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Rollup merge of rust-lang#98280 - compiler-errors:better-call-closure…
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…-on-type-err, r=estebank

Improve suggestion for calling fn-like expr on type mismatch

1.) Suggest calling values of with RPIT types (and probably TAIT) when we expect `Ty` and have `impl Fn() -> Ty`
2.) Suggest calling closures even when they're not assigned to a local variable first
3.) Drive-by fix of a pretty-printing bug (`impl Fn()-> Ty` => `impl Fn() -> Ty`)

r? ```@estebank```
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JohnTitor authored Jun 24, 2022
2 parents 33eb3c0 + d15fed7 commit 964fc41
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Showing 11 changed files with 143 additions and 125 deletions.
2 changes: 1 addition & 1 deletion compiler/rustc_middle/src/ty/print/pretty.rs
Original file line number Diff line number Diff line change
Expand Up @@ -856,7 +856,7 @@ pub trait PrettyPrinter<'tcx>:
p!(")");
if let Term::Ty(ty) = return_ty.skip_binder() {
if !ty.is_unit() {
p!("-> ", print(return_ty));
p!(" -> ", print(return_ty));
}
}
p!(write("{}", if paren_needed { ")" } else { "" }));
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189 changes: 76 additions & 113 deletions compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,15 +8,14 @@ use rustc_hir as hir;
use rustc_hir::def::{CtorOf, DefKind};
use rustc_hir::lang_items::LangItem;
use rustc_hir::{
Expr, ExprKind, GenericBound, ItemKind, Node, Path, QPath, Stmt, StmtKind, TyKind,
WherePredicate,
Expr, ExprKind, GenericBound, Node, Path, QPath, Stmt, StmtKind, TyKind, WherePredicate,
};
use rustc_infer::infer::{self, TyCtxtInferExt};
use rustc_infer::traits;
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::subst::GenericArgKind;
use rustc_middle::ty::{self, Binder, IsSuggestable, ToPredicate, Ty};
use rustc_span::symbol::{kw, sym};
use rustc_middle::ty::{self, Binder, IsSuggestable, Subst, ToPredicate, Ty};
use rustc_span::symbol::sym;
use rustc_span::Span;
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;

Expand Down Expand Up @@ -78,124 +77,88 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
expected: Ty<'tcx>,
found: Ty<'tcx>,
) -> bool {
let hir = self.tcx.hir();
let (def_id, sig) = match *found.kind() {
ty::FnDef(def_id, _) => (def_id, found.fn_sig(self.tcx)),
ty::Closure(def_id, substs) => (def_id, substs.as_closure().sig()),
let (def_id, output, inputs) = match *found.kind() {
ty::FnDef(def_id, _) => {
let fn_sig = found.fn_sig(self.tcx);
(def_id, fn_sig.output(), fn_sig.inputs().skip_binder().len())
}
ty::Closure(def_id, substs) => {
let fn_sig = substs.as_closure().sig();
(def_id, fn_sig.output(), fn_sig.inputs().skip_binder().len() - 1)
}
ty::Opaque(def_id, substs) => {
let sig = self.tcx.bound_item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
if let ty::PredicateKind::Projection(proj) = pred.kind().skip_binder()
&& Some(proj.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output()
// args tuple will always be substs[1]
&& let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
{
Some((
pred.kind().rebind(proj.term.ty().unwrap()),
args.len(),
))
} else {
None
}
});
if let Some((output, inputs)) = sig {
(def_id, output, inputs)
} else {
return false;
}
}
_ => return false,
};

let sig = self.replace_bound_vars_with_fresh_vars(expr.span, infer::FnCall, sig);
let sig = self.normalize_associated_types_in(expr.span, sig);
if self.can_coerce(sig.output(), expected) {
let (mut sugg_call, applicability) = if sig.inputs().is_empty() {
(String::new(), Applicability::MachineApplicable)
} else {
("...".to_string(), Applicability::HasPlaceholders)
let output = self.replace_bound_vars_with_fresh_vars(expr.span, infer::FnCall, output);
let output = self.normalize_associated_types_in(expr.span, output);
if !output.is_ty_var() && self.can_coerce(output, expected) {
let (sugg_call, mut applicability) = match inputs {
0 => ("".to_string(), Applicability::MachineApplicable),
1..=4 => (
(0..inputs).map(|_| "_").collect::<Vec<_>>().join(", "),
Applicability::MachineApplicable,
),
_ => ("...".to_string(), Applicability::HasPlaceholders),
};
let mut msg = "call this function";
match hir.get_if_local(def_id) {
Some(
Node::Item(hir::Item { kind: ItemKind::Fn(.., body_id), .. })
| Node::ImplItem(hir::ImplItem {
kind: hir::ImplItemKind::Fn(_, body_id), ..
})
| Node::TraitItem(hir::TraitItem {
kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Provided(body_id)),
..
}),
) => {
let body = hir.body(*body_id);
sugg_call = body
.params
.iter()
.map(|param| match &param.pat.kind {
hir::PatKind::Binding(_, _, ident, None)
if ident.name != kw::SelfLower =>
{
ident.to_string()
}
_ => "_".to_string(),
})
.collect::<Vec<_>>()
.join(", ");
}
Some(Node::Expr(hir::Expr {
kind: ExprKind::Closure { body: body_id, .. },
span: full_closure_span,
..
})) => {
if *full_closure_span == expr.span {
return false;
}
msg = "call this closure";
let body = hir.body(*body_id);
sugg_call = body
.params
.iter()
.map(|param| match &param.pat.kind {
hir::PatKind::Binding(_, _, ident, None)
if ident.name != kw::SelfLower =>
{
ident.to_string()
}
_ => "_".to_string(),
})
.collect::<Vec<_>>()
.join(", ");
}
Some(Node::Ctor(hir::VariantData::Tuple(fields, _))) => {
sugg_call = fields.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
match def_id.as_local().map(|def_id| self.tcx.def_kind(def_id)) {
Some(DefKind::Ctor(hir::def::CtorOf::Variant, _)) => {
msg = "instantiate this tuple variant";
}
Some(DefKind::Ctor(CtorOf::Struct, _)) => {
msg = "instantiate this tuple struct";
}
_ => {}
}

