Update contype and conaffinity if fusestatic is true. Fixes #1577.

PiperOrigin-RevId: 628073529
Change-Id: I2fe88736d12ec16d72bbd4dce5d349b930147b50

src/user/user_model.cc

@@ -2955,6 +2955,15 @@ void mjCModel::FuseStatic(void) {
     sites.clear();
     FuseReindex(bodies[0]);
 
+    // recompute parent contype, conaffinity, and margin
+    par->contype = par->conaffinity = 0;
+    par->margin = 0;
+    for (const auto& geom : geoms) {
+      par->contype |= geom->contype;
+      par->conaffinity |= geom->conaffinity;
+      par->margin = mju_max(par->margin, geom->margin);
+    }
+
     //------------- delete body (without deleting children)
 
     // delete allocation

test/user/user_model_test.cc

@@ -248,9 +248,9 @@ TEST_F(FuseStaticTest, FuseStaticEquivalent) {
     <worldbody>
       <body>
         <joint axis="1 0 0"/>
-        <geom size="0.5" pos="1 0 0"/>
+        <geom size="0.5" pos="1 0 0" contype="0" conaffinity="0"/>
         <body>
-          <geom size="0.5" pos="0 1 0"/>
+          <geom size="0.5" pos="0 1 0" contype="1" conaffinity="1"/>
         </body>
       </body>
     </worldbody>
@@ -268,6 +268,11 @@ TEST_F(FuseStaticTest, FuseStaticEquivalent) {
   EXPECT_EQ(m_fuse->nbody, 2) << "Expecting a world body and one other body";
   EXPECT_EQ(m_no_fuse->nbody, 3) << "Expecting a world body and two others";
 
+  EXPECT_EQ(m_no_fuse->body_contype[2], 1);
+  EXPECT_EQ(m_no_fuse->body_conaffinity[2], 1);
+  EXPECT_EQ(m_fuse->body_contype[1], 1);
+  EXPECT_EQ(m_fuse->body_conaffinity[1], 1);
+
   mjData* d_fuse = mj_makeData(m_fuse);
   mjData* d_no_fuse = mj_makeData(m_no_fuse);