use check::{autoderef, FnCtxt, UnresolvedTypeAction};
-use middle::infer::{self, Coercion, TypeOrigin};
-use middle::traits::{self, ObligationCause};
-use middle::traits::{predicate_for_trait_def, report_selection_error};
-use middle::ty::adjustment::{AutoAdjustment, AutoDerefRef, AdjustDerefRef};
-use middle::ty::adjustment::{AutoPtr, AutoUnsafe, AdjustReifyFnPointer};
-use middle::ty::adjustment::{AdjustUnsafeFnPointer, AdjustMutToConstPointer};
-use middle::ty::{self, LvaluePreference, TypeAndMut, Ty};
-use middle::ty::fold::TypeFoldable;
-use middle::ty::error::TypeError;
-use middle::ty::relate::RelateResult;
+use rustc::infer::{Coercion, InferOk, TypeOrigin, TypeTrace};
+use rustc::traits::{self, ObligationCause};
+use rustc::traits::{predicate_for_trait_def, report_selection_error};
+use rustc::ty::adjustment::{AutoAdjustment, AutoDerefRef, AdjustDerefRef};
+use rustc::ty::adjustment::{AutoPtr, AutoUnsafe, AdjustReifyFnPointer};
+use rustc::ty::adjustment::{AdjustUnsafeFnPointer, AdjustMutToConstPointer};
+use rustc::ty::{self, LvaluePreference, TypeAndMut, Ty, TyCtxt};
+use rustc::ty::fold::TypeFoldable;
+use rustc::ty::error::TypeError;
+use rustc::ty::relate::{RelateResult, TypeRelation};
use util::common::indent;
use std::cell::RefCell;
use std::collections::VecDeque;
-use rustc_front::hir;
+use rustc::hir;
struct Coerce<'a, 'tcx: 'a> {
fcx: &'a FnCtxt<'a, 'tcx>,
- origin: infer::TypeOrigin,
+ origin: TypeOrigin,
+ use_lub: bool,
unsizing_obligations: RefCell<Vec<traits::PredicateObligation<'tcx>>>,
}
-type CoerceResult<'tcx> = RelateResult<'tcx, Option<AutoAdjustment<'tcx>>>;
+type CoerceResult<'tcx> = RelateResult<'tcx, (Ty<'tcx>, AutoAdjustment<'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> {
+ fn new(fcx: &'f FnCtxt<'f, 'tcx>, origin: TypeOrigin) -> Self {
+ Coerce {
+ fcx: fcx,
+ origin: origin,
+ use_lub: false,
+ unsizing_obligations: RefCell::new(vec![])
+ }
+ }
+
+ fn tcx(&self) -> &TyCtxt<'tcx> {
self.fcx.tcx()
}
- 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>) -> RelateResult<'tcx, Ty<'tcx>> {
+ let infcx = self.fcx.infcx();
+ infcx.commit_if_ok(|_| {
+ let trace = TypeTrace::types(self.origin, false, a, b);
+ if self.use_lub {
+ infcx.lub(false, trace, &a, &b)
+ .map(|InferOk { value, obligations }| {
+ // FIXME(#32730) propagate obligations
+ assert!(obligations.is_empty());
+ value
+ })
+ } else {
+ infcx.sub(false, trace, &a, &b)
+ .map(|InferOk { value, obligations }| {
+ // FIXME(#32730) propagate obligations
+ assert!(obligations.is_empty());
+ value
+ })
+ }
+ })
}
- fn unpack_actual_value<T, F>(&self, a: Ty<'tcx>, f: F) -> T where
- F: FnOnce(Ty<'tcx>) -> T,
- {
- f(self.fcx.infcx().shallow_resolve(a))
+ /// Unify two types (using sub or lub) and produce a noop coercion.
+ fn unify_and_identity(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
+ self.unify(&a, &b).and_then(|ty| self.identity(ty))
}
- fn coerce(&self,
- expr_a: &hir::Expr,
- a: Ty<'tcx>,
- b: Ty<'tcx>)
- -> CoerceResult<'tcx> {
- debug!("Coerce.tys({:?} => {:?})",
- a,
- b);
+ /// Synthesize an identity adjustment.
