state
+    return (
+      <div className="files-changed-header">
+        <div className="commits-displayed">
+          Showing changes from all commits
+        </div>
+        <DiffOptions
+          isInteractiveDiff={false}
+          hideWhitespaceChanges={hideWhitespaceInDiff}
+          onHideWhitespaceChangesChanged={this.onHideWhitespaceInDiffChanged}
+          showSideBySideDiff={showSideBySideDiff}
+          onShowSideBySideDiffChanged={this.onShowSideBySideDiffChanged}
+          onDiffOptionsOpened={this.onDiffOptionsOpened}
+        />
+      </div>
+    )
+  }
+
+  private renderFileList() {
+    const { files, selectedFile, fileListWidth } = this.props
+
+    return (
+      <Resizable
+        width={fileListWidth.value}
+        minimumWidth={fileListWidth.min}
+        maximumWidth={fileListWidth.max}
+        onResize={this.onFileListResize}
+        onReset={this.onFileListSizeReset}
+      >
+        <FileList
+          files={files}
+          onSelectedFileChanged={this.onFileSelected}
+          selectedFile={selectedFile}
+          availableWidth={clamp(fileListWidth)}
+          onContextMenu={this.onFileContextMenu}
+        />
+      </Resizable>
+    )
+  }
+
+  private renderDiff() {
+    const { selectedFile } = this.props
+
+    if (selectedFile === null) {
+      return
+    }
+
+    const { diff, repository, imageDiffType, hideWhitespaceInDiff } = this.props
+
+    const { showSideBySideDiff } = this.state
+
+    return (
+      <SeamlessDiffSwitcher
+        repository={repository}
+        imageDiffType={imageDiffType}
+        file={selectedFile}
+        diff={diff}
+        readOnly={true}
+        hideWhitespaceInDiff={hideWhitespaceInDiff}
+        showSideBySideDiff={showSideBySideDiff}
+        onOpenBinaryFile={this.onOpenBinaryFile}
+        onChangeImageDiffType={this.onChangeImageDiffType}
+        onHideWhitespaceInDiffChanged={this.onHideWhitespaceInDiffChanged}
+      />
+    )
+  }
+
+  public render() {
+    return (
+      <div className="pull-request-files-changed">
+        {this.renderHeader()}
+        <div className="files-diff-viewer">
+          {this.renderFileList()}
+          {this.renderDiff()}
+        </div>
+      </div>
+    )
+  }
+}

app/src/ui/open-pull-request/pull-request-merge-status.tsx

@@ -0,0 +1,68 @@
+import * as React from 'react'
+import { assertNever } from '../../lib/fatal-error'
+import { ComputedAction } from '../../models/computed-action'
+import { MergeTreeResult } from '../../models/merge'
+import { Octicon } from '../octicons'
+import * as OcticonSymbol from '../octicons/octicons.generated'
+
+interface IPullRequestMergeStatusProps {
+  /** The result of merging the pull request branch into the base branch */
+  readonly mergeStatus: MergeTreeResult | null
+}
+
+/** The component to display message about the result of merging the pull
+ * request. */
+export class PullRequestMergeStatus extends React.Component<IPullRequestMergeStatusProps> {
+  private getMergeStatusDescription = () => {
+    const { mergeStatus } = this.props
+    if (mergeStatus === null) {
+      return ''
+    }
+
+    const { kind } = mergeStatus
+    switch (kind) {
+      case ComputedAction.Loading:
+        return (
+          <span className="pr-merge-status-loading">
+            <strong>Checking mergeability&hellip;</strong> Don’t worry, you can
+            still create the pull request.
+          </span>
+        )
+      case ComputedAction.Invalid:
+        return (
+          <span className="pr-merge-status-invalid">
+            <strong>Error checking merge status.</strong> Unable to merge
+            unrelated histories in this repository
+          </span>
+        )
+      case ComputedAction.Clean:
+        return (
+          <span className="pr-merge-status-clean">
+            <strong>
+              <Octicon symbol={OcticonSymbol.check} /> Able to merge.
+            </strong>{' '}
+            These branches can be automatically merged.
+          </span>
+        )
+      case ComputedAction.Conflicts:
+        return (
+          <span className="pr-merge-status-conflicts">
+            <strong>
+              <Octicon symbol={OcticonSymbol.x} /> Can't automatically merge.
+            </strong>{' '}
+            Don’t worry, you can still create the pull request.
+          </span>
+        )
+      default:
+        return assertNever(kind, `Unknown merge status kind of ${kind}.`)
+    }
+  }
+
+  public render() {
+    return (
+      <div className="pull-request-merge-status">
+        {this.getMergeStatusDescription()}
+      </div>
+    )
+  }
+}

