Allow run-script output to have comment-lines and blank lines.

This makes the run-script output a little more lenient, so one could
output blank lines or comments to make things more readable for
debugging.

src/tup/parser.c

@@ -1032,10 +1032,6 @@ int exec_run_script(struct tupfile *tf, const char *cmdline, int lno)
 	while(p[0]) {
 		char *newline;
 		rslno++;
-		if(p[0] != ':') {
-			fprintf(tf->f, "tup error: run-script line %i is not a :-rule - '%s'\n", rslno, p);
-			goto out_err;
-		}
 		newline = strchr(p, '\n');
 		if(!newline) {
 			fprintf(tf->f, "tup error: Missing newline from :-rule in run script: '%s'\n", p);
@@ -1044,8 +1040,18 @@ int exec_run_script(struct tupfile *tf, const char *cmdline, int lno)
 		*newline = 0;
 		if(debug_run)
 			fprintf(tf->f, "%s\n", p);
-		if(parse_rule(tf, p+1, lno) < 0) {
-			fprintf(tf->f, "tup error: Unable to parse :-rule from run script: '%s'\n", p);
+		if(p[0] == ':') {
+			if(parse_rule(tf, p+1, lno) < 0) {
+				fprintf(tf->f, "tup error: Unable to parse :-rule from run script: '%s'\n", p);
+				goto out_err;
+			}
+		} else if(p[0] == '#' || p[0] == 0) {
+			/* Skip comments and blank lines */
+			if(debug_run) {
+				fprintf(tf->f, "Skipping non :-rule line %i: %s\n", rslno, p);
+			}
+		} else {
+			fprintf(tf->f, "tup error: run-script line %i is not a :-rule - '%s'\n", rslno, p);
 			goto out_err;
 		}
 		p = newline + 1;

test/t2247-run-blankline.sh

@@ -0,0 +1,38 @@
+#! /bin/sh -e
+# tup - A file-based build system
+#
+# Copyright (C) 2024  Mike Shal <[email protected]>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+# Make sure run script can ignore blank lines.
+
+. ./tup.sh
+check_no_windows run-script
+
+cat > gen.sh << HERE
+#! /usr/bin/env bash
+for i in *; do
+	echo ": |> echo \$i |>"
+	echo ""
+done
+HERE
+chmod +x gen.sh
+
+cat > Tupfile << HERE
+run ./gen.sh
+HERE
+update
+
+eotup

test/t2248-run-comments.sh

@@ -0,0 +1,38 @@
+#! /bin/sh -e
+# tup - A file-based build system
+#
+# Copyright (C) 2024  Mike Shal <[email protected]>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+# Make sure run script can ignore comments.
+
+. ./tup.sh
+check_no_windows run-script
+
+cat > gen.sh << HERE
+#! /usr/bin/env bash
+for i in *; do
+	echo "# basic echo rule"
+	echo ": |> echo \$i |>"
+done
+HERE
+chmod +x gen.sh
+
+cat > Tupfile << HERE
+run ./gen.sh
+HERE
+update
+
+eotup