add compare with master command

package.json

@@ -15,6 +15,11 @@
         "category": "Git",
         "command": "git-differ.compareWithCommit",
         "title": "Git Differ: Compare with Commit"
+      },
+      {
+        "category": "Git",
+        "command": "git-differ.compareWithMaster",
+        "title": "Git Differ: Compare with Master"
       }
     ],
     "configuration": {
@@ -43,6 +48,11 @@
           "command": "git-differ.compareWithCommit",
           "group": "Git@15",
           "when": "!explorerResourceIsFolder"
+        },
+        {
+          "command": "git-differ.compareWithMaster",
+          "group": "Git@15",
+          "when": "!explorerResourceIsFolder"
         }
       ],
       "editor/title/context": [
@@ -55,6 +65,11 @@
           "command": "git-differ.compareWithCommit",
           "group": "Git@15",
           "when": "true"
+        },
+        {
+          "command": "git-differ.compareWithMaster",
+          "group": "Git@15",
+          "when": "true"
         }
       ]
     }

src/cmd/compareWithBranch.ts

@@ -9,6 +9,39 @@ type Branch = {
   remote?: string;
 };
 
+export async function executeDiffComparison(
+  gitApi: API,
+  uri: vscode.Uri,
+  branchName: string
+): Promise<void> {
+  const gitUri = gitApi.toGitUri(uri, branchName);
+  const filePath = uri.path.split("/").pop() || uri.path;
+
+  await vscode.commands.executeCommand("vscode.diff", gitUri, uri, `${branchName} ↔ ${filePath}`);
+}
+
+export async function findMasterBranch(gitApi: API, uri: vscode.Uri): Promise<Branch | null> {
+  try {
+    const localBranches = await getBranches(gitApi, uri, false);
+
+    let masterBranch = localBranches.find((branch) => branch.name === "master");
+    if (!masterBranch) {
+      masterBranch = localBranches.find((branch) => branch.name === "main");
+    }
+
+    if (!masterBranch) {
+      const remoteBranches = await getBranches(gitApi, uri, true);
+      masterBranch = remoteBranches.find(
+        (branch) => branch.name === "origin/master" || branch.name === "origin/main"
+      );
+    }
+
+    return masterBranch || null;
+  } catch (error) {
+    return null;
+  }
+}
+
 export function newCompareWithBranch(gitApi: API): vscode.Disposable {
   return vscode.commands.registerCommand(
     "git-differ.compareWithBranch",
@@ -47,15 +80,11 @@ export function newCompareWithBranch(gitApi: API): vscode.Disposable {
         return;
       }
 
-      const gitUri = gitApi.toGitUri(uri, branch.name);
-      const filePath = uri.path.split("/").pop() || uri.path;
-
-      vscode.commands.executeCommand(
-        "vscode.diff",
-        gitUri,
-        uri,
-        `${branch.name} compared with "${filePath}"`
-      );
+      try {
+        await executeDiffComparison(gitApi, uri, branch.name);
+      } catch (error) {
+        vscode.window.showErrorMessage(`An error occurred: ${error}`);
+      }
     }
   );
 }

src/cmd/compareWithMaster.ts

@@ -0,0 +1,31 @@
+import * as vscode from "vscode";
+import { API } from "../git";
+import { findMasterBranch, executeDiffComparison } from "./compareWithBranch";
+
+export function newCompareWithMaster(gitApi: API): vscode.Disposable {
+  return vscode.commands.registerCommand(
+    "git-differ.compareWithMaster",
+    async (uri: vscode.Uri | undefined) => {
+      if (!uri) {
+        uri = vscode.window.activeTextEditor?.document.uri;
+      }
+      if (!uri) {
+        vscode.window.showErrorMessage("No file selected");
+        return;
+      }
+
+      try {
+        const masterBranch = await findMasterBranch(gitApi, uri);
+
+        if (!masterBranch || !masterBranch.name) {
+          vscode.window.showErrorMessage("Could not find master or main branch");
+          return;
+        }
+
+        await executeDiffComparison(gitApi, uri, masterBranch.name);
+      } catch (error) {
+        vscode.window.showErrorMessage(`An error occurred: ${error}`);
+      }
+    }
+  );
+}

src/extension.ts

@@ -1,17 +1,18 @@
 import * as vscode from "vscode";
 import { newCompareWithBranch } from "./cmd/compareWithBranch";
 import { newCompareWithCommit } from "./cmd/compareWithCommit";
+import { newCompareWithMaster } from "./cmd/compareWithMaster";
 import { API, GitExtension } from "./git";
 
 export function activate(context: vscode.ExtensionContext) {
   const gitExtension = vscode.extensions.getExtension<GitExtension>("vscode.git")!.exports;
   const gitApi: API = gitExtension.getAPI(1);
 
   const compareWithCommit = newCompareWithCommit(gitApi);
-
   const compareWithBranch = newCompareWithBranch(gitApi);
+  const compareWithMaster = newCompareWithMaster(gitApi);
 
-  context.subscriptions.push(compareWithBranch, compareWithCommit);
+  context.subscriptions.push(compareWithBranch, compareWithCommit, compareWithMaster);
 }
 
 export function deactivate() {}