Relations between various id's in HIR and ways to query HIR trees

1

For the context, what I am working on right now is to prototype a codegen backend of some tree representation of a downstream language, so I figured it might be helpful to generate from HIR instead of MIR (because structures like if are lost). Now in my codegen function, I am having an Instance, and I want to obtain the corresponding HIR representation.

I have read https://rustc-dev-guide.rust-lang.org/hir.html but I am still puzzled by the relations between various id's. I thought that different id's should essentially correspond each other, but it doesn't seem to be the case. For example, as_local_node_id gives an Option. It doesn't quite ring a bell to me because according to the doc, NodeId is some absolute identifier of a tree so if I am given a DefId, in what case the NodeId doesn't exist? What's the recommended way to obtain an HIR tree from a DefId?

Currently, in order to obtain an HirId, I am doing:

let hirid = tcx.hir().node_id_to_hir_id(tcx.hir().as_local_node_id(instance.def_id()).unwrap());
let hir = tcx.hir().find(hirid);

Does that make sense?

2

For example, as_local_node_id gives an Option. It doesn't quite ring a bell to me because according to the doc, NodeId is some absolute identifier of a tree so if I am given a DefId, in what case the NodeId doesn't exist?

The name is a hint. It returns None when DefId does not refer to a node in the local crate.

3

This topic was automatically closed 90 days after the last reply. New replies are no longer allowed.