When a member access names an interface member, perform impl lookup to
find the impl and its corresponding member.
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Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
A couple of minor functional changes here:
- We now always create a `name_ref` for the name referred to by the
right-hand operand of member access. Previously we skipped creating this
instruction if the referenced name was a field, and just created the
field access instruction. This makes our processing of member accesses
and our SemIR representation a bit more uniform.
- We now perform lookup into the type of the left-hand operand if it's
any type with a scope, not just for classes. This means we do lookup
into interface types. However, doing so isn't really useful yet because
it always finds an associated entity that isn't usable by itself. This
changes the diagnostic in
`toolchain/check/testdata/interface/fail_todo_facet_lookup.carbon`.
The member access logic is fairly large, and will be growing with the
addition of impl lookup. Factor it out to separate the logic for dealing
with handling the parse node and updating the node stack from the logic
that checks and builds the member access expression.
Richard SmithandJon Ross-Perkins