//! sort of a minor point so I've opted to leave it for later---after all
//! we may want to adjust precisely when coercions occur.
-use check::{autoderef, FnCtxt, LvaluePreference, UnresolvedTypeAction};
+use check::{Diverges, FnCtxt};
-use middle::infer::{self, Coercion};
-use middle::traits::{self, ObligationCause};
-use middle::traits::{predicate_for_trait_def, report_selection_error};
-use middle::ty::{AutoDerefRef, AdjustDerefRef};
-use middle::ty::{self, TypeAndMut, Ty, TypeError};
-use middle::ty_relate::RelateResult;
-use util::common::indent;
+use rustc::hir;
+use rustc::hir::def_id::DefId;
+use rustc::infer::{Coercion, InferResult, InferOk};
+use rustc::infer::type_variable::TypeVariableOrigin;
+use rustc::traits::{self, ObligationCause, ObligationCauseCode};
+use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow};
+use rustc::ty::{self, LvaluePreference, TypeAndMut,
+ Ty, ClosureSubsts};
+use rustc::ty::fold::TypeFoldable;
+use rustc::ty::error::TypeError;
+use rustc::ty::relate::RelateResult;
+use rustc::ty::subst::Subst;
+use errors::DiagnosticBuilder;
+use syntax::abi;
+use syntax::feature_gate;
+use syntax::ptr::P;
+use syntax_pos;
-use std::cell::RefCell;
use std::collections::VecDeque;
-use syntax::ast;
+use std::ops::Deref;
-struct Coerce<'a, 'tcx: 'a> {
- fcx: &'a FnCtxt<'a, 'tcx>,
- origin: infer::TypeOrigin,
- unsizing_obligations: RefCell<Vec<traits::PredicateObligation<'tcx>>>,
+struct Coerce<'a, 'gcx: 'a + 'tcx, 'tcx: 'a> {
+ fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
+ cause: ObligationCause<'tcx>,
+ use_lub: bool,
}
-type CoerceResult<'tcx> = RelateResult<'tcx, Option<ty::AutoAdjustment<'tcx>>>;
+impl<'a, 'gcx, 'tcx> Deref for Coerce<'a, 'gcx, 'tcx> {
+ type Target = FnCtxt<'a, 'gcx, 'tcx>;
+ fn deref(&self) -> &Self::Target {
+ &self.fcx
+ }
+}
+
+type CoerceResult<'tcx> = InferResult<'tcx, (Vec<Adjustment<'tcx>>, Ty<'tcx>)>;
+
+fn coerce_mutbls<'tcx>(from_mutbl: hir::Mutability,
+ to_mutbl: hir::Mutability)
+ -> RelateResult<'tcx, ()> {
+ match (from_mutbl, to_mutbl) {
+ (hir::MutMutable, hir::MutMutable) |
+ (hir::MutImmutable, hir::MutImmutable) |
+ (hir::MutMutable, hir::MutImmutable) => Ok(()),
+ (hir::MutImmutable, hir::MutMutable) => Err(TypeError::Mutability),
+ }
+}
-impl<'f, 'tcx> Coerce<'f, 'tcx> {
- fn tcx(&self) -> &ty::ctxt<'tcx> {
- self.fcx.tcx()
+fn identity(_: Ty) -> Vec<Adjustment> { vec![] }
+
+fn simple<'tcx>(kind: Adjust<'tcx>) -> impl FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>> {
+ move |target| vec![Adjustment { kind, target }]
+}
+
+fn success<'tcx>(adj: Vec<Adjustment<'tcx>>,
+ target: Ty<'tcx>,
+ obligations: traits::PredicateObligations<'tcx>)
+ -> CoerceResult<'tcx> {
+ Ok(InferOk {
+ value: (adj, target),
+ obligations
+ })
+}
+
+impl<'f, 'gcx, 'tcx> Coerce<'f, 'gcx, 'tcx> {
+ fn new(fcx: &'f FnCtxt<'f, 'gcx, 'tcx>, cause: ObligationCause<'tcx>) -> Self {
+ Coerce {
+ fcx,
+ cause,
+ use_lub: false,
+ }
}
- fn subtype(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
- try!(self.fcx.infcx().sub_types(false, self.origin.clone(), a, b));
- Ok(None) // No coercion required.
+ fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> {
+ self.commit_if_ok(|_| {
+ if self.use_lub {
+ self.at(&self.cause, self.fcx.param_env)
+ .lub(b, a)
+ } else {
+ self.at(&self.cause, self.fcx.param_env)
+ .sup(b, a)
+ .map(|InferOk { value: (), obligations }| InferOk { value: a, obligations })
+ }
+ })
}
- fn unpack_actual_value<T, F>(&self, a: Ty<'tcx>, f: F) -> T where
- F: FnOnce(Ty<'tcx>) -> T,
+ /// Unify two types (using sub or lub) and produce a specific coercion.
+ fn unify_and<F>(&self, a: Ty<'tcx>, b: Ty<'tcx>, f: F)
+ -> CoerceResult<'tcx>
+ where F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>
{
- f(self.fcx.infcx().shallow_resolve(a))
+ self.unify(&a, &b).and_then(|InferOk { value: ty, obligations }| {
+ success(f(ty), ty, obligations)
+ })
}
- fn coerce(&self,
- expr_a: &ast::Expr,
- a: Ty<'tcx>,
- b: Ty<'tcx>)
- -> CoerceResult<'tcx> {
- debug!("Coerce.tys({:?} => {:?})",
- a,
- b);
+ fn coerce(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
+ let a = self.shallow_resolve(a);
+ debug!("Coerce.tys({:?} => {:?})", a, b);
+
+ // Just ignore error types.
+ if a.references_error() || b.references_error() {
+ return success(vec![], b, vec![]);
+ }
+
+ if a.is_never() {
+ // Subtle: If we are coercing from `!` to `?T`, where `?T` is an unbound
+ // type variable, we want `?T` to fallback to `!` if not
+ // otherwise constrained. An example where this arises:
+ //
+ // let _: Option<?T> = Some({ return; });
+ //
+ // here, we would coerce from `!` to `?T`.
+ let b = self.shallow_resolve(b);
+ return if self.shallow_resolve(b).is_ty_var() {
+ // micro-optimization: no need for this if `b` is
+ // already resolved in some way.
+ let diverging_ty = self.next_diverging_ty_var(
+ TypeVariableOrigin::AdjustmentType(self.cause.span));
+ self.unify_and(&b, &diverging_ty, simple(Adjust::NeverToAny))
+ } else {
+ success(simple(Adjust::NeverToAny)(b), b, vec![])
+ };
+ }
// Consider coercing the subtype to a DST
- let unsize = self.unpack_actual_value(a, |a| {
- self.coerce_unsized(a, b)
- });
+ //
+ // NOTE: this is wrapped in a `commit_if_ok` because it creates
+ // a "spurious" type variable, and we don't want to have that
+ // type variable in memory if the coercion fails.
+ let unsize = self.commit_if_ok(|_| self.coerce_unsized(a, b));
if unsize.is_ok() {
+ debug!("coerce: unsize successful");
return unsize;
}
+ debug!("coerce: unsize failed");
// Examine the supertype and consider auto-borrowing.
