Auto merge of #116828 - compiler-errors:nightlyify-rustc_type_ir, r=<try>

Begin to abstract `rustc_type_ir` for rust-analyzer

Not totally happy with this yet, but if the new trait solver is ever to be used by external users, we need to make rustc-type-ir build without internal deps. This adds the "nightly" feature which is used by the compiler, and falls back to more simple implementations when that is not active.

r? `@lcnr` or `@jackh726` -- happy to block this pr on a discussion about design and long-term direction for rustc-type-ir tho

Author: bors

compiler/rustc_type_ir/Cargo.toml

@@ -7,8 +7,19 @@ edition = "2021"
 
 [dependencies]
 bitflags = "1.2.1"
-rustc_index = { path = "../rustc_index" }
-rustc_serialize = { path = "../rustc_serialize" }
-rustc_data_structures = { path = "../rustc_data_structures" }
-rustc_macros = { path = "../rustc_macros" }
-smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
+rustc_index = { path = "../rustc_index", default-features = false }
+rustc_serialize = { path = "../rustc_serialize", optional = true }
+rustc_data_structures = { path = "../rustc_data_structures", optional = true }
+rustc_macros = { path = "../rustc_macros", optional = true }
+smallvec = { version = "1.8.1" }
+
+[features]
+default = ["nightly"]
+nightly = [
+    "smallvec/may_dangle",
+    "smallvec/union",
+    "rustc_index/nightly",
+    "rustc_serialize",
+    "rustc_data_structures",
+    "rustc_macros"
+]

compiler/rustc_type_ir/src/fold.rs

@@ -46,6 +46,12 @@
 //! ```
 use crate::{visit::TypeVisitable, Interner};
 
+#[cfg(feature = "nightly")]
+type Never = !;
+
+#[cfg(not(feature = "nightly"))]
+type Never = std::convert::Infallible;
+
 /// This trait is implemented for every type that can be folded,
 /// providing the skeleton of the traversal.
 ///
@@ -74,7 +80,10 @@ pub trait TypeFoldable<I: Interner>: TypeVisitable<I> {
     /// folders. Do not override this method, to ensure coherence with
     /// `try_fold_with`.
     fn fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
-        self.try_fold_with(folder).into_ok()
+        match self.try_fold_with(folder) {
+            Ok(t) => t,
+            Err(_) => unreachable!(),
+        }
     }
 }
 
@@ -95,7 +104,10 @@ pub trait TypeSuperFoldable<I: Interner>: TypeFoldable<I> {
     /// infallible folders. Do not override this method, to ensure coherence
     /// with `try_super_fold_with`.
     fn super_fold_with<F: TypeFolder<I>>(self, folder: &mut F) -> Self {
-        self.try_super_fold_with(folder).into_ok()
+        match self.try_super_fold_with(folder) {
+            Ok(t) => t,
+            Err(_) => unreachable!(),
+        }
     }
 }
 
@@ -108,7 +120,7 @@ pub trait TypeSuperFoldable<I: Interner>: TypeFoldable<I> {
 /// A blanket implementation of [`FallibleTypeFolder`] will defer to
 /// the infallible methods of this trait to ensure that the two APIs
 /// are coherent.
-pub trait TypeFolder<I: Interner>: FallibleTypeFolder<I, Error = !> {
+pub trait TypeFolder<I: Interner>: FallibleTypeFolder<I, Error = Never> {
     fn interner(&self) -> I;
 
     fn fold_binder<T>(&mut self, t: I::Binder<T>) -> I::Binder<T>
@@ -203,39 +215,39 @@ impl<I: Interner, F> FallibleTypeFolder<I> for F
 where
     F: TypeFolder<I>,
 {
-    type Error = !;
+    type Error = Never;
 
     fn interner(&self) -> I {
         TypeFolder::interner(self)
     }
 
-    fn try_fold_binder<T>(&mut self, t: I::Binder<T>) -> Result<I::Binder<T>, !>
+    fn try_fold_binder<T>(&mut self, t: I::Binder<T>) -> Result<I::Binder<T>, Never>
     where
         T: TypeFoldable<I>,
         I::Binder<T>: TypeSuperFoldable<I>,
     {
         Ok(self.fold_binder(t))
     }
 
-    fn try_fold_ty(&mut self, t: I::Ty) -> Result<I::Ty, !>
+    fn try_fold_ty(&mut self, t: I::Ty) -> Result<I::Ty, Never>
     where
         I::Ty: TypeSuperFoldable<I>,
     {
         Ok(self.fold_ty(t))
     }
 
-    fn try_fold_region(&mut self, r: I::Region) -> Result<I::Region, !> {
+    fn try_fold_region(&mut self, r: I::Region) -> Result<I::Region, Never> {
         Ok(self.fold_region(r))
     }
 
-    fn try_fold_const(&mut self, c: I::Const) -> Result<I::Const, !>
+    fn try_fold_const(&mut self, c: I::Const) -> Result<I::Const, Never>
     where
         I::Const: TypeSuperFoldable<I>,
     {
         Ok(self.fold_const(c))
     }
 
