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Auto merge of #79169 - LeSeulArtichaut:ty-lib, r=nikomatsakis

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Create `rustc_type_ir`

Decided to start small 😄

This PR creates a `rustc_type_ir` crate as part of the WG-Traits plan to create a shared type library.
~~There already exists a `rustc_ty` crate, so I named the new crate `rustc_ty_library`. However I think it would make sense to rename the current `rustc_ty` to something else (e.g. `rustc_ty_passes`) to free the name for this new crate.~~

r? `@jackh726`
This commit is contained in:
bors
2020-12-12 12:36:18 +00:00
parent c3ed6681ff 0cf5a8ad15
commit 3f2088aa60
6 changed files with 234 additions and 194 deletions
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110
compiler/rustc_middle/src/ty/sty.rs
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@@ -1289,53 +1289,6 @@ impl<'tcx> ParamConst {
}
}
rustc_index::newtype_index! {
/// A [De Bruijn index][dbi] is a standard means of representing
/// regions (and perhaps later types) in a higher-ranked setting. In
/// particular, imagine a type like this:
///
/// for<'a> fn(for<'b> fn(&'b isize, &'a isize), &'a char)
/// ^ ^ | | |
/// | | | | |
/// | +------------+ 0 | |
/// | | |
/// +----------------------------------+ 1 |
/// | |
/// +----------------------------------------------+ 0
///
/// In this type, there are two binders (the outer fn and the inner
/// fn). We need to be able to determine, for any given region, which
/// fn type it is bound by, the inner or the outer one. There are
/// various ways you can do this, but a De Bruijn index is one of the
/// more convenient and has some nice properties. The basic idea is to
/// count the number of binders, inside out. Some examples should help
/// clarify what I mean.
///
/// Let's start with the reference type `&'b isize` that is the first
/// argument to the inner function. This region `'b` is assigned a De
/// Bruijn index of 0, meaning "the innermost binder" (in this case, a
/// fn). The region `'a` that appears in the second argument type (`&'a
/// isize`) would then be assigned a De Bruijn index of 1, meaning "the
/// second-innermost binder". (These indices are written on the arrays
/// in the diagram).
///
/// What is interesting is that De Bruijn index attached to a particular
/// variable will vary depending on where it appears. For example,
/// the final type `&'a char` also refers to the region `'a` declared on
/// the outermost fn. But this time, this reference is not nested within
/// any other binders (i.e., it is not an argument to the inner fn, but
/// rather the outer one). Therefore, in this case, it is assigned a
/// De Bruijn index of 0, because the innermost binder in that location
/// is the outer fn.
///
/// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
#[derive(HashStable)]
pub struct DebruijnIndex {
DEBUG_FORMAT = "DebruijnIndex({})",
const INNERMOST = 0,
}
}
pub type Region<'tcx> = &'tcx RegionKind;
/// Representation of regions. Note that the NLL checker uses a distinct
@@ -1450,7 +1403,7 @@ pub enum RegionKind {
/// Region bound in a function scope, which will be substituted when the
/// function is called.
ReLateBound(DebruijnIndex, BoundRegion),
ReLateBound(ty::DebruijnIndex, BoundRegion),
/// When checking a function body, the types of all arguments and so forth
/// that refer to bound region parameters are modified to refer to free
@@ -1614,65 +1567,6 @@ impl<'tcx> PolyExistentialProjection<'tcx> {
}
}
impl DebruijnIndex {
/// Returns the resulting index when this value is moved into
/// `amount` number of new binders. So, e.g., if you had
///
/// for<'a> fn(&'a x)
///
/// and you wanted to change it to
///
/// for<'a> fn(for<'b> fn(&'a x))
///
/// you would need to shift the index for `'a` into a new binder.
#[must_use]
pub fn shifted_in(self, amount: u32) -> DebruijnIndex {
DebruijnIndex::from_u32(self.as_u32() + amount)
}
/// Update this index in place by shifting it "in" through
/// `amount` number of binders.
pub fn shift_in(&mut self, amount: u32) {
*self = self.shifted_in(amount);
}
/// Returns the resulting index when this value is moved out from
/// `amount` number of new binders.
#[must_use]
pub fn shifted_out(self, amount: u32) -> DebruijnIndex {
DebruijnIndex::from_u32(self.as_u32() - amount)
}
/// Update in place by shifting out from `amount` binders.
pub fn shift_out(&mut self, amount: u32) {
*self = self.shifted_out(amount);
}
/// Adjusts any De Bruijn indices so as to make `to_binder` the
/// innermost binder. That is, if we have something bound at `to_binder`,
/// it will now be bound at INNERMOST. This is an appropriate thing to do
/// when moving a region out from inside binders:
///
/// ```
/// for<'a> fn(for<'b> for<'c> fn(&'a u32), _)
/// // Binder: D3 D2 D1 ^^
/// ```
///
/// Here, the region `'a` would have the De Bruijn index D3,
/// because it is the bound 3 binders out. However, if we wanted
/// to refer to that region `'a` in the second argument (the `_`),
/// those two binders would not be in scope. In that case, we
/// might invoke `shift_out_to_binder(D3)`. This would adjust the
/// De Bruijn index of `'a` to D1 (the innermost binder).
///
/// If we invoke `shift_out_to_binder` and the region is in fact
/// bound by one of the binders we are shifting out of, that is an
/// error (and should fail an assertion failure).
pub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self {
self.shifted_out(to_binder.as_u32() - INNERMOST.as_u32())
}
}
/// Region utilities
impl RegionKind {
/// Is this region named by the user?
@@ -1703,7 +1597,7 @@ impl RegionKind {
}
}
pub fn bound_at_or_above_binder(&self, index: DebruijnIndex) -> bool {
pub fn bound_at_or_above_binder(&self, index: ty::DebruijnIndex) -> bool {
match *self {
ty::ReLateBound(debruijn, _) => debruijn >= index,
_ => false,