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Add more .await suggestions on E0308
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@estebank
estebank committed Oct 23, 2020
1 parent 1829b4a commit c548511
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Showing 12 changed files with 167 additions and 188 deletions.
157 changes: 119 additions & 38 deletions compiler/rustc_infer/src/infer/error_reporting/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -50,7 +50,6 @@ use super::region_constraints::GenericKind;
use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePairs};

use crate::infer;
use crate::infer::OriginalQueryValues;
use crate::traits::error_reporting::report_object_safety_error;
use crate::traits::{
IfExpressionCause, MatchExpressionArmCause, ObligationCause, ObligationCauseCode,
Expand All @@ -65,7 +64,6 @@ use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_hir::{Item, ItemKind, Node};
use rustc_middle::ty::error::TypeError;
use rustc_middle::ty::ParamEnvAnd;
use rustc_middle::ty::{
self,
subst::{Subst, SubstsRef},
Expand Down Expand Up @@ -1621,6 +1619,16 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
Mismatch::Variable(exp_found) => Some(exp_found),
Mismatch::Fixed(_) => None,
};
let exp_found = match terr {
// `terr` has more accurate type information than `exp_found` in match expressions.
ty::error::TypeError::Sorts(terr)
if exp_found.map_or(false, |ef| terr.found == ef.found) =>
{
Some(*terr)
}
_ => exp_found,
};
debug!("exp_found {:?} terr {:?}", exp_found, terr);
if let Some(exp_found) = exp_found {
self.suggest_as_ref_where_appropriate(span, &exp_found, diag);
self.suggest_await_on_expect_found(cause, span, &exp_found, diag);
Expand All @@ -1642,6 +1650,53 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
self.note_error_origin(diag, cause, exp_found);
}

fn get_impl_future_output_ty(&self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
if let ty::Opaque(def_id, substs) = ty.kind() {
let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
// Future::Output
let item_def_id = self
.tcx
.associated_items(future_trait)
.in_definition_order()
.next()
.unwrap()
.def_id;

let bounds = self.tcx.explicit_item_bounds(*def_id);

for (predicate, _) in bounds {
let predicate = predicate.subst(self.tcx, substs);
if let ty::PredicateAtom::Projection(projection_predicate) =
predicate.skip_binders()
{
if projection_predicate.projection_ty.item_def_id == item_def_id {
// We don't account for multiple `Future::Output = Ty` contraints.
return Some(projection_predicate.ty);
}
}
}
}
None
}

/// A possible error is to forget to add `.await` when using futures:
///
/// ```
/// async fn make_u32() -> u32 {
/// 22
/// }
///
/// fn take_u32(x: u32) {}
///
/// async fn foo() {
/// let x = make_u32();
/// take_u32(x);
/// }
/// ```
///
/// This routine checks if the found type `T` implements `Future<Output=U>` where `U` is the
/// expected type. If this is the case, and we are inside of an async body, it suggests adding
/// `.await` to the tail of the expression.
fn suggest_await_on_expect_found(
&self,
cause: &ObligationCause<'tcx>,
Expand All @@ -1651,50 +1706,76 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
) {
debug!(
"suggest_await_on_expect_found: exp_span={:?}, expected_ty={:?}, found_ty={:?}",
exp_span, exp_found.expected, exp_found.found
exp_span, exp_found.expected, exp_found.found,
);

if let ty::Opaque(def_id, _) = *exp_found.expected.kind() {
let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
// Future::Output
let item_def_id = self
.tcx
.associated_items(future_trait)
.in_definition_order()
.next()
.unwrap()
.def_id;
if let ObligationCauseCode::CompareImplMethodObligation { .. } = &cause.code {
return;
}

