Adds compare with branch command

Adds branches quick pick

src/commands/diffWithBranch.ts

@@ -0,0 +1,47 @@
+'use strict';
+import { commands, TextEditor, Uri, window } from 'vscode';
+import { ActiveEditorCommand, Commands } from './commands';
+import { BuiltInCommands } from '../constants';
+import { GitService, GitUri } from '../gitService';
+import { Logger } from '../logger';
+import { CommandQuickPickItem, BranchesQuickPick } from '../quickPicks';
+import * as path from 'path';
+
+export class DiffWithBranchCommand extends ActiveEditorCommand {
+
+    constructor(private git: GitService) {
+        super(Commands.DiffWithBranch);
+    }
+
+    async execute(editor: TextEditor, uri?: Uri, goBackCommand?: CommandQuickPickItem): Promise<any> {
+        if (!(uri instanceof Uri)) {
+            if (!editor || !editor.document) return undefined;
+            uri = editor.document.uri;
+        }
+
+        const line = (editor && editor.selection.active.line) || 0;
+
+        const gitUri = await GitUri.fromUri(uri, this.git);
+
+        const branches = await this.git.getBranches(gitUri.repoPath);
+        const pick = await BranchesQuickPick.show(branches, gitUri, goBackCommand);
+        if (!pick) return undefined;
+
+        if (pick instanceof CommandQuickPickItem) {
+            return pick.execute();
+        }
+
+        const branch = pick.branch.name;
+        if (!branch) return undefined;
+
+        try {
+            const compare = await this.git.getVersionedFile(gitUri.repoPath, gitUri.fsPath, branch);
+            await commands.executeCommand(BuiltInCommands.Diff, Uri.file(compare), gitUri.fileUri(), `${path.basename(gitUri.fsPath)} (${branch}) ↔ ${path.basename(gitUri.fsPath)}`);
+            return await commands.executeCommand(BuiltInCommands.RevealLine, { lineNumber: line, at: 'center' });
+        }
+        catch (ex) {
+            Logger.error('[GitLens.DiffWithBranchCommand]', 'getVersionedFile', ex);
+            return window.showErrorMessage(`Unable to open diff. See output channel for more details`);
+        }
+    }
+}