app/src/ui/preferences/preferences.tsx

@@ -54,6 +54,7 @@ interface IPreferencesProps {
   readonly confirmRepositoryRemoval: boolean
   readonly confirmDiscardChanges: boolean
   readonly confirmDiscardChangesPermanently: boolean
+  readonly confirmDiscardStash: boolean
   readonly confirmForcePush: boolean
   readonly confirmUndoCommit: boolean
   readonly uncommittedChangesStrategy: UncommittedChangesStrategy
@@ -79,6 +80,7 @@ interface IPreferencesState {
   readonly confirmRepositoryRemoval: boolean
   readonly confirmDiscardChanges: boolean
   readonly confirmDiscardChangesPermanently: boolean
+  readonly confirmDiscardStash: boolean
   readonly confirmForcePush: boolean
   readonly confirmUndoCommit: boolean
   readonly uncommittedChangesStrategy: UncommittedChangesStrategy
@@ -121,6 +123,7 @@ export class Preferences extends React.Component<
       confirmRepositoryRemoval: false,
       confirmDiscardChanges: false,
       confirmDiscardChangesPermanently: false,
+      confirmDiscardStash: false,
       confirmForcePush: false,
       confirmUndoCommit: false,
       uncommittedChangesStrategy: defaultUncommittedChangesStrategy,
@@ -178,6 +181,7 @@ export class Preferences extends React.Component<
       confirmDiscardChanges: this.props.confirmDiscardChanges,
       confirmDiscardChangesPermanently:
         this.props.confirmDiscardChangesPermanently,
+      confirmDiscardStash: this.props.confirmDiscardStash,
       confirmForcePush: this.props.confirmForcePush,
       confirmUndoCommit: this.props.confirmUndoCommit,
       uncommittedChangesStrategy: this.props.uncommittedChangesStrategy,
@@ -333,12 +337,14 @@ export class Preferences extends React.Component<
             confirmDiscardChangesPermanently={
               this.state.confirmDiscardChangesPermanently
             }
+            confirmDiscardStash={this.state.confirmDiscardStash}
             confirmForcePush={this.state.confirmForcePush}
             confirmUndoCommit={this.state.confirmUndoCommit}
             onConfirmRepositoryRemovalChanged={
               this.onConfirmRepositoryRemovalChanged
             }
             onConfirmDiscardChangesChanged={this.onConfirmDiscardChangesChanged}
+            onConfirmDiscardStashChanged={this.onConfirmDiscardStashChanged}
             onConfirmForcePushChanged={this.onConfirmForcePushChanged}
             onConfirmDiscardChangesPermanentlyChanged={
               this.onConfirmDiscardChangesPermanentlyChanged
@@ -410,6 +416,10 @@ export class Preferences extends React.Component<
     this.setState({ confirmDiscardChanges: value })
   }
 
+  private onConfirmDiscardStashChanged = (value: boolean) => {
+    this.setState({ confirmDiscardStash: value })
+  }
+
   private onConfirmDiscardChangesPermanentlyChanged = (value: boolean) => {
     this.setState({ confirmDiscardChangesPermanently: value })
   }
@@ -562,6 +572,10 @@ export class Preferences extends React.Component<
       this.state.confirmForcePush
     )
 
+    await this.props.dispatcher.setConfirmDiscardStashSetting(
+      this.state.confirmDiscardStash
+    )
+
     await this.props.dispatcher.setConfirmUndoCommitSetting(
       this.state.confirmUndoCommit
     )