let projection_ty = self.tcx.projection_ty_from_predicates((def_id, item_def_id));
if let Some(projection_ty) = projection_ty {
let projection_query = self.canonicalize_query(
&ParamEnvAnd { param_env: self.tcx.param_env(def_id), value: projection_ty },
&mut OriginalQueryValues::default(),
);
if let Ok(resp) = self.tcx.normalize_projection_ty(projection_query) {
let normalized_ty = resp.value.value.normalized_ty;
debug!("suggest_await_on_expect_found: normalized={:?}", normalized_ty);
if ty::TyS::same_type(normalized_ty, exp_found.found) {
let span = if let ObligationCauseCode::Pattern {
span,
origin_expr: _,
root_ty: _,
} = cause.code
{
// scrutinee's span
span.unwrap_or(exp_span)
} else {
exp_span
};
diag.span_suggestion_verbose(
span.shrink_to_hi(),
"consider awaiting on the future",
".await".to_string(),
match (
self.get_impl_future_output_ty(exp_found.expected),
self.get_impl_future_output_ty(exp_found.found),
) {
(Some(exp), Some(found)) if ty::TyS::same_type(exp, found) => match &cause.code {
ObligationCauseCode::IfExpression(box IfExpressionCause { then, .. }) => {
diag.multipart_suggestion(
"consider `await`ing on both `Future`s",
vec![
(then.shrink_to_hi(), ".await".to_string()),
(exp_span.shrink_to_hi(), ".await".to_string()),
],
Applicability::MaybeIncorrect,
);
}
ObligationCauseCode::MatchExpressionArm(box MatchExpressionArmCause {
prior_arms,
..
}) => {
if let [.., arm_span] = &prior_arms[..] {
diag.multipart_suggestion(
"consider `await`ing on both `Future`s",
vec![
(arm_span.shrink_to_hi(), ".await".to_string()),
(exp_span.shrink_to_hi(), ".await".to_string()),
],
Applicability::MaybeIncorrect,
);
} else {
diag.help("consider `await`ing on both `Future`s");
}
}
_ => {
diag.help("consider `await`ing on both `Future`s");
}
},
(_, Some(ty)) if ty::TyS::same_type(exp_found.expected, ty) => {
let span = match cause.code {
// scrutinee's span
ObligationCauseCode::Pattern { span: Some(span), .. } => span,
_ => exp_span,
};
diag.span_suggestion_verbose(
span.shrink_to_hi(),
"consider `await`ing on the `Future`",
".await".to_string(),
Applicability::MaybeIncorrect,
);
}
(Some(ty), _) if ty::TyS::same_type(ty, exp_found.found) => {
let span = match cause.code {
// scrutinee's span
ObligationCauseCode::Pattern { span: Some(span), .. } => span,
_ => exp_span,
};
diag.span_suggestion_verbose(
span.shrink_to_hi(),
"consider `await`ing on the `Future`",
".await".to_string(),
Applicability::MaybeIncorrect,
);
}
_ => {}
}
}

Expand Down
37 changes: 13 additions & 24 deletions compiler/rustc_middle/src/ty/error.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -334,26 +334,15 @@ impl<'tcx> TyCtxt<'tcx> {
debug!("note_and_explain_type_err err={:?} cause={:?}", err, cause);
match err {
Sorts(values) => {
let expected_str = values.expected.sort_string(self);
let found_str = values.found.sort_string(self);
if expected_str == found_str && expected_str == "closure" {
db.note("no two closures, even if identical, have the same type");
db.help("consider boxing your closure and/or using it as a trait object");
}
if expected_str == found_str && expected_str == "opaque type" {
// Issue #63167
db.note("distinct uses of `impl Trait` result in different opaque types");
let e_str = values.expected.to_string();
let f_str = values.found.to_string();
if e_str == f_str && &e_str == "impl std::future::Future" {
// FIXME: use non-string based check.
db.help(
"if both `Future`s have the same `Output` type, consider \
`.await`ing on both of them",
);
}
}
match (values.expected.kind(), values.found.kind()) {
(ty::Closure(..), ty::Closure(..)) => {
db.note("no two closures, even if identical, have the same type");
db.help("consider boxing your closure and/or using it as a trait object");
}
(ty::Opaque(..), ty::Opaque(..)) => {
// Issue #63167
db.note("distinct uses of `impl Trait` result in different opaque types");
}
(ty::Float(_), ty::Infer(ty::IntVar(_))) => {
if let Ok(
// Issue #53280
Expand Down Expand Up @@ -382,12 +371,12 @@ impl<'tcx> TyCtxt<'tcx> {
}
db.note(
"a type parameter was expected, but a different one was found; \
you might be missing a type parameter or trait bound",
you might be missing a type parameter or trait bound",
);
db.note(
"for more information, visit \
https://doc.rust-lang.org/book/ch10-02-traits.html\
#traits-as-parameters",
https://doc.rust-lang.org/book/ch10-02-traits.html\
#traits-as-parameters",
);
}
(ty::Projection(_), ty::Projection(_)) => {
Expand Down Expand Up @@ -471,8 +460,8 @@ impl<T> Trait<T> for X {
}
db.note(
"for more information, visit \
https://doc.rust-lang.org/book/ch10-02-traits.html\
#traits-as-parameters",
https://doc.rust-lang.org/book/ch10-02-traits.html\
#traits-as-parameters",
);
}
(ty::Param(p), ty::Closure(..) | ty::Generator(..)) => {
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_typeck/src/check/demand.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
return;
}
self.suggest_boxing_when_appropriate(err, expr, expected, expr_ty);
self.suggest_missing_await(err, expr, expected, expr_ty);
self.suggest_missing_parentheses(err, expr);
self.note_need_for_fn_pointer(err, expected, expr_ty);
self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
Expand Down
79 changes: 0 additions & 79 deletions compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,6 @@ use crate::astconv::AstConv;

