strv: introduce strv_find_closest()

Follow-up for 1e1ac5d53b.

src/basic/strv.c

@@ -66,7 +66,28 @@ char* strv_find_startswith(char * const *l, const char *name) {
         return NULL;
 }
 
-char* strv_find_closest_by_levenshtein(char * const *l, const char *name) {
+static char* strv_find_closest_prefix(char * const *l, const char *name) {
+        size_t best_distance = SIZE_MAX;
+        char *best = NULL;
+
+        assert(name);
+
+        STRV_FOREACH(s, l) {
+                char *e = startswith(*s, name);
+                if (!e)
+                        continue;
+
+                size_t n = strlen(e);
+                if (n < best_distance) {
+                        best_distance = n;
+                        best = *s;
+                }
+        }
+
+        return best;
+}
+
+static char* strv_find_closest_by_levenshtein(char * const *l, const char *name) {
         ssize_t best_distance = SSIZE_MAX;
         char *best = NULL;
 
@@ -93,6 +114,20 @@ char* strv_find_closest_by_levenshtein(char * const *l, const char *name) {
         return best;
 }
 
+char* strv_find_closest(char * const *l, const char *name) {
+        assert(name);
+
+        /* Be more helpful to the user, and give a hint what the user might have wanted to type. We search
+         * with two mechanisms: a simple prefix match and – if that didn't yield results –, a Levenshtein
+         * word distance based match. */
+
+        char *found = strv_find_closest_prefix(l, name);
+        if (found)
+                return found;
+
+        return strv_find_closest_by_levenshtein(l, name);
+}
+
 char* strv_find_first_field(char * const *needles, char * const *haystack) {
         STRV_FOREACH(k, needles) {
                 char *value = strv_env_pairs_get((char **)haystack, *k);

src/basic/strv.h

@@ -17,7 +17,7 @@ char* strv_find(char * const *l, const char *name) _pure_;
 char* strv_find_case(char * const *l, const char *name) _pure_;
 char* strv_find_prefix(char * const *l, const char *name) _pure_;
 char* strv_find_startswith(char * const *l, const char *name) _pure_;
-char* strv_find_closest_by_levenshtein(char * const *l, const char *name) _pure_;
+char* strv_find_closest(char * const *l, const char *name) _pure_;
 /* Given two vectors, the first a list of keys and the second a list of key-value pairs, returns the value
  * of the first key from the first vector that is found in the second vector. */
 char* strv_find_first_field(char * const *needles, char * const *haystack) _pure_;