Handle absent build options

[glossy turret]

I want to write a build step that will use msdf-atlas-gen tool (https://github.com/Chlumsky/msdf-atlas-gen)

I have two build options that are passed to the tool:
font_filename and font_size.

The question is: How can I handle absence of the build options?

My current implementation looks like this:

    const font_size = b.option(u16, "font_size", "Size of glyph in font atlas generated with msdf-atlas-gen");

    const msdf_atlas_gen = b.addSystemCommand(&.{"msdf-atlas-gen"});

    if (font_filename != null and font_size != null) {
        msdf_atlas_gen.addArgs(&.{
            b.fmt("-font {s}.ttf", .{font_filename.?}),
            b.fmt("-size {}", .{font_size.?}),
            "-type msdf",
            "-yorigin top",
            b.fmt("-imageout {s}.png", .{font_filename.?}),
            b.fmt("-json {s}.json", .{font_filename.?}),
            "-charset assets/charset.txt",
            "-uniformgrid",
            "-uniformorigin on",
            "-pxpadding 4",
        });
    }

    const atlas_gen = b.step("atlas_gen", "Generate .png font atlas and .json metrics data using msdf-atlas-gen");
    atlas_gen.dependOn(&msdf_atlas_gen.step);```

[coral niche]

in the else case, you can msdf_atlas_gen depend on b.fail("...")

you might also want to consider using a LazyPath rather than []const u8 for the filename, and having msdf atlas gen output a LazyPath (using addPrefixedFileArg & addOutputFileArg), that way it can integrate with zig's cache system and not re-run if the source files haven't changed