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name async generators something more human friendly in type error diagnostic #81496

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Feb 19, 2021
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24 changes: 22 additions & 2 deletions compiler/rustc_hir/src/hir.rs
Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
// ignore-tidy-filelength
use crate::def::{DefKind, Namespace, Res};
use crate::def_id::DefId;
crate use crate::hir_id::HirId;
Expand Down Expand Up @@ -1274,7 +1275,7 @@ impl Body<'hir> {
}

/// The type of source expression that caused this generator to be created.
#[derive(Clone, PartialEq, Eq, HashStable_Generic, Encodable, Decodable, Debug, Copy)]
#[derive(Clone, PartialEq, Eq, Hash, HashStable_Generic, Encodable, Decodable, Debug, Copy)]
pub enum GeneratorKind {
/// An explicit `async` block or the body of an async function.
Async(AsyncGeneratorKind),
Expand All @@ -1292,12 +1293,21 @@ impl fmt::Display for GeneratorKind {
}
}

impl GeneratorKind {
pub fn descr(&self) -> &'static str {
match self {
GeneratorKind::Async(ask) => ask.descr(),
GeneratorKind::Gen => "generator",
}
}
}

/// In the case of a generator created as part of an async construct,
/// which kind of async construct caused it to be created?
///
/// This helps error messages but is also used to drive coercions in
/// type-checking (see #60424).
#[derive(Clone, PartialEq, Eq, HashStable_Generic, Encodable, Decodable, Debug, Copy)]
#[derive(Clone, PartialEq, Eq, Hash, HashStable_Generic, Encodable, Decodable, Debug, Copy)]
pub enum AsyncGeneratorKind {
/// An explicit `async` block written by the user.
Block,
Expand All @@ -1319,6 +1329,16 @@ impl fmt::Display for AsyncGeneratorKind {
}
}

impl AsyncGeneratorKind {
pub fn descr(&self) -> &'static str {
match self {
AsyncGeneratorKind::Block => "`async` block",
AsyncGeneratorKind::Closure => "`async` closure body",
AsyncGeneratorKind::Fn => "`async fn` body",
}
}
}

#[derive(Copy, Clone, Debug)]
pub enum BodyOwnerKind {
/// Functions and methods.
Expand Down
16 changes: 9 additions & 7 deletions compiler/rustc_infer/src/infer/error_reporting/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1509,7 +1509,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {

impl<'tcx> ty::fold::TypeVisitor<'tcx> for OpaqueTypesVisitor<'tcx> {
fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
if let Some((kind, def_id)) = TyCategory::from_ty(t) {
if let Some((kind, def_id)) = TyCategory::from_ty(self.tcx, t) {
let span = self.tcx.def_span(def_id);
// Avoid cluttering the output when the "found" and error span overlap:
//
Expand Down Expand Up @@ -1582,11 +1582,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
};
if let Some((expected, found)) = expected_found {
let expected_label = match exp_found {
Mismatch::Variable(ef) => ef.expected.prefix_string(),
Mismatch::Variable(ef) => ef.expected.prefix_string(self.tcx),
Mismatch::Fixed(s) => s.into(),
};
let found_label = match exp_found {
Mismatch::Variable(ef) => ef.found.prefix_string(),
Mismatch::Variable(ef) => ef.found.prefix_string(self.tcx),
Mismatch::Fixed(s) => s.into(),
};
let exp_found = match exp_found {
Expand Down Expand Up @@ -2436,7 +2436,7 @@ impl<'tcx> ObligationCauseExt<'tcx> for ObligationCause<'tcx> {
pub enum TyCategory {
Closure,
Opaque,
Generator,
Generator(hir::GeneratorKind),
Foreign,
}

Expand All @@ -2445,16 +2445,18 @@ impl TyCategory {
match self {
Self::Closure => "closure",
Self::Opaque => "opaque type",
Self::Generator => "generator",
Self::Generator(gk) => gk.descr(),
Self::Foreign => "foreign type",
}
}

pub fn from_ty(ty: Ty<'_>) -> Option<(Self, DefId)> {
pub fn from_ty(tcx: TyCtxt<'_>, ty: Ty<'_>) -> Option<(Self, DefId)> {
match *ty.kind() {
ty::Closure(def_id, _) => Some((Self::Closure, def_id)),
ty::Opaque(def_id, _) => Some((Self::Opaque, def_id)),
ty::Generator(def_id, ..) => Some((Self::Generator, def_id)),
ty::Generator(def_id, ..) => {
Some((Self::Generator(tcx.generator_kind(def_id).unwrap()), def_id))
}
ty::Foreign(def_id) => Some((Self::Foreign, def_id)),
_ => None,
}
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -383,7 +383,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
InferenceDiagnosticsData {
name: s,
span: None,
kind: UnderspecifiedArgKind::Type { prefix: ty.prefix_string() },
kind: UnderspecifiedArgKind::Type { prefix: ty.prefix_string(self.tcx) },
parent: None,
}
}
Expand Down
6 changes: 3 additions & 3 deletions compiler/rustc_middle/src/ty/error.rs
Original file line number Diff line number Diff line change
Expand Up @@ -264,7 +264,7 @@ impl<'tcx> ty::TyS<'tcx> {
}
}
ty::Closure(..) => "closure".into(),
ty::Generator(..) => "generator".into(),
ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(),
ty::GeneratorWitness(..) => "generator witness".into(),
ty::Tuple(..) => "tuple".into(),
ty::Infer(ty::TyVar(_)) => "inferred type".into(),
Expand All @@ -282,7 +282,7 @@ impl<'tcx> ty::TyS<'tcx> {
}
}