+ fn identity(&self, ty: Ty<'tcx>) -> CoerceResult<'tcx> {
+ Ok((ty, AdjustDerefRef(AutoDerefRef {
+ autoderefs: 0,
+ autoref: None,
+ unsize: None
+ })))
+ }
+
+ fn coerce<'a, E, I>(&self,
+ exprs: &E,
+ a: Ty<'tcx>,
+ b: Ty<'tcx>)
+ -> CoerceResult<'tcx>
+ // FIXME(eddyb) use copyable iterators when that becomes ergonomic.
+ where E: Fn() -> I,
+ I: IntoIterator<Item=&'a hir::Expr> {
let a = self.fcx.infcx().shallow_resolve(a);
+ debug!("Coerce.tys({:?} => {:?})", a, b);
// Just ignore error types.
if a.references_error() || b.references_error() {
- return Ok(None);
+ return self.identity(b);
}
// Consider coercing the subtype to a DST
return self.coerce_unsafe_ptr(a, b, mt_b.mutbl);
}
- ty::TyRef(_, mt_b) => {
- return self.coerce_borrowed_pointer(expr_a, a, b, mt_b.mutbl);
+ ty::TyRef(r_b, mt_b) => {
+ return self.coerce_borrowed_pointer(exprs, a, b, r_b, mt_b);
}
_ => {}
}
match a.sty {
- ty::TyBareFn(Some(_), a_f) => {
+ ty::TyFnDef(_, _, 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) => {
+ ty::TyFnPtr(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)
+ // Otherwise, just use unification rules.
+ self.unify_and_identity(a, b)
}
}
}
/// 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: &hir::Expr,
- a: Ty<'tcx>,
- b: Ty<'tcx>,
- mutbl_b: hir::Mutability)
- -> CoerceResult<'tcx> {
- debug!("coerce_borrowed_pointer(a={:?}, b={:?})",
- a,
- b);
+ fn coerce_borrowed_pointer<'a, E, I>(&self,
+ exprs: &E,
+ a: Ty<'tcx>,
+ b: Ty<'tcx>,
+ r_b: &'tcx ty::Region,
+ mt_b: TypeAndMut<'tcx>)
+ -> CoerceResult<'tcx>
+ // FIXME(eddyb) use copyable iterators when that becomes ergonomic.
+ where E: Fn() -> I,
+ I: IntoIterator<Item=&'a hir::Expr> {
+
+ 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_identity(a, b)
+ };
- 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(AutoPtr(r_borrow, mutbl_b));
+ let span = self.origin.span();
- let lvalue_pref = LvaluePreference::from_mutbl(mutbl_b);
+ let lvalue_pref = LvaluePreference::from_mutbl(mt_b.mutbl);
let mut first_error = None;
- let (_, autoderefs, success) = autoderef(self.fcx,
- expr_a.span,
- a,
- Some(expr_a),
+ let mut r_borrow_var = None;
+ let (_, autoderefs, success) = autoderef(self.fcx, span, a, exprs,
UnresolvedTypeAction::Ignore,
lvalue_pref,
- |inner_ty, autoderef| {
+ |referent_ty, autoderef|
+ {
if autoderef == 0 {
// Don't let this pass, otherwise it would cause
// &T to autoref to &&T.
return None;
}
- 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 autoderef == 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.fcx.infcx().next_region_var(coercion);
+ r_borrow_var = Some(self.tcx().mk_region(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(ty) => Some(ty),
+ Err(err) => {
+ if first_error.is_none() {
+ first_error = Some(err);
+ }
+ None
+ }
}
});
- 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 ty = match success {
+ Some(ty) => ty,
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);
}
+ };
+
+ // Now apply the autoref. We have to extract the region out of
+ // the final ref type we got.
