Never create empty databases.

When pkg_add(1)ing packages installing manual pages into some directory,
the database in that directory automatically gets created or updated,
no change so far.  This patch causes the database file to be
automatically unlinked when pkg_delete(1)ing the last package having
manual pages in that directory, to leave less cruft behind.

Suggested by ajacoutot@.

2 files changed, 25 insertions, 0 deletions

diff --git a/makewhatis.8 b/makewhatis.8
index 080a9b79..cf675e89 100644
--- a/makewhatis.8
+++ b/makewhatis.8
@@ -74,6 +74,8 @@ and
 .Sm on
 in that directory.
 Existing databases are replaced.
+If a directory contains no manual pages, no database is created in that
+directory.
 If
 .Ar dir
 is not provided,
@@ -130,6 +132,7 @@ Remove
 .Ar
 from the database in
 .Ar dir .
+If that causes the database to become empty, also delete the database file.
 .El
 .Pp
 If fatal parse errors are encountered while parsing, the offending file
diff --git a/mandocdb.c b/mandocdb.c
index 6990bbed..b74c31bd 100644
--- a/mandocdb.c
+++ b/mandocdb.c
@@ -2122,6 +2122,23 @@ dbwrite(struct dba *dba)
 	int		 status;
 	pid_t		 child;
 
+	/*
+	 * Do not write empty databases, and delete existing ones
+	 * when makewhatis -u causes them to become empty.
+	 */
+
+	dba_array_start(dba->pages);
+	if (dba_array_next(dba->pages) == NULL) {
+		if (unlink(MANDOC_DB) == -1)
+			say(MANDOC_DB, "&unlink");
+		return;
+	}
+
+	/*
+	 * Build the database in a temporary file,
+	 * then atomically move it into place.
+	 */
+
 	if (dba_write(MANDOC_DB "~", dba) != -1) {
 		if (rename(MANDOC_DB "~", MANDOC_DB) == -1) {
 			exitcode = (int)MANDOCLEVEL_SYSERR;
@@ -2131,6 +2148,11 @@ dbwrite(struct dba *dba)
 		return;
 	}
 
+	/*
+	 * We lack write permission and cannot replace the database
+	 * file, but let's at least check whether the data changed.
+	 */
+
 	(void)strlcpy(tfn, "/tmp/mandocdb.XXXXXXXX", sizeof(tfn));
 	if (mkdtemp(tfn) == NULL) {
 		exitcode = (int)MANDOCLEVEL_SYSERR;