Function flatten

pub fn flatten<'a, I>(nodes: I) -> IndexMap<String, FlatNode>
where
    I: IntoIterator<Item = &'a IfcxNode>,

Merges input nodes into one FlatNode per path.

This borrows the nodes, so every attribute value is copied into the result. When the nodes are not needed afterwards, flatten_owned gives the same result without copying them, which is several times faster on large models.

nodes must be in layer order, weakest first: the nodes of one file in file order, and for a layer stack the nodes of each layer after those of the layers it overrides. Later nodes win, as described on FlatNode::merge.

The result is keyed by path, in order of each path’s first appearance. Every map keeps insertion order. Upstream stores these maps in JavaScript objects, which list integer-like keys such as "2" first; that ordering quirk is not reproduced, the content is the same. Paths are compared as plain strings, so a/b is a node of its own here; composition applies it to child b of a.

use openbim_ifcx::{flatten, IfcxNode};

let layers: Vec<IfcxNode> = serde_json::from_str(r#"[
    {"path": "w", "children": {"Body": "b1"}, "inherits": {"Type": "t"},
     "attributes": {"x::height": 2.5}},
    {"path": "w", "children": {"Body": null}, "inherits": {"Type": null},
     "attributes": {"x::height": 3.0}}
]"#)?;
let flat = flatten(&layers);
let wall = &flat["w"];
assert_eq!(wall.children["Body"], None);
assert!(wall.inherits.is_empty());
assert_eq!(*wall.attributes["x::height"], 3.0);