Streamline project build.zig

Offload as much work as possible into new `jetzigInit` function provided
by Jetzig's `build.zig`. This means that a new Jetzig project's
`build.zig` is now almost completely vanilla with the exception of two
extra lines:

```zig
const jetzig = @import("jetzig");
```

```zig
    try jetzig.jetzigInit(b, exe, .{});
```

build.zig

@@ -67,3 +67,47 @@ pub fn build(b: *std.Build) !void {
     const test_step = b.step("test", "Run library tests");
     test_step.dependOn(&run_main_tests.step);
 }
+
+/// Placeholder for potential options we may add in future without breaking
+/// backward-compatibility.
+pub const JetzigInitOptions = struct {};
+
+pub fn jetzigInit(b: *std.Build, exe: *std.Build.Step.Compile, options: JetzigInitOptions) !void {
+    _ = options;
+    const target = b.host;
+    const optimize = exe.root_module.optimize orelse .Debug;
+    const jetzig_dep = b.dependency(
+        "jetzig",
+        .{ .optimize = optimize, .target = b.host },
+    );
+    const jetzig_module = jetzig_dep.module("jetzig");
+    const zmpl_module = jetzig_dep.module("zmpl");
+
+    exe.root_module.addImport("jetzig", jetzig_module);
+    exe.root_module.addImport("zmpl", zmpl_module);
+
+    var generate_routes = try GenerateRoutes.init(b.allocator, "src/app/views");
+    try generate_routes.generateRoutes();
+    const write_files = b.addWriteFiles();
+    const routes_file = write_files.add("routes.zig", generate_routes.buffer.items);
+    for (generate_routes.static_routes.items) |route| _ = write_files.add(route.path, route.source);
+    for (generate_routes.dynamic_routes.items) |route| _ = write_files.add(route.path, route.source);
+    const routes_module = b.createModule(.{ .root_source_file = routes_file });
+
+    const exe_static_routes = b.addExecutable(.{
+        .name = "static",
+        .root_source_file = jetzig_dep.path("src/compile_static_routes.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+
+    exe.root_module.addImport("routes", routes_module);
+    routes_module.addImport("jetzig", jetzig_module);
+
+    exe_static_routes.root_module.addImport("routes", routes_module);
+    exe_static_routes.root_module.addImport("jetzig", jetzig_module);
+    exe_static_routes.root_module.addImport("zmpl", zmpl_module);
+
+    const run_static_routes_cmd = b.addRunArtifact(exe_static_routes);
+    exe.step.dependOn(&run_static_routes_cmd.step);
+}

demo/build.zig

@@ -1,23 +1,9 @@
 const std = @import("std");
-const jetzig_build = @import("jetzig");
+const jetzig = @import("jetzig");
-pub const zmpl = jetzig_build.zmpl;
-
-const GenerateRoutes = @import("jetzig").GenerateRoutes;
 
 pub fn build(b: *std.Build) !void {
     const target = b.standardTargetOptions(.{});
-
     const optimize = b.standardOptimizeOption(.{});
-    const jetzig_dep = b.dependency("jetzig", .{ .optimize = optimize, .target = target });
-
-    const lib = b.addStaticLibrary(.{
-        .name = "jetzig-demo",
-        .root_source_file = .{ .path = "src/main.zig" },
-        .target = target,
-        .optimize = optimize,
-    });
-
-    b.installArtifact(lib);
 
     const exe = b.addExecutable(.{
         .name = "jetzig-demo",
@@ -26,48 +12,14 @@ pub fn build(b: *std.Build) !void {
         .optimize = optimize,
     });
 
-    const jetzig_module = jetzig_dep.module("jetzig");
+    try jetzig.jetzigInit(b, exe, .{});
-    const zmpl_module = jetzig_dep.module("zmpl");
-
-    exe.root_module.addImport("jetzig", jetzig_module);
-    lib.root_module.addImport("jetzig", jetzig_module);
-    exe.root_module.addImport("zmpl", zmpl_module);
-    lib.root_module.addImport("zmpl", zmpl_module);
 
     b.installArtifact(exe);
 
-    var generate_routes = try GenerateRoutes.init(b.allocator, "src/app/views");
-    try generate_routes.generateRoutes();
-    const write_files = b.addWriteFiles();
-    const routes_file = write_files.add("routes.zig", generate_routes.buffer.items);
-    for (generate_routes.static_routes.items) |route| _ = write_files.add(route.path, route.source);
-    for (generate_routes.dynamic_routes.items) |route| _ = write_files.add(route.path, route.source);
-    const routes_module = b.createModule(.{ .root_source_file = routes_file });
-
-    const exe_static_routes = b.addExecutable(.{
-        .name = "static",
-        .root_source_file = jetzig_dep.path("src/compile_static_routes.zig"),
-        .target = target,
-        .optimize = optimize,
-    });
-
-    exe.root_module.addImport("routes", routes_module);
-    lib.root_module.addImport("routes", routes_module);
-    routes_module.addImport("jetzig", jetzig_module);
-
-    exe_static_routes.root_module.addImport("routes", routes_module);
-    exe_static_routes.root_module.addImport("jetzig", jetzig_module);
-    exe_static_routes.root_module.addImport("zmpl", zmpl_module);
-
-    const run_static_routes_cmd = b.addRunArtifact(exe_static_routes);
-    exe.step.dependOn(&run_static_routes_cmd.step);
-
     const run_cmd = b.addRunArtifact(exe);
     run_cmd.step.dependOn(b.getInstallStep());
 
-    if (b.args) |args| {
+    if (b.args) |args| run_cmd.addArgs(args);
-        run_cmd.addArgs(args);
-    }
 
     const run_step = b.step("run", "Run the app");
     run_step.dependOn(&run_cmd.step);