Support literal numbers with explicit plus sign (#633)

[volsa]

Hi, #633 looked like a beginner friendly issue so I thought I'd give it a shot; the PR should be hopefully OK :)

[codecov-commenter]

Codecov Report

Base: 93.76% // Head: 93.76% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (87b6040) compared to base (35842fa).
Patch coverage: 76.47% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #640   +/-   ##
=======================================
  Coverage   93.76%   93.76%           
=======================================
  Files          46       46           
  Lines       17604    17620   +16     
=======================================
+ Hits        16506    16522   +16     
  Misses       1098     1098           

Impacted Files	Coverage Δ
src/parser/expressions_parser.rs	94.60% <76.47%> (+0.11%)	⬆️

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[riederm]

hi @volsa, thx for the PR!
the check-style-step of the build failed, you can fix the formatting via: cargo fmt

[riederm]

this ST-code is not 100% correct. it should maybe look like this:

PROGRAM exp
   VAR
      x : INT;
   END_VAR
   x := 1;
   x := +1;
END_PROGRAM

[volsa]

Out of curiosity, would the following ST-code also be wrong because it's missing a VAR block?

PROGRAM exp 
x := NULL;
END_PROGRAM

(taken from the assignment_to_null() test)

[riederm]

Out of curiosity, would the following ST-code also be wrong because it's missing a VAR block?

PROGRAM exp 
x := NULL;
END_PROGRAM

(taken from the assignment_to_null() test)

so technically this works, if x is declared somewhere as a global variable. When we do parse tests, we often dont have semantically correct cases: (e.g. we dont care if x would resolve to something meaningful or not).
your sourcode mixed a statement and a declaration, you cannot have declarations outside of VAR-blocks.

I was really surprised that the parser actually returned something 😄 . but if you look at your assignment, the parser created something very strange:
Assignment{ left: "DINT", right: "1" }

so the parser thought that DINT is an identifer to a variable.

[volsa]

Yeah that makes sense, thanks for clarifying.

[riederm]

I did some experiments and it looks like this code only covers behavior for literals. Can we also fix & test the behavior for reference?

like: ? x := +x;. I know it does nothing, but we should be able to parse it. I think this would just require a small tweak in

rusty/src/parser/expressions_parser.rs

Lines 171 to 178 in 44bad56

	fn parse_unary_expression(lexer: &mut ParseSession) -> AstStatement {
	let operator = match lexer.token {
	OperatorNot => Some(Operator::Not),
	OperatorMinus => Some(Operator::Minus),
	OperatorAmp => Some(Operator::Address),
	_ => None,
	};

to also allow the plus sign.

[volsa]

Done! Fingers crossed the style-checker doesn't throw an error :P

[riederm]

very nice, thx! 👍