Stage 1: ISO 10303-21 STEP text parser (kofem-geom crate)

[mkofler96]

Goal

Create the kofem-geom crate and implement a parser for the ISO 10303-21 exchange format used by all STEP files.

Background

new_bracket_2.stp (72 765 lines) is our reference file. Analysis shows it contains:

• 26 691 CARTESIAN_POINT entities
• 486 ADVANCED_FACE entities
• 1 133 EDGE_CURVE entities
• 651 VERTEX_POINT entities
• 520 B_SPLINE_CURVE_WITH_KNOTS, 15 B_SPLINE_SURFACE_WITH_KNOTS

What to build

File: crates/kofem-geom/src/step/parser.rs

Parse the ASCII exchange format:

ISO-10303-21;
HEADER; … ENDSEC;
DATA;
#1 = CARTESIAN_POINT('', (0., 0., 0.));
#2 = LINE('label', #1, #3);
ENDSEC;
END-ISO-10303-21;

Each entity is #id = TYPE(arg, arg, …); and may span multiple lines.

Output types:

pub struct StepEntity {
    pub id: u64,
    pub type_name: String,
    pub args: Vec<Arg>,
}

pub enum Arg {
    String(String),
    Real(f64),
    Integer(i64),
    Ref(u64),       // #42
    List(Vec<Arg>), // (a, b, c)
    Enum(String),   // .FORWARD.
    Omitted,        // $
}

pub type StepFile = HashMap<u64, StepEntity>;

pub fn parse(text: &str) -> Result<StepFile, ParseError>;

TDD test cases

// RED → GREEN 1: entity count
#[test]
fn parses_bracket_entity_count() {
    let file = parse(include_str!("../../../test_files/new_bracket_2.stp")).unwrap();
    assert!(file.len() > 30_000);
}

// RED → GREEN 2: CARTESIAN_POINT args
#[test]
fn parses_cartesian_point_coords() {
    let snippet = "ISO-10303-21;\nHEADER;\nFILE_DESCRIPTION((''));\nENDSEC;\nDATA;\n\
        #97=CARTESIAN_POINT('',(4.388981755810E-8,1.467728130595E1,3.159218055376E1));\n\
        ENDSEC;\nEND-ISO-10303-21;";
    let file = parse(snippet).unwrap();
    let e = file.get(&97).unwrap();
    assert_eq!(e.type_name, "CARTESIAN_POINT");
    if let Arg::List(coords) = &e.args[1] {
        assert_eq!(coords.len(), 3);
        if let Arg::Real(x) = coords[0] { assert!((x - 4.388981755810E-8).abs() < 1e-15); }
    } else { panic!("expected List"); }
}

// RED → GREEN 3: count faces
#[test]
fn bracket_has_486_advanced_faces() {
    let file = parse(include_str!("../../../test_files/new_bracket_2.stp")).unwrap();
    let n = file.values().filter(|e| e.type_name == "ADVANCED_FACE").count();
    assert_eq!(n, 486);
}

Implementation notes

• Handle multi-line entities by stripping \n from the DATA section before splitting on ;
• String literals use '' for an escaped apostrophe
• Enums look like .FORWARD.
• $ means omitted / null
• Ref: #\d+

Acceptance criteria

• All three tests pass
• cargo test -p kofem-geom is clean
• cargo clippy -p kofem-geom -- -D warnings is clean