+ if ty == a && mt_a.mutbl == hir::MutImmutable && autoderefs == 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 self.identity(ty);
}
+ let r_borrow = match ty.sty {
+ ty::TyRef(r_borrow, _) => r_borrow,
+ _ => span_bug!(span, "expected a ref type, got {:?}", ty)
+ };
+ let autoref = Some(AutoPtr(r_borrow, mt_b.mutbl));
+ debug!("coerce_borrowed_pointer: succeeded ty={:?} autoderefs={:?} autoref={:?}",
+ ty, autoderefs, autoref);
+ Ok((ty, AdjustDerefRef(AutoDerefRef {
+ autoderefs: autoderefs,
+ autoref: autoref,
+ unsize: None
+ })))
}
// Handle reborrows before selecting `Source: CoerceUnsized<Target>`.
let (source, 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);
(mt_a.ty, Some(AutoPtr(region, mt_b.mutbl)))
}
(&ty::TyRef(_, mt_a), &ty::TyRawPtr(mt_b)) => {
- try!(coerce_mutbls(mt_a.mutbl, mt_b.mutbl));
+ coerce_mutbls(mt_a.mutbl, mt_b.mutbl)?;
(mt_a.ty, Some(AutoUnsafe(mt_b.mutbl)))
}
_ => (source, None)
}
}
- let mut obligations = self.unsizing_obligations.borrow_mut();
- assert!(obligations.is_empty());
- *obligations = leftover_predicates;
+ *self.unsizing_obligations.borrow_mut() = leftover_predicates;
let adjustment = AutoDerefRef {
autoderefs: if reborrow.is_some() { 1 } else { 0 },
unsize: Some(target)
};
debug!("Success, coerced with {:?}", adjustment);
- Ok(Some(AdjustDerefRef(adjustment)))
+ Ok((target, AdjustDerefRef(adjustment)))
}
fn coerce_from_fn_pointer(&self,
* into a closure or a `proc`.
*/
- self.unpack_actual_value(b, |b| {
- debug!("coerce_from_fn_pointer(a={:?}, b={:?})",
- a, b);
+ let b = self.fcx.infcx().shallow_resolve(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) {
- (hir::Unsafety::Normal, hir::Unsafety::Unsafe) => {
- let unsafe_a = self.tcx().safe_to_unsafe_fn_ty(fn_ty_a);
- try!(self.subtype(unsafe_a, b));
- return Ok(Some(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_identity(unsafe_a, b).map(|(ty, _)| {
+ (ty, AdjustUnsafeFnPointer)
+ });
}
+ _ => {}
}
- self.subtype(a, b)
- })
+ }
+ self.unify_and_identity(a, b)
}
fn coerce_from_fn_item(&self,
* into a closure or a `proc`.
*/
- self.unpack_actual_value(b, |b| {
- debug!("coerce_from_fn_item(a={:?}, b={:?})",
- a, b);
+ let b = self.fcx.infcx().shallow_resolve(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(AdjustReifyFnPointer))
- }
- _ => self.subtype(a, b)
+ match b.sty {
+ ty::TyFnPtr(_) => {
+ let a_fn_pointer = self.tcx().mk_ty(ty::TyFnPtr(fn_ty_a));
+ self.unify_and_identity(a_fn_pointer, b).map(|(ty, _)| {
+ (ty, AdjustReifyFnPointer)
+ })
}
- })
+ _ => self.unify_and_identity(a, b)
+ }
}
fn coerce_unsafe_ptr(&self,
ty::TyRef(_, mt) => (true, mt),
ty::TyRawPtr(mt) => (false, mt),
_ => {
- return self.subtype(a, b);
+ return self.unify_and_identity(a, b);
}
};
// 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 (ty, noop) = self.unify_and_identity(a_unsafe, b)?;
+ coerce_mutbls(mt_a.mutbl, mutbl_b)?;
// Although references and unsafe ptrs have the same
// representation, we still register an AutoDerefRef so that
// regionck knows that the region for `a` must be valid here.
- if is_ref {
- Ok(Some(AdjustDerefRef(AutoDerefRef {
+ Ok((ty, if is_ref {
+ AdjustDerefRef(AutoDerefRef {
autoderefs: 1,
autoref: Some(AutoUnsafe(mutbl_b)),
unsize: None
- })))
+ })
} else if mt_a.mutbl != mutbl_b {
- Ok(Some(AdjustMutToConstPointer))
+ AdjustMutToConstPointer
} else {
- Ok(None)
- }
+ noop
+ }))
}
}
-pub fn mk_assignty<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
- expr: &hir::Expr,
+fn apply<'a, 'b, 'tcx, E, I>(coerce: &mut Coerce<'a, 'tcx>,
+ exprs: &E,
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: TypeOrigin::ExprAssignable(expr.span),
- unsizing_obligations: RefCell::new(vec![])
- };
- let adjustment = try!(coerce.coerce(expr, a, b));
- unsizing_obligations = coerce.unsizing_obligations.into_inner();
- Ok(adjustment)
- })
- }));
+ -> CoerceResult<'tcx>
+ where E: Fn() -> I,
+ I: IntoIterator<Item=&'b hir::Expr> {
- if let Some(AdjustDerefRef(auto)) = adjustment {
+ let (ty, adjustment) = indent(|| coerce.coerce(exprs, a, b))?;
+
+ let fcx = coerce.fcx;
+ if let AdjustDerefRef(auto) = adjustment {
if auto.unsize.is_some() {
- for obligation in unsizing_obligations {
+ let mut obligations = coerce.unsizing_obligations.borrow_mut();
+ for obligation in obligations.drain(..) {
fcx.register_predicate(obligation);
}
}
}
- if let Some(adjustment) = adjustment {
- debug!("Success, coerced with {:?}", adjustment);
- fcx.write_adjustment(expr.id, adjustment);
- }
- Ok(())
+ Ok((ty, adjustment))
}
-fn coerce_mutbls<'tcx>(from_mutbl: hir::Mutability,
- to_mutbl: hir::Mutability)
- -> CoerceResult<'tcx> {
- match (from_mutbl, to_mutbl) {
- (hir::MutMutable, hir::MutMutable) |
- (hir::MutImmutable, hir::MutImmutable) |
- (hir::MutMutable, hir::MutImmutable) => Ok(None),
- (hir::MutImmutable, hir::MutMutable) => Err(TypeError::Mutability)
+/// 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<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
+ expr: &hir::Expr,
+ target: Ty<'tcx>)
+ -> RelateResult<'tcx, Ty<'tcx>> {
+ let source = fcx.resolve_type_vars_if_possible(fcx.expr_ty(expr));
+ debug!("coercion::try({:?}: {:?} -> {:?})", expr, source, target);
+
+ let mut coerce = Coerce::new(fcx, TypeOrigin::ExprAssignable(expr.span));
+ fcx.infcx().commit_if_ok(|_| {
+ let (ty, adjustment) =
+ apply(&mut coerce, &|| Some(expr), source, target)?;
+ if !adjustment.is_identity() {
+ debug!("Success, coerced with {:?}", adjustment);
+ assert!(!fcx.inh.tables.borrow().adjustments.contains_key(&expr.id));
+ fcx.write_adjustment(expr.id, adjustment);
+ }
+ Ok(ty)
+ })
+}
+
+/// 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").
+pub fn try_find_lub<'a, 'b, 'tcx, E, I>(fcx: &FnCtxt<'a, 'tcx>,
+ origin: TypeOrigin,
+ exprs: E,
+ prev_ty: Ty<'tcx>,
+ new: &'b hir::Expr)
+ -> RelateResult<'tcx, Ty<'tcx>>
+ // FIXME(eddyb) use copyable iterators when that becomes ergonomic.
+ where E: Fn() -> I,
+ I: IntoIterator<Item=&'b hir::Expr> {
+
+ let prev_ty = fcx.resolve_type_vars_if_possible(prev_ty);
+ let new_ty = fcx.resolve_type_vars_if_possible(fcx.expr_ty(new));
+ debug!("coercion::try_find_lub({:?}, {:?})", prev_ty, new_ty);
+
+ let trace = TypeTrace::types(origin, true, prev_ty, new_ty);
+
+ // Special-case that coercion alone cannot handle:
+ // Two function item types of differing IDs or Substs.