//
// See above for details.
match b.sty {
ty::TyRawPtr(mt_b) => {
- return self.unpack_actual_value(a, |a| {
- self.coerce_unsafe_ptr(a, b, mt_b.mutbl)
- });
+ return self.coerce_unsafe_ptr(a, b, mt_b.mutbl);
}
- ty::TyRef(_, mt_b) => {
- return self.unpack_actual_value(a, |a| {
- self.coerce_borrowed_pointer(expr_a, a, b, mt_b.mutbl)
- });
+ ty::TyRef(r_b, mt_b) => {
+ return self.coerce_borrowed_pointer(a, b, r_b, mt_b);
}
_ => {}
}
- self.unpack_actual_value(a, |a| {
- match a.sty {
- ty::TyBareFn(Some(_), a_f) => {
- // Function items are coercible to any closure
- // type; function pointers are not (that would
- // require double indirection).
- self.coerce_from_fn_item(a, a_f, b)
- }
- ty::TyBareFn(None, a_f) => {
- // We permit coercion of fn pointers to drop the
- // unsafe qualifier.
- self.coerce_from_fn_pointer(a, a_f, b)
- }
- _ => {
- // Otherwise, just use subtyping rules.
- self.subtype(a, b)
- }
+ match a.sty {
+ ty::TyFnDef(..) => {
+ // Function items are coercible to any closure
+ // type; function pointers are not (that would
+ // require double indirection).
+ // Additionally, we permit coercion of function
+ // items to drop the unsafe qualifier.
+ self.coerce_from_fn_item(a, b)
}
- })
+ ty::TyFnPtr(a_f) => {
+ // We permit coercion of fn pointers to drop the
+ // unsafe qualifier.
+ self.coerce_from_fn_pointer(a, a_f, b)
+ }
+ ty::TyClosure(def_id_a, substs_a) => {
+ // Non-capturing closures are coercible to
+ // function pointers
+ self.coerce_closure_to_fn(a, def_id_a, substs_a, b)
+ }
+ _ => {
+ // Otherwise, just use unification rules.
+ self.unify_and(a, b, identity)
+ }
+ }
}
/// Reborrows `&mut A` to `&mut B` and `&(mut) A` to `&B`.
/// To match `A` with `B`, autoderef will be performed,
/// calling `deref`/`deref_mut` where necessary.
fn coerce_borrowed_pointer(&self,
- expr_a: &ast::Expr,
a: Ty<'tcx>,
b: Ty<'tcx>,
- mutbl_b: ast::Mutability)
+ r_b: ty::Region<'tcx>,
+ mt_b: TypeAndMut<'tcx>)
-> CoerceResult<'tcx> {
- debug!("coerce_borrowed_pointer(a={:?}, b={:?})",
- a,
- b);
+
+ debug!("coerce_borrowed_pointer(a={:?}, b={:?})", a, b);
// If we have a parameter of type `&M T_a` and the value
// provided is `expr`, we will be adding an implicit borrow,
// to type check, we will construct the type that `&M*expr` would
// yield.
- match a.sty {
- ty::TyRef(_, mt_a) => {
- try!(coerce_mutbls(mt_a.mutbl, mutbl_b));
+ let (r_a, mt_a) = match a.sty {
+ ty::TyRef(r_a, mt_a) => {
+ coerce_mutbls(mt_a.mutbl, mt_b.mutbl)?;
+ (r_a, mt_a)
}
- _ => return self.subtype(a, b)
- }
+ _ => return self.unify_and(a, b, identity),
+ };
- let coercion = Coercion(self.origin.span());
- let r_borrow = self.fcx.infcx().next_region_var(coercion);
- let r_borrow = self.tcx().mk_region(r_borrow);
- let autoref = Some(ty::AutoPtr(r_borrow, mutbl_b));
+ let span = self.cause.span;
- let lvalue_pref = LvaluePreference::from_mutbl(mutbl_b);
let mut first_error = None;
- let (_, autoderefs, success) = autoderef(self.fcx,
- expr_a.span,
- a,
- Some(expr_a),
- UnresolvedTypeAction::Ignore,
- lvalue_pref,
- |inner_ty, autoderef| {
- if autoderef == 0 {
+ let mut r_borrow_var = None;
+ let mut autoderef = self.autoderef(span, a);
+ let mut found = None;
+
+ for (referent_ty, autoderefs) in autoderef.by_ref() {
+ if autoderefs == 0 {
// Don't let this pass, otherwise it would cause
// &T to autoref to &&T.
- return None;
+ continue;
}
- let ty = self.tcx().mk_ref(r_borrow,
- TypeAndMut {ty: inner_ty, mutbl: mutbl_b});
- if let Err(err) = self.subtype(ty, b) {
- if first_error.is_none() {
- first_error = Some(err);
- }
- None
+
+ // At this point, we have deref'd `a` to `referent_ty`. So
+ // imagine we are coercing from `&'a mut Vec<T>` to `&'b mut [T]`.
+ // In the autoderef loop for `&'a mut Vec<T>`, we would get
+ // three callbacks:
+ //
+ // - `&'a mut Vec<T>` -- 0 derefs, just ignore it
+ // - `Vec<T>` -- 1 deref
+ // - `[T]` -- 2 deref
+ //
+ // At each point after the first callback, we want to
+ // check to see whether this would match out target type
+ // (`&'b mut [T]`) if we autoref'd it. We can't just
+ // compare the referent types, though, because we still
+ // have to consider the mutability. E.g., in the case
+ // we've been considering, we have an `&mut` reference, so
+ // the `T` in `[T]` needs to be unified with equality.
+ //
+ // Therefore, we construct reference types reflecting what
+ // the types will be after we do the final auto-ref and
+ // compare those. Note that this means we use the target
+ // mutability [1], since it may be that we are coercing
+ // from `&mut T` to `&U`.
+ //
+ // One fine point concerns the region that we use. We
+ // choose the region such that the region of the final
+ // type that results from `unify` will be the region we
+ // want for the autoref:
+ //
+ // - if in sub mode, that means we want to use `'b` (the
+ // region from the target reference) for both
+ // pointers [2]. This is because sub mode (somewhat
+ // arbitrarily) returns the subtype region. In the case
+ // where we are coercing to a target type, we know we
+ // want to use that target type region (`'b`) because --
+ // for the program to type-check -- it must be the
+ // smaller of the two.
+ // - One fine point. It may be surprising that we can
+ // use `'b` without relating `'a` and `'b`. The reason
+ // that this is ok is that what we produce is
+ // effectively a `&'b *x` expression (if you could
+ // annotate the region of a borrow), and regionck has
+ // code that adds edges from the region of a borrow
+ // (`'b`, here) into the regions in the borrowed
+ // expression (`*x`, here). (Search for "link".)
+ // - if in lub mode, things can get fairly complicated. The
+ // easiest thing is just to make a fresh
+ // region variable [4], which effectively means we defer
+ // the decision to region inference (and regionck, which will add
+ // some more edges to this variable). However, this can wind up
+ // creating a crippling number of variables in some cases --
+ // e.g. #32278 -- so we optimize one particular case [3].
