Adds error messages for failed operations

Adds showHistory command support to CodeLens
Fixes and improve the showHistory explorer
Refactoring

src/commands/diffLineWithPrevious.ts

@@ -0,0 +1,52 @@
+'use strict';
+import { commands, TextEditor, TextEditorEdit, Uri, window } from 'vscode';
+import { EditorCommand } from './commands';
+import { Commands } from '../constants';
+import GitProvider, { GitCommit } from '../gitProvider';
+import { Logger } from '../logger';
+
+export default class DiffLineWithPreviousCommand extends EditorCommand {
+    constructor(private git: GitProvider) {
+        super(Commands.DiffLineWithPrevious);
+    }
+
+    async execute(editor: TextEditor, edit: TextEditorEdit): Promise<any>;
+    async execute(editor: TextEditor, edit: TextEditorEdit, uri?: Uri, commit?: GitCommit, line?: number): Promise<any> {
+        line = line || editor.selection.active.line;
+
+        if (!commit || GitProvider.isUncommitted(commit.sha)) {
+            if (!(uri instanceof Uri)) {
+                if (!editor.document) return undefined;
+                uri = editor.document.uri;
+            }
+
+            try {
+                const blame = await this.git.getBlameForLine(uri.fsPath, line);
+                if (!blame) return window.showWarningMessage(`Unable to open diff. File is probably not under source control`);
+
+                // If the line is uncommitted, find the previous commit
+                commit = blame.commit;
+                if (commit.isUncommitted) {
+                    try {
+                        const prevBlame = await this.git.getBlameForLine(commit.previousUri.fsPath, blame.line.originalLine + 1, commit.previousSha, commit.repoPath);
+                        if (!prevBlame) return undefined;
+
+                        const prevCommit = prevBlame.commit;
+                        commit = new GitCommit(commit.repoPath, commit.sha, commit.fileName, commit.author, commit.date, commit.message, commit.lines, commit.originalFileName, prevCommit.sha, prevCommit.fileName);
+                        line = blame.line.originalLine + 1;
+                    }
+                    catch (ex) {
+                        Logger.error('[GitLens.DiffWithPreviousLineCommand]', `getBlameForLine(${blame.line.originalLine}, ${commit.previousSha})`, ex);
+                        return window.showErrorMessage(`Unable to open diff. See output channel for more details`);
+                    }
+                }
+            }
+            catch (ex) {
+                Logger.error('[GitLens.DiffWithPreviousLineCommand]', `getBlameForLine(${line})`, ex);
+                return window.showErrorMessage(`Unable to open diff. See output channel for more details`);
+            }
+        }
+
+        return commands.executeCommand(Commands.DiffWithPrevious, commit.uri, commit, line);
+    }
+}