-    fn try_fold_predicate(&mut self, p: I::Predicate) -> Result<I::Predicate, !>
+    fn try_fold_predicate(&mut self, p: I::Predicate) -> Result<I::Predicate, Never>
     where
         I::Predicate: TypeSuperFoldable<I>,
     {

compiler/rustc_type_ir/src/index.rs

@@ -0,0 +1,76 @@
+#[derive(Copy, Clone, Hash, Eq, PartialEq, Ord, PartialOrd, Debug)]
+pub struct DebruijnIndex {
+    pub(crate) private: u32,
+}
+
+impl DebruijnIndex {
+    pub const fn from_u32(u: u32) -> Self {
+        Self { private: u }
+    }
+
+    pub const fn as_u32(self) -> u32 {
+        self.private
+    }
+}
+
+pub const INNERMOST: DebruijnIndex = DebruijnIndex { private: 0 };
+
+#[derive(Copy, Clone, Hash, Eq, PartialEq, Ord, PartialOrd, Debug)]
+pub struct UniverseIndex {
+    pub(crate) private: u32,
+}
+
+impl UniverseIndex {
+    pub const fn from_u32(u: u32) -> Self {
+        Self { private: u }
+    }
+
+    pub const fn as_u32(self) -> u32 {
+        self.private
+    }
+}
+
+#[derive(Copy, Clone, Hash, Eq, PartialEq, Ord, PartialOrd, Debug)]
+pub struct TyVid {
+    pub(crate) private: u32,
+}
+
+impl TyVid {
+    pub const fn from_u32(u: u32) -> Self {
+        Self { private: u }
+    }
+
+    pub const fn as_u32(self) -> u32 {
+        self.private
+    }
+}
+
+#[derive(Copy, Clone, Hash, Eq, PartialEq, Ord, PartialOrd, Debug)]
+pub struct FloatVid {
+    pub(crate) private: u32,
+}
+
+impl FloatVid {
+    pub const fn from_u32(u: u32) -> Self {
+        Self { private: u }
+    }
+
+    pub const fn as_u32(self) -> u32 {
+        self.private
+    }
+}
+
+#[derive(Copy, Clone, Hash, Eq, PartialEq, Ord, PartialOrd, Debug)]
+pub struct IntVid {
+    pub(crate) private: u32,
+}
+
+impl IntVid {
+    pub const fn from_u32(u: u32) -> Self {
+        Self { private: u }
+    }
+
+    pub const fn as_u32(self) -> u32 {
+        self.private
+    }
+}

compiler/rustc_type_ir/src/index_nightly.rs

@@ -0,0 +1,105 @@
+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:
+    /// ```ignore (illustrative)
+    ///    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 arrows
+    /// 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_Generic)]
+    #[debug_format = "DebruijnIndex({})"]
+    pub struct DebruijnIndex {
+        const INNERMOST = 0;
+    }
+}
+
+rustc_index::newtype_index! {
+    /// A **ty**pe **v**ariable **ID**.
+    #[debug_format = "?{}t"]
+    pub struct TyVid {}
+}
+
+rustc_index::newtype_index! {
+    /// An **int**egral (`u32`, `i32`, `usize`, etc.) type **v**ariable **ID**.
+    #[debug_format = "?{}i"]
+    pub struct IntVid {}
+}
+
+rustc_index::newtype_index! {
+    /// A **float**ing-point (`f32` or `f64`) type **v**ariable **ID**.
+    #[debug_format = "?{}f"]
+    pub struct FloatVid {}
+}
+
+rustc_index::newtype_index! {
+    /// "Universes" are used during type- and trait-checking in the
+    /// presence of `for<..>` binders to control what sets of names are
+    /// visible. Universes are arranged into a tree: the root universe
+    /// contains names that are always visible. Each child then adds a new
+    /// set of names that are visible, in addition to those of its parent.
+    /// We say that the child universe "extends" the parent universe with
+    /// new names.
+    ///
+    /// To make this more concrete, consider this program:
+    ///
+    /// ```ignore (illustrative)
+    /// struct Foo { }
+    /// fn bar<T>(x: T) {
+    ///   let y: for<'a> fn(&'a u8, Foo) = ...;
+    /// }
+    /// ```
+    ///
+    /// The struct name `Foo` is in the root universe U0. But the type
+    /// parameter `T`, introduced on `bar`, is in an extended universe U1
+    /// -- i.e., within `bar`, we can name both `T` and `Foo`, but outside
+    /// of `bar`, we cannot name `T`. Then, within the type of `y`, the
+    /// region `'a` is in a universe U2 that extends U1, because we can
+    /// name it inside the fn type but not outside.
+    ///
+    /// Universes are used to do type- and trait-checking around these
+    /// "forall" binders (also called **universal quantification**). The
+    /// idea is that when, in the body of `bar`, we refer to `T` as a
+    /// type, we aren't referring to any type in particular, but rather a
+    /// kind of "fresh" type that is distinct from all other types we have
+    /// actually declared. This is called a **placeholder** type, and we
+    /// use universes to talk about this. In other words, a type name in
+    /// universe 0 always corresponds to some "ground" type that the user
+    /// declared, but a type name in a non-zero universe is a placeholder
+    /// type -- an idealized representative of "types in general" that we
+    /// use for checking generic functions.
+    #[derive(HashStable_Generic)]
+    #[debug_format = "U{}"]
+    pub struct UniverseIndex {}
+}