add "open old file" git command

this implements #23011

extensions/git/package.json

@@ -59,6 +59,11 @@
           "dark": "resources/icons/dark/open-file.svg"
         }
       },
+      {
+        "command": "git.openOldFile",
+        "title": "%command.openOldFile%",
+        "category": "Git"
+      },
       {
         "command": "git.stage",
         "title": "%command.stage%",
@@ -226,6 +231,10 @@
           "command": "git.openFile",
           "when": "config.git.enabled && scmProvider == git && gitState == idle"
         },
+        {
+          "command": "git.openOldFile",
+          "when": "config.git.enabled && scmProvider == git && gitState == idle"
+        },
         {
           "command": "git.openChange",
           "when": "config.git.enabled && scmProvider == git && gitState == idle"
@@ -477,6 +486,11 @@
           "when": "config.git.enabled && scmProvider == git && gitState == idle && scmResourceGroup == index",
           "group": "navigation"
         },
+        {
+          "command": "git.openOldFile",
+          "when": "config.git.enabled && scmProvider == git && gitState == idle && scmResourceGroup == index",
+          "group": "navigation"
+        },
         {
           "command": "git.unstage",
           "when": "config.git.enabled && scmProvider == git && gitState == idle && scmResourceGroup == index",
@@ -492,6 +506,11 @@
           "when": "config.git.enabled && scmProvider == git && gitState == idle && scmResourceGroup == workingTree",
           "group": "navigation"
         },
+        {
+          "command": "git.openOldFile",
+          "when": "config.git.enabled && scmProvider == git && gitState == idle && scmResourceGroup == workingTree",
+          "group": "navigation"
+        },
         {
           "command": "git.openFile",
           "when": "config.git.enabled && scmProvider == git && gitState == idle && scmResourceGroup == workingTree",

extensions/git/package.nls.json

@@ -4,6 +4,7 @@
 	"command.refresh": "Refresh",
 	"command.openChange": "Open Changes",
 	"command.openFile": "Open File",
+	"command.openOldFile": "Open Old File",
 	"command.stage": "Stage Changes",
 	"command.stageAll": "Stage All Changes",
 	"command.stageSelectedRanges": "Stage Selected Ranges",

extensions/git/src/commands.ts

@@ -275,6 +275,35 @@ export class CommandCenter {
 		return await commands.executeCommand<void>('vscode.open', uri);
 	}
 
+	@command('git.openOldFile')
+	async openOldFile(arg?: Resource | Uri): Promise<void> {
+		let resource: Resource | undefined = undefined;
+
+		if (arg instanceof Resource) {
+			resource = arg;
+
+		} else if (arg instanceof Uri) {
+			resource = this.getSCMResource(arg);
+		} else {
+			resource = this.getSCMResource();
+		}
+
+		if (!resource) {
+			return;
+		}
+		return await this._openOldResource(resource);
+	}
+
+	private async _openOldResource(resource: Resource): Promise<void> {
+		const old = this.getLeftResource(resource);
+		const current = this.getRightResource(resource);
+
+		if (!old) {
+			return await commands.executeCommand<void>('vscode.open', current);
+		}
+		return await commands.executeCommand<void>('vscode.open', old);
+	}
+
 	@command('git.openChange')
 	async openChange(arg?: Resource | Uri): Promise<void> {
 		let resource: Resource | undefined = undefined;
@@ -290,7 +319,6 @@ export class CommandCenter {
 		if (!resource) {
 			return;
 		}
-
 		return await this._openResource(resource);
 	}