From 477a14dcb28a29851a283ebd4c5d4979a5e81292 Mon Sep 17 00:00:00 2001
From: Google DeepMind <noreply@deepmind.com>
Date: Mon, 15 Dec 2025 11:56:41 -0800
Subject: [PATCH] Add WASM binding for `mj_compile`.

It does not support model assets management via VFS yet.

PiperOrigin-RevId: 844864882
Change-Id: I422d7896ed024fc6f5c3fa923a58cdc9059f3bee
---
 wasm/codegen/generated/bindings.cc   | 11 +++++++++++
 wasm/codegen/generators/constants.py |  2 +-
 wasm/codegen/templates/bindings.cc   | 10 ++++++++++
 wasm/tests/bindings_test.ts          | 24 ++++++++++++++++++++++++
 4 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/wasm/codegen/generated/bindings.cc b/wasm/codegen/generated/bindings.cc
index a0763b9e..27ce3adb 100644
--- a/wasm/codegen/generated/bindings.cc
+++ b/wasm/codegen/generated/bindings.cc
@@ -33,6 +33,7 @@
 #include <mujoco/mjmodel.h>
 #include <mujoco/mjvisualize.h>
 #include <mujoco/mujoco.h>
+#include <mujoco/mjspec.h>
 #include "engine/engine_util_errmem.h"
 #include "wasm/unpack.h"
 
@@ -7823,6 +7824,15 @@ std::unique_ptr<MjSpec> parseXMLString_wrapper(const std::string &xml) {
   return std::unique_ptr<MjSpec>(new MjSpec(ptr));
 }
 
+std::unique_ptr<MjModel> mj_compile_wrapper(const MjSpec& spec) {
+  mjSpec* spec_ptr = spec.get();
+  mjModel* model = mj_compile(spec_ptr, nullptr);
+  if (!model || mjs_isWarning(spec_ptr)) {
+    mju_error("%s", mjs_getError(spec_ptr));
+  }
+  return std::unique_ptr<MjModel>(new MjModel(model));
+}
+
 void error_wrapper(const String& msg) { mju_error("%s\n", msg.as<const std::string>().data()); }
 
 int mj_saveLastXML_wrapper(const String& filename, const MjModel& m) {
@@ -12308,6 +12318,7 @@ EMSCRIPTEN_BINDINGS(mujoco_bindings) {
   function("mj_comPos", &mj_comPos_wrapper);
   function("mj_comVel", &mj_comVel_wrapper);
   function("mj_compareFwdInv", &mj_compareFwdInv_wrapper);
+  function("mj_compile", &mj_compile_wrapper);
   function("mj_constraintUpdate", &mj_constraintUpdate_wrapper);
   function("mj_contactForce", &mj_contactForce_wrapper);
   function("mj_copyBack", &mj_copyBack_wrapper);
diff --git a/wasm/codegen/generators/constants.py b/wasm/codegen/generators/constants.py
index 1cb0ef23..8bd3d71f 100644
--- a/wasm/codegen/generators/constants.py
+++ b/wasm/codegen/generators/constants.py
@@ -64,7 +64,6 @@ _SKIPPED_PLUGIN_FUNCTIONS: tuple[str, ...] = (
 # Functions that are bound as class methods
 _SKIPPED_CLASS_METHODS: tuple[str, ...] = (
     # go/keep-sorted start
-    "mj_compile",
     "mj_copyData",
     "mj_copyModel",
     "mj_copySpec",
@@ -192,6 +191,7 @@ _SKIPPED_UTILITY_FUNCTIONS: tuple[str, ...] = (
 # These functions are not bound automatically but are written by hand instead.
 MANUAL_WRAPPER_FUNCTIONS: tuple[str, ...] = (
     # go/keep-sorted start
+    "mj_compile",
     "mj_saveLastXML",
     "mj_setLengthRange",
     "mju_error",
diff --git a/wasm/codegen/templates/bindings.cc b/wasm/codegen/templates/bindings.cc
index e74ab501..dfae0925 100644
--- a/wasm/codegen/templates/bindings.cc
+++ b/wasm/codegen/templates/bindings.cc
@@ -33,6 +33,7 @@
 #include <mujoco/mjmodel.h>
 #include <mujoco/mjvisualize.h>
 #include <mujoco/mujoco.h>
+#include <mujoco/mjspec.h>
 #include "engine/engine_util_errmem.h"
 #include "wasm/unpack.h"
 
@@ -406,6 +407,15 @@ std::unique_ptr<MjSpec> parseXMLString_wrapper(const std::string &xml) {
   return std::unique_ptr<MjSpec>(new MjSpec(ptr));
 }
 
+std::unique_ptr<MjModel> mj_compile_wrapper(const MjSpec& spec) {
+  mjSpec* spec_ptr = spec.get();
+  mjModel* model = mj_compile(spec_ptr, nullptr);
+  if (!model || mjs_isWarning(spec_ptr)) {
+    mju_error("%s", mjs_getError(spec_ptr));
+  }
+  return std::unique_ptr<MjModel>(new MjModel(model));
+}
+
 void error_wrapper(const String& msg) { mju_error("%s\n", msg.as<const std::string>().data()); }
 
 int mj_saveLastXML_wrapper(const String& filename, const MjModel& m) {
diff --git a/wasm/tests/bindings_test.ts b/wasm/tests/bindings_test.ts
index cc14f9dd..56614d8b 100644
--- a/wasm/tests/bindings_test.ts
+++ b/wasm/tests/bindings_test.ts
@@ -1802,4 +1802,28 @@ describe('MuJoCo WASM Bindings', () => {
       unlinkXMLFile(tempXmlFilename);
     }
   });
+
+  it('should compile a spec from XML string', () => {
+    let spec = null;
+    let model = null;
+    try {
+      spec = mujoco.parseXMLString(TEST_XML);
+      expect(spec).not.toBeNull();
+
+      model = mujoco.mj_compile(spec);
+      expect(model).not.toBeNull();
+      expect(model.nq).toBeGreaterThan(0);
+
+      const jointId =
+          mujoco.mj_name2id(model, mujoco.mjtObj.mjOBJ_JOINT.value, 'myhinge');
+      expect(jointId).toBeGreaterThanOrEqual(0);
+    } finally {
+      if (spec) {
+        spec.delete();
+      }
+      if (model) {
+        model.delete();
+      }
+    }
+  });
 });