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Improve trait/impl method discrepancy errors #84014

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Apr 12, 2021
Merged

Improve trait/impl method discrepancy errors #84014

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d43ede1
Use more accurate spans for trait/impl method arg divergence
estebank Apr 8, 2021
147649d
Suggest changing impl parameter types to match trait
estebank Apr 8, 2021
5af3dec
Suggest return type
estebank Apr 8, 2021
bb502c4
Provide verbose suggestion for new output type
estebank Apr 8, 2021
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13 changes: 8 additions & 5 deletions compiler/rustc_middle/src/ty/error.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@ pub enum TypeError<'tcx> {
UnsafetyMismatch(ExpectedFound<hir::Unsafety>),
AbiMismatch(ExpectedFound<abi::Abi>),
Mutability,
ArgumentMutability(usize),
TupleSize(ExpectedFound<usize>),
FixedArraySize(ExpectedFound<u64>),
ArgCount,
Expand All @@ -46,6 +47,7 @@ pub enum TypeError<'tcx> {
RegionsPlaceholderMismatch,

Sorts(ExpectedFound<Ty<'tcx>>),
ArgumentSorts(ExpectedFound<Ty<'tcx>>, usize),
IntMismatch(ExpectedFound<ty::IntVarValue>),
FloatMismatch(ExpectedFound<ty::FloatTy>),
Traits(ExpectedFound<DefId>),
Expand Down Expand Up @@ -110,7 +112,7 @@ impl<'tcx> fmt::Display for TypeError<'tcx> {
AbiMismatch(values) => {
write!(f, "expected {} fn, found {} fn", values.expected, values.found)
}
Mutability => write!(f, "types differ in mutability"),
ArgumentMutability(_) | Mutability => write!(f, "types differ in mutability"),
TupleSize(values) => write!(
f,
"expected a tuple with {} element{}, \
Expand Down Expand Up @@ -142,7 +144,7 @@ impl<'tcx> fmt::Display for TypeError<'tcx> {
br_string(br)
),
RegionsPlaceholderMismatch => write!(f, "one type is more general than the other"),
Sorts(values) => ty::tls::with(|tcx| {
ArgumentSorts(values, _) | Sorts(values) => ty::tls::with(|tcx| {
report_maybe_different(
f,
&values.expected.sort_string(tcx),
Expand Down Expand Up @@ -199,10 +201,11 @@ impl<'tcx> TypeError<'tcx> {
use self::TypeError::*;
match self {
CyclicTy(_) | CyclicConst(_) | UnsafetyMismatch(_) | Mismatch | AbiMismatch(_)
| FixedArraySize(_) | Sorts(_) | IntMismatch(_) | FloatMismatch(_)
| VariadicMismatch(_) | TargetFeatureCast(_) => false,
| FixedArraySize(_) | ArgumentSorts(..) | Sorts(_) | IntMismatch(_)
| FloatMismatch(_) | VariadicMismatch(_) | TargetFeatureCast(_) => false,

