bjoernager/rust
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introduce new fallback algorithm

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We now fallback type variables using the following rules:

* Construct a coercion graph `A -> B` where `A` and `B` are unresolved
  type variables or the `!` type.
* Let D be those variables that are reachable from `!`.
* Let N be those variables that are reachable from a variable not in
D.
* All variables in (D \ N) fallback to `!`.
* All variables in (D & N) fallback to `()`.
This commit is contained in:
Niko Matsakis 2020-11-22 09:58:58 -05:00 • committed by Mark Rousskov
parent e0c38af27c
commit 2ee89144e2
7 changed files with 347 additions and 55 deletions
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13
compiler/rustc_infer/src/infer/mod.rs
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@ -707,11 +707,17 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
/// No attempt is made to resolve `ty`.
pub fn type_var_diverges(&'a self, ty: Ty<'_>) -> Diverging {
match *ty.kind() {
ty::Infer(ty::TyVar(vid)) => self.inner.borrow_mut().type_variables().var_diverges(vid),
ty::Infer(ty::TyVar(vid)) => self.ty_vid_diverges(vid),
_ => Diverging::NotDiverging,
}
}
/// Returns true if the type inference variable `vid` was created
/// as a diverging type variable. No attempt is made to resolve `vid`.
pub fn ty_vid_diverges(&'a self, vid: ty::TyVid) -> Diverging {
self.inner.borrow_mut().type_variables().var_diverges(vid)
}
/// Returns the origin of the type variable identified by `vid`, or `None`
/// if this is not a type variable.
///
@ -1070,6 +1076,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
})
}
/// Number of type variables created so far.
pub fn num_ty_vars(&self) -> usize {
self.inner.borrow_mut().type_variables().num_vars()
}
pub fn next_ty_var_id(&self, diverging: Diverging, origin: TypeVariableOrigin) -> TyVid {
self.inner.borrow_mut().type_variables().new_var(self.universe(), diverging, origin)
}