use lazyDependency to optimize dependency fetching

Helps hexops/mach#1197

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

build.zig

@@ -5,18 +5,11 @@ pub fn build(b: *std.Build) !void {
     const optimize = b.standardOptimizeOption(.{});
     const target = b.standardTargetOptions(.{});
 
-    const glfw_dep = b.dependency("glfw", .{
-        .target = target,
-        .optimize = optimize,
-    });
-
     var module = b.addModule("mach-glfw", .{
         .target = target,
         .optimize = optimize,
         .root_source_file = .{ .path = "src/main.zig" },
     });
-    module.linkLibrary(glfw_dep.artifact("glfw"));
-    @import("glfw").addPaths(module);
 
     const test_step = b.step("test", "Run library tests");
     const main_tests = b.addTest(.{
@@ -25,11 +18,18 @@ pub fn build(b: *std.Build) !void {
         .target = target,
         .optimize = optimize,
     });
-    main_tests.linkLibrary(glfw_dep.artifact("glfw"));
-    @import("glfw").addPaths(&main_tests.root_module);
     b.installArtifact(main_tests);
-
     test_step.dependOn(&b.addRunArtifact(main_tests).step);
+
+    if (b.lazyDependency("glfw", .{
+        .target = target,
+        .optimize = optimize,
+    })) |dep| {
+        module.linkLibrary(dep.artifact("glfw"));
+        @import("glfw").addPaths(module);
+        main_tests.linkLibrary(dep.artifact("glfw"));
+        @import("glfw").addPaths(&main_tests.root_module);
+    }
 }
 
 comptime {

build.zig.zon

@@ -14,6 +14,7 @@
         .glfw = .{
             .url = "https://pkg.machengine.org/glfw/8f7ca982913c0ab64df44d79d6ad2fb592e5ec39.tar.gz",
             .hash = "122085745c053e68fea3772c7239c7c87bcc7f042fa3189592b30e0e39cbb9603d79",
+            .lazy = true,
         },
     },
 }