Improve zigup default and zigup list output

Default command now also points to the actual directory if default
compiler is master.

List command now also marks which one is the master also also marks the
default compiler with ``(default)``.

zigup.zig

@@ -458,6 +458,12 @@ fn listCompilers(allocator: Allocator) !void {
     };
     defer install_dir.close();
 
+    const default_compiler = try getDefaultCompiler(allocator);
+    defer if (default_compiler) |default| allocator.free(default);
+
+    const master_dir = try getMasterDir(allocator, &install_dir);
+    defer if (master_dir) |master| allocator.free(master);
+
     const stdout = std.io.getStdOut().writer();
     {
         var it = install_dir.iterate();
@@ -466,7 +472,24 @@ fn listCompilers(allocator: Allocator) !void {
                 continue;
             if (std.mem.endsWith(u8, entry.name, ".installing"))
                 continue;
-            try stdout.print("{s}\n", .{entry.name});
+
+            try stdout.print("{s}", .{entry.name});
+
+            const is_master = if (master_dir) |master|
+                (if (mem.eql(u8, master, entry.name)) true else false)
+                else false;
+
+            if (is_master) {
+                try stdout.writeAll(" -> master");
+            }
+
+            if (default_compiler) |default| {
+                if (mem.eql(u8, default, entry.name) or (is_master and mem.eql(u8, default, "master"))) {
+                    try stdout.writeAll(" (default)");
+                }
+            }
+
+            try stdout.writeByte('\n');
         }
     }
 }
@@ -604,7 +627,26 @@ fn printDefaultCompiler(allocator: Allocator) !void {
     defer if (default_compiler_opt) |default_compiler| allocator.free(default_compiler);
     const stdout = std.io.getStdOut().writer();
     if (default_compiler_opt) |default_compiler| {
-        try stdout.print("{s}\n", .{default_compiler});
+        if (mem.eql(u8, default_compiler, "master")) {
+            const install_dir_string = try getInstallDir(allocator, .{ .create = false });
+            defer allocator.free(install_dir_string);
+
+            var install_dir = std.fs.openDirAbsolute(install_dir_string, .{ .iterate = true }) catch |e| switch (e) {
+                error.FileNotFound => return,
+                else => return e,
+            };
+            defer install_dir.close();
+
+            const master_dir = try getMasterDir(allocator, &install_dir);
+            defer if (master_dir) |master| allocator.free(master);
+
+            if (master_dir) |master| {
+                try stdout.print("master -> {s}\n", .{master});
+            }
+        }
+        else {
+            try stdout.print("{s}\n", .{default_compiler});
+        }
     } else {
         try stdout.writeAll("<no-default>\n");
     }