+ // Let me try to explain with some examples:
+ // - The "running example" above represents the simple case,
+ // where we have one `&` reference at the outer level and
+ // ownership all the rest of the way down. In this case,
+ // we want `LUB('a, 'b)` as the resulting region.
+ // - However, if there are nested borrows, that region is
+ // too strong. Consider a coercion from `&'a &'x Rc<T>` to
+ // `&'b T`. In this case, `'a` is actually irrelevant.
+ // The pointer we want is `LUB('x, 'b`). If we choose `LUB('a,'b)`
+ // we get spurious errors (`run-pass/regions-lub-ref-ref-rc.rs`).
+ // (The errors actually show up in borrowck, typically, because
+ // this extra edge causes the region `'a` to be inferred to something
+ // too big, which then results in borrowck errors.)
+ // - We could track the innermost shared reference, but there is already
+ // code in regionck that has the job of creating links between
+ // the region of a borrow and the regions in the thing being
+ // borrowed (here, `'a` and `'x`), and it knows how to handle
+ // all the various cases. So instead we just make a region variable
+ // and let regionck figure it out.
+ let r = if !self.use_lub {
+ r_b // [2] above
+ } else if autoderefs == 1 {
+ r_a // [3] above
} else {
- Some(())
+ if r_borrow_var.is_none() {
+ // create var lazilly, at most once
+ let coercion = Coercion(span);
+ let r = self.next_region_var(coercion);
+ r_borrow_var = Some(r); // [4] above
+ }
+ r_borrow_var.unwrap()
+ };
+ let derefd_ty_a = self.tcx.mk_ref(r,
+ TypeAndMut {
+ ty: referent_ty,
+ mutbl: mt_b.mutbl, // [1] above
+ });
+ match self.unify(derefd_ty_a, b) {
+ Ok(ok) => {
+ found = Some(ok);
+ break;
+ }
+ Err(err) => {
+ if first_error.is_none() {
+ first_error = Some(err);
+ }
+ }
}
- });
+ }
- match success {
- Some(_) => {
- Ok(Some(AdjustDerefRef(AutoDerefRef {
- autoderefs: autoderefs,
- autoref: autoref,
- unsize: None
- })))
- }
+ // Extract type or return an error. We return the first error
+ // we got, which should be from relating the "base" type
+ // (e.g., in example above, the failure from relating `Vec<T>`
+ // to the target type), since that should be the least
+ // confusing.
+ let InferOk { value: ty, mut obligations } = match found {
+ Some(d) => d,
None => {
- // Return original error as if overloaded deref was never
- // attempted, to avoid irrelevant/confusing error messages.
- Err(first_error.expect("coerce_borrowed_pointer failed with no error?"))
+ let err = first_error.expect("coerce_borrowed_pointer had no error");
+ debug!("coerce_borrowed_pointer: failed with err = {:?}", err);
+ return Err(err);
}
+ };
+
+ if ty == a && mt_a.mutbl == hir::MutImmutable && autoderef.step_count() == 1 {
+ // As a special case, if we would produce `&'a *x`, that's
+ // a total no-op. We end up with the type `&'a T` just as
+ // we started with. In that case, just skip it
+ // altogether. This is just an optimization.
+ //
+ // Note that for `&mut`, we DO want to reborrow --
+ // otherwise, this would be a move, which might be an
+ // error. For example `foo(self.x)` where `self` and
+ // `self.x` both have `&mut `type would be a move of
+ // `self.x`, but we auto-coerce it to `foo(&mut *self.x)`,
+ // which is a borrow.
+ assert_eq!(mt_b.mutbl, hir::MutImmutable); // can only coerce &T -> &U
+ return success(vec![], ty, obligations);
}
+
+ let pref = LvaluePreference::from_mutbl(mt_b.mutbl);
+ let InferOk { value: mut adjustments, obligations: o }
+ = autoderef.adjust_steps_as_infer_ok(pref);
+ obligations.extend(o);
+ obligations.extend(autoderef.into_obligations());
+
+ // Now apply the autoref. We have to extract the region out of
+ // the final ref type we got.
+ let r_borrow = match ty.sty {
+ ty::TyRef(r_borrow, _) => r_borrow,
+ _ => span_bug!(span, "expected a ref type, got {:?}", ty),
+ };
+ adjustments.push(Adjustment {
+ kind: Adjust::Borrow(AutoBorrow::Ref(r_borrow, mt_b.mutbl)),
+ target: ty
+ });
+
+ debug!("coerce_borrowed_pointer: succeeded ty={:?} adjustments={:?}",
+ ty,
+ adjustments);
+
+ success(adjustments, ty, obligations)
}
// &[T; n] or &mut [T; n] -> &[T]
// or &mut [T; n] -> &mut [T]
// or &Concrete -> &Trait, etc.
- fn coerce_unsized(&self,
- source: Ty<'tcx>,
- target: Ty<'tcx>)
- -> CoerceResult<'tcx> {
- debug!("coerce_unsized(source={:?}, target={:?})",
- source,
- target);
+ fn coerce_unsized(&self, source: Ty<'tcx>, target: Ty<'tcx>) -> CoerceResult<'tcx> {
+ debug!("coerce_unsized(source={:?}, target={:?})", source, target);
- let traits = (self.tcx().lang_items.unsize_trait(),
- self.tcx().lang_items.coerce_unsized_trait());
+ let traits = (self.tcx.lang_items().unsize_trait(),
+ self.tcx.lang_items().coerce_unsized_trait());
let (unsize_did, coerce_unsized_did) = if let (Some(u), Some(cu)) = traits {
(u, cu)
} else {
// that, at which point we will need extra checks on the target here.
// Handle reborrows before selecting `Source: CoerceUnsized<Target>`.
- let (source, reborrow) = match (&source.sty, &target.sty) {
+ let reborrow = match (&source.sty, &target.sty) {
(&ty::TyRef(_, mt_a), &ty::TyRef(_, mt_b)) => {
- try!(coerce_mutbls(mt_a.mutbl, mt_b.mutbl));
+ coerce_mutbls(mt_a.mutbl, mt_b.mutbl)?;
- let coercion = Coercion(self.origin.span());
- let r_borrow = self.fcx.infcx().next_region_var(coercion);
- let region = self.tcx().mk_region(r_borrow);
- (mt_a.ty, Some(ty::AutoPtr(region, mt_b.mutbl)))
+ let coercion = Coercion(self.cause.span);
+ let r_borrow = self.next_region_var(coercion);
+ Some((Adjustment {
+ kind: Adjust::Deref(None),
+ target: mt_a.ty
+ }, Adjustment {
+ kind: Adjust::Borrow(AutoBorrow::Ref(r_borrow, mt_b.mutbl)),
+ target: self.tcx.mk_ref(r_borrow, ty::TypeAndMut {
+ mutbl: mt_b.mutbl,
+ ty: mt_a.ty
+ })
+ }))
}
(&ty::TyRef(_, mt_a), &ty::TyRawPtr(mt_b)) => {
- try!(coerce_mutbls(mt_a.mutbl, mt_b.mutbl));
- (mt_a.ty, Some(ty::AutoUnsafe(mt_b.mutbl)))
+ coerce_mutbls(mt_a.mutbl, mt_b.mutbl)?;
+
+ Some((Adjustment {
+ kind: Adjust::Deref(None),
+ target: mt_a.ty
+ }, Adjustment {
+ kind: Adjust::Borrow(AutoBorrow::RawPtr(mt_b.mutbl)),
+ target: self.tcx.mk_ptr(ty::TypeAndMut {
+ mutbl: mt_b.mutbl,
+ ty: mt_a.ty
+ })
+ }))
}
- _ => (source, None)
+ _ => None,
};
- let source = source.adjust_for_autoref(self.tcx(), reborrow);
+ let coerce_source = reborrow.as_ref().map_or(source, |&(_, ref r)| r.target);
+
+ // Setup either a subtyping or a LUB relationship between
+ // the `CoerceUnsized` target type and the expected type.