let msg = match self.tcx.def_kind(def_id) {
DefKind::Fn => "call this function",
DefKind::Closure | DefKind::OpaqueTy => "call this closure",
DefKind::Ctor(CtorOf::Struct, _) => "instantiate this tuple struct",
DefKind::Ctor(CtorOf::Variant, _) => "instantiate this tuple variant",
_ => "call this function",
};

let sugg = match expr.kind {
hir::ExprKind::Call(..)
| hir::ExprKind::Path(..)
| hir::ExprKind::Index(..)
| hir::ExprKind::Lit(..) => {
vec![(expr.span.shrink_to_hi(), format!("({sugg_call})"))]
}
Some(Node::ForeignItem(hir::ForeignItem {
kind: hir::ForeignItemKind::Fn(_, idents, _),
..
})) => {
sugg_call = idents
.iter()
.map(|ident| {
if ident.name != kw::SelfLower {
ident.to_string()
} else {
"_".to_string()
}
})
.collect::<Vec<_>>()
.join(", ")
hir::ExprKind::Closure { .. } => {
// Might be `{ expr } || { bool }`
applicability = Applicability::MaybeIncorrect;
vec![
(expr.span.shrink_to_lo(), "(".to_string()),
(expr.span.shrink_to_hi(), format!(")({sugg_call})")),
]
}
Some(Node::TraitItem(hir::TraitItem {
kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Required(idents)),
..
})) => {
sugg_call = idents
.iter()
.map(|ident| {
if ident.name != kw::SelfLower {
ident.to_string()
} else {
"_".to_string()
}
})
.collect::<Vec<_>>()
.join(", ")
_ => {
vec![
(expr.span.shrink_to_lo(), "(".to_string()),
(expr.span.shrink_to_hi(), format!(")({sugg_call})")),
]
}
_ => {}
}
err.span_suggestion_verbose(
expr.span.shrink_to_hi(),
&format!("use parentheses to {}", msg),
format!("({})", sugg_call),
};

err.multipart_suggestion_verbose(
format!("use parentheses to {msg}"),
sugg,
applicability,
);

return true;
}
false
Expand Down
12 changes: 12 additions & 0 deletions src/test/ui/impl-trait/suggest-calling-rpit-closure.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
fn whatever() -> i32 {
opaque()
//~^ ERROR mismatched types
}

fn opaque() -> impl Fn() -> i32 {
|| 0
}

fn main() {
let _ = whatever();
}
21 changes: 21 additions & 0 deletions src/test/ui/impl-trait/suggest-calling-rpit-closure.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,21 @@
error[E0308]: mismatched types
--> $DIR/suggest-calling-rpit-closure.rs:2:5
|
LL | fn whatever() -> i32 {
| --- expected `i32` because of return type
LL | opaque()
| ^^^^^^^^ expected `i32`, found opaque type
...
LL | fn opaque() -> impl Fn() -> i32 {
| ---------------- the found opaque type
|
= note: expected type `i32`
found opaque type `impl Fn() -> i32`
help: use parentheses to call this closure
|
LL | opaque()()
| ++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
4 changes: 4 additions & 0 deletions src/test/ui/parser/expr-as-stmt.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -201,6 +201,10 @@ LL | { true } || { true }
|
= note: expected type `bool`
found closure `[closure@$DIR/expr-as-stmt.rs:51:14: 51:25]`
help: use parentheses to call this closure
|
LL | { true } (|| { true })()
| + +++
help: parentheses are required to parse this as an expression
|
LL | ({ true }) || { true }
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,12 @@ LL | | }.hi() {
|
= note: expected type `bool`
found closure `[closure@$DIR/struct-literal-restrictions-in-lamda.rs:12:11: 14:11]`
help: use parentheses to call this closure
|
LL ~ while (|| Foo {
LL | x: 3
LL ~ }.hi())() {
|