Mutability
| ArgumentMutability(_)
| TupleSize(_)
| ArgCount
| RegionsDoesNotOutlive(..)
Expand Down Expand Up @@ -339,7 +342,7 @@ impl<'tcx> TyCtxt<'tcx> {
use self::TypeError::*;
debug!("note_and_explain_type_err err={:?} cause={:?}", err, cause);
match err {
Sorts(values) => {
ArgumentSorts(values, _) | Sorts(values) => {
match (values.expected.kind(), values.found.kind()) {
(ty::Closure(..), ty::Closure(..)) => {
db.note("no two closures, even if identical, have the same type");
Expand Down
6 changes: 6 additions & 0 deletions compiler/rustc_middle/src/ty/relate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -179,6 +179,12 @@ impl<'tcx> Relate<'tcx> for ty::FnSig<'tcx> {
} else {
relation.relate_with_variance(ty::Contravariant, a, b)
}
})
.enumerate()
.map(|(i, r)| match r {
Err(TypeError::Sorts(exp_found)) => Err(TypeError::ArgumentSorts(exp_found, i)),
Err(TypeError::Mutability) => Err(TypeError::ArgumentMutability(i)),
r => r,
});
Ok(ty::FnSig {
inputs_and_output: tcx.mk_type_list(inputs_and_output)?,
Expand Down
2 changes: 2 additions & 0 deletions compiler/rustc_middle/src/ty/structural_impls.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -587,6 +587,7 @@ impl<'a, 'tcx> Lift<'tcx> for ty::error::TypeError<'a> {
UnsafetyMismatch(x) => UnsafetyMismatch(x),
AbiMismatch(x) => AbiMismatch(x),
Mutability => Mutability,
ArgumentMutability(i) => ArgumentMutability(i),
TupleSize(x) => TupleSize(x),
FixedArraySize(x) => FixedArraySize(x),
ArgCount => ArgCount,
Expand All @@ -607,6 +608,7 @@ impl<'a, 'tcx> Lift<'tcx> for ty::error::TypeError<'a> {
CyclicTy(t) => return tcx.lift(t).map(|t| CyclicTy(t)),
CyclicConst(ct) => return tcx.lift(ct).map(|ct| CyclicConst(ct)),
ProjectionMismatched(x) => ProjectionMismatched(x),
ArgumentSorts(x, i) => return tcx.lift(x).map(|x| ArgumentSorts(x, i)),
Sorts(x) => return tcx.lift(x).map(Sorts),
ExistentialMismatch(x) => return tcx.lift(x).map(ExistentialMismatch),
ConstMismatch(x) => return tcx.lift(x).map(ConstMismatch),
Expand Down
168 changes: 87 additions & 81 deletions compiler/rustc_typeck/src/check/compare_method.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -278,9 +278,8 @@ fn compare_predicate_entailment<'tcx>(
if let Err(terr) = sub_result {
debug!("sub_types failed: impl ty {:?}, trait ty {:?}", impl_fty, trait_fty);

let (impl_err_span, trait_err_span) = extract_spans_for_error_reporting(
&infcx, param_env, &terr, &cause, impl_m, impl_sig, trait_m, trait_sig,
);
let (impl_err_span, trait_err_span) =
extract_spans_for_error_reporting(&infcx, &terr, &cause, impl_m, trait_m);

cause.make_mut().span = impl_err_span;

Expand All @@ -291,18 +290,79 @@ fn compare_predicate_entailment<'tcx>(
"method `{}` has an incompatible type for trait",
trait_m.ident
);
if let TypeError::Mutability = terr {
if let Some(trait_err_span) = trait_err_span {
if let Ok(trait_err_str) = tcx.sess.source_map().span_to_snippet(trait_err_span)
match &terr {
TypeError::ArgumentMutability(0) | TypeError::ArgumentSorts(_, 0)
if trait_m.fn_has_self_parameter =>
{
let ty = trait_sig.inputs()[0];
let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty())
{
ExplicitSelf::ByValue => "self".to_owned(),
ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
ExplicitSelf::ByReference(_, hir::Mutability::Mut) => {
"&mut self".to_owned()
}
_ => format!("self: {}", ty),
};

// When the `impl` receiver is an arbitrary self type, like `self: Box<Self>`, the
// span points only at the type `Box<Self`>, but we want to cover the whole
// argument pattern and type.
let impl_m_hir_id =
tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
let span = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
ImplItemKind::Fn(ref sig, body) => tcx
.hir()
.body_param_names(body)
.zip(sig.decl.inputs.iter())
.map(|(param, ty)| param.span.to(ty.span))
.next()
.unwrap_or(impl_err_span),
_ => bug!("{:?} is not a method", impl_m),
};

diag.span_suggestion(
span,
"change the self-receiver type to match the trait",
sugg,
Applicability::MachineApplicable,
);
}
TypeError::ArgumentMutability(i) | TypeError::ArgumentSorts(_, i) => {
if trait_sig.inputs().len() == *i {
// Suggestion to change output type. We do not suggest in `async` functions
// to avoid complex logic or incorrect output.
let impl_m_hir_id =
tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
ImplItemKind::Fn(ref sig, _)
if sig.header.asyncness == hir::IsAsync::NotAsync =>
{
let msg = "change the output type to match the trait";
let ap = Applicability::MachineApplicable;
match sig.decl.output {
hir::FnRetTy::DefaultReturn(sp) => {
let sugg = format!("-> {} ", trait_sig.output());
diag.span_suggestion_verbose(sp, msg, sugg, ap);
}
hir::FnRetTy::Return(hir_ty) => {
let sugg = trait_sig.output().to_string();
diag.span_suggestion(hir_ty.span, msg, sugg, ap);
}
};
}
_ => {}
};
} else if let Some(trait_ty) = trait_sig.inputs().get(*i) {
diag.span_suggestion(
impl_err_span,
"consider changing the mutability to match the trait",
trait_err_str,
"change the parameter type to match the trait",
trait_ty.to_string(),
Applicability::MachineApplicable,
);
}
}
_ => {}
}

infcx.note_type_err(
Expand Down Expand Up @@ -385,86 +445,35 @@ fn check_region_bounds_on_impl_item<'tcx>(

fn extract_spans_for_error_reporting<'a, 'tcx>(
infcx: &infer::InferCtxt<'a, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
terr: &TypeError<'_>,
cause: &ObligationCause<'tcx>,
impl_m: &ty::AssocItem,
impl_sig: ty::FnSig<'tcx>,
trait_m: &ty::AssocItem,
trait_sig: ty::FnSig<'tcx>,
) -> (Span, Option<Span>) {
let tcx = infcx.tcx;
let impl_m_hir_id = tcx.hir().local_def_id_to_hir_id(impl_m.def_id.expect_local());
let (impl_m_output, impl_m_iter) = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
ImplItemKind::Fn(ref impl_m_sig, _) => {
(&impl_m_sig.decl.output, impl_m_sig.decl.inputs.iter())
let mut impl_args = match tcx.hir().expect_impl_item(impl_m_hir_id).kind {
ImplItemKind::Fn(ref sig, _) => {
sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
}
_ => bug!("{:?} is not a method", impl_m),
};

match *terr {
TypeError::Mutability => {
if let Some(def_id) = trait_m.def_id.as_local() {
let trait_m_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
let trait_m_iter = match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
TraitItemKind::Fn(ref trait_m_sig, _) => trait_m_sig.decl.inputs.iter(),
_ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
};

iter::zip(impl_m_iter, trait_m_iter)
.find(|&(ref impl_arg, ref trait_arg)| {
match (&impl_arg.kind, &trait_arg.kind) {
(
&hir::TyKind::Rptr(_, ref impl_mt),
&hir::TyKind::Rptr(_, ref trait_mt),
)
| (&hir::TyKind::Ptr(ref impl_mt), &hir::TyKind::Ptr(ref trait_mt)) => {
impl_mt.mutbl != trait_mt.mutbl
}
_ => false,
}
})
.map(|(ref impl_arg, ref trait_arg)| (impl_arg.span, Some(trait_arg.span)))
.unwrap_or_else(|| (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)))
} else {
(cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
let trait_args = trait_m.def_id.as_local().map(|def_id| {
let trait_m_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
TraitItemKind::Fn(ref sig, _) => {
sig.decl.inputs.iter().map(|t| t.span).chain(iter::once(sig.decl.output.span()))
}
_ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
}
TypeError::Sorts(ExpectedFound { .. }) => {
if let Some(def_id) = trait_m.def_id.as_local() {
let trait_m_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
let (trait_m_output, trait_m_iter) =
match tcx.hir().expect_trait_item(trait_m_hir_id).kind {
TraitItemKind::Fn(ref trait_m_sig, _) => {
(&trait_m_sig.decl.output, trait_m_sig.decl.inputs.iter())
}
_ => bug!("{:?} is not a TraitItemKind::Fn", trait_m),
};
});

let impl_iter = impl_sig.inputs().iter();
let trait_iter = trait_sig.inputs().iter();
iter::zip(iter::zip(impl_iter, trait_iter), iter::zip(impl_m_iter, trait_m_iter))
.find_map(|((&impl_arg_ty, &trait_arg_ty), (impl_arg, trait_arg))| match infcx
.at(&cause, param_env)
.sub(trait_arg_ty, impl_arg_ty)
{
Ok(_) => None,
Err(_) => Some((impl_arg.span, Some(trait_arg.span))),
})
.unwrap_or_else(|| {
if infcx
.at(&cause, param_env)
.sup(trait_sig.output(), impl_sig.output())
.is_err()
{
(impl_m_output.span(), Some(trait_m_output.span()))
} else {
(cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
}
})
} else {
(cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id))
}
match *terr {
TypeError::ArgumentMutability(i) => {
(impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
}
TypeError::ArgumentSorts(ExpectedFound { .. }, i) => {
(impl_args.nth(i).unwrap(), trait_args.and_then(|mut args| args.nth(i)))
}
_ => (cause.span(tcx), tcx.hir().span_if_local(trait_m.def_id)),
}
Expand Down Expand Up @@ -514,8 +523,7 @@ fn compare_self_type<'tcx>(
tcx.sess,
impl_m_span,
E0185,
"method `{}` has a `{}` declaration in the impl, but \
not in the trait",
"method `{}` has a `{}` declaration in the impl, but not in the trait",
trait_m.ident,
self_descr
);
Expand All @@ -535,8 +543,7 @@ fn compare_self_type<'tcx>(
tcx.sess,
impl_m_span,
E0186,
"method `{}` has a `{}` declaration in the trait, but \
not in the impl",
"method `{}` has a `{}` declaration in the trait, but not in the impl",
trait_m.ident,
self_descr
);
Expand Down Expand Up @@ -993,8 +1000,7 @@ crate fn compare_const_impl<'tcx>(
tcx.sess,
cause.span,
E0326,
"implemented const `{}` has an incompatible type for \
trait",
"implemented const `{}` has an incompatible type for trait",
trait_c.ident
);

Expand Down
10 changes: 8 additions & 2 deletions src/test/ui/associated-types/defaults-specialization.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,10 @@ LL | fn make() -> Self::Ty {
| -------- type in trait
...
LL | fn make() -> u8 { 0 }
| ^^ expected associated type, found `u8`
| ^^
| |
| expected associated type, found `u8`
| help: change the output type to match the trait: `<A<T> as Tr>::Ty`
|
= note: expected fn pointer `fn() -> <A<T> as Tr>::Ty`
found fn pointer `fn() -> u8`
Expand All @@ -30,7 +33,10 @@ LL | default type Ty = bool;
| ----------------------- expected this associated type
LL |
LL | fn make() -> bool { true }
| ^^^^ expected associated type, found `bool`
| ^^^^
| |
| expected associated type, found `bool`
| help: change the output type to match the trait: `<B<T> as Tr>::Ty`
|
= note: expected fn pointer `fn() -> <B<T> as Tr>::Ty`
found fn pointer `fn() -> bool`
Expand Down
26 changes: 26 additions & 0 deletions src/test/ui/compare-method/bad-self-type.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
use std::future::Future;
use std::task::{Context, Poll};

fn main() {}

struct MyFuture {}

impl Future for MyFuture {
type Output = ();
fn poll(self, _: &mut Context<'_>) -> Poll<()> {
//~^ ERROR method `poll` has an incompatible type for trait
todo!()
}
}

trait T {
fn foo(self);
fn bar(self) -> Option<()>;
}

impl T for MyFuture {
fn foo(self: Box<Self>) {}
//~^ ERROR method `foo` has an incompatible type for trait
fn bar(self) {}
//~^ ERROR method `bar` has an incompatible type for trait
}
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