+ // We only have the latter, so we use an inference variable
+ // for the former and let type inference do the rest.
+ let origin = TypeVariableOrigin::MiscVariable(self.cause.span);
+ let coerce_target = self.next_ty_var(origin);
+ let mut coercion = self.unify_and(coerce_target, target, |target| {
+ let unsize = Adjustment {
+ kind: Adjust::Unsize,
+ target
+ };
+ match reborrow {
+ None => vec![unsize],
+ Some((ref deref, ref autoref)) => {
+ vec![deref.clone(), autoref.clone(), unsize]
+ }
+ }
+ })?;
- let mut selcx = traits::SelectionContext::new(self.fcx.infcx());
+ let mut selcx = traits::SelectionContext::new(self);
// Use a FIFO queue for this custom fulfillment procedure.
let mut queue = VecDeque::new();
- let mut leftover_predicates = vec![];
// Create an obligation for `Source: CoerceUnsized<Target>`.
- let cause = ObligationCause::misc(self.origin.span(), self.fcx.body_id);
- queue.push_back(predicate_for_trait_def(self.tcx(),
- cause,
- coerce_unsized_did,
- 0,
- source,
- vec![target]));
+ let cause = ObligationCause::misc(self.cause.span, self.body_id);
+ queue.push_back(self.tcx.predicate_for_trait_def(self.fcx.param_env,
+ cause,
+ coerce_unsized_did,
+ 0,
+ coerce_source,
+ &[coerce_target]));
+
+ let mut has_unsized_tuple_coercion = false;
// Keep resolving `CoerceUnsized` and `Unsize` predicates to avoid
// emitting a coercion in cases like `Foo<$1>` -> `Foo<$2>`, where
let traits = [coerce_unsized_did, unsize_did];
while let Some(obligation) = queue.pop_front() {
debug!("coerce_unsized resolve step: {:?}", obligation);
- let trait_ref = match obligation.predicate {
+ let trait_ref = match obligation.predicate {
ty::Predicate::Trait(ref tr) if traits.contains(&tr.def_id()) => {
+ if unsize_did == tr.def_id() {
+ if let ty::TyTuple(..) = tr.0.input_types().nth(1).unwrap().sty {
+ debug!("coerce_unsized: found unsized tuple coercion");
+ has_unsized_tuple_coercion = true;
+ }
+ }
tr.clone()
}
_ => {
- leftover_predicates.push(obligation);
+ coercion.obligations.push(obligation);
continue;
}
};
match selcx.select(&obligation.with(trait_ref)) {
// Uncertain or unimplemented.
- Ok(None) | Err(traits::Unimplemented) => {
+ Ok(None) |
+ Err(traits::Unimplemented) => {
debug!("coerce_unsized: early return - can't prove obligation");
return Err(TypeError::Mismatch);
}
// Object safety violations or miscellaneous.
Err(err) => {
- report_selection_error(self.fcx.infcx(), &obligation, &err);
+ self.report_selection_error(&obligation, &err);
// Treat this like an obligation and follow through
// with the unsizing - the lack of a coercion should
// be silent, as it causes a type mismatch later.
}
}
- let mut obligations = self.unsizing_obligations.borrow_mut();
- assert!(obligations.is_empty());
- *obligations = leftover_predicates;
+ if has_unsized_tuple_coercion && !self.tcx.sess.features.borrow().unsized_tuple_coercion {
+ feature_gate::emit_feature_err(&self.tcx.sess.parse_sess,
+ "unsized_tuple_coercion",
+ self.cause.span,
+ feature_gate::GateIssue::Language,
+ feature_gate::EXPLAIN_UNSIZED_TUPLE_COERCION);
+ }
- let adjustment = AutoDerefRef {
- autoderefs: if reborrow.is_some() { 1 } else { 0 },
- autoref: reborrow,
- unsize: Some(target)
- };
- debug!("Success, coerced with {:?}", adjustment);
- Ok(Some(AdjustDerefRef(adjustment)))
+ Ok(coercion)
}
- fn coerce_from_fn_pointer(&self,
- a: Ty<'tcx>,
- fn_ty_a: &'tcx ty::BareFnTy<'tcx>,
- b: Ty<'tcx>)
- -> CoerceResult<'tcx>
+ fn coerce_from_safe_fn<F, G>(&self,
+ a: Ty<'tcx>,
+ fn_ty_a: ty::PolyFnSig<'tcx>,
+ b: Ty<'tcx>,
+ to_unsafe: F,
+ normal: G)
+ -> CoerceResult<'tcx>
+ where F: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>,
+ G: FnOnce(Ty<'tcx>) -> Vec<Adjustment<'tcx>>
{
- /*!
- * Attempts to coerce from the type of a Rust function item
- * into a closure or a `proc`.
- */
-
- self.unpack_actual_value(b, |b| {
- debug!("coerce_from_fn_pointer(a={:?}, b={:?})",
- a, b);
-
- if let ty::TyBareFn(None, fn_ty_b) = b.sty {
- match (fn_ty_a.unsafety, fn_ty_b.unsafety) {
- (ast::Unsafety::Normal, ast::Unsafety::Unsafe) => {
- let unsafe_a = self.tcx().safe_to_unsafe_fn_ty(fn_ty_a);
- try!(self.subtype(unsafe_a, b));
- return Ok(Some(ty::AdjustUnsafeFnPointer));
- }
- _ => {}
+ if let ty::TyFnPtr(fn_ty_b) = b.sty {
+ match (fn_ty_a.unsafety(), fn_ty_b.unsafety()) {
+ (hir::Unsafety::Normal, hir::Unsafety::Unsafe) => {
+ let unsafe_a = self.tcx.safe_to_unsafe_fn_ty(fn_ty_a);
+ return self.unify_and(unsafe_a, b, to_unsafe);
}
+ _ => {}
}
- self.subtype(a, b)
- })
+ }
+ self.unify_and(a, b, normal)
+ }
+
+ fn coerce_from_fn_pointer(&self,
+ a: Ty<'tcx>,
+ fn_ty_a: ty::PolyFnSig<'tcx>,
+ b: Ty<'tcx>)
+ -> CoerceResult<'tcx> {
+ //! Attempts to coerce from the type of a Rust function item
+ //! into a closure or a `proc`.
