Clean up engine selection

build.zig

@@ -14,6 +14,7 @@
 
 const std = @import("std");
 const builtin = @import("builtin");
+const EngineType = @import("src/api.zig").EngineType;
 
 const pkgs = packages("");
 
@@ -40,7 +41,7 @@ pub fn build(b: *std.Build) !void {
 
     // TODO: install only bench or shell with zig build <cmd>
 
-    const options = try buildOptions(b);
+    const options = buildOptions(b);
 
     // bench
     // -----
@@ -132,31 +133,16 @@ pub fn build(b: *std.Build) !void {
     test_step.dependOn(&run_tests.step);
 }
 
-const Engine = enum {
-    v8,
-};
-
 pub const Options = struct {
-    engine: Engine,
+    engine: EngineType,
     opts: *std.Build.Step.Options,
 };
 
-pub fn buildOptions(b: *std.Build) !Options {
+pub fn buildOptions(b: *std.Build) Options {
+    const engine = b.option(EngineType, "engine", "JS engine (v8)") orelse .v8;
     const options = b.addOptions();
-    const engine = b.option([]const u8, "engine", "JS engine (v8)");
-    var eng: Engine = undefined;
-    if (engine == null) {
-        // default
-        eng = .v8;
-    } else {
-        if (std.mem.eql(u8, engine.?, "v8")) {
-            eng = .v8;
-        } else {
-            return error.EngineUnknown;
-        }
-    }
-    options.addOption(?[]const u8, "engine", engine);
-    return .{ .engine = eng, .opts = options };
+    options.addOption(EngineType, "engine", engine);
+    return .{ .engine = engine, .opts = options };
 }
 
 fn common(
@@ -166,9 +152,11 @@ fn common(
 ) !void {
     m.addOptions("jsruntime_build_options", options.opts);
     m.addImport("tigerbeetle-io", pkgs.tigerbeetle_io(b));
-    if (options.engine == .v8) {
-        try pkgs.v8(m);
-        m.addImport("v8", pkgs.zig_v8(b));
+    switch (options.engine) {
+        .v8 => {
+            try pkgs.v8(m);
+            m.addImport("v8", pkgs.zig_v8(b));
+        },
     }
 }
 

src/api.zig

@@ -87,6 +87,6 @@ pub const Inspector = Engine.Inspector;
 pub const InspectorOnResponseFn = *const fn (ctx: *anyopaque, call_id: u32, msg: []const u8) void;
 pub const InspectorOnEventFn = *const fn (ctx: *anyopaque, msg: []const u8) void;
 
-pub const engineType = enum {
+pub const EngineType = enum {
     v8,
 };

src/engines/v8/v8.zig

@@ -90,7 +90,7 @@ pub const Env = struct {
 
     js_ctx: ?v8.Context = null,
 
-    pub fn engine() public.engineType {
+    pub fn engine() public.EngineType {
         return .v8;
     }
 

src/interfaces.zig

@@ -52,7 +52,7 @@ pub fn Env(
 ) void {
 
     // engine()
-    assertDecl(T, "engine", fn () public.engineType);
+    assertDecl(T, "engine", fn () public.EngineType);
 
     // init()
     assertDecl(T, "init", fn (self: *T, alloc: std.mem.Allocator, loop: *public.Loop, userctx: ?public.UserContext) void);

src/private_api.zig

@@ -14,6 +14,7 @@
 
 const std = @import("std");
 
+const build_opts = @import("jsruntime_build_options");
 const interfaces = @import("interfaces.zig");
 
 fn checkInterfaces(engine: anytype) void {
@@ -44,31 +45,13 @@ fn checkInterfaces(engine: anytype) void {
     // private api
 }
 
-pub const Engine = blk: {
-
-    // retrieve JS engine
-
-    // - as a build option
-    const build_opts = @import("jsruntime_build_options");
-    if (@hasDecl(build_opts, "engine")) {
-        // use v8 by default.
-        const eng = build_opts.engine orelse "v8";
-        if (std.mem.eql(u8, eng, "v8")) {
-            const engine = @import("engines/v8/v8.zig");
-            checkInterfaces(engine);
-            break :blk engine;
-        }
-        @compileError("unknwon -Dengine '" ++ eng ++ "'");
-    }
-
-    // - as a root declaration
-    const root = @import("root");
-    if (@hasDecl(root, "JSEngine")) {
-        checkInterfaces(root.JSEngine);
-        break :blk root.JSEngine;
-    }
-
-    @compileError("you need to specify a JS engine as a build option (-Dengine) or as a root file declaration (pub const JSEngine)");
+// retrieve JS engine
+pub const Engine = switch (build_opts.engine) {
+    .v8 => blk: {
+        const engine = @import("engines/v8/v8.zig");
+        checkInterfaces(engine);
+        break :blk engine;
+    },
 };
 
 pub const API = Engine.API;