Latest zig requires immutable vars to be 'const'

src/Parser.zig

@@ -366,7 +366,7 @@ fn putMatchedArg(self: *Parser, arg: *const Arg, value: arg_matches.MatchedArgVa
     try self.verifyValuesLength(arg, value.count());
 
     var matches = &self.arg_matches;
-    var maybe_old_value = matches.args.getPtr(arg.name);
+    const maybe_old_value = matches.args.getPtr(arg.name);
 
     if (maybe_old_value) |old_value| {
         // To fix the const error

src/arg_matches.zig

@@ -74,7 +74,7 @@ pub const ArgMatches = struct {
     pub fn setSubcommand(self: *ArgMatches, subcommand: MatchedSubCommand) !void {
         if (self.subcommand != null) return;
 
-        var alloc_subcmd = try self.allocator.create(MatchedSubCommand);
+        const alloc_subcmd = try self.allocator.create(MatchedSubCommand);
         alloc_subcmd.* = subcommand;
         self.subcommand = alloc_subcmd;
     }

src/help.zig

@@ -62,7 +62,7 @@ pub const Help = struct {
 
     pub fn writeAll(self: *Help, stream: anytype) !void {
         var buffer = std.io.bufferedWriter(stream);
-        var writer = buffer.writer();
+        const writer = buffer.writer();
 
         try self.writeDescription(writer);
         try self.writeHeader(writer);

src/test.zig

@@ -207,7 +207,7 @@ test "Option with allowed values" {
     var app = App.init(allocator, "clang", null);
     errdefer app.deinit();
 
-    var stdd = Arg.singleValueOptionWithValidValues(
+    const stdd = Arg.singleValueOptionWithValidValues(
         "std",
         null,
         null,