Add more tab completion support for ALTER TABLE ADD in psql

This includes the detection of new patterns for various constraint
types, with the addition of USING INDEX for unique indexes of a table
on primary keys and unique constraints.

Author: Dagfinn Ilmari Mannsåker
Discussion: https://postgr.es/m/87bl6ehhpl.fsf@wibble.ilmari.org

src/bin/psql/tab-complete.c

@@ -776,6 +776,10 @@ static const SchemaQuery Query_for_list_of_collations = {
 "       and pg_catalog.quote_ident(c1.relname)='%s'"\
 "       and pg_catalog.pg_table_is_visible(c2.oid)"
 
+#define Query_for_unique_index_of_table \
+Query_for_index_of_table \
+"       and i.indisunique"
+
 /* the silly-looking length condition is just to eat up the current word */
 #define Query_for_constraint_of_table \
 "SELECT pg_catalog.quote_ident(conname) "\
@@ -2019,6 +2023,45 @@ psql_completion(const char *text, int start, int end)
 					  "OWNER TO", "SET", "VALIDATE CONSTRAINT",
 					  "REPLICA IDENTITY", "ATTACH PARTITION",
 					  "DETACH PARTITION", "FORCE ROW LEVEL SECURITY");
+	/* ALTER TABLE xxx ADD */
+	else if (Matches("ALTER", "TABLE", MatchAny, "ADD"))
+		COMPLETE_WITH("COLUMN", "CONSTRAINT", "CHECK", "UNIQUE", "PRIMARY KEY",
+					  "EXCLUDE", "FOREIGN KEY");
+	/* ALTER TABLE xxx ADD CONSTRAINT yyy */
+	else if (Matches("ALTER", "TABLE", MatchAny, "ADD", "CONSTRAINT", MatchAny))
+		COMPLETE_WITH("CHECK", "UNIQUE", "PRIMARY KEY", "EXCLUDE", "FOREIGN KEY");
+	/* ALTER TABLE xxx ADD [CONSTRAINT yyy] (PRIMARY KEY|UNIQUE) */
+	else if (Matches("ALTER", "TABLE", MatchAny, "ADD", "PRIMARY", "KEY") ||
+			 Matches("ALTER", "TABLE", MatchAny, "ADD", "UNIQUE") ||
+			 Matches("ALTER", "TABLE", MatchAny, "ADD", "CONSTRAINT", MatchAny, "PRIMARY", "KEY") ||
+			 Matches("ALTER", "TABLE", MatchAny, "ADD", "CONSTRAINT", MatchAny, "UNIQUE"))
+		COMPLETE_WITH("(", "USING INDEX");
+	/* ALTER TABLE xxx ADD PRIMARY KEY USING INDEX */
+	else if (Matches("ALTER", "TABLE", MatchAny, "ADD", "PRIMARY", "KEY", "USING", "INDEX"))
+	{
+		completion_info_charp = prev6_wd;
+		COMPLETE_WITH_QUERY(Query_for_unique_index_of_table);
+	}
+	/* ALTER TABLE xxx ADD UNIQUE USING INDEX */
+	else if (Matches("ALTER", "TABLE", MatchAny, "ADD", "UNIQUE", "USING", "INDEX"))
+	{
+		completion_info_charp = prev5_wd;
+		COMPLETE_WITH_QUERY(Query_for_unique_index_of_table);
+	}
+	/* ALTER TABLE xxx ADD CONSTRAINT yyy PRIMARY KEY USING INDEX */
+	else if (Matches("ALTER", "TABLE", MatchAny, "ADD", "CONSTRAINT", MatchAny,
+					 "PRIMARY", "KEY", "USING", "INDEX"))
+	{
+		completion_info_charp = prev8_wd;
+		COMPLETE_WITH_QUERY(Query_for_unique_index_of_table);
+	}
+	/* ALTER TABLE xxx ADD CONSTRAINT yyy UNIQUE USING INDEX */
+	else if (Matches("ALTER", "TABLE", MatchAny, "ADD", "CONSTRAINT", MatchAny,
+					 "UNIQUE", "USING", "INDEX"))
+	{
+		completion_info_charp = prev7_wd;
+		COMPLETE_WITH_QUERY(Query_for_unique_index_of_table);
+	}
 	/* ALTER TABLE xxx ENABLE */
 	else if (Matches("ALTER", "TABLE", MatchAny, "ENABLE"))
 		COMPLETE_WITH("ALWAYS", "REPLICA", "ROW LEVEL SECURITY", "RULE",