grep.c: display column number of first match

To prepare for 'git grep' learning '--column', teach grep.c's
show_line() how to show the column of the first match on non-context
lines.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

grep.c

@@ -1405,7 +1405,7 @@ static int next_match(struct grep_opt *opt, char *bol, char *eol,
 }
 
 static void show_line(struct grep_opt *opt, char *bol, char *eol,
-		      const char *name, unsigned lno, char sign)
+		      const char *name, unsigned lno, ssize_t cno, char sign)
 {
 	int rest = eol - bol;
 	const char *match_color, *line_color = NULL;
@@ -1440,6 +1440,17 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
 		output_color(opt, buf, strlen(buf), opt->color_lineno);
 		output_sep(opt, sign);
 	}
+	/*
+	 * Treat 'cno' as the 1-indexed offset from the start of a non-context
+	 * line to its first match. Otherwise, 'cno' is 0 indicating that we are
+	 * being called with a context line.
+	 */
+	if (opt->columnnum && cno) {
+		char buf[32];
+		xsnprintf(buf, sizeof(buf), "%"PRIuMAX, (uintmax_t)cno);
+		output_color(opt, buf, strlen(buf), opt->color_columnno);
+		output_sep(opt, sign);
+	}
 	if (opt->color) {
 		regmatch_t match;
 		enum grep_context ctx = GREP_CONTEXT_BODY;
@@ -1545,7 +1556,7 @@ static void show_funcname_line(struct grep_opt *opt, struct grep_source *gs,
 			break;
 
 		if (match_funcname(opt, gs, bol, eol)) {
-			show_line(opt, bol, eol, gs->name, lno, '=');
+			show_line(opt, bol, eol, gs->name, lno, 0, '=');
 			break;
 		}
 	}
@@ -1610,7 +1621,7 @@ static void show_pre_context(struct grep_opt *opt, struct grep_source *gs,
 
 		while (*eol != '\n')
 			eol++;
-		show_line(opt, bol, eol, gs->name, cur, sign);
+		show_line(opt, bol, eol, gs->name, cur, 0, sign);
 		bol = eol + 1;
 		cur++;
 	}
@@ -1809,6 +1820,7 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
 	while (left) {
 		char *eol, ch;
 		int hit;
+		ssize_t cno;
 		ssize_t col = -1, icol = -1;
 
 		/*
@@ -1874,7 +1886,18 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
 				show_pre_context(opt, gs, bol, eol, lno);
 			else if (opt->funcname)
 				show_funcname_line(opt, gs, bol, lno);
-			show_line(opt, bol, eol, gs->name, lno, ':');
+			cno = opt->invert ? icol : col;
+			if (cno < 0) {
+				/*
+				 * A negative cno indicates that there was no
+				 * match on the line. We are thus inverted and
+				 * being asked to show all lines that _don't_
+				 * match a given expression. Therefore, set cno
+				 * to 0 to suggest the whole line matches.
+				 */
+				cno = 0;
+			}
+			show_line(opt, bol, eol, gs->name, lno, cno + 1, ':');
 			last_hit = lno;
 			if (opt->funcbody)
 				show_function = 1;
@@ -1903,7 +1926,7 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
 			/* If the last hit is within the post context,
 			 * we need to show this line.
 			 */
-			show_line(opt, bol, eol, gs->name, lno, '-');
+			show_line(opt, bol, eol, gs->name, lno, col + 1, '-');
 		}
 
 	next_line: