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//! Code for type-checking closure expressions.
use super::{check_fn, Expectation, FnCtxt, GeneratorTypes};
use crate::astconv::AstConv;
use crate::middle::region;
use rustc::hir::def_id::DefId;
use rustc::infer::{InferOk, InferResult};
use rustc::infer::LateBoundRegionConversionTime;
use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc::traits::Obligation;
use rustc::traits::error_reporting::ArgKind;
use rustc::ty::{self, Ty, GenericParamDefKind};
use rustc::ty::fold::TypeFoldable;
use rustc::ty::subst::InternalSubsts;
use std::cmp;
use std::iter;
use rustc_target::spec::abi::Abi;
use syntax::source_map::Span;
use rustc::hir;
/// What signature do we *expect* the closure to have from context?
#[derive(Debug)]
struct ExpectedSig<'tcx> {
/// Span that gave us this expectation, if we know that.
cause_span: Option<Span>,
sig: ty::FnSig<'tcx>,
}
struct ClosureSignatures<'tcx> {
bound_sig: ty::PolyFnSig<'tcx>,
liberated_sig: ty::FnSig<'tcx>,
}
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
pub fn check_expr_closure(
&self,
expr: &hir::Expr,
_capture: hir::CaptureClause,
decl: &'tcx hir::FnDecl,
body_id: hir::BodyId,
gen: Option<hir::GeneratorMovability>,
expected: Expectation<'tcx>,
) -> Ty<'tcx> {
debug!(
"check_expr_closure(expr={:?},expected={:?})",
expr, expected
);
// It's always helpful for inference if we know the kind of
// closure sooner rather than later, so first examine the expected
// type, and see if can glean a closure kind from there.
let (expected_sig, expected_kind) = match expected.to_option(self) {
Some(ty) => self.deduce_expectations_from_expected_type(ty),
None => (None, None),
};
let body = self.tcx.hir().body(body_id);
self.check_closure(expr, expected_kind, decl, body, gen, expected_sig)
}
fn check_closure(
&self,
expr: &hir::Expr,
opt_kind: Option<ty::ClosureKind>,
decl: &'tcx hir::FnDecl,
body: &'tcx hir::Body,
gen: Option<hir::GeneratorMovability>,
expected_sig: Option<ExpectedSig<'tcx>>,
) -> Ty<'tcx> {
debug!(
"check_closure(opt_kind={:?}, expected_sig={:?})",
opt_kind, expected_sig
);
let expr_def_id = self.tcx.hir().local_def_id(expr.hir_id);
let ClosureSignatures {
bound_sig,
liberated_sig,
} = self.sig_of_closure(expr_def_id, decl, body, expected_sig);
debug!("check_closure: ty_of_closure returns {:?}", liberated_sig);
let generator_types = check_fn(
self,
self.param_env,
liberated_sig,
decl,
expr.hir_id,
body,
gen,
).1;
// Create type variables (for now) to represent the transformed
// types of upvars. These will be unified during the upvar
// inference phase (`upvar.rs`).
let base_substs =
InternalSubsts::identity_for_item(self.tcx, self.tcx.closure_base_def_id(expr_def_id));
let substs = base_substs.extend_to(self.tcx,expr_def_id, |param, _| {
match param.kind {
GenericParamDefKind::Lifetime => {
span_bug!(expr.span, "closure has lifetime param")
}
GenericParamDefKind::Type { .. } => {
self.infcx.next_ty_var(TypeVariableOrigin {
kind: TypeVariableOriginKind::ClosureSynthetic,
span: expr.span,
}).into()
}
GenericParamDefKind::Const => {
span_bug!(expr.span, "closure has const param")
}
}
});
if let Some(GeneratorTypes { yield_ty, interior, movability }) = generator_types {
let substs = ty::GeneratorSubsts { substs };
self.demand_eqtype(
expr.span,
yield_ty,
substs.yield_ty(expr_def_id, self.tcx),
);
self.demand_eqtype(
expr.span,
liberated_sig.output(),
substs.return_ty(expr_def_id, self.tcx),
);
self.demand_eqtype(
expr.span,
interior,
substs.witness(expr_def_id, self.tcx),
);
return self.tcx.mk_generator(expr_def_id, substs, movability);
}
let substs = ty::ClosureSubsts { substs };
let closure_type = self.tcx.mk_closure(expr_def_id, substs);
debug!(
"check_closure: expr.hir_id={:?} closure_type={:?}",
expr.hir_id, closure_type
);
// Tuple up the arguments and insert the resulting function type into
// the `closures` table.
let sig = bound_sig.map_bound(|sig| {
self.tcx.mk_fn_sig(
iter::once(self.tcx.intern_tup(sig.inputs())),
sig.output(),
sig.c_variadic,
sig.unsafety,
sig.abi,
)
});
debug!(
"check_closure: expr_def_id={:?}, sig={:?}, opt_kind={:?}",
expr_def_id, sig, opt_kind
);
let sig_fn_ptr_ty = self.tcx.mk_fn_ptr(sig);
self.demand_eqtype(
expr.span,
sig_fn_ptr_ty,
substs.closure_sig_ty(expr_def_id, self.tcx),
);
if let Some(kind) = opt_kind {
self.demand_eqtype(
expr.span,
kind.to_ty(self.tcx),
substs.closure_kind_ty(expr_def_id, self.tcx),
);
}
closure_type
}
/// Given the expected type, figures out what it can about this closure we
/// are about to type check:
fn deduce_expectations_from_expected_type(
&self,
expected_ty: Ty<'tcx>,
) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
debug!(
"deduce_expectations_from_expected_type(expected_ty={:?})",
expected_ty
);
match expected_ty.sty {
ty::Dynamic(ref object_type, ..) => {
let sig = object_type
.projection_bounds()
.filter_map(|pb| {
let pb = pb.with_self_ty(self.tcx, self.tcx.types.err);
self.deduce_sig_from_projection(None, &pb)
})
.next();
let kind = object_type.principal_def_id().and_then(|did| {
self.tcx.lang_items().fn_trait_kind(did)
});
(sig, kind)
}
ty::Infer(ty::TyVar(vid)) => self.deduce_expectations_from_obligations(vid),
ty::FnPtr(sig) => {
let expected_sig = ExpectedSig {
cause_span: None,
sig: sig.skip_binder().clone(),
};
(Some(expected_sig), Some(ty::ClosureKind::Fn))
}
_ => (None, None),
}
}
fn deduce_expectations_from_obligations(
&self,
expected_vid: ty::TyVid,
) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
let expected_sig = self.obligations_for_self_ty(expected_vid)
.find_map(|(_, obligation)| {
debug!(
"deduce_expectations_from_obligations: obligation.predicate={:?}",
obligation.predicate
);
if let ty::Predicate::Projection(ref proj_predicate) = obligation.predicate {
// Given a Projection predicate, we can potentially infer
// the complete signature.
self.deduce_sig_from_projection(
Some(obligation.cause.span),
proj_predicate
)
} else {
None
}
});
// Even if we can't infer the full signature, we may be able to
// infer the kind. This can occur if there is a trait-reference
// like `F : Fn<A>`. Note that due to subtyping we could encounter
// many viable options, so pick the most restrictive.
let expected_kind = self.obligations_for_self_ty(expected_vid)
.filter_map(|(tr, _)| self.tcx.lang_items().fn_trait_kind(tr.def_id()))
.fold(None, |best, cur| {
Some(best.map_or(cur, |best| cmp::min(best, cur)))
});
(expected_sig, expected_kind)
}
/// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
/// everything we need to know about a closure or generator.
