Add the support for '-f' option in dropdb utility.

Specifying '-f' will add the 'force' option to the DROP DATABASE command
sent to the server.  This will try to terminate all existing connections
to the target database before dropping it.

Author: Pavel Stehule
Reviewed-by: Vignesh C and Amit Kapila
Discussion: https://postgr.es/m/CAP_rwwmLJJbn70vLOZFpxGw3XD7nLB_7+NKz46H5EOO2k5H7OQ@mail.gmail.com

doc/src/sgml/ref/dropdb.sgml

@@ -86,6 +86,18 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>-f</option></term>
+      <term><option>--force</option></term>
+      <listitem>
+       <para>
+        Attempt to terminate all existing connections to the target database
+        before dropping it.   See <xref linkend="sql-dropdatabase"/> for more
+        information on this option.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
        <term><option>-V</option></term>
        <term><option>--version</option></term>

src/bin/scripts/dropdb.c

@@ -34,6 +34,7 @@ main(int argc, char *argv[])
 		{"interactive", no_argument, NULL, 'i'},
 		{"if-exists", no_argument, &if_exists, 1},
 		{"maintenance-db", required_argument, NULL, 2},
+		{"force", no_argument, NULL, 'f'},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -49,6 +50,7 @@ main(int argc, char *argv[])
 	enum trivalue prompt_password = TRI_DEFAULT;
 	bool		echo = false;
 	bool		interactive = false;
+	bool		force = false;
 
 	PQExpBufferData sql;
 
@@ -61,7 +63,7 @@ main(int argc, char *argv[])
 
 	handle_help_version_opts(argc, argv, "dropdb", help);
 
-	while ((c = getopt_long(argc, argv, "h:p:U:wWei", long_options, &optindex)) != -1)
+	while ((c = getopt_long(argc, argv, "h:p:U:wWeif", long_options, &optindex)) != -1)
 	{
 		switch (c)
 		{
@@ -86,6 +88,9 @@ main(int argc, char *argv[])
 			case 'i':
 				interactive = true;
 				break;
+			case 'f':
+				force = true;
+				break;
 			case 0:
 				/* this covers the long options */
 				break;
@@ -123,8 +128,10 @@ main(int argc, char *argv[])
 
 	initPQExpBuffer(&sql);
 
-	appendPQExpBuffer(&sql, "DROP DATABASE %s%s;",
+	appendPQExpBuffer(&sql, "DROP DATABASE %s%s%s;",
-					  (if_exists ? "IF EXISTS " : ""), fmtId(dbname));
+					  (if_exists ? "IF EXISTS " : ""),
+					  fmtId(dbname),
+					  force ? " WITH (FORCE)" : "");
 
 	/* Avoid trying to drop postgres db while we are connected to it. */
 	if (maintenance_db == NULL && strcmp(dbname, "postgres") == 0)
@@ -159,6 +166,7 @@ help(const char *progname)
 	printf(_("\nOptions:\n"));
 	printf(_("  -e, --echo                show the commands being sent to the server\n"));
 	printf(_("  -i, --interactive         prompt before deleting anything\n"));
+	printf(_("  -f, --force               try to terminate other connections before dropping\n"));
 	printf(_("  -V, --version             output version information, then exit\n"));
 	printf(_("  --if-exists               don't report error if database doesn't exist\n"));
 	printf(_("  -?, --help                show this help, then exit\n"));

src/bin/scripts/t/050_dropdb.pl

@@ -3,7 +3,7 @@ use warnings;
 
 use PostgresNode;
 use TestLib;
-use Test::More tests => 11;
+use Test::More tests => 13;
 
 program_help_ok('dropdb');
 program_version_ok('dropdb');
@@ -19,5 +19,11 @@ $node->issues_sql_like(
 	qr/statement: DROP DATABASE foobar1/,
 	'SQL DROP DATABASE run');
 
+$node->safe_psql('postgres', 'CREATE DATABASE foobar2');
+$node->issues_sql_like(
+	[ 'dropdb', '--force', 'foobar2' ],
+	qr/statement: DROP DATABASE foobar2 WITH \(FORCE\);/,
+	'SQL DROP DATABASE (FORCE) run');
+
 $node->command_fails([ 'dropdb', 'nonexistent' ],
 	'fails with nonexistent database');