vis: introduce registers 0-9 and & to capture search matches

These are currently only updated for `x` and `y` sam commands,
whether they should be updated for other search related activities
(`/`, `?`, `n`, `N`, `*`, `#` etc.) needs to be investigated.

man/vis.1

@@ -116,6 +116,13 @@ system clipboard integration via shell script
 .Xr vis-clipboard 1
 .It \(dq0
 yank register, most recently yanked range
+.It \(dq1-\(dq9
+.It \(dq&
+sub expression matches of most recent
+.Ic x
+or
+.Ic y
+command
 .It \(dq/
 search register, most recently used search pattern
 .It \(dq:
@@ -518,6 +525,12 @@ If the regular expression and its slashes are omitted,
 .Li "/.*\[rs]n/"
 is assumed.
 Null string matches potentially occur before every character of the range and at the end of the range.
+.Pp
+The
+.Ic \(dq1-\(dq9
+and
+.Ic \(dq&
+registers are updated with the (sub) expression matches of the pattern.
 .It Ic y/regexp/ Bq command
 Like
 .Ic x ,

sam.c

@@ -1181,11 +1181,14 @@ static bool cmd_extract(Vis *vis, Win *win, Command *cmd, const char *argv[], Cu
 	if (cmd->regex) {
 		bool trailing_match = false;
 		size_t start = range->start, end = range->end, last_start = EPOS;
-		RegexMatch match[1];
+		size_t nsub = 1 + text_regex_nsub(cmd->regex);
+		if (nsub > 10)
+			nsub = 10;
+		RegexMatch match[nsub];
 		while (start < end || trailing_match) {
 			trailing_match = false;
 			bool found = text_search_range_forward(txt, start,
-				end - start, cmd->regex, 1, match,
+				end - start, cmd->regex, nsub, match,
 				start > range->start ? REG_NOTBOL : 0) == 0;
 			Filerange r = text_range_empty();
 			if (found) {
@@ -1216,6 +1219,12 @@ static bool cmd_extract(Vis *vis, Win *win, Command *cmd, const char *argv[], Cu
 			}
 
 			if (text_range_valid(&r)) {
+				if (found) {
+					for (size_t i = 0; i < nsub; i++) {
+						Register *reg = &vis->registers[VIS_REG_AMPERSAND+i];
+						register_put_range(vis, reg, txt, &match[i]);
+					}
+				}
 				ret &= sam_execute(vis, win, cmd->cmd, NULL, &r);
 				last_start = start;
 			}

vis.c

@@ -37,6 +37,16 @@ const MarkDef vis_marks[] = {
 const RegisterDef vis_registers[] = {
 	[VIS_REG_DEFAULT]    = { '"', "Unnamed register"                                 },
 	[VIS_REG_ZERO]       = { '0', "Yank register"                                    },
+	[VIS_REG_1]          = { '1', "1st sub-expression match"                         },
+	[VIS_REG_2]          = { '2', "2nd sub-expression match"                         },
+	[VIS_REG_3]          = { '3', "3rd sub-expression match"                         },
+	[VIS_REG_4]          = { '4', "4th sub-expression match"                         },
+	[VIS_REG_5]          = { '5', "5th sub-expression match"                         },
+	[VIS_REG_6]          = { '6', "6th sub-expression match"                         },
+	[VIS_REG_7]          = { '7', "7th sub-expression match"                         },
+	[VIS_REG_8]          = { '8', "8th sub-expression match"                         },
+	[VIS_REG_9]          = { '9', "9th sub-expression match"                         },
+	[VIS_REG_AMPERSAND]  = { '&', "Last regex match"                                 },
 	[VIS_REG_BLACKHOLE]  = { '_', "/dev/null register"                               },
 	[VIS_REG_CLIPBOARD]  = { '*', "System clipboard register, see vis-clipboard(1)"  },
 	[VIS_MACRO_REPEAT]   = { '.', "Last inserted text"                               },

vis.h

@@ -400,6 +400,16 @@ void vis_mark_set(Vis*, enum VisMark mark, size_t pos);
 enum VisRegister {
 	VIS_REG_DEFAULT,    /* used when no other register is specified */
 	VIS_REG_ZERO,       /* yank register */
+	VIS_REG_AMPERSAND,  /* last regex match */
+	VIS_REG_1,	    /* 1-9 last sub-expression matches */
+	VIS_REG_2,
+	VIS_REG_3,
+	VIS_REG_4,
+	VIS_REG_5,
+	VIS_REG_6,
+	VIS_REG_7,
+	VIS_REG_8,
+	VIS_REG_9,
 	VIS_REG_BLACKHOLE,  /* /dev/null register */
 	VIS_REG_CLIPBOARD,  /* system clipboard register */
 	VIS_MACRO_REPEAT,   /* copy of the above macro once the recording is finished */