How to add two strings together at compile time zig

[soft topaz]

I'm trying to use an environment variable and do not know how I can add another path on top of the environment variable in the build.zig

here's what I currently have:

    const vk_path = b.graph.env_map.get("VULKAN_SDK") orelse
        b.graph.env_map.get("VK_SDK_PATH") orelse
        std.debug.panic("Error getting VK_SDK_PATH or VULKAN_SDK environment variable!", .{});
    std.debug.print("{s}", .{vk_path});

    const mod = b.addModule("root", .{
        .root_source_file = b.path("src/root.zig"),
        .target = target,
    });

    const vulkan = b.dependency("vulkan_zig", .{
        .registry = b.pathFromRoot(std.fmt.comptimePrint("{s}/share/vulkan/registry/vk.xml", .{vk_path})),
    }).module("vulkan-zig");

[static thorn]

in build.zig you can use b.fmt("{s}{s}", .{"a", "b"})

alternatively if things are known at comptime (which is not the case for environment variables in ENV_MAP):
comptime 1: "a" ++ "b" -> "ab"
comptime 2: std.fmt.comptimePrint("{s}{s}", .{"a", "b"});

[soft topaz]

alright well now i'm doing:

   const vulkan = b.dependency("vulkan_zig", .{
       .registry = b.pathFromRoot(b.fmt("{s}{s}", .{vk_path, "/share/vulkan/registry/vk.xml"})),
   }).module("vulkan-zig");

but it still gives the error:

error: option 'registry' has unsupported type: []u8
                else => @compileError("option '" ++ field.name ++ "' has unsupported type: " ++ @typeName(T)),

[static thorn]

that's because of how b.dependency is. you need to @as([]const u8, b.pathFromRoot(...))

also I think it's supposed to be a LazyPath. so actually you want std.Build.LazyPath{ .cwd_relative = b.fmt("{s}{s}", .{})

and in that case you can do (std.Build.LazyPath{ .cwd_relative = vk_root}).path("share/vulkan/registry/vk.xml") and don't need b.fmt at all

[soft topaz]

well I have another problem as well. now it doesn't want to read my actual environment variables which is a problem that I need to figure out.

[soft topaz]

that is a much nicer way

[soft topaz]

is that just casting it from I assume a u8 array to const u8 array?

[static thorn]

yeah (implicit cast)

because b.dependency is switching on the type of the thing. and it has

[]const u8 => ...,
else => @compileError()

[soft topaz]

that does not work. little confused on the error too

build.zig:19:68: error: member function expected 2 argument(s), found 1
        .registry = (std.Build.LazyPath{ .cwd_relative = vk_path }).path("share/vulkan/registry/vk.xml"),
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
C:\Users\\AppData\Roaming\Code\User\globalStorage\ziglang.vscode-zig\zig\x86_64-windows-0.15.0-dev.734+adc4418ba\lib\std\Build.zig:2585:9: note: function declared here
    pub fn path(lazy_path: LazyPath, b: *Build, sub_path: []const u8) LazyPath 

[static thorn]

should be .path(b, "share/...")

[soft topaz]

yeah figured that out

[static thorn]

it says expected 2 arguments even though there's 3 arguments because the first one is getting passed implicitly