finish implementing "default master"

test.zig

@@ -24,6 +24,11 @@ pub fn main() !void {
     defer allocator_store.deinit();
     const allocator = allocator_store.allocator();
 
+    {
+        const result = try runCaptureOuts(allocator, ".", zigup_args ++ &[_][]const u8 {"default", "master"});
+        defer { allocator.free(result.stdout); allocator.free(result.stderr); }
+        try testing.expect(std.mem.containsAtLeast(u8, result.stderr, 1, "master has not been fetched"));
+    }
     {
         const result = try runCaptureOuts(allocator, ".", zigup_args ++ &[_][]const u8 {"-h"});
         defer { allocator.free(result.stdout); allocator.free(result.stderr); }

zigup.zig

@@ -288,9 +288,27 @@ pub fn main2() !u8 {
         }
         if (args.len == 2) {
             const version_string = args[1];
-            const install_dir = try getInstallDir(allocator, .{ .create = true });
-            defer allocator.free(install_dir);
-            const compiler_dir = try std.fs.path.join(allocator, &[_][]const u8{ install_dir, version_string });
+            const install_dir_string = try getInstallDir(allocator, .{ .create = true });
+            defer allocator.free(install_dir_string);
+            const resolved_version_string = init_resolved: {
+                if (!std.mem.eql(u8, version_string, "master"))
+                    break :init_resolved version_string;
+
+                var optional_master_dir: ?[]const u8 = blk: {
+                    var install_dir = std.fs.openDirAbsolute(install_dir_string, .{ .iterate = true }) catch |e| switch (e) {
+                        error.FileNotFound => break :blk null,
+                        else => return e,
+                    };
+                    defer install_dir.close();
+                    break :blk try getMasterDir(allocator, &install_dir);
+                };
+                // no need to free master_dir, this is a short lived program
+                break :init_resolved optional_master_dir orelse {
+                    std.debug.print("Error: master has not been fetched\n", .{});
+                    return 1;
+                };
+            };
+            const compiler_dir = try std.fs.path.join(allocator, &[_][]const u8{ install_dir_string, resolved_version_string });
             defer allocator.free(compiler_dir);
             try setDefaultCompiler(allocator, compiler_dir, .verify_existence);
             return 0;