///
/// The `cause_span` should be the span that caused us to
/// have this expected signature, or `None` if we can't readily
/// know that.
fn deduce_sig_from_projection(
&self,
cause_span: Option<Span>,
projection: &ty::PolyProjectionPredicate<'tcx>,
) -> Option<ExpectedSig<'tcx>> {
let tcx = self.tcx;
debug!("deduce_sig_from_projection({:?})", projection);
let trait_ref = projection.to_poly_trait_ref(tcx);
let is_fn = tcx.lang_items().fn_trait_kind(trait_ref.def_id()).is_some();
let gen_trait = tcx.lang_items().gen_trait().unwrap();
let is_gen = gen_trait == trait_ref.def_id();
if !is_fn && !is_gen {
debug!("deduce_sig_from_projection: not fn or generator");
return None;
}
if is_gen {
// Check that we deduce the signature from the `<_ as std::ops::Generator>::Return`
// associated item and not yield.
let return_assoc_item = self.tcx.associated_items(gen_trait).nth(1).unwrap().def_id;
if return_assoc_item != projection.projection_def_id() {
debug!("deduce_sig_from_projection: not return assoc item of generator");
return None;
}
}
let input_tys = if is_fn {
let arg_param_ty = trait_ref.skip_binder().substs.type_at(1);
let arg_param_ty = self.resolve_vars_if_possible(&arg_param_ty);
debug!("deduce_sig_from_projection: arg_param_ty={:?}", arg_param_ty);
match arg_param_ty.sty {
ty::Tuple(tys) => tys.into_iter().map(|k| k.expect_ty()).collect::<Vec<_>>(),
_ => return None,
}
} else {
// Generators cannot have explicit arguments.
vec![]
};
let ret_param_ty = projection.skip_binder().ty;
let ret_param_ty = self.resolve_vars_if_possible(&ret_param_ty);
debug!("deduce_sig_from_projection: ret_param_ty={:?}", ret_param_ty);
let sig = self.tcx.mk_fn_sig(
input_tys.iter(),
&ret_param_ty,
false,
hir::Unsafety::Normal,
Abi::Rust,
);
debug!("deduce_sig_from_projection: sig={:?}", sig);
Some(ExpectedSig { cause_span, sig })
}
fn sig_of_closure(
&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
expected_sig: Option<ExpectedSig<'tcx>>,
) -> ClosureSignatures<'tcx> {
if let Some(e) = expected_sig {
self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
} else {
self.sig_of_closure_no_expectation(expr_def_id, decl, body)
}
}
/// If there is no expected signature, then we will convert the
/// types that the user gave into a signature.
fn sig_of_closure_no_expectation(
&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
) -> ClosureSignatures<'tcx> {
debug!("sig_of_closure_no_expectation()");
let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl);
self.closure_sigs(expr_def_id, body, bound_sig)
}
/// Invoked to compute the signature of a closure expression. This
/// combines any user-provided type annotations (e.g., `|x: u32|
/// -> u32 { .. }`) with the expected signature.
///
/// The approach is as follows:
///
/// - Let `S` be the (higher-ranked) signature that we derive from the user's annotations.
/// - Let `E` be the (higher-ranked) signature that we derive from the expectations, if any.
/// - If we have no expectation `E`, then the signature of the closure is `S`.
/// - Otherwise, the signature of the closure is E. Moreover:
/// - Skolemize the late-bound regions in `E`, yielding `E'`.
/// - Instantiate all the late-bound regions bound in the closure within `S`
/// with fresh (existential) variables, yielding `S'`
/// - Require that `E' = S'`
/// - We could use some kind of subtyping relationship here,
/// I imagine, but equality is easier and works fine for
/// our purposes.
///
/// The key intuition here is that the user's types must be valid
/// from "the inside" of the closure, but the expectation
/// ultimately drives the overall signature.
///
/// # Examples
///
/// ```
/// fn with_closure<F>(_: F)
/// where F: Fn(&u32) -> &u32 { .. }
///
/// with_closure(|x: &u32| { ... })
/// ```
///
/// Here:
/// - E would be `fn(&u32) -> &u32`.
/// - S would be `fn(&u32) ->
/// - E' is `&'!0 u32 -> &'!0 u32`
/// - S' is `&'?0 u32 -> ?T`
///
/// S' can be unified with E' with `['?0 = '!0, ?T = &'!10 u32]`.
///
/// # Arguments
///
/// - `expr_def_id`: the `DefId` of the closure expression
/// - `decl`: the HIR declaration of the closure
/// - `body`: the body of the closure
/// - `expected_sig`: the expected signature (if any). Note that
/// this is missing a binder: that is, there may be late-bound
/// regions with depth 1, which are bound then by the closure.
fn sig_of_closure_with_expectation(
&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
expected_sig: ExpectedSig<'tcx>,
) -> ClosureSignatures<'tcx> {
debug!(
"sig_of_closure_with_expectation(expected_sig={:?})",
expected_sig
);
// Watch out for some surprises and just ignore the
// expectation if things don't see to match up with what we
// expect.
if expected_sig.sig.c_variadic != decl.c_variadic {
return self.sig_of_closure_no_expectation(expr_def_id, decl, body);
} else if expected_sig.sig.inputs_and_output.len() != decl.inputs.len() + 1 {
return self.sig_of_closure_with_mismatched_number_of_arguments(
expr_def_id,
decl,
body,
expected_sig,
);
}
// Create a `PolyFnSig`. Note the oddity that late bound
// regions appearing free in `expected_sig` are now bound up
// in this binder we are creating.
assert!(!expected_sig.sig.has_vars_bound_above(ty::INNERMOST));
let bound_sig = ty::Binder::bind(self.tcx.mk_fn_sig(
expected_sig.sig.inputs().iter().cloned(),
expected_sig.sig.output(),
decl.c_variadic,
hir::Unsafety::Normal,
Abi::RustCall,
));
// `deduce_expectations_from_expected_type` introduces
// late-bound lifetimes defined elsewhere, which we now
// anonymize away, so as not to confuse the user.
let bound_sig = self.tcx.anonymize_late_bound_regions(&bound_sig);
let closure_sigs = self.closure_sigs(expr_def_id, body, bound_sig);
// Up till this point, we have ignored the annotations that the user
// gave. This function will check that they unify successfully.
// Along the way, it also writes out entries for types that the user
// wrote into our tables, which are then later used by the privacy
// check.
match self.check_supplied_sig_against_expectation(expr_def_id, decl, body, &closure_sigs) {
Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
Err(_) => return self.sig_of_closure_no_expectation(expr_def_id, decl, body),
}
closure_sigs
}
fn sig_of_closure_with_mismatched_number_of_arguments(
&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
expected_sig: ExpectedSig<'tcx>,
) -> ClosureSignatures<'tcx> {
let expr_map_node = self.tcx.hir().get_if_local(expr_def_id).unwrap();
let expected_args: Vec<_> = expected_sig
.sig
.inputs()
.iter()
.map(|ty| ArgKind::from_expected_ty(ty, None))
.collect();
let (closure_span, found_args) = self.get_fn_like_arguments(expr_map_node);
let expected_span = expected_sig.cause_span.unwrap_or(closure_span);
self.report_arg_count_mismatch(
expected_span,
Some(closure_span),
expected_args,
found_args,
true,
).emit();
let error_sig = self.error_sig_of_closure(decl);
self.closure_sigs(expr_def_id, body, error_sig)
}
/// Enforce the user's types against the expectation. See
/// `sig_of_closure_with_expectation` for details on the overall
/// strategy.
fn check_supplied_sig_against_expectation(
&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
expected_sigs: &ClosureSignatures<'tcx>,
) -> InferResult<'tcx, ()> {
// Get the signature S that the user gave.
//
// (See comment on `sig_of_closure_with_expectation` for the
// meaning of these letters.)
let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl);
debug!(
"check_supplied_sig_against_expectation: supplied_sig={:?}",
supplied_sig
);
// FIXME(#45727): As discussed in [this comment][c1], naively
// forcing equality here actually results in suboptimal error
// messages in some cases. For now, if there would have been
// an obvious error, we fallback to declaring the type of the
// closure to be the one the user gave, which allows other
// error message code to trigger.
//
// However, I think [there is potential to do even better
// here][c2], since in *this* code we have the precise span of
// the type parameter in question in hand when we report the
// error.
//
// [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706
// [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796
self.infcx.commit_if_ok(|_| {
let mut all_obligations = vec![];
// The liberated version of this signature should be a subtype
// of the liberated form of the expectation.
for ((hir_ty, &supplied_ty), expected_ty) in decl.inputs.iter()
.zip(*supplied_sig.inputs().skip_binder()) // binder moved to (*) below
.zip(expected_sigs.liberated_sig.inputs())
// `liberated_sig` is E'.
{
// Instantiate (this part of..) S to S', i.e., with fresh variables.
let (supplied_ty, _) = self.infcx.replace_bound_vars_with_fresh_vars(
hir_ty.span,
LateBoundRegionConversionTime::FnCall,
&ty::Binder::bind(supplied_ty),
); // recreated from (*) above
// Check that E' = S'.
let cause = &self.misc(hir_ty.span);
let InferOk {
value: (),
obligations,
} = self.at(cause, self.param_env)
.eq(*expected_ty, supplied_ty)?;
all_obligations.extend(obligations);
// Also, require that the supplied type must outlive
// the closure body.
let closure_body_region = self.tcx.mk_region(
ty::ReScope(
region::Scope {
id: body.value.hir_id.local_id,
data: region::ScopeData::Node,
},
),
);
all_obligations.push(
Obligation::new(
cause.clone(),
self.param_env,
ty::Predicate::TypeOutlives(
ty::Binder::dummy(
ty::OutlivesPredicate(
supplied_ty,
closure_body_region,
),
),
),
),
);
}
let (supplied_output_ty, _) = self.infcx.replace_bound_vars_with_fresh_vars(
decl.output.span(),
LateBoundRegionConversionTime::FnCall,
&supplied_sig.output(),
);
let cause = &self.misc(decl.output.span());
let InferOk {
value: (),
obligations,
} = self.at(cause, self.param_env)
.eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?;
all_obligations.extend(obligations);
Ok(InferOk {
value: (),
obligations: all_obligations,
})
})
}
/// If there is no expected signature, then we will convert the
/// types that the user gave into a signature.
///
/// Also, record this closure signature for later.
fn supplied_sig_of_closure(
&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
) -> ty::PolyFnSig<'tcx> {
let astconv: &dyn AstConv<'_> = self;
// First, convert the types that the user supplied (if any).
let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
let supplied_return = match decl.output {
hir::Return(ref output) => astconv.ast_ty_to_ty(&output),
hir::DefaultReturn(_) => astconv.ty_infer(None, decl.output.span()),
};
let result = ty::Binder::bind(self.tcx.mk_fn_sig(
supplied_arguments,
supplied_return,
decl.c_variadic,
hir::Unsafety::Normal,
Abi::RustCall,
));
debug!("supplied_sig_of_closure: result={:?}", result);
let c_result = self.inh.infcx.canonicalize_response(&result);
self.tables.borrow_mut().user_provided_sigs.insert(
expr_def_id,
c_result,
);
result
}
/// Converts the types that the user supplied, in case that doing
/// so should yield an error, but returns back a signature where
/// all parameters are of type `TyErr`.
fn error_sig_of_closure(&self, decl: &hir::FnDecl) -> ty::PolyFnSig<'tcx> {
let astconv: &dyn AstConv<'_> = self;
let supplied_arguments = decl.inputs.iter().map(|a| {
// Convert the types that the user supplied (if any), but ignore them.
astconv.ast_ty_to_ty(a);
self.tcx.types.err
});
if let hir::Return(ref output) = decl.output {
astconv.ast_ty_to_ty(&output);
}
let result = ty::Binder::bind(self.tcx.mk_fn_sig(
supplied_arguments,
self.tcx.types.err,
decl.c_variadic,
hir::Unsafety::Normal,
Abi::RustCall,
));
debug!("supplied_sig_of_closure: result={:?}", result);
result
}
fn closure_sigs(
&self,
expr_def_id: DefId,
body: &hir::Body,
bound_sig: ty::PolyFnSig<'tcx>,
) -> ClosureSignatures<'tcx> {
let liberated_sig = self.tcx()
.liberate_late_bound_regions(expr_def_id, &bound_sig);
let liberated_sig = self.inh.normalize_associated_types_in(
body.value.span,
body.value.hir_id,
self.param_env,
&liberated_sig,
);
ClosureSignatures {
bound_sig,
liberated_sig,
}
}
}
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