vis: introduce vis_keys_utf8

libutf.h

@@ -23,7 +23,7 @@ typedef unsigned long Rune;
 #endif
 #endif
 
-#define UTFmax 6 /* maximum bytes per rune */
+#define UTFmax 4 /* maximum bytes per rune */
 
 #define Runeself 0x80             /* rune and utf are equal (<) */
 #define Runemax  RUNE_C(0x10FFFF) /* maximum rune value */

vis.c

@@ -962,6 +962,15 @@ long vis_keys_codepoint(Vis *vis, const char *keys) {
 	return -1;
 }
 
+bool vis_keys_utf8(Vis *vis, const char *keys, char utf8[static UTFmax+1]) {
+	Rune rune = vis_keys_codepoint(vis, keys);
+	if (rune == (Rune)-1)
+		return false;
+	size_t len = runetochar(utf8, &rune);
+	utf8[len] = '\0';
+	return true;
+}
+
 static void vis_keys_process(Vis *vis, size_t pos) {
 	Buffer *buf = vis->keys;
 	char *keys = buf->data + pos, *start = keys, *cur = keys, *end = keys, *binding_end = keys;;

vis.h

@@ -12,6 +12,7 @@ typedef struct Win Win;
 #include "ui.h"
 #include "view.h"
 #include "text-regex.h"
+#include "libutf.h"
 
 /* simplify utility renames by distribution packagers */
 #ifndef VIS_MENU
@@ -503,6 +504,9 @@ int vis_pipe_collect(Vis *vis, Filerange *range, const char *argv[], char **out,
 const char *vis_keys_next(Vis*, const char *keys);
 /* Tries to convert next symbolic key to a raw code point, returns -1 for unknown keys */
 long vis_keys_codepoint(Vis*, const char *keys);
+/* Tries to convert next symbolic key to a UTF-8 sequence. Returns false for unknown keys
+ * and leaves `utf8` untouched. Guarantees that `utf8` is NUL terminated on success */
+bool vis_keys_utf8(Vis*, const char *keys, char utf8[static UTFmax+1]);
 /* vis operates as a finite state machine (FSM), feeding keys from an input
  * queue (or a previously recorded macro) to key handling functions (see struct
  * KeyAction) which consume the input.