app/src/ui/preferences/prompts.tsx

@@ -6,10 +6,12 @@ interface IPromptsPreferencesProps {
   readonly confirmRepositoryRemoval: boolean
   readonly confirmDiscardChanges: boolean
   readonly confirmDiscardChangesPermanently: boolean
+  readonly confirmDiscardStash: boolean
   readonly confirmForcePush: boolean
   readonly confirmUndoCommit: boolean
   readonly onConfirmDiscardChangesChanged: (checked: boolean) => void
   readonly onConfirmDiscardChangesPermanentlyChanged: (checked: boolean) => void
+  readonly onConfirmDiscardStashChanged: (checked: boolean) => void
   readonly onConfirmRepositoryRemovalChanged: (checked: boolean) => void
   readonly onConfirmForcePushChanged: (checked: boolean) => void
   readonly onConfirmUndoCommitChanged: (checked: boolean) => void
@@ -19,6 +21,7 @@ interface IPromptsPreferencesState {
   readonly confirmRepositoryRemoval: boolean
   readonly confirmDiscardChanges: boolean
   readonly confirmDiscardChangesPermanently: boolean
+  readonly confirmDiscardStash: boolean
   readonly confirmForcePush: boolean
   readonly confirmUndoCommit: boolean
 }
@@ -35,6 +38,7 @@ export class Prompts extends React.Component<
       confirmDiscardChanges: this.props.confirmDiscardChanges,
       confirmDiscardChangesPermanently:
         this.props.confirmDiscardChangesPermanently,
+      confirmDiscardStash: this.props.confirmDiscardStash,
       confirmForcePush: this.props.confirmForcePush,
       confirmUndoCommit: this.props.confirmUndoCommit,
     }
@@ -58,6 +62,15 @@ export class Prompts extends React.Component<
     this.props.onConfirmDiscardChangesPermanentlyChanged(value)
   }
 
+  private onConfirmDiscardStashChanged = (
+    event: React.FormEvent<HTMLInputElement>
+  ) => {
+    const value = event.currentTarget.checked
+
+    this.setState({ confirmDiscardStash: value })
+    this.props.onConfirmDiscardStashChanged(value)
+  }
+
   private onConfirmForcePushChanged = (
     event: React.FormEvent<HTMLInputElement>
   ) => {
@@ -116,6 +129,15 @@ export class Prompts extends React.Component<
           }
           onChange={this.onConfirmDiscardChangesPermanentlyChanged}
         />
+        <Checkbox
+          label="Discarding stash"
+          value={
+            this.state.confirmDiscardStash
+              ? CheckboxValue.On
+              : CheckboxValue.Off
+          }
+          onChange={this.onConfirmDiscardStashChanged}
+        />
         <Checkbox
           label="Force pushing"
           value={

app/src/ui/repository.tsx

@@ -50,6 +50,7 @@ interface IRepositoryViewProps {
   readonly hideWhitespaceInHistoryDiff: boolean
   readonly showSideBySideDiff: boolean
   readonly askForConfirmationOnDiscardChanges: boolean
+  readonly askForConfirmationOnDiscardStash: boolean
   readonly focusCommitMessage: boolean
   readonly commitSpellcheckEnabled: boolean
   readonly accounts: ReadonlyArray<Account>
@@ -355,6 +356,9 @@ export class RepositoryView extends React.Component<
           fileListWidth={this.props.stashedFilesWidth}
           repository={this.props.repository}
           dispatcher={this.props.dispatcher}
+          askForConfirmationOnDiscardStash={
+            this.props.askForConfirmationOnDiscardStash
+          }
           isWorkingTreeClean={isWorkingTreeClean}
           showSideBySideDiff={this.props.showSideBySideDiff}
           onOpenBinaryFile={this.onOpenBinaryFile}

app/src/ui/stashing/confirm-discard-stash.tsx

@@ -5,16 +5,19 @@ import { Dispatcher } from '../dispatcher'
 import { Row } from '../lib/row'
 import { IStashEntry } from '../../models/stash-entry'
 import { OkCancelButtonGroup } from '../dialog/ok-cancel-button-group'
+import { Checkbox, CheckboxValue } from '../lib/checkbox'
 
 interface IConfirmDiscardStashProps {
   readonly dispatcher: Dispatcher
   readonly repository: Repository
   readonly stash: IStashEntry
+  readonly askForConfirmationOnDiscardStash: boolean
   readonly onDismissed: () => void
 }
 
 interface IConfirmDiscardStashState {
   readonly isDiscarding: boolean
+  readonly confirmDiscardStash: boolean
 }
 /**
  * Dialog to confirm dropping a stash
@@ -28,6 +31,7 @@ export class ConfirmDiscardStashDialog extends React.Component<
 
     this.state = {
       isDiscarding: false,
+      confirmDiscardStash: props.askForConfirmationOnDiscardStash,
     }
   }
 
