util: add a free_clear() helper to reset after free

Same as e.g. g_clear_pointer(). Switch a number of obvious call sites
over to use this, the rest will come over time.

Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1472>

src/libinput-plugin-lua.c

@@ -375,8 +375,7 @@ remove_device(struct libinput_lua_plugin *plugin, EvdevDevice *evdev)
 	list_for_each_safe(prop, &evdev->udev_properties_list, link) {
 		udev_property_destroy(prop);
 	}
-	free(evdev->name);
-	evdev->name = NULL;
+	free_clear(&evdev->name);
 	evdev->device = libinput_device_unref(evdev->device);
 
 	/* This device no longer exists but our lua code may have a

src/util-bits.h

@@ -36,6 +36,7 @@
 #include <stdlib.h>
 
 #include "util-macros.h"
+#include "util-mem.h"
 
 #define bit(x_) (1UL << (x_))
 #define NBITS(b) (b * 8)
@@ -281,8 +282,7 @@ infmask_new(void)
 
 _nonnull_(1) static inline void infmask_reset(infmask_t *mask)
 {
-	free(mask->mask);
-	mask->mask = NULL;
+	free_clear(&mask->mask);
 	mask->nmasks = 0;
 }
 

src/util-mem.h

@@ -186,3 +186,14 @@ steal_fd(int *fd)
 	*fd = -1;
 	return copy;
 }
+
+/**
+ * Frees the pointer content and resets the data to NULL.
+ */
+#define free_clear(ptr_)                  \
+	do {                              \
+		typeof((ptr_)) _pp = (ptr_);  \
+		typeof(*(ptr_)) _p = *_pp;    \
+		*_pp = NULL;                  \
+		free(_p);                     \
+	} while(0)

src/util-stringbuf.h

@@ -53,8 +53,7 @@ stringbuf_is_empty(struct stringbuf *b)
 static inline void
 stringbuf_reset(struct stringbuf *b)
 {
-	free(b->data);
-	b->data = NULL;
+	free_clear(&b->data);
 	b->sz = 0;
 	b->len = 0;
 }

tools/libinput-record.c

@@ -2372,8 +2372,7 @@ mainloop(struct record_context *ctx)
 				}
 			}
 		}
-		free(ctx->output_file.name_with_suffix);
-		ctx->output_file.name_with_suffix = NULL;
+		free_clear(&ctx->output_file.name_with_suffix);
 	} while (autorestart && !ctx->stop);
 
 	sigprocmask(SIG_UNBLOCK, &mask, NULL);