+ //!
+
+ let b = self.shallow_resolve(b);
+ debug!("coerce_from_fn_pointer(a={:?}, b={:?})", a, b);
+
+ self.coerce_from_safe_fn(a, fn_ty_a, b,
+ simple(Adjust::UnsafeFnPointer), identity)
}
fn coerce_from_fn_item(&self,
a: Ty<'tcx>,
- fn_ty_a: &'tcx ty::BareFnTy<'tcx>,
b: Ty<'tcx>)
-> CoerceResult<'tcx> {
- /*!
- * Attempts to coerce from the type of a Rust function item
- * into a closure or a `proc`.
- */
-
- self.unpack_actual_value(b, |b| {
- debug!("coerce_from_fn_item(a={:?}, b={:?})",
- a, b);
-
- match b.sty {
- ty::TyBareFn(None, _) => {
- let a_fn_pointer = self.tcx().mk_fn(None, fn_ty_a);
- try!(self.subtype(a_fn_pointer, b));
- Ok(Some(ty::AdjustReifyFnPointer))
- }
- _ => self.subtype(a, b)
+ //! Attempts to coerce from the type of a Rust function item
+ //! into a closure or a `proc`.
+ //!
+
+ let b = self.shallow_resolve(b);
+ debug!("coerce_from_fn_item(a={:?}, b={:?})", a, b);
+
+ match b.sty {
+ ty::TyFnPtr(_) => {
+ let a_sig = a.fn_sig(self.tcx);
+ let InferOk { value: a_sig, mut obligations } =
+ self.normalize_associated_types_in_as_infer_ok(self.cause.span, &a_sig);
+
+ let a_fn_pointer = self.tcx.mk_fn_ptr(a_sig);
+ let InferOk { value, obligations: o2 } =
+ self.coerce_from_safe_fn(a_fn_pointer, a_sig, b,
+ simple(Adjust::ReifyFnPointer), simple(Adjust::ReifyFnPointer))?;
+
+ obligations.extend(o2);
+ Ok(InferOk { value, obligations })
}
- })
+ _ => self.unify_and(a, b, identity),
+ }
+ }
+
+ fn coerce_closure_to_fn(&self,
+ a: Ty<'tcx>,
+ def_id_a: DefId,
+ substs_a: ClosureSubsts<'tcx>,
+ b: Ty<'tcx>)
+ -> CoerceResult<'tcx> {
+ //! Attempts to coerce from the type of a non-capturing closure
+ //! into a function pointer.
+ //!
+
+ let b = self.shallow_resolve(b);
+
+ let node_id_a = self.tcx.hir.as_local_node_id(def_id_a).unwrap();
+ match b.sty {
+ ty::TyFnPtr(_) if self.tcx.with_freevars(node_id_a, |v| v.is_empty()) => {
+ // We coerce the closure, which has fn type
+ // `extern "rust-call" fn((arg0,arg1,...)) -> _`
+ // to
+ // `fn(arg0,arg1,...) -> _`
+ let sig = self.fn_sig(def_id_a).subst(self.tcx, substs_a.substs);
+ let converted_sig = sig.map_bound(|s| {
+ let params_iter = match s.inputs()[0].sty {
+ ty::TyTuple(params, _) => {
+ params.into_iter().cloned()
+ }
+ _ => bug!(),
+ };
+ self.tcx.mk_fn_sig(
+ params_iter,
+ s.output(),
+ s.variadic,
+ hir::Unsafety::Normal,
+ abi::Abi::Rust
+ )
+ });
+ let pointer_ty = self.tcx.mk_fn_ptr(converted_sig);
+ debug!("coerce_closure_to_fn(a={:?}, b={:?}, pty={:?})",
+ a, b, pointer_ty);
+ self.unify_and(pointer_ty, b, simple(Adjust::ClosureFnPointer))
+ }
+ _ => self.unify_and(a, b, identity),
+ }
}
fn coerce_unsafe_ptr(&self,
a: Ty<'tcx>,
b: Ty<'tcx>,
- mutbl_b: ast::Mutability)
+ mutbl_b: hir::Mutability)
-> CoerceResult<'tcx> {
- debug!("coerce_unsafe_ptr(a={:?}, b={:?})",
- a,
- b);
+ debug!("coerce_unsafe_ptr(a={:?}, b={:?})", a, b);
let (is_ref, mt_a) = match a.sty {
ty::TyRef(_, mt) => (true, mt),
ty::TyRawPtr(mt) => (false, mt),
_ => {
- return self.subtype(a, b);
+ return self.unify_and(a, b, identity);
}
};
// Check that the types which they point at are compatible.
- let a_unsafe = self.tcx().mk_ptr(ty::TypeAndMut{ mutbl: mutbl_b, ty: mt_a.ty });
- try!(self.subtype(a_unsafe, b));
- try!(coerce_mutbls(mt_a.mutbl, mutbl_b));
-
+ let a_unsafe = self.tcx.mk_ptr(ty::TypeAndMut {
+ mutbl: mutbl_b,
+ ty: mt_a.ty,
+ });
+ coerce_mutbls(mt_a.mutbl, mutbl_b)?;
// Although references and unsafe ptrs have the same
- // representation, we still register an AutoDerefRef so that
+ // representation, we still register an Adjust::DerefRef so that
// regionck knows that the region for `a` must be valid here.
if is_ref {
- Ok(Some(AdjustDerefRef(AutoDerefRef {
- autoderefs: 1,
- autoref: Some(ty::AutoUnsafe(mutbl_b)),
- unsize: None
- })))
+ self.unify_and(a_unsafe, b, |target| {
+ vec![Adjustment {
+ kind: Adjust::Deref(None),
+ target: mt_a.ty
+ }, Adjustment {
+ kind: Adjust::Borrow(AutoBorrow::RawPtr(mutbl_b)),
+ target
+ }]
+ })
+ } else if mt_a.mutbl != mutbl_b {
+ self.unify_and(a_unsafe, b, simple(Adjust::MutToConstPointer))
} else {
- Ok(None)
+ self.unify_and(a_unsafe, b, identity)
}
}
}
-pub fn mk_assignty<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
- expr: &ast::Expr,
- a: Ty<'tcx>,
- b: Ty<'tcx>)
- -> RelateResult<'tcx, ()> {
- debug!("mk_assignty({:?} -> {:?})", a, b);
- let mut unsizing_obligations = vec![];
- let adjustment = try!(indent(|| {
- fcx.infcx().commit_if_ok(|_| {
- let coerce = Coerce {
- fcx: fcx,
- origin: infer::ExprAssignable(expr.span),
- unsizing_obligations: RefCell::new(vec![])
+impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
+ /// Attempt to coerce an expression to a type, and return the
+ /// adjusted type of the expression, if successful.
+ /// Adjustments are only recorded if the coercion succeeded.
+ /// The expressions *must not* have any pre-existing adjustments.
