doc: parse gives :incomplete for such input

fixes JuliaLang#9505
[ci skip]

doc/stdlib/base.rst

@@ -541,7 +541,7 @@ Syntax
 
 .. function:: parse(str, start; greedy=true, raise=true)
 
- Parse the expression string and return an expression (which could later be passed to eval for execution). Start is the index of the first character to start parsing. If ``greedy`` is true (default), ``parse`` will try to consume as much input as it can; otherwise, it will stop as soon as it has parsed a valid expression. If ``raise`` is true (default), syntax errors will raise an error; otherwise, ``parse`` will return an expression that will raise an error upon evaluation.
+ Parse the expression string and return an expression (which could later be passed to eval for execution). Start is the index of the first character to start parsing. If ``greedy`` is true (default), ``parse`` will try to consume as much input as it can; otherwise, it will stop as soon as it has parsed a valid expression. Incomplete but otherwise syntactically valid expressions will return ``Expr(:incomplete, "(error message)")``. If ``raise`` is true (default), syntax errors other than incomplete expressions will raise an error. If ``raise`` is false, ``parse`` will return an expression that will raise an error upon evaluation.
 
 .. function:: parse(str; raise=true)