error: aborting due to 2 previous errors

Expand Down
4 changes: 0 additions & 4 deletions src/test/ui/reify-intrinsic.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -8,10 +8,6 @@ LL | let _: unsafe extern "rust-intrinsic" fn(isize) -> usize = std::mem::tr
|
= note: expected fn pointer `unsafe extern "rust-intrinsic" fn(isize) -> usize`
found fn item `unsafe extern "rust-intrinsic" fn(_) -> _ {transmute::<_, _>}`
help: use parentheses to call this function
|
LL | let _: unsafe extern "rust-intrinsic" fn(isize) -> usize = std::mem::transmute(...);
| +++++

error[E0606]: casting `unsafe extern "rust-intrinsic" fn(_) -> _ {transmute::<_, _>}` as `unsafe extern "rust-intrinsic" fn(isize) -> usize` is invalid
--> $DIR/reify-intrinsic.rs:11:13
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -1118,6 +1118,10 @@ LL | if let Range { start: F, end } = F..|| true {}
|
= note: expected type `bool`
found closure `[closure@$DIR/disallowed-positions.rs:136:41: 136:48]`
help: use parentheses to call this closure
|
LL | if let Range { start: F, end } = F..(|| true)() {}
| + +++

error[E0308]: mismatched types
--> $DIR/disallowed-positions.rs:136:8
Expand Down Expand Up @@ -1314,6 +1318,10 @@ LL | while let Range { start: F, end } = F..|| true {}
|
= note: expected type `bool`
found closure `[closure@$DIR/disallowed-positions.rs:200:44: 200:51]`
help: use parentheses to call this closure
|
LL | while let Range { start: F, end } = F..(|| true)() {}
| + +++

error[E0308]: mismatched types
--> $DIR/disallowed-positions.rs:200:11
Expand Down
4 changes: 4 additions & 0 deletions src/test/ui/span/move-closure.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,10 @@ LL | let x: () = move || ();
|
= note: expected unit type `()`
found closure `[closure@$DIR/move-closure.rs:5:17: 5:27]`
help: use parentheses to call this closure
|
LL | let x: () = (move || ())();
| + +++

error: aborting due to previous error

Expand Down
14 changes: 7 additions & 7 deletions src/test/ui/suggestions/fn-or-tuple-struct-without-args.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ LL | let _: usize = foo;
found fn item `fn(usize, usize) -> usize {foo}`
help: use parentheses to call this function
|
LL | let _: usize = foo(a, b);
LL | let _: usize = foo(_, _);
| ++++++

error[E0308]: mismatched types
Expand Down Expand Up @@ -105,7 +105,7 @@ LL | let _: usize = T::baz;
found fn item `fn(usize, usize) -> usize {<_ as T>::baz}`
help: use parentheses to call this function
|
LL | let _: usize = T::baz(x, y);
LL | let _: usize = T::baz(_, _);
| ++++++

error[E0308]: mismatched types
Expand All @@ -123,7 +123,7 @@ LL | let _: usize = T::bat;
found fn item `fn(usize) -> usize {<_ as T>::bat}`
help: use parentheses to call this function
|
LL | let _: usize = T::bat(x);
LL | let _: usize = T::bat(_);
| +++

error[E0308]: mismatched types
Expand Down Expand Up @@ -159,7 +159,7 @@ LL | let _: usize = X::baz;
found fn item `fn(usize, usize) -> usize {<X as T>::baz}`
help: use parentheses to call this function
|
LL | let _: usize = X::baz(x, y);
LL | let _: usize = X::baz(_, _);
| ++++++

error[E0308]: mismatched types
Expand All @@ -177,7 +177,7 @@ LL | let _: usize = X::bat;
found fn item `fn(usize) -> usize {<X as T>::bat}`
help: use parentheses to call this function
|
LL | let _: usize = X::bat(x);
LL | let _: usize = X::bat(_);
| +++

error[E0308]: mismatched types
Expand All @@ -195,7 +195,7 @@ LL | let _: usize = X::bax;
found fn item `fn(usize) -> usize {<X as T>::bax}`
help: use parentheses to call this function
|
LL | let _: usize = X::bax(x);
LL | let _: usize = X::bax(_);
| +++

error[E0308]: mismatched types
Expand All @@ -213,7 +213,7 @@ LL | let _: usize = X::bach;
found fn item `fn(usize) -> usize {<X as T>::bach}`
help: use parentheses to call this function
|
LL | let _: usize = X::bach(x);
LL | let _: usize = X::bach(_);
| +++

error[E0308]: mismatched types
Expand Down
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