wasm: log should use stack allocated memory first

This allows log messages to come through even when OOM.

src/os/wasm/log.zig

@@ -9,12 +9,25 @@ pub fn log(
     comptime format: []const u8,
     args: anytype,
 ) void {
+    // The buffer for putting our log message. We try to use a stack-allocated
+    // buffer first because we want to avoid allocation. If we are logging
+    // an error DUE to an OOM, allocating will of course fail and we'd like
+    // to see the error message so we prefer to use this.
+    var buf: [2048]u8 = undefined;
+
     // 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);
+
+    // Format. We attempt to use a stack-allocated string first and if that
+    // fails we'll try to allocate.
+    var allocated: bool = false;
+    const str = nosuspend std.fmt.bufPrint(&buf, txt, args) catch str: {
+        allocated = true;
+        break :str std.fmt.allocPrint(wasm.alloc, txt, args) catch return;
+    };
+    defer if (allocated) wasm.alloc.free(str);
 
     // Send it over to the JS side
     JS.log(str.ptr, str.len);