use rustc_ast::util::parser::ExprPrecedence;
use rustc_span::{self, Span};
use rustc_trait_selection::traits;

use rustc_errors::{Applicability, DiagnosticBuilder};
use rustc_hir as hir;
Expand All @@ -13,7 +12,6 @@ use rustc_hir::{ExprKind, ItemKind, Node};
use rustc_infer::infer;
use rustc_middle::ty::{self, Ty};
use rustc_span::symbol::kw;
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;

use std::iter;

Expand Down Expand Up @@ -433,83 +431,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}
}

/// A possible error is to forget to add `.await` when using futures:
///
/// ```
/// async fn make_u32() -> u32 {
/// 22
/// }
///
/// fn take_u32(x: u32) {}
///
/// async fn foo() {
/// let x = make_u32();
/// take_u32(x);
/// }
/// ```
///
/// This routine checks if the found type `T` implements `Future<Output=U>` where `U` is the
/// expected type. If this is the case, and we are inside of an async body, it suggests adding
/// `.await` to the tail of the expression.
pub(in super::super) fn suggest_missing_await(
&self,
err: &mut DiagnosticBuilder<'_>,
expr: &hir::Expr<'_>,
expected: Ty<'tcx>,
found: Ty<'tcx>,
) {
debug!("suggest_missing_await: expr={:?} expected={:?}, found={:?}", expr, expected, found);
// `.await` is not permitted outside of `async` bodies, so don't bother to suggest if the
// body isn't `async`.
let item_id = self.tcx().hir().get_parent_node(self.body_id);
if let Some(body_id) = self.tcx().hir().maybe_body_owned_by(item_id) {
let body = self.tcx().hir().body(body_id);
if let Some(hir::GeneratorKind::Async(_)) = body.generator_kind {
let sp = expr.span;
// Check for `Future` implementations by constructing a predicate to
// prove: `<T as Future>::Output == U`
let future_trait = self.tcx.require_lang_item(LangItem::Future, Some(sp));
let item_def_id = self
.tcx
.associated_items(future_trait)
.in_definition_order()
.next()
.unwrap()
.def_id;
// `<T as Future>::Output`
let projection_ty = ty::ProjectionTy {
// `T`
substs: self
.tcx
.mk_substs_trait(found, self.fresh_substs_for_item(sp, item_def_id)),
// `Future::Output`
item_def_id,
};

let predicate = ty::PredicateAtom::Projection(ty::ProjectionPredicate {
projection_ty,
ty: expected,
})
.potentially_quantified(self.tcx, ty::PredicateKind::ForAll);
let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);

debug!("suggest_missing_await: trying obligation {:?}", obligation);

if self.infcx.predicate_may_hold(&obligation) {
debug!("suggest_missing_await: obligation held: {:?}", obligation);
err.span_suggestion_verbose(
sp.shrink_to_hi(),
"consider `await`ing on the `Future`",
".await".to_string(),
Applicability::MaybeIncorrect,
);
} else {
debug!("suggest_missing_await: obligation did not hold: {:?}", obligation)
}
}
}
}

pub(in super::super) fn suggest_missing_parentheses(
&self,
err: &mut DiagnosticBuilder<'_>,
Expand Down
4 changes: 4 additions & 0 deletions src/test/ui/async-await/dont-suggest-missing-await.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,10 @@ LL | take_u32(x)
|
= note: expected type `u32`
found opaque type `impl Future`
help: consider `await`ing on the `Future`
|
LL | take_u32(x.await)
| ^^^^^^

error: aborting due to previous error

Expand Down
4 changes: 4 additions & 0 deletions src/test/ui/async-await/issue-61076.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,10 @@ LL | Tuple(_) => {}
|
= note: expected opaque type `impl Future`
found struct `Tuple`
help: consider `await`ing on the `Future`
|
LL | match tuple().await {
| ^^^^^^

error: aborting due to 6 previous errors

Expand Down
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