logging works for wasm

build.zig

@@ -137,6 +137,7 @@ pub fn build(b: *std.build.Builder) !void {
         const main_test = b.addTest("src/main_wasm.zig");
         main_test.setTarget(.{ .cpu_arch = .wasm32, .os_tag = .wasi });
         main_test.addOptions("build_options", exe_options);
+        main_test.addPackage(js.pkg);
         test_step.dependOn(&main_test.step);
     }
 

src/font/Atlas.zig

@@ -307,7 +307,7 @@ pub fn clear(self: *Atlas) void {
 pub const Wasm = struct {
     // If you're copying this file (Atlas.zig) out to a separate project,
     // just replace this with the allocator you want to use.
-    const wasm = @import("../wasm.zig");
+    const wasm = @import("../os/wasm.zig");
     const alloc = wasm.alloc;
 
     export fn atlas_new(size: u32, format: u8) ?*Atlas {

src/font/face/web_canvas.zig

@@ -73,7 +73,7 @@ pub const Face = struct {
 
 /// The wasm-compatible API.
 pub const Wasm = struct {
-    const wasm = @import("../../wasm.zig");
+    const wasm = @import("../../os/wasm.zig");
     const alloc = wasm.alloc;
 
     export fn face_new(ptr: [*]const u8, len: usize, pts: u16) ?*Face {

src/main_wasm.zig

@@ -1,5 +1,6 @@
 // This is the main file for the WASM module. The WASM module has to
 // export a C ABI compatible API.
 
-pub usingnamespace @import("wasm.zig");
+pub usingnamespace @import("os/wasm.zig");
+pub usingnamespace @import("os/wasm/log.zig");
 pub usingnamespace @import("font/main.zig");

src/os/wasm/log.zig

@@ -0,0 +1,27 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const wasm = @import("../wasm.zig");
+
+// The function std.log will call.
+pub fn log(
+    comptime level: std.log.Level,
+    comptime scope: @TypeOf(.EnumLiteral),
+    comptime format: []const u8,
+    args: anytype,
+) void {
+    // Build the string
+    const level_txt = comptime level.asText();
+    const prefix = if (scope == .default) ": " else "(" ++ @tagName(scope) ++ "): ";
+    const txt = level_txt ++ prefix ++ format;
+    const str = nosuspend std.fmt.allocPrint(wasm.alloc, txt, args) catch return;
+    defer wasm.alloc.free(str);
+
+    // Send it over to the JS side
+    JS.log(str.ptr, str.len);
+}
+
+// We wrap our externs in this namespace so we can reuse symbols, otherwise
+// "log" would collide.
+const JS = struct {
+    extern "env" fn log(ptr: [*]const u8, len: usize) void;
+};