+ pub fn try_coerce(&self,
+ expr: &hir::Expr,
+ expr_ty: Ty<'tcx>,
+ expr_diverges: Diverges,
+ target: Ty<'tcx>)
+ -> RelateResult<'tcx, Ty<'tcx>> {
+ let source = self.resolve_type_vars_with_obligations(expr_ty);
+ debug!("coercion::try({:?}: {:?} -> {:?})", expr, source, target);
+
+ // Special-ish case: we can coerce any type `T` into the `!`
+ // type, but only if the source expression diverges.
+ if target.is_never() && expr_diverges.always() {
+ debug!("permit coercion to `!` because expr diverges");
+ return Ok(target);
+ }
+
+ let cause = self.cause(expr.span, ObligationCauseCode::ExprAssignable);
+ let coerce = Coerce::new(self, cause);
+ let ok = self.commit_if_ok(|_| coerce.coerce(source, target))?;
+
+ let (adjustments, _) = self.register_infer_ok_obligations(ok);
+ self.apply_adjustments(expr, adjustments);
+ Ok(target)
+ }
+
+ /// Same as `try_coerce()`, but without side-effects.
+ pub fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
+ let source = self.resolve_type_vars_with_obligations(expr_ty);
+ debug!("coercion::can({:?} -> {:?})", source, target);
+
+ let cause = self.cause(syntax_pos::DUMMY_SP, ObligationCauseCode::ExprAssignable);
+ let coerce = Coerce::new(self, cause);
+ self.probe(|_| coerce.coerce(source, target)).is_ok()
+ }
+
+ /// Given some expressions, their known unified type and another expression,
+ /// tries to unify the types, potentially inserting coercions on any of the
+ /// provided expressions and returns their LUB (aka "common supertype").
+ ///
+ /// This is really an internal helper. From outside the coercion
+ /// module, you should instantiate a `CoerceMany` instance.
+ fn try_find_coercion_lub<E>(&self,
+ cause: &ObligationCause<'tcx>,
+ exprs: &[E],
+ prev_ty: Ty<'tcx>,
+ new: &hir::Expr,
+ new_ty: Ty<'tcx>,
+ new_diverges: Diverges)
+ -> RelateResult<'tcx, Ty<'tcx>>
+ where E: AsCoercionSite
+ {
+ let prev_ty = self.resolve_type_vars_with_obligations(prev_ty);
+ let new_ty = self.resolve_type_vars_with_obligations(new_ty);
+ debug!("coercion::try_find_coercion_lub({:?}, {:?})", prev_ty, new_ty);
+
+ // Special-ish case: we can coerce any type `T` into the `!`
+ // type, but only if the source expression diverges.
+ if prev_ty.is_never() && new_diverges.always() {
+ debug!("permit coercion to `!` because expr diverges");
+ return Ok(prev_ty);
+ }
+
+ // Special-case that coercion alone cannot handle:
+ // Two function item types of differing IDs or Substs.
+ if let (&ty::TyFnDef(..), &ty::TyFnDef(..)) = (&prev_ty.sty, &new_ty.sty) {
+ // Don't reify if the function types have a LUB, i.e. they
+ // are the same function and their parameters have a LUB.
+ let lub_ty = self.commit_if_ok(|_| {
+ self.at(cause, self.param_env)
+ .lub(prev_ty, new_ty)
+ }).map(|ok| self.register_infer_ok_obligations(ok));
+
+ if lub_ty.is_ok() {
+ // We have a LUB of prev_ty and new_ty, just return it.
+ return lub_ty;
+ }
+
+ // The signature must match.
+ let a_sig = prev_ty.fn_sig(self.tcx);
+ let a_sig = self.normalize_associated_types_in(new.span, &a_sig);
+ let b_sig = new_ty.fn_sig(self.tcx);
+ let b_sig = self.normalize_associated_types_in(new.span, &b_sig);
+ let sig = self.at(cause, self.param_env)
+ .trace(prev_ty, new_ty)
+ .lub(&a_sig, &b_sig)
+ .map(|ok| self.register_infer_ok_obligations(ok))?;
+
+ // Reify both sides and return the reified fn pointer type.
+ let fn_ptr = self.tcx.mk_fn_ptr(sig);
+ for expr in exprs.iter().map(|e| e.as_coercion_site()).chain(Some(new)) {
+ // The only adjustment that can produce an fn item is
+ // `NeverToAny`, so this should always be valid.
+ self.apply_adjustments(expr, vec![Adjustment {
+ kind: Adjust::ReifyFnPointer,
+ target: fn_ptr
+ }]);
+ }
+ return Ok(fn_ptr);
+ }
+
+ let mut coerce = Coerce::new(self, cause.clone());
+ coerce.use_lub = true;
+
+ // First try to coerce the new expression to the type of the previous ones,
+ // but only if the new expression has no coercion already applied to it.
+ let mut first_error = None;
+ if !self.tables.borrow().adjustments().contains_key(new.hir_id) {
+ let result = self.commit_if_ok(|_| coerce.coerce(new_ty, prev_ty));
+ match result {
+ Ok(ok) => {
+ let (adjustments, target) = self.register_infer_ok_obligations(ok);
+ self.apply_adjustments(new, adjustments);
+ return Ok(target);
+ }
+ Err(e) => first_error = Some(e),
+ }
+ }
+
+ // Then try to coerce the previous expressions to the type of the new one.
+ // This requires ensuring there are no coercions applied to *any* of the
+ // previous expressions, other than noop reborrows (ignoring lifetimes).
+ for expr in exprs {
+ let expr = expr.as_coercion_site();
+ let noop = match self.tables.borrow().expr_adjustments(expr) {
+ &[
+ Adjustment { kind: Adjust::Deref(_), .. },
+ Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(_, mutbl_adj)), .. }
+ ] => {
+ match self.node_ty(expr.hir_id).sty {
+ ty::TyRef(_, mt_orig) => {
+ // Reborrow that we can safely ignore, because
+ // the next adjustment can only be a Deref
+ // which will be merged into it.
+ mutbl_adj == mt_orig.mutbl
+ }
+ _ => false,
+ }
+ }
+ &[Adjustment { kind: Adjust::NeverToAny, .. }] | &[] => true,
+ _ => false,
};
- let adjustment = try!(coerce.coerce(expr, a, b));
- unsizing_obligations = coerce.unsizing_obligations.into_inner();
- Ok(adjustment)
- })
- }));
- if let Some(AdjustDerefRef(auto)) = adjustment {
- if auto.unsize.is_some() {
- for obligation in unsizing_obligations {
- fcx.register_predicate(obligation);
+ if !noop {
+ return self.commit_if_ok(|_| {
+ self.at(cause, self.param_env)
+ .lub(prev_ty, new_ty)
+ }).map(|ok| self.register_infer_ok_obligations(ok));
+ }
+ }
+
+ match self.commit_if_ok(|_| coerce.coerce(prev_ty, new_ty)) {
+ Err(_) => {
+ // Avoid giving strange errors on failed attempts.