pub fn prefix_string(&self) -> Cow<'static, str> {
pub fn prefix_string(&self, tcx: TyCtxt<'_>) -> Cow<'static, str> {
match *self.kind() {
ty::Infer(_)
| ty::Error(_)
Expand All @@ -308,7 +308,7 @@ impl<'tcx> ty::TyS<'tcx> {
ty::FnPtr(_) => "fn pointer".into(),
ty::Dynamic(..) => "trait object".into(),
ty::Closure(..) => "closure".into(),
ty::Generator(..) => "generator".into(),
ty::Generator(def_id, ..) => tcx.generator_kind(def_id).unwrap().descr().into(),
ty::GeneratorWitness(..) => "generator witness".into(),
ty::Tuple(..) => "tuple".into(),
ty::Placeholder(..) => "higher-ranked type".into(),
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -1366,8 +1366,8 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
Some(t) => Some(t),
None => {
let ty = parent_trait_ref.skip_binder().self_ty();
let span =
TyCategory::from_ty(ty).map(|(_, def_id)| self.tcx.def_span(def_id));
let span = TyCategory::from_ty(self.tcx, ty)
.map(|(_, def_id)| self.tcx.def_span(def_id));
Some((ty.to_string(), span))
}
}
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_typeck/src/check/method/suggest.rs
Original file line number Diff line number Diff line change
Expand Up @@ -390,7 +390,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
"no {} named `{}` found for {} `{}` in the current scope",
item_kind,
item_name,
actual.prefix_string(),
actual.prefix_string(self.tcx),
ty_str,
);
if let Mode::MethodCall = mode {
Expand Down Expand Up @@ -728,7 +728,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
.map(|(_, path)| path)
.collect::<Vec<_>>()
.join("\n");
let actual_prefix = actual.prefix_string();
let actual_prefix = actual.prefix_string(self.tcx);
err.set_primary_message(&format!(
"the {item_kind} `{item_name}` exists for {actual_prefix} `{ty_str}`, but its trait bounds were not satisfied"
));
Expand Down
16 changes: 16 additions & 0 deletions src/test/ui/async-await/generator-desc.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
// edition:2018
#![feature(async_closure)]
use std::future::Future;

async fn one() {}
async fn two() {}

fn fun<F: Future<Output = ()>>(f1: F, f2: F) {}
fn main() {
fun(async {}, async {});
//~^ ERROR mismatched types
fun(one(), two());
//~^ ERROR mismatched types
fun((async || {})(), (async || {})());
//~^ ERROR mismatched types
}
49 changes: 49 additions & 0 deletions src/test/ui/async-await/generator-desc.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,49 @@
error[E0308]: mismatched types
--> $DIR/generator-desc.rs:10:25
|
LL | fun(async {}, async {});
| -- ^^ expected `async` block, found a different `async` block
| |
| the expected `async` block
|
= note: expected `async` block `[static generator@$DIR/generator-desc.rs:10:15: 10:17]`
found `async` block `[static generator@$DIR/generator-desc.rs:10:25: 10:27]`

error[E0308]: mismatched types
--> $DIR/generator-desc.rs:12:16
|
LL | async fn one() {}
| - the `Output` of this `async fn`'s expected opaque type
LL | async fn two() {}
| - the `Output` of this `async fn`'s found opaque type
...
LL | fun(one(), two());
| ^^^^^ expected opaque type, found a different opaque type
|
= note: expected opaque type `impl Future` (opaque type at <$DIR/generator-desc.rs:5:16>)
found opaque type `impl Future` (opaque type at <$DIR/generator-desc.rs:6:16>)
= help: consider `await`ing on both `Future`s
= note: distinct uses of `impl Trait` result in different opaque types

error[E0308]: mismatched types
--> $DIR/generator-desc.rs:14:26
|
LL | fun((async || {})(), (async || {})());
| -- ^^^^^^^^^^^^^^^ expected `async` closure body, found a different `async` closure body
| |
| the expected `async` closure body
|
::: $SRC_DIR/core/src/future/mod.rs:LL:COL
|
LL | pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
| -------------------------------
| |
| the expected opaque type
| the found opaque type
|
= note: expected opaque type `impl Future` (`async` closure body)
found opaque type `impl Future` (`async` closure body)

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0308`.