associated_item table is not populated after type error.

[nrc]

This is the underlying cause of the ICE in #39957. I worked around it in save-analysis, but @eddyb (cc) asked me to file an issue since it might cause bugs elsewhere.

Example code:

#![feature(try_from)]
use std::convert::TryFrom;

struct Test;
impl Test {
    fn foo(&self) -> &'static str {
        "asdf"
    }
}

impl TryFrom for Test {} //~ ERROR: wrong number of type arguments: expected 1, found 0

Because of the error on the last line, we never create the associated_item table on the tcx, which means that both impl_of_method and trait_of_item return None for foo.

[arielb1]

associated_item is constructed on demand:

rust/src/librustc/ty/mod.rs

Line 2051 in 042728e

pub fn associated_item(self, def_id: DefId) -> AssociatedItem {

, so I wonder what is going on here. Can you confirm that impl_of_method returns None?

[eddyb]

@arielb1 The solution proposed on IRC is to remove both of those and instead have a way of checking if a an arbitrary DefId is an associated item and/or get an Option<ty::AssociatedItem> from it.
It's fairly simple, for cross-crate you check describe_def and locally the variant of hir::map::Node.

[arielb1]

@eddyb

Well, now that we have "HIR" AssociatedItem, we can move it to the HIR map.

[eddyb]

Right, that'd make sense. There's a bunch of these that should be moved to HIR.