+ match (&prev_ty.sty, &new_ty.sty) {
+ (&ty::TyFnDef(a_def_id, a_substs, a_fty),
+ &ty::TyFnDef(b_def_id, b_substs, b_fty)) => {
+ // The signature must always match.
+ let fty = fcx.infcx().lub(true, trace.clone(), a_fty, b_fty)
+ .map(|InferOk { value, obligations }| {
+ // FIXME(#32730) propagate obligations
+ assert!(obligations.is_empty());
+ value
+ })?;
+
+ if a_def_id == b_def_id {
+ // Same function, maybe the parameters match.
+ let substs = fcx.infcx().commit_if_ok(|_| {
+ fcx.infcx().lub(true, trace.clone(), a_substs, b_substs)
+ .map(|InferOk { value, obligations }| {
+ // FIXME(#32730) propagate obligations
+ assert!(obligations.is_empty());
+ value
+ })
+ }).map(|s| fcx.tcx().mk_substs(s));
+
+ if let Ok(substs) = substs {
+ // We have a LUB of prev_ty and new_ty, just return it.
+ return Ok(fcx.tcx().mk_fn_def(a_def_id, substs, fty));
+ }
+ }
+
+ // Reify both sides and return the reified fn pointer type.
+ for expr in exprs().into_iter().chain(Some(new)) {
+ // No adjustments can produce a fn item, so this should never trip.
+ assert!(!fcx.inh.tables.borrow().adjustments.contains_key(&expr.id));
+ fcx.write_adjustment(expr.id, AdjustReifyFnPointer);
+ }
+ return Ok(fcx.tcx().mk_fn_ptr(fty));
+ }
+ _ => {}
+ }
+
+ let mut coerce = Coerce::new(fcx, origin);
+ 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 !fcx.inh.tables.borrow().adjustments.contains_key(&new.id) {
+ let result = fcx.infcx().commit_if_ok(|_| {
+ apply(&mut coerce, &|| Some(new), new_ty, prev_ty)
+ });
+ match result {
+ Ok((ty, adjustment)) => {
+ if !adjustment.is_identity() {
+ fcx.write_adjustment(new.id, adjustment);
+ }
+ return Ok(ty);
+ }
+ 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 noop = match fcx.inh.tables.borrow().adjustments.get(&expr.id) {
+ Some(&AdjustDerefRef(AutoDerefRef {
+ autoderefs: 1,
+ autoref: Some(AutoPtr(_, mutbl_adj)),
+ unsize: None
+ })) => match fcx.expr_ty(expr).sty {
+ ty::TyRef(_, mt_orig) => {
+ // Reborrow that we can safely ignore.
+ mutbl_adj == mt_orig.mutbl
+ }
+ _ => false
+ },
+ Some(_) => false,
+ None => true
+ };
+
+ if !noop {
+ return fcx.infcx().commit_if_ok(|_| {
+ fcx.infcx().lub(true, trace.clone(), &prev_ty, &new_ty)
+ .map(|InferOk { value, obligations }| {
+ // FIXME(#32730) propagate obligations
+ assert!(obligations.is_empty());
+ value
+ })
+ });
+ }
+ }
+
+ match fcx.infcx().commit_if_ok(|_| apply(&mut coerce, &exprs, prev_ty, new_ty)) {
+ Err(_) => {
+ // Avoid giving strange errors on failed attempts.
+ if let Some(e) = first_error {
+ Err(e)
+ } else {
+ fcx.infcx().commit_if_ok(|_| {
+ fcx.infcx().lub(true, trace, &prev_ty, &new_ty)
+ .map(|InferOk { value, obligations }| {
+ // FIXME(#32730) propagate obligations
+ assert!(obligations.is_empty());
+ value
+ })
+ })
+ }
+ }
+ Ok((ty, adjustment)) => {
+ if !adjustment.is_identity() {
+ for expr in exprs() {
+ fcx.write_adjustment(expr.id, adjustment);
+ }
+ }
+ Ok(ty)
+ }
}
}
projects / rustc.git / blobdiff