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Auto merge of rust-lang#97705 - compiler-errors:guide-inference, r=lcnr
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Fix inference issues with unconstrained base expr in `type_changing_struct_update`

Use fresh infer vars to guide inference along in `type_changing_struct_update`.

Fixes rust-lang#96878
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@bors
bors committed Jun 11, 2022
2 parents 99930ac + 5052911 commit e652caa
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Showing 2 changed files with 116 additions and 67 deletions.
152 changes: 85 additions & 67 deletions compiler/rustc_typeck/src/check/expr.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -41,8 +41,7 @@ use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKi
use rustc_infer::infer::InferOk;
use rustc_middle::middle::stability;
use rustc_middle::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase};
use rustc_middle::ty::error::ExpectedFound;
use rustc_middle::ty::error::TypeError::{FieldMisMatch, Sorts};
use rustc_middle::ty::error::TypeError::FieldMisMatch;
use rustc_middle::ty::subst::SubstsRef;
use rustc_middle::ty::{self, AdtKind, DefIdTree, Ty, TypeFoldable};
use rustc_session::parse::feature_err;
Expand All @@ -65,7 +64,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Ty<'tcx>,
extend_err: impl Fn(&mut Diagnostic),
extend_err: impl FnMut(&mut Diagnostic),
) -> Ty<'tcx> {
self.check_expr_meets_expectation_or_error(expr, ExpectHasType(expected), extend_err)
}
Expand All @@ -74,7 +73,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
&self,
expr: &'tcx hir::Expr<'tcx>,
expected: Expectation<'tcx>,
extend_err: impl Fn(&mut Diagnostic),
mut extend_err: impl FnMut(&mut Diagnostic),
) -> Ty<'tcx> {
let expected_ty = expected.to_option(&self).unwrap_or(self.tcx.types.bool);
let mut ty = self.check_expr_with_expectation(expr, expected);
Expand Down Expand Up @@ -1480,10 +1479,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
// re-link the regions that EIfEO can erase.
self.demand_eqtype(span, adt_ty_hint, adt_ty);

let (substs, adt_kind, kind_name) = match adt_ty.kind() {
ty::Adt(adt, substs) => (substs, adt.adt_kind(), adt.variant_descr()),
_ => span_bug!(span, "non-ADT passed to check_expr_struct_fields"),
let ty::Adt(adt, substs) = adt_ty.kind() else {
span_bug!(span, "non-ADT passed to check_expr_struct_fields");
};
let adt_kind = adt.adt_kind();

let mut remaining_fields = variant
.fields
Expand Down Expand Up @@ -1521,7 +1520,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
});
} else {
self.report_unknown_field(
adt_ty, variant, field, ast_fields, kind_name, expr_span,
adt_ty,
variant,
field,
ast_fields,
adt.variant_descr(),
expr_span,
);
}

Expand All @@ -1534,7 +1538,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}