@@ -46,6 +50,17 @@ export class ConfirmDiscardStashDialog extends React.Component<
       >
         <DialogContent>
           <Row>Are you sure you want to discard these stashed changes?</Row>
+          <Row>
+            <Checkbox
+              label="Do not show this message again"
+              value={
+                this.state.confirmDiscardStash
+                  ? CheckboxValue.Off
+                  : CheckboxValue.On
+              }
+              onChange={this.onAskForConfirmationOnDiscardStashChanged}
+            />
+          </Row>
         </DialogContent>
         <DialogFooter>
           <OkCancelButtonGroup destructive={true} okButtonText="Discard" />
@@ -54,6 +69,14 @@ export class ConfirmDiscardStashDialog extends React.Component<
     )
   }
 
+  private onAskForConfirmationOnDiscardStashChanged = (
+    event: React.FormEvent<HTMLInputElement>
+  ) => {
+    const value = !event.currentTarget.checked
+
+    this.setState({ confirmDiscardStash: value })
+  }
+
   private onSubmit = async () => {
     const { dispatcher, repository, stash, onDismissed } = this.props
 
@@ -62,6 +85,7 @@ export class ConfirmDiscardStashDialog extends React.Component<
     })
 
     try {
+      dispatcher.setConfirmDiscardStashSetting(this.state.confirmDiscardStash)
       await dispatcher.dropStash(repository, stash)
     } finally {
       this.setState({

app/src/ui/stashing/stash-diff-header.tsx

@@ -11,11 +11,13 @@ interface IStashDiffHeaderProps {
   readonly stashEntry: IStashEntry
   readonly repository: Repository
   readonly dispatcher: Dispatcher
+  readonly askForConfirmationOnDiscardStash: boolean
   readonly isWorkingTreeClean: boolean
 }
 
 interface IStashDiffHeaderState {
   readonly isRestoring: boolean
+  readonly isDiscarding: boolean
 }
 
 /**
@@ -31,12 +33,13 @@ export class StashDiffHeader extends React.Component<
 
     this.state = {
       isRestoring: false,
+      isDiscarding: false,
     }
   }
 
   public render() {
     const { isWorkingTreeClean } = this.props
-    const { isRestoring } = this.state
+    const { isRestoring, isDiscarding } = this.state
 
     return (
       <div className="header">
@@ -44,10 +47,12 @@ export class StashDiffHeader extends React.Component<
         <div className="row">
           <OkCancelButtonGroup
             okButtonText="Restore"
-            okButtonDisabled={isRestoring || !isWorkingTreeClean}
+            okButtonDisabled={
+              isRestoring || !isWorkingTreeClean || isDiscarding
+            }
             onOkButtonClick={this.onRestoreClick}
             cancelButtonText="Discard"
-            cancelButtonDisabled={isRestoring}
+            cancelButtonDisabled={isRestoring || isDiscarding}
             onCancelButtonClick={this.onDiscardClick}
           />
           {this.renderExplanatoryText()}
@@ -80,13 +85,33 @@ export class StashDiffHeader extends React.Component<
     )
   }
 
-  private onDiscardClick = () => {
-    const { dispatcher, repository, stashEntry } = this.props
-    dispatcher.showPopup({
-      type: PopupType.ConfirmDiscardStash,
-      stash: stashEntry,
+  private onDiscardClick = async () => {
+    const {
+      dispatcher,
       repository,
-    })
+      stashEntry,
+      askForConfirmationOnDiscardStash,
+    } = this.props
+
+    if (!askForConfirmationOnDiscardStash) {
+      this.setState({
+        isDiscarding: true,
+      })
+
+      try {
+        await dispatcher.dropStash(repository, stashEntry)
+      } finally {
+        this.setState({
+          isDiscarding: false,
+        })
+      }
+    } else {
+      dispatcher.showPopup({
+        type: PopupType.ConfirmDiscardStash,
+        stash: stashEntry,
+        repository,
+      })
+    }
   }
 
   private onRestoreClick = async () => {

app/src/ui/stashing/stash-diff-viewer.tsx

@@ -27,6 +27,9 @@ interface IStashDiffViewerProps {
   readonly repository: Repository
   readonly dispatcher: Dispatcher
 
