There's a funny bug with the way newlines are handled

[Michael-F-Bryan]

TL;DR:

/// For some reason we were parsing the G90, then an empty G01 and the
/// actual G01.
#[test]
fn funny_bug_in_crate_example() {
    let src = "G90 \n G01 X50.0 Y-10";
    let expected = vec![
        GCode::new(Mnemonic::General, 90.0, Span::PLACEHOLDER),
        GCode::new(Mnemonic::General, 1.0, Span::PLACEHOLDER)
            .with_argument(Word::new('X', 50.0, Span::PLACEHOLDER))
            .with_argument(Word::new('Y', -10.0, Span::PLACEHOLDER)),
    ];

    let got: Vec<_> = crate::parse(src).collect();

    assert_eq!(got, expected);
}

Fails with

thread 'parser::tests::funny_bug_in_crate_example' panicked at 'assertion failed: `(left == right)`
  left: `[GCode { mnemonic: General, number: 90.0, arguments: [], span: Span { start: 0, end: 3, line: 0 } }, GCode { mnemonic: General, number: 1.0, arguments: [], span: Span { start: 6, end: 9, line: 1 } }, GCode { mnemonic: General, number: 1.0, arguments: [Word { letter: 'X', value: 50.0, span: Span { start: 10, end: 15, line: 1 } }, Word { letter: 'Y', value: -10.0, span: Span { start: 16, end: 20, line: 1 } }], span: Span { start: 6, end: 9, line: 1 } }]`,
 right: `[GCode { mnemonic: General, number: 90.0, arguments: [], span: <placeholder> }, GCode { mnemonic: General, number: 1.0, arguments: [Word { letter: 'X', value: 50.0, span: <placeholder> }, Word { letter: 'Y', value: -10.0, span: <placeholder> }], span: <placeholder> }]`', gcode/src/parser.rs:437:9

(note the G01 with no arguments in the middle)

I've been able to consistently reproduce this bug with the following code:

extern crate gcode;

fn main() {
    let gcode_string = "G0 X1\nG1 Y2";
    let parse_result: Vec<_> = gcode::parse(gcode_string).collect();
    assert_eq!(parse_result.len(), 2);
}

This fails with actual length 3 instead of 2.

Prepending line numbers for every line seems to solve it:

let gcode_string = "N0 G0 X1\nN1 G1 Y2";

This correctly returns 2 commands.
I've analyzed the parser more closely by using the full_parse_with_callback function and found that Line 0 thinks it contains 2 GCodes and Line 1 contains 1 GCode, but when printing out the actual GCodes returned i see 1 GCode on line 0 and 2 GCodes on line 1: The empty one and the correct one. So there seems to be the difference.

Finally, the parser runs correct when i use 2 empty G-codes:

let gcode_string = "G0\nG1";

This returns 2 commands.