// Make sure the programmer specified correct number of fields.
if kind_name == "union" {
if adt_kind == AdtKind::Union {
if ast_fields.len() != 1 {
struct_span_err!(
tcx.sess,
Expand All @@ -1557,67 +1561,81 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
// FIXME: We are currently creating two branches here in order to maintain
// consistency. But they should be merged as much as possible.
let fru_tys = if self.tcx.features().type_changing_struct_update {
let base_ty = self.check_expr(base_expr);
match adt_ty.kind() {
ty::Adt(adt, substs) if adt.is_struct() => {
match base_ty.kind() {
ty::Adt(base_adt, base_subs) if adt == base_adt => {
variant
.fields
.iter()
.map(|f| {
let fru_ty = self.normalize_associated_types_in(
expr_span,
self.field_ty(base_expr.span, f, base_subs),
);
let ident = self
.tcx
.adjust_ident(f.ident(self.tcx), variant.def_id);
if let Some(_) = remaining_fields.remove(&ident) {
let target_ty =
self.field_ty(base_expr.span, f, substs);
let cause = self.misc(base_expr.span);
match self
.at(&cause, self.param_env)
.sup(target_ty, fru_ty)
{
Ok(InferOk { obligations, value: () }) => {
self.register_predicates(obligations)
}
// FIXME: Need better diagnostics for `FieldMisMatch` error
Err(_) => {
self.report_mismatched_types(
&cause,
target_ty,
fru_ty,
FieldMisMatch(variant.name, ident.name),
)
.emit();
}
}
if let ty::Adt(adt, substs) = adt_ty.kind() && adt.is_struct() {
// Make an ADT with fresh inference substitutions. This
// will allow us to guide inference along so that, e.g.
// ```
// let x = MyStruct<'a, B, const C: usize> {
// f: 1,
// ..Default::default()
// };
// ```
// will have the default base expression constrained to
// `MyStruct<'_, _, _>`, as opposed to just `_`... This
// will allow us to then do a subtyping relation on all
// of the `remaining_fields` below, per the RFC.
let fresh_substs = self.fresh_substs_for_item(base_expr.span, adt.did());
let fresh_base_ty = self.tcx.mk_adt(*adt, fresh_substs);
let base_ty = self.check_expr_has_type_or_error(
base_expr,
fresh_base_ty,
|_| {
error_happened = true;
},
);
let base_ty = self.shallow_resolve(base_ty);
if let ty::Adt(base_adt, base_substs) = base_ty.kind() && adt == base_adt {
variant
.fields
.iter()
.map(|f| {
let fru_ty = self.normalize_associated_types_in(
expr_span,
self.field_ty(base_expr.span, f, base_substs),
);
let ident = self
.tcx
.adjust_ident(f.ident(self.tcx), variant.def_id);
if let Some(_) = remaining_fields.remove(&ident) {
let target_ty =
self.field_ty(base_expr.span, f, substs);
let cause = self.misc(base_expr.span);
match self
.at(&cause, self.param_env)
.sup(target_ty, fru_ty)
{
Ok(InferOk { obligations, value: () }) => {
self.register_predicates(obligations)
}
fru_ty
})
.collect()
}
_ => {
self.report_mismatched_types(
&self.misc(base_expr.span),
adt_ty,
base_ty,
Sorts(ExpectedFound::new(true, adt_ty, base_ty)),
)
.emit();
return;
}
// FIXME: Need better diagnostics for `FieldMisMatch` error
Err(_) => {
self.report_mismatched_types(
&cause,
target_ty,
fru_ty,
FieldMisMatch(variant.name, ident.name),
)
.emit();
}
}
}
self.resolve_vars_if_possible(fru_ty)
})
.collect()
} else {
if !error_happened && !base_ty.references_error() {
span_bug!(base_expr.span, "expected an error to have been reported in `check_expr_has_type_or_error`");
}
}
_ => {
self.tcx
.sess
.emit_err(FunctionalRecordUpdateOnNonStruct { span: base_expr.span });
return;
}
} else {
// Check the base_expr, regardless of a bad expected adt_ty, so we can get
// type errors on that expression, too.
self.check_expr(base_expr);
self.tcx
.sess
.emit_err(FunctionalRecordUpdateOnNonStruct { span: base_expr.span });
return;
}
} else {
self.check_expr_has_type_or_error(base_expr, adt_ty, |_| {
Expand Down Expand Up @@ -1653,7 +1671,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}
};
self.typeck_results.borrow_mut().fru_field_types_mut().insert(expr_id, fru_tys);
} else if kind_name != "union" && !remaining_fields.is_empty() {
} else if adt_kind != AdtKind::Union && !remaining_fields.is_empty() {
let inaccessible_remaining_fields = remaining_fields.iter().any(|(_, (_, field))| {
!field.vis.is_accessible_from(tcx.parent_module(expr_id).to_def_id(), tcx)
});
Expand Down
31 changes: 31 additions & 0 deletions src/test/ui/rfcs/rfc-2528-type-changing-struct-update/issue-96878.rs
View file
Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
// check-pass

#![feature(type_changing_struct_update)]
#![allow(incomplete_features)]

use std::borrow::Cow;
use std::marker::PhantomData;

#[derive(Default)]
struct NonGeneric {
field1: usize,
}

#[derive(Default)]
struct Generic<T, U> {
field1: T,
field2: U,
}

#[derive(Default)]
struct MoreGeneric<'a, const N: usize> {
// If only `for<const N: usize> [u32; N]: Default`...
field1: PhantomData<[u32; N]>,
field2: Cow<'a, str>,
}

fn main() {
let default1 = NonGeneric { ..Default::default() };
let default2: Generic<i32, f32> = Generic { ..Default::default() };
let default3: MoreGeneric<'static, 12> = MoreGeneric { ..Default::default() };
}

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