Enable compiler errors for implicit switch case fallthroughs.

Also unify warning options across Clang and GCC and fix minor issues that was surfaced by this.

PiperOrigin-RevId: 508619655
Change-Id: I59b777bf2dfea4422485670e2427c7d3f5cf6405

src/cc/array_safety.h

@@ -73,7 +73,16 @@ static inline int sprintf_arr(char (&dest)[N], const char* format, ...) {
 // dest is guaranteed to be null-terminated
 template <std::size_t N>
 static inline char* strcat_arr(char (&dest)[N], const char* src) {
-  return std::strncat(dest, src, sizeof_arr(dest) - strlen_arr(dest) - 1);
+  const std::size_t dest_len = strlen_arr(dest);
+  const std::size_t dest_size = sizeof_arr(dest);
+  for (std::size_t i = dest_len; i < dest_size; ++i) {
+    dest[i] = src[i - dest_len];
+    if (!dest[i]) {
+      break;
+    }
+  }
+  dest[dest_size - 1] = '\0';
+  return dest;
 }
 
 // like std::strcpy but won't write beyond the bound of dest

src/engine/engine_collision_box.c

@@ -316,7 +316,7 @@ int mjc_CapsuleBox(const mjModel* m, const mjData* d, mjContact* con,
         };
         mjtNum c[2];
       } d2;
-      d2 p, s, d, c /*, tmp1*/;
+      d2 p, s, d /*, c, tmp1*/;
       mjtNum u, v, w, e1, best /* ,e2 */, l /* , e3, e4 */;
 
       bestdist = bestdistmax;
@@ -366,8 +366,8 @@ int mjc_CapsuleBox(const mjModel* m, const mjData* d, mjContact* con,
         }
       }
 
-      c.x = s.x * ((c1 / 2) ? -1 : 1);
-      c.y = s.y * ((c1 % 2) ? -1 : 1);
+      // c.x = s.x * ((c1 / 2) ? -1 : 1);
+      // c.y = s.y * ((c1 % 2) ? -1 : 1);
 
       e1 = fabs(w) / l;
       // e2 = best / l;

src/engine/engine_core_constraint.c

@@ -540,6 +540,7 @@ void mj_instantiateEquality(const mjModel* m, mjData* d) {
 
       case mjEQ_DISTANCE:
         mju_error("distance equality constraints are no longer supported");
+        break;
 
       default:                    // SHOULD NOT OCCUR
         mju_error_i("Invalid equality constraint type %d", m->eq_type[i]);

src/engine/engine_core_smooth.c

@@ -21,6 +21,7 @@
 #include <mujoco/mjmodel.h>
 #include "engine/engine_callback.h"
 #include "engine/engine_core_constraint.h"
+#include "engine/engine_crossplatform.h"
 #include "engine/engine_io.h"
 #include "engine/engine_macro.h"
 #include "engine/engine_plugin.h"
@@ -236,6 +237,7 @@ void mj_comPos(const mjModel* m, mjData* d) {
 
       // rotation components: same as ball
       skip = 18;
+      mjFALLTHROUGH;
 
     case mjJNT_BALL:
       for (int i=0; i<3; i++) {
@@ -1283,6 +1285,7 @@ void mj_comVel(const mjModel* m, mjData* d) {
 
         // continue with rotations
         j += 3;
+        mjFALLTHROUGH;
 
       case mjJNT_BALL:
         // compute all 3 cdofdots using parent velocity
@@ -1349,6 +1352,7 @@ void mj_passive(const mjModel* m, mjData* d) {
       // continue with rotations
       dadr += 3;
       padr += 3;
+      mjFALLTHROUGH;
 
     case mjJNT_BALL:
       // covert quatertion difference into angular "velocity"
@@ -2032,6 +2036,7 @@ void mj_rnePostConstraint(const mjModel* m, mjData* d) {
 
     case mjEQ_DISTANCE:
       mju_error("distance equality constraints are no longer supported");
+      break;
 
     default:
       mju_error_i("Unknown constraint type type %d", m->eq_type[id]);    // SHOULD NOT OCCUR

src/engine/engine_crossplatform.h

@@ -46,8 +46,10 @@
   #endif
 #endif
 
-#if defined(__GNUC__) && __GNUC__ >= 7
-  #define mjFALLTHROUGH __attribute__ ((fallthrough))
+#if defined(__cplusplus)
+  #define mjFALLTHROUGH [[fallthrough]]
+#elif defined(__clang__) || (defined(__GNUC__) && __GNUC__ >= 7)
+  #define mjFALLTHROUGH __attribute__((fallthrough))
 #else
   #define mjFALLTHROUGH ((void) 0)
 #endif

src/engine/engine_derivative.c

@@ -22,6 +22,7 @@
 #include "engine/engine_core_smooth.h"
 #include "engine/engine_forward.h"
 #include "engine/engine_core_constraint.h"
+#include "engine/engine_crossplatform.h"
 #include "engine/engine_io.h"
 #include "engine/engine_inverse.h"
 #include "engine/engine_macro.h"
@@ -402,6 +403,7 @@ static void mjd_comVel_vel(const mjModel* m, mjData* d, mjtNum* Dcvel, mjtNum* D
 
         // continue with rotations
         j += 3;
+        mjFALLTHROUGH;
 
       case mjJNT_BALL:
         // Dcdofdot = D crossMotion(cvel, cdof)

src/engine/engine_sensor.c

@@ -21,6 +21,7 @@
 #include <mujoco/mjplugin.h>
 #include "engine/engine_callback.h"
 #include "engine/engine_core_smooth.h"
+#include "engine/engine_crossplatform.h"
 #include "engine/engine_io.h"
 #include "engine/engine_macro.h"
 #include "engine/engine_plugin.h"
@@ -804,6 +805,7 @@ void mj_energyPos(const mjModel* m, mjData* d) {
 
         // continue with rotations
         padr += 3;
+        mjFALLTHROUGH;
 
       case mjJNT_BALL:
         // covert quatertion difference into angular "velocity"

src/engine/engine_support.c

@@ -1270,7 +1270,8 @@ void mj_differentiatePos(const mjModel* m, mjtNum* qvel, mjtNum dt,
       vadr += 3;
       padr += 3;
 
-    // continute with rotations
+      // continute with rotations
+      mjFALLTHROUGH;
 
     case mjJNT_BALL:
       mju_negQuat(neg, qpos1+padr);           // solve:  qpos1 * dif = qpos2
@@ -1304,7 +1305,8 @@ void mj_integratePos(const mjModel* m, mjtNum* qpos, const mjtNum* qvel, mjtNum
       padr += 3;
       vadr += 3;
 
-    // continue with rotation update
+      // continue with rotation update
+      mjFALLTHROUGH;
 
     case mjJNT_BALL:
       // quaternion update

src/engine/engine_vis_visualize.c

@@ -62,6 +62,7 @@ static void makeLabel(const mjModel* m, mjtObj type, int id, char* label) {
 
   // copy result into label
   strncpy(label, txt, 99);
+  label[99] = '\0';
 }
 
 

src/user/user_mesh.cc

@@ -1854,9 +1854,9 @@ void mjCSkin::LoadSKN(const mjVFS* vfs) {
 
     // read name
     char txt[40];
-    strncpy(txt, (char*)(pdata+cnt), 40);
+    strncpy(txt, (char*)(pdata+cnt), 39);
+    txt[39] = '\0';
     cnt += 10;
-    txt[39] = 0;
     bodyname.push_back(txt);
 
     // read bindpos