+  /** Should the app propt the user to confirm a discard stash */
+  readonly askForConfirmationOnDiscardStash: boolean
+
   /** Whether we should display side by side diffs. */
   readonly showSideBySideDiff: boolean
 
@@ -113,6 +116,9 @@ export class StashDiffViewer extends React.PureComponent<IStashDiffViewerProps>
           repository={repository}
           dispatcher={dispatcher}
           isWorkingTreeClean={isWorkingTreeClean}
+          askForConfirmationOnDiscardStash={
+            this.props.askForConfirmationOnDiscardStash
+          }
         />
         <div className="commit-details">
           <Resizable

app/styles/_ui.scss

@@ -99,4 +99,7 @@
 @import 'ui/_pull-request-quick-view';
 @import 'ui/discard-changes-retry';
 @import 'ui/_git-email-not-found-warning';
-@import 'ui/_branch-select.scss';
+@import 'ui/_branch-select';
+@import 'ui/_popover-dropdown';
+@import 'ui/_pull-request-files-changed';
+@import 'ui/_pull-request-merge-status';

app/styles/ui/_branch-select.scss

@@ -1,66 +0,0 @@
-.branch-select-component {
-  display: inline-flex;
-
-  .base-label {
-    font-weight: var(--font-weight-semibold);
-    color: var(--text-secondary-color);
-    margin: 0 var(--spacing-half);
-  }
-
-  button {
-    border: none;
-    background-color: inherit;
-    border: none;
-    padding: 0;
-    margin: 0;
-    font-style: normal;
-    font-family: var(--font-family-monospace);
-
-    .ref-component {
-      padding: 1px;
-    }
-
-    &.button-component {
-      overflow: visible;
-
-      &:hover,
-      &:focus {
-        border: none;
-        box-shadow: none;
-
-        .ref-component {
-          border-color: var(--path-segment-background-focus);
-          box-shadow: 0 0 0 1px var(--path-segment-background-focus);
-        }
-      }
-    }
-  }
-
-  .ref-component {
-    display: inline-flex;
-    align-items: center;
-  }
-
-  .branch-select-dropdown {
-    position: absolute;
-    min-height: 200px;
-    width: 365px;
-    padding: 0;
-    margin-top: 25px;
-
-    .branch-select-dropdown-header {
-      padding: var(--spacing);
-      font-weight: var(--font-weight-semibold);
-      display: flex;
-      border-bottom: var(--base-border);
-
-      .close {
-        margin-right: 0;
-      }
-    }
-
-    .branch-select-dropdown-list {
-      display: flex;
-    }
-  }
-}

app/styles/ui/_popover-dropdown.scss

@@ -0,0 +1,36 @@
+.popover-dropdown-component {
+  display: inline-flex;
+
+  .button-content,
+  .popover-dropdown-button-label {
+    font-weight: var(--font-weight-semibold);
+  }
+
+  .popover-dropdown-button-label {
+    color: var(--text-secondary-color);
+    margin: 0 var(--spacing-half);
+  }
+
+  .popover-dropdown-popover {
+    position: absolute;
+    min-height: 200px;
+    width: 365px;
+    padding: 0;
+    margin-top: 25px;
+
+    .popover-dropdown-header {
+      padding: var(--spacing);
+      font-weight: var(--font-weight-semibold);
+      display: flex;
+      border-bottom: var(--base-border);
+
+      .close {
+        margin-right: 0;
+      }
+    }
+
+    .popover-dropdown-content {
+      display: flex;
+    }
+  }
+}

app/styles/ui/_pull-request-files-changed.scss

@@ -0,0 +1,23 @@
+.pull-request-files-changed {
+  border: var(--base-border);
+  border-radius: var(--border-radius);
+
+  .files-changed-header {
+    padding: var(--spacing);
+    border-bottom: var(--base-border);
+    display: flex;
+
+    .commits-displayed {
+      flex-grow: 1;
+    }
+  }
+
+  .files-diff-viewer {
+    height: 500px;
+    display: flex;
+  }
+
+  .file-list {
+    border-right: var(--base-border);
+  }
+}

