That's not a problem with the line joining stuff. Both `return' and `{ foo: bar }' are ENTIRE VALID statements in their own right.

returnStmt ::= "return" [ expression ] (";" or EOL)

Note that expression is optional, so it's the choice of `return' by itself being a valid statement on its own that "causes problems".

Plus, this is not really a problem that can be solved by simply putting semicolons everywhere. You can't change the parser rules by including or not semicolons.

Also, same thing with break/continue:

breakStmt ::= "break" [ label ] (";" or EOL)

continueStmt ::= "continue" [ label ] (";" or EOL)