Change taglist_get_tagstring to support 'unlimited' tag list size

Previous taglist_get_tagstring signature/implementation did not allow
handling of cases where inputted buffer could not contain all tags.
New implementation allocates buffer based on pre-computed size allowing to
insert all tags in the returned string.

Added get_taglist_string in qthelper to handle conversion to QString
Added TestTagList with tests for taglist_get_tagstring

Signed-off-by: Jeremie Guichard <djebrest@gmail.com>

core/dive.c

@@ -12,6 +12,7 @@
 #include "divelist.h"
 #include "qthelper.h"
 #include "metadata.h"
+#include "membuffer.h"
 
 /* one could argue about the best place to have this variable -
  * it's used in the UI, but it seems to make the most sense to have it
@@ -3020,30 +3021,28 @@ void taglist_cleanup(struct tag_entry **tag_list)
 	}
 }
 
-int taglist_get_tagstring(struct tag_entry *tag_list, char *buffer, int len)
+char *taglist_get_tagstring(struct tag_entry *tag_list)
 {
-	int i = 0;
-	struct tag_entry *tmp;
-	tmp = tag_list;
-	memset(buffer, 0, len);
+	bool first_tag = true;
+	struct membuffer b = { 0 };
+	struct tag_entry *tmp = tag_list;
 	while (tmp != NULL) {
-		int newlength = strlen(tmp->tag->name);
-		if (i > 0)
-			newlength += 2;
-		if ((i + newlength) < len) {
-			if (i > 0) {
-				strcpy(buffer + i, ", ");
-				strcpy(buffer + i + 2, tmp->tag->name);
+		if (!empty_string(tmp->tag->name)) {
+			if (first_tag) {
+				put_format(&b, "%s", tmp->tag->name);
+				first_tag = false;
 			} else {
-				strcpy(buffer, tmp->tag->name);
+				put_format(&b, ", %s", tmp->tag->name);
 			}
-		} else {
-			return i;
 		}
-		i += newlength;
 		tmp = tmp->next;
 	}
-	return i;
+	/* Ensures we do return null terminated empty string for:
+	 *  - empty tag list
+	 *  - tag list with empty tag only
+	 */
+	mb_cstring(&b);
+	return detach_buffer(&b);
 }
 
 static inline void taglist_free_divetag(struct divetag *tag)

core/dive.h

@@ -264,10 +264,13 @@ struct tag_entry *taglist_added(struct tag_entry *original_list, struct tag_entr
 void dump_taglist(const char *intro, struct tag_entry *tl);
 
 /*
- * Writes all divetags in tag_list to buffer, limited by the buffer's (len)gth.
- * Returns the characters written
+ * Writes all divetags form tag_list into internally allocated buffer
+ * Function returns pointer to allocated buffer
+ * Buffer contains comma separated list of tags names or null terminated string
+ *
+ * NOTE! The returned buffer must be freed once used.
  */
-int taglist_get_tagstring(struct tag_entry *tag_list, char *buffer, int len);
+char *taglist_get_tagstring(struct tag_entry *tag_list);
 
 /* cleans up a list: removes empty tags and duplicates */
 void taglist_cleanup(struct tag_entry **tag_list);

core/qthelper.cpp

@@ -1282,6 +1282,14 @@ QString get_divepoint_gas_string(struct dive *d, const divedatapoint &p)
 	return get_gas_string(d->cylinder[idx].gasmix);
 }
 
+QString get_taglist_string(struct tag_entry *tag_list)
+{
+	char *buffer = taglist_get_tagstring(tag_list);
+	QString ret = QString::fromUtf8(buffer);
+	free(buffer);
+	return ret;
+}
+
 weight_t string_to_weight(const char *str)
 {
 	const char *end;

core/qthelper.h

@@ -30,6 +30,7 @@ bool gpsHasChanged(struct dive *dive, struct dive *master, const QString &gps_te
 QList<int> getDivesInTrip(dive_trip_t *trip);
 QString get_gas_string(struct gasmix gas);
 QString get_divepoint_gas_string(struct dive *d, const divedatapoint& dp);
+QString get_taglist_string(struct tag_entry *tag_list);
 void read_hashes();
 void write_hashes();
 void updateHash(struct picture *picture);

core/subsurface-qt/DiveObjectHelper.cpp

@@ -192,9 +192,7 @@ QString DiveObjectHelper::notes() const
 
 QString DiveObjectHelper::tags() const
 {
-	static char buffer[256];
-	taglist_get_tagstring(m_dive->tag_list, buffer, 256);
-	return QString(buffer);
+	return get_taglist_string(m_dive->tag_list);
 }
 
 QString DiveObjectHelper::gas() const