app/styles/ui/_pull-request-merge-status.scss

@@ -0,0 +1,31 @@
+.pull-request-merge-status {
+  flex-grow: 1;
+  color: var(--text-secondary-color);
+
+  .octicon {
+    vertical-align: text-bottom;
+  }
+
+  strong {
+    font-weight: var(--font-weight-semibold);
+  }
+
+  .pr-merge-status-loading {
+    strong {
+      color: var(--file-warning-color);
+    }
+  }
+
+  .pr-merge-status-invalid,
+  .pr-merge-status-conflicts {
+    strong {
+      color: var(--status-error-color);
+    }
+  }
+
+  .pr-merge-status-clean {
+    strong {
+      color: var(--status-success-color);
+    }
+  }
+}

app/styles/ui/dialogs/_open-pull-request.scss

@@ -1,4 +1,7 @@
 .open-pull-request {
+  width: 850px;
+  max-width: none;
+
   header.dialog-header {
     padding-bottom: var(--spacing);
 
@@ -15,4 +18,25 @@
       padding: var(--spacing-half);
     }
   }
+
+  .open-pull-request-content {
+    padding: var(--spacing);
+  }
+
+  .open-pull-request-no-changes {
+    height: 100%;
+    display: flex;
+    align-items: center;
+    text-align: center;
+    justify-content: center;
+    padding: var(--spacing-double);
+  }
+
+  .dialog-footer {
+    flex-direction: row;
+  }
+
+  .pull-request-merge-status {
+    flex-grow: 1;
+  }
 }

app/styles/ui/window/_tooltips.scss

@@ -11,6 +11,7 @@ body > .tooltip,
   max-width: 300px;
 
   word-wrap: break-word;
+  word-break: break-word;
   overflow-wrap: break-word;
 
   background-color: var(--tooltip-background-color);

app/test/unit/git/diff-test.ts

@@ -575,9 +575,38 @@ describe('git/diff', () => {
         'feature-branch',
         'irrelevantToTest'
       )
+
+      expect(changesetData).not.toBeNull()
+      if (changesetData === null) {
+        return
+      }
+
       expect(changesetData.files).toHaveLength(1)
       expect(changesetData.files[0].path).toBe('feature.md')
     })
+
+    it('returns null for unrelated histories', async () => {
+      // create a second branch that's orphaned from our current branch
+      await GitProcess.exec(
+        ['checkout', '--orphan', 'orphaned-branch'],
+        repository.path
+      )
+
+      // add a commit to this new branch
+      await GitProcess.exec(
+        ['commit', '--allow-empty', '-m', `first commit on gh-pages`],
+        repository.path
+      )
+
+      const changesetData = await getBranchMergeBaseChangedFiles(
+        repository,
+        'master',
+        'feature-branch',
+        'irrelevantToTest'
+      )
+
+      expect(changesetData).toBeNull()
+    })
   })
 
   describe('getBranchMergeBaseDiff', () => {

changelog.json

@@ -1,6 +1,12 @@
 {
   "releases": {
     "3.1.2": ["[Improved] Upgrade embedded Git to 2.35.5"],
+    "3.1.2-beta1": [
+      "[Added] You can preview the changes a pull request from your current branch would make - #11517",
+      "[Fixed] App correctly remembers undo commit prompt setting - #15408",
+      "[Improved] Add support for zooming out at the 67%, 75%, 80% and 90% zoom levels - #15401. Thanks @sathvikrijo!",
+      "[Improved] Add option to disable discard stash confirmation - #15379. Thanks @tsvetilian-ty!"
+    ],
     "3.1.1": [
       "[Fixed] App correctly remembers undo commit prompt setting - #15408"
     ],

docs/contributing/setup.md

@@ -19,13 +19,13 @@ versions look similar to the below output:
 
 ```shellsession
 $ node -v
-v10.15.4
+v16.13.0
 
 $ yarn -v
-1.15.2
+1.21.1
 
 $ python --version
-Python 2.7.15
+Python 3.9.x
 ```
 
 There are also [additional resources](tooling.md) to configure your favorite

script/package.ts

@@ -102,7 +102,11 @@ function packageWindows() {
   }
 
   if (shouldMakeDelta()) {
-    options.remoteReleases = getUpdatesURL()
+    const url = new URL(getUpdatesURL())
+    // Make sure Squirrel.Windows isn't affected by partially or completely
+    // disabled releases.
+    url.searchParams.set('bypassStaggeredRelease', '1')
+    options.remoteReleases = url.toString()
   }
 
   if (isAppveyor() || isGitHubActions()) {