ls(1): actually restore proper behavior

Highlights:
- CLICOLOR in the environment should imply --color=auto to maintain
  compatibility with historical behavior
- -G should set CLICOLOR and imply --color=auto

The manpage has been updated to draw the connection between -G and --color;
the former is in-fact a sort of compromise between --color=always and
--color=auto, where we'll output color regardless of the environment lacking
CLICOLOR/COLORTERM assuming stdout is a tty.

X-MFC-With: r361318

bin/ls/ls.1

@@ -32,7 +32,7 @@
 .\"     @(#)ls.1	8.7 (Berkeley) 7/29/94
 .\" $FreeBSD$
 .\"
-.Dd May 20, 2020
+.Dd May 21, 2020
 .Dt LS 1
 .Os
 .Sh NAME
@@ -135,7 +135,8 @@ This option is equivalent to defining
 .Ev CLICOLOR
 or
 .Ev COLORTERM
-in the environment.
+in the environment and setting
+.Fl -color Ns = Ns Ar auto .
 (See below.)
 This functionality can be compiled out by removing the definition of
 .Ev COLORLS .

bin/ls/ls.c

@@ -265,6 +265,13 @@ main(int argc, char *argv[])
 	fts_options = FTS_PHYSICAL;
 	if (getenv("LS_SAMESORT"))
 		f_samesort = 1;
+
+	/*
+	 * For historical compatibility, we'll use our autodetection if CLICOLOR
+	 * is set.
+	 */
+	if (getenv("CLICOLOR"))
+		colorflag = COLORFLAG_AUTO;
 	while ((ch = getopt_long(argc, argv,
 	    "+1ABCD:FGHILPRSTUWXZabcdfghiklmnopqrstuwxy,", long_opts,
 	    NULL)) != -1) {
@@ -342,7 +349,13 @@ main(int argc, char *argv[])
 			f_slash = 0;
 			break;
 		case 'G':
+			/*
+			 * We both set CLICOLOR here and set colorflag to
+			 * COLORFLAG_AUTO, because -G should not force color if
+			 * stdout isn't a tty.
+			 */
 			setenv("CLICOLOR", "", 1);
+			colorflag = COLORFLAG_AUTO;
 			break;
 		case 'H':
 			fts_options |= FTS_COMFOLLOW;