Make switch fallthrough markers compatible with clang and C23

Uses _X_FALLTHROUGH from xproto 7.0.34 if available,
local fallback if xproto is older than that.

Clears warnings from clang 19.1.7 of the form:

mouse.c:1219:17: warning: unannotated fall-through between switch labels
 [-Wimplicit-fallthrough]
 1219 |                 default:
      |                 ^
mouse.c:1219:17: note: insert '[[fallthrough]];' to silence this warning
 1219 |                 default:
      |                 ^
      |                 [[fallthrough]];
mouse.c:1219:17: note: insert 'break;' to avoid fall-through
 1219 |                 default:
      |                 ^
      |                 break;

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Part-of: <https://gitlab.freedesktop.org/xorg/driver/xf86-input-mouse/-/merge_requests/23>

configure.ac

@@ -48,7 +48,7 @@ XORG_WITH_LINT
 AC_CHECK_FUNCS([asprintf timingsafe_memcmp])
 
 # Obtain compiler/linker options from server and required extensions
-PKG_CHECK_MODULES(XORG, [xorg-server >= 1.10] xproto inputproto)
+PKG_CHECK_MODULES(XORG, [xorg-server >= 1.10 xproto >= 7.0.27 inputproto])
 
 # Define a configure option for an alternate input module directory
 AC_ARG_WITH(xorg-module-dir,

src/mouse.c

@@ -1214,7 +1214,7 @@ MouseReadInput(InputInfoPtr pInfo)
                 case PROT_GLIDE:
                 case PROT_THINKING:
                     buttons |= ((int)(u & 0x10) >> 1);
-                    /* fall through */
+                    _X_FALLTHROUGH; /* fall through */
 
                 default:
                     buttons |= ((int)(u & 0x20) >> 4) |
@@ -3641,7 +3641,7 @@ autoGood(MouseDevPtr pMse)
     case AUTOPROBE_H_VALIDATE2:
         if (mPriv->goodCount < PROBE_UNCERTAINTY/2)
             return TRUE;
-        /* FALLTHROUGH */
+        _X_FALLTHROUGH; /* FALLTHROUGH */
     default:
         return FALSE;
     }

src/mouse.h

@@ -30,6 +30,16 @@
 #ifndef _XF86OSMOUSE_H_
 #define _XF86OSMOUSE_H_
 
+#include <X11/Xfuncproto.h>
+
+#ifndef _X_FALLTHROUGH /* xproto < 7.0.34 */
+# if  __has_attribute(fallthrough)
+#  define _X_FALLTHROUGH __attribute__((fallthrough))
+# else
+#  define _X_FALLTHROUGH (void)0
+# endif
+#endif
+
 #include "xf86Xinput.h"
 
 #if GET_ABI_MAJOR(ABI_XINPUT_VERSION) < 18

src/sun_mouse.c

@@ -752,7 +752,7 @@ vuidMouseProc(DeviceIntPtr pPointer, int what)
             if (m != NULL)
                 m->next = pVuidMse->next;
         }
-        /* fallthrough */
+        _X_FALLTHROUGH; /* fallthrough */
     case DEVICE_OFF:
         if (pInfo->fd != -1) {
             if (pVuidMse->strmod) {