+ if let Some(e) = first_error {
+ Err(e)
+ } else {
+ self.commit_if_ok(|_| {
+ self.at(cause, self.param_env)
+ .lub(prev_ty, new_ty)
+ }).map(|ok| self.register_infer_ok_obligations(ok))
+ }
+ }
+ Ok(ok) => {
+ let (adjustments, target) = self.register_infer_ok_obligations(ok);
+ for expr in exprs {
+ let expr = expr.as_coercion_site();
+ self.apply_adjustments(expr, adjustments.clone());
+ }
+ Ok(target)
+ }
+ }
+ }
+}
+
+/// CoerceMany encapsulates the pattern you should use when you have
+/// many expressions that are all getting coerced to a common
+/// type. This arises, for example, when you have a match (the result
+/// of each arm is coerced to a common type). It also arises in less
+/// obvious places, such as when you have many `break foo` expressions
+/// that target the same loop, or the various `return` expressions in
+/// a function.
+///
+/// The basic protocol is as follows:
+///
+/// - Instantiate the `CoerceMany` with an initial `expected_ty`.
+/// This will also serve as the "starting LUB". The expectation is
+/// that this type is something which all of the expressions *must*
+/// be coercible to. Use a fresh type variable if needed.
+/// - For each expression whose result is to be coerced, invoke `coerce()` with.
+/// - In some cases we wish to coerce "non-expressions" whose types are implicitly
+/// unit. This happens for example if you have a `break` with no expression,
+/// or an `if` with no `else`. In that case, invoke `coerce_forced_unit()`.
+/// - `coerce()` and `coerce_forced_unit()` may report errors. They hide this
+/// from you so that you don't have to worry your pretty head about it.
+/// But if an error is reported, the final type will be `err`.
+/// - Invoking `coerce()` may cause us to go and adjust the "adjustments" on
+/// previously coerced expressions.
+/// - When all done, invoke `complete()`. This will return the LUB of
+/// all your expressions.
+/// - WARNING: I don't believe this final type is guaranteed to be
+/// related to your initial `expected_ty` in any particular way,
+/// although it will typically be a subtype, so you should check it.
+/// - Invoking `complete()` may cause us to go and adjust the "adjustments" on
+/// previously coerced expressions.
+///
+/// Example:
+///
+/// ```
+/// let mut coerce = CoerceMany::new(expected_ty);
+/// for expr in exprs {
+/// let expr_ty = fcx.check_expr_with_expectation(expr, expected);
+/// coerce.coerce(fcx, &cause, expr, expr_ty);
+/// }
+/// let final_ty = coerce.complete(fcx);
+/// ```
+pub struct CoerceMany<'gcx, 'tcx, 'exprs, E>
+ where 'gcx: 'tcx, E: 'exprs + AsCoercionSite,
+{
+ expected_ty: Ty<'tcx>,
+ final_ty: Option<Ty<'tcx>>,
+ expressions: Expressions<'gcx, 'exprs, E>,
+ pushed: usize,
+}
+
+/// The type of a `CoerceMany` that is storing up the expressions into
+/// a buffer. We use this in `check/mod.rs` for things like `break`.
+pub type DynamicCoerceMany<'gcx, 'tcx> = CoerceMany<'gcx, 'tcx, 'gcx, P<hir::Expr>>;
+
+enum Expressions<'gcx, 'exprs, E>
+ where E: 'exprs + AsCoercionSite,
+{
+ Dynamic(Vec<&'gcx hir::Expr>),
+ UpFront(&'exprs [E]),
+}
+
+impl<'gcx, 'tcx, 'exprs, E> CoerceMany<'gcx, 'tcx, 'exprs, E>
+ where 'gcx: 'tcx, E: 'exprs + AsCoercionSite,
+{
+ /// The usual case; collect the set of expressions dynamically.
+ /// If the full set of coercion sites is known before hand,
+ /// consider `with_coercion_sites()` instead to avoid allocation.
+ pub fn new(expected_ty: Ty<'tcx>) -> Self {
+ Self::make(expected_ty, Expressions::Dynamic(vec![]))
+ }
+
+ /// As an optimization, you can create a `CoerceMany` with a
+ /// pre-existing slice of expressions. In this case, you are
+ /// expected to pass each element in the slice to `coerce(...)` in
+ /// order. This is used with arrays in particular to avoid
+ /// needlessly cloning the slice.
+ pub fn with_coercion_sites(expected_ty: Ty<'tcx>,
+ coercion_sites: &'exprs [E])
+ -> Self {
+ Self::make(expected_ty, Expressions::UpFront(coercion_sites))
+ }
+
+ fn make(expected_ty: Ty<'tcx>, expressions: Expressions<'gcx, 'exprs, E>) -> Self {
+ CoerceMany {
+ expected_ty,
+ final_ty: None,
+ expressions,
+ pushed: 0,
+ }
+ }
+
+ /// Return the "expected type" with which this coercion was
+ /// constructed. This represents the "downward propagated" type
+ /// that was given to us at the start of typing whatever construct
+ /// we are typing (e.g., the match expression).
+ ///
+ /// Typically, this is used as the expected type when
+ /// type-checking each of the alternative expressions whose types
+ /// we are trying to merge.
+ pub fn expected_ty(&self) -> Ty<'tcx> {
+ self.expected_ty
+ }
+
+ /// Returns the current "merged type", representing our best-guess
+ /// at the LUB of the expressions we've seen so far (if any). This
+ /// isn't *final* until you call `self.final()`, which will return
+ /// the merged type.
+ pub fn merged_ty(&self) -> Ty<'tcx> {
+ self.final_ty.unwrap_or(self.expected_ty)
+ }
+
+ /// Indicates that the value generated by `expression`, which is
+ /// of type `expression_ty`, is one of the possibility that we
+ /// could coerce from. This will record `expression` and later
+ /// calls to `coerce` may come back and add adjustments and things
+ /// if necessary.
+ pub fn coerce<'a>(&mut self,
+ fcx: &FnCtxt<'a, 'gcx, 'tcx>,
+ cause: &ObligationCause<'tcx>,
+ expression: &'gcx hir::Expr,
+ expression_ty: Ty<'tcx>,
+ expression_diverges: Diverges)
+ {
+ self.coerce_inner(fcx,
+ cause,
+ Some(expression),
+ expression_ty,
+ expression_diverges,
+ None, false)
+ }
+
+ /// Indicates that one of the inputs is a "forced unit". This
+ /// occurs in a case like `if foo { ... };`, where the missing else
+ /// generates a "forced unit". Another example is a `loop { break;
+ /// }`, where the `break` has no argument expression. We treat
+ /// these cases slightly differently for error-reporting
+ /// purposes. Note that these tend to correspond to cases where
+ /// the `()` expression is implicit in the source, and hence we do
+ /// not take an expression argument.
+ ///
+ /// The `augment_error` gives you a chance to extend the error
+ /// message, in case any results (e.g., we use this to suggest
+ /// removing a `;`).
+ pub fn coerce_forced_unit<'a>(&mut self,
+ fcx: &FnCtxt<'a, 'gcx, 'tcx>,
+ cause: &ObligationCause<'tcx>,
+ augment_error: &mut FnMut(&mut DiagnosticBuilder),
+ label_unit_as_expected: bool)
+ {
+ self.coerce_inner(fcx,
+ cause,
+ None,
+ fcx.tcx.mk_nil(),
+ Diverges::Maybe,
+ Some(augment_error),
+ label_unit_as_expected)
+ }
+
+ /// The inner coercion "engine". If `expression` is `None`, this
+ /// is a forced-unit case, and hence `expression_ty` must be
+ /// `Nil`.
