feat(git): Implement git checkout

For now this only lets you check out branches, not files.

packages/git/src/subcommands/__exports__.js

@@ -19,6 +19,7 @@
 // Generated by /tools/gen.js
 import module_add from './add.js'
 import module_branch from './branch.js'
+import module_checkout from './checkout.js'
 import module_clone from './clone.js'
 import module_commit from './commit.js'
 import module_config from './config.js'
@@ -34,6 +35,7 @@ import module_version from './version.js'
 export default {
     "add": module_add,
     "branch": module_branch,
+    "checkout": module_checkout,
     "clone": module_clone,
     "commit": module_commit,
     "config": module_config,

packages/git/src/subcommands/checkout.js

@@ -0,0 +1,155 @@
+/*
+ * Copyright (C) 2024  Puter Technologies Inc.
+ *
+ * This file is part of Puter's Git client.
+ *
+ * Puter's Git client is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+import git from 'isomorphic-git';
+import { find_repo_root } from '../git-helpers.js';
+import { SHOW_USAGE } from '../help.js';
+
+const CHECKOUT = {
+    name: 'checkout',
+    usage: [
+        'git checkout [--force] <branch>',
+        'git checkout (-b | -B) [--force] <new-branch> [<start-point>]',
+    ],
+    description: `Switch branches.`,
+    args: {
+        allowPositionals: true,
+        tokens: true,
+        strict: false,
+        options: {
+            'new-branch': {
+                description: 'Create a new branch and then check it out.',
+                type: 'boolean',
+                short: 'b',
+                default: false,
+            },
+            'force': {
+                description: 'Perform the checkout forcefully. For --new-branch, ignores whether the branch already exists. For checking out branches, ignores and overwrites any unstaged changes.',
+                type: 'boolean',
+                short: 'f',
+            },
+        },
+    },
+    execute: async (ctx) => {
+        const { io, fs, env, args } = ctx;
+        const { stdout, stderr } = io;
+        const { options, positionals, tokens } = args;
+        const cache = {};
+
+        for (const token of tokens) {
+            if (token.kind !== 'option') continue;
+
+            if (token.name === 'B') {
+                options['new-branch'] = true;
+                options.force = true;
+                delete options['B'];
+                continue;
+            }
+
+            // Report any options that we don't recognize
+            let option_recognized = false;
+            for (const [key, value] of Object.entries(CHECKOUT.args.options)) {
+                if (key === token.name || value.short === token.name) {
+                    option_recognized = true;
+                    break;
+                }
+            }
+            if (!option_recognized) {
+                stderr(`Unrecognized option: ${token.rawName}`);
+                throw SHOW_USAGE;
+            }
+        }
+
+        const { repository_dir, git_dir } = await find_repo_root(fs, env.PWD);
+
+        // DRY: Copied from branch.js
+        const get_current_branch = async () => git.currentBranch({
+            fs,
+            dir: repository_dir,
+            gitdir: git_dir,
+            test: true,
+        });
+        const get_all_branches = async () => git.listBranches({
+            fs,
+            dir: repository_dir,
+            gitdir: git_dir,
+        });
+        const get_branch_data = async () => {
+            const [branches, current_branch] = await Promise.all([
+                get_all_branches(),
+                get_current_branch(),
+            ]);
+            return { branches, current_branch };
+        }
+
+        if (options['new-branch']) {
+            const { branches, current_branch } = await get_branch_data();
+            if (positionals.length === 0 || positionals.length > 2) {
+                stderr('error: Expected 1 or 2 arguments, for <new-branch> [<start-point>].');
+                throw SHOW_USAGE;
+            }
+            const branch_name = positionals.shift();
+            const starting_point = positionals.shift() ?? current_branch;
+
+            if (branches.includes(branch_name) && !options.force)
+                throw new Error(`A branch named '${branch_name}' already exists.`);
+
+            await git.branch({
+                fs,
+                dir: repository_dir,
+                gitdir: git_dir,
+                ref: branch_name,
+                object: starting_point,
+                checkout: true,
+                force: options.force,
+            });
+            stdout(`Switched to a new branch '${branch_name}'`);
+            return;
+        }
+
+        // Check out a branch
+        // TODO: Check out files.
+        {
+            if (positionals.length === 0 || positionals.length > 1) {
+                stderr('error: Expected 1 argument, for <branch>.');
+                throw SHOW_USAGE;
+            }
+            const { branches, current_branch } = await get_branch_data();
+            const branch_name = positionals.shift();
+
+            if (branch_name === current_branch) {
+                stdout(`Already on '${branch_name}'`);
+                return;
+            }
+
+            if (!branches.includes(branch_name))
+                throw new Error(`Branch '${branch_name}' not found.`);
+
+            await git.checkout({
+                fs,
+                dir: repository_dir,
+                gitdir: git_dir,
+                cache,
+                ref: branch_name,
+                force: options.force,
+            });
+            stdout(`Switched to branch '${branch_name}'`);
+        }
+    }
+};
+export default CHECKOUT;