"DO:" contains only one statement

Rule "do1" gives this warning when it finds a DO: ... END block that contains only one statement.
The statement will work without the DO/END block around it.

Actually, the rule only looks at DO/END blocks in the THEN or ELSE branches of an IF statement:

IF condition THEN DO:
   /* this block is inspected */
END.
ELSE DO:
   /* this block is also inspected */
END.
DO:
  /* this block is not inspected because it is
     not in a THEN or ELSE branch. */
END.

Furthermore, the rule does NOT raise a warning when the DO...END block contains an IF statement. That is because an IF statement inside an IF statement is usually hard to read but adding a DO...END block improves readability. So, you get a bonus for improving readability :-)

IF condition THEN DO:
   /* only 1 statement in the DO..END block 
      but no warning, because it's an IF statement */
   IF a=b THEN 
      a = a + 8.
   ELSE
      a = b * b.
END.

Likewise, the rule does not warn if the only statement is a CASE, FOR, DO or REPEAT statement. This list is set in prolint.properties.p (see property "rules.do1.StatementSkipList") so you can customize it.

the risc:

The DO/END-block wastes about 60 bytes in R-code and affects run-time performance.

how to solve this:

Just remove the DO: and END.