+ fn coerce_inner<'a>(&mut self,
+ fcx: &FnCtxt<'a, 'gcx, 'tcx>,
+ cause: &ObligationCause<'tcx>,
+ expression: Option<&'gcx hir::Expr>,
+ mut expression_ty: Ty<'tcx>,
+ expression_diverges: Diverges,
+ augment_error: Option<&mut FnMut(&mut DiagnosticBuilder)>,
+ label_expression_as_expected: bool)
+ {
+ // Incorporate whatever type inference information we have
+ // until now; in principle we might also want to process
+ // pending obligations, but doing so should only improve
+ // compatibility (hopefully that is true) by helping us
+ // uncover never types better.
+ if expression_ty.is_ty_var() {
+ expression_ty = fcx.infcx.shallow_resolve(expression_ty);
+ }
+
+ // If we see any error types, just propagate that error
+ // upwards.
+ if expression_ty.references_error() || self.merged_ty().references_error() {
+ self.final_ty = Some(fcx.tcx.types.err);
+ return;
+ }
+
+ // Handle the actual type unification etc.
+ let result = if let Some(expression) = expression {
+ if self.pushed == 0 {
+ // Special-case the first expression we are coercing.
+ // To be honest, I'm not entirely sure why we do this.
+ fcx.try_coerce(expression, expression_ty, expression_diverges, self.expected_ty)
+ } else {
+ match self.expressions {
+ Expressions::Dynamic(ref exprs) =>
+ fcx.try_find_coercion_lub(cause,
+ exprs,
+ self.merged_ty(),
+ expression,
+ expression_ty,
+ expression_diverges),
+ Expressions::UpFront(ref coercion_sites) =>
+ fcx.try_find_coercion_lub(cause,
+ &coercion_sites[0..self.pushed],
+ self.merged_ty(),
+ expression,
+ expression_ty,
+ expression_diverges),
+ }
+ }
+ } else {
+ // this is a hack for cases where we default to `()` because
+ // the expression etc has been omitted from the source. An
+ // example is an `if let` without an else:
+ //
+ // if let Some(x) = ... { }
+ //
+ // we wind up with a second match arm that is like `_ =>
+ // ()`. That is the case we are considering here. We take
+ // a different path to get the right "expected, found"
+ // message and so forth (and because we know that
+ // `expression_ty` will be unit).
+ //
+ // Another example is `break` with no argument expression.
+ assert!(expression_ty.is_nil());
+ assert!(expression_ty.is_nil(), "if let hack without unit type");
+ fcx.at(cause, fcx.param_env)
+ .eq_exp(label_expression_as_expected, expression_ty, self.merged_ty())
+ .map(|infer_ok| {
+ fcx.register_infer_ok_obligations(infer_ok);
+ expression_ty
+ })
+ };
+
+ match result {
+ Ok(v) => {
+ self.final_ty = Some(v);
+ if let Some(e) = expression {
+ match self.expressions {
+ Expressions::Dynamic(ref mut buffer) => buffer.push(e),
+ Expressions::UpFront(coercion_sites) => {
+ // if the user gave us an array to validate, check that we got
+ // the next expression in the list, as expected
+ assert_eq!(coercion_sites[self.pushed].as_coercion_site().id, e.id);
+ }
+ }
+ self.pushed += 1;
+ }
+ }
+ Err(err) => {
+ let (expected, found) = if label_expression_as_expected {
+ // In the case where this is a "forced unit", like
+ // `break`, we want to call the `()` "expected"
+ // since it is implied by the syntax.
+ // (Note: not all force-units work this way.)"
+ (expression_ty, self.final_ty.unwrap_or(self.expected_ty))
+ } else {
+ // Otherwise, the "expected" type for error
+ // reporting is the current unification type,
+ // which is basically the LUB of the expressions
+ // we've seen so far (combined with the expected
+ // type)
+ (self.final_ty.unwrap_or(self.expected_ty), expression_ty)
+ };
+
+ let mut db;
+ match cause.code {
+ ObligationCauseCode::ReturnNoExpression => {
+ db = struct_span_err!(
+ fcx.tcx.sess, cause.span, E0069,
+ "`return;` in a function whose return type is not `()`");
+ db.span_label(cause.span, "return type is not ()");
+ }
+ ObligationCauseCode::BlockTailExpression(blk_id) => {
+ db = fcx.report_mismatched_types(cause, expected, found, err);
+
+ let expr = expression.unwrap_or_else(|| {
+ span_bug!(cause.span,
+ "supposed to be part of a block tail expression, but the \
+ expression is empty");
+ });
+ fcx.suggest_mismatched_types_on_tail(&mut db, expr,
+ expected, found,
+ cause.span, blk_id);
+ }
+ _ => {
+ db = fcx.report_mismatched_types(cause, expected, found, err);
+ }
+ }
+
+ if let Some(augment_error) = augment_error {
+ augment_error(&mut db);
+ }
+
+ db.emit();
+
+ self.final_ty = Some(fcx.tcx.types.err);
}
}
}
- if let Some(adjustment) = adjustment {
- debug!("Success, coerced with {:?}", adjustment);
- fcx.write_adjustment(expr.id, adjustment);
+ pub fn complete<'a>(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx> {
+ if let Some(final_ty) = self.final_ty {
+ final_ty
+ } else {
+ // If we only had inputs that were of type `!` (or no
+ // inputs at all), then the final type is `!`.
+ assert_eq!(self.pushed, 0);
+ fcx.tcx.types.never
+ }
}
- Ok(())
}
-fn coerce_mutbls<'tcx>(from_mutbl: ast::Mutability,
- to_mutbl: ast::Mutability)
- -> CoerceResult<'tcx> {
- match (from_mutbl, to_mutbl) {
- (ast::MutMutable, ast::MutMutable) |
- (ast::MutImmutable, ast::MutImmutable) |
- (ast::MutMutable, ast::MutImmutable) => Ok(None),
- (ast::MutImmutable, ast::MutMutable) => Err(TypeError::Mutability)
+/// Something that can be converted into an expression to which we can
+/// apply a coercion.
+pub trait AsCoercionSite {
+ fn as_coercion_site(&self) -> &hir::Expr;
+}
+
+impl AsCoercionSite for hir::Expr {
+ fn as_coercion_site(&self) -> &hir::Expr {
+ self
+ }
+}
+
+impl AsCoercionSite for P<hir::Expr> {
+ fn as_coercion_site(&self) -> &hir::Expr {
+ self
+ }
+}
+
+impl<'a, T> AsCoercionSite for &'a T
+ where T: AsCoercionSite
+{
+ fn as_coercion_site(&self) -> &hir::Expr {
+ (**self).as_coercion_site()
+ }
+}
+
+impl AsCoercionSite for ! {
+ fn as_coercion_site(&self) -> &hir::Expr {
+ unreachable!()
+ }
+}
+
+impl AsCoercionSite for hir::Arm {
+ fn as_coercion_site(&self) -> &hir::Expr {
+ &self.body
}
}
projects / rustc.git / blobdiff