Rename `subst::Kind` to `subst::GenericArg`
And `subst::UnpackedKind` to `subst::GenericArgKind`. Individual variable names (e.g. `kind`) are not renamed, which would be an infeasible mission.
Fixes https://github.com/rust-lang/rust/issues/64352.
r? @eddyb
reserve `impl<T> From<!> for T`
this is necessary for never-type stabilization.
cc #57012#35121
I think we wanted a crater run for this @nikomatsakis?
r? @nikomatsakis
Remove blanket silencing of "type annotation needed" errors
Remove blanket check for existence of other errors before emitting "type annotation needed" errors, and add some eager checks to avoid adding obligations when they refer to types that reference `[type error]` in order to reduce unneeded errors.
Fix#64084.
Remove blanket check for existence of other errors before emitting
"type annotation needed" errors, and add some eager checks to avoid
adding obligations when they refer to types that reference
`[type error]` in order to reduce unneded errors.
Fixes#63677
RFC #2071 (impl-trait-existential-types) does not explicitly state how
impl trait type alises should interact with coherence. However, there's
only one choice which makes sense - coherence should look at the
underlying type (i.e. the 'defining' type of the impl trait) of the type
alias, just like we do for non-impl-trait type aliases.
Specifically, impl trait type alises which resolve to a local type
should be treated like a local type with respect to coherence (e.g.
impl trait type aliases which resolve to a forieign type should be
treated as a foreign type, and those that resolve to a local type should
be treated as a local type).
Since neither inherent impls nor direct trait impl (i.e. `impl MyType`
or `impl MyTrait for MyType`) are allowd for type aliases, this
usually does not come up. Before we ever attempt to do coherence
checking, we will have errored out if an impl trait type alias was used
directly in an 'impl' clause.
However, during trait selection, we sometimes need to prove bounds like
'T: Sized' for some type 'T'. If 'T' is an impl trait type alias, this
requires to know the coherence behavior for impl trait type aliases when
we perform coherence checking.
Note: Since determining the underlying type of an impl trait type alias
requires us to perform body type checking, this commit causes us to type
check some bodies easlier than we otherwise would have. However, since
this is done through a query, this shouldn't cause any problems
For completeness, I've added an additional test of the coherence-related
behavior of impl trait type aliases.
The super-hot call site of `inlined_shallow_resolve()` basically does
`r.inlined_shallow_resolve(ty) != ty`. This commit introduces a
version of that function specialized for that particular call pattern,
`shallow_resolve_changed()`. Incredibly, this reduces the instruction
count for `keccak` by 5%.
The commit also renames `inlined_shallow_resolve()` as
`shallow_resolve()` and removes the `inline(always)` annotation, as it's
no longer nearly so hot.
Minimize uses of `LocalInternedString`
`LocalInternedString` is described as "An alternative to `Symbol` and `InternedString`, useful when the chars within the symbol need to be accessed. It is best used for temporary values."
This PR makes the code match that comment, by removing all non-local uses of `LocalInternedString`. This allows the removal of a number of operations on `LocalInternedString` and a couple of uses of `unsafe`.
