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Split out opaque collection from from type_of #111862

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May 25, 2023
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Split out opaque collection from from type_of #111862

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310 changes: 5 additions & 305 deletions compiler/rustc_hir_analysis/src/collect/type_of.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,7 @@
use rustc_errors::{Applicability, StashKey};
use rustc_hir as hir;
use rustc_hir::def_id::LocalDefId;
use rustc_hir::intravisit;
use rustc_hir::intravisit::Visitor;
use rustc_hir::{HirId, Node};
use rustc_middle::hir::nested_filter;
use rustc_hir::HirId;
use rustc_middle::ty::print::with_forced_trimmed_paths;
use rustc_middle::ty::subst::InternalSubsts;
use rustc_middle::ty::util::IntTypeExt;
Expand All @@ -14,7 +11,8 @@ use rustc_span::{Span, DUMMY_SP};

use super::ItemCtxt;
use super::{bad_placeholder, is_suggestable_infer_ty};
use crate::errors::UnconstrainedOpaqueType;

mod opaque;

fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
use hir::*;
Expand Down Expand Up @@ -429,7 +427,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
ItemKind::OpaqueTy(OpaqueTy {
origin: hir::OpaqueTyOrigin::TyAlias { .. },
..
}) => find_opaque_ty_constraints_for_tait(tcx, def_id),
}) => opaque::find_opaque_ty_constraints_for_tait(tcx, def_id),
// Opaque types desugared from `impl Trait`.
ItemKind::OpaqueTy(OpaqueTy {
origin:
Expand All @@ -443,7 +441,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
"tried to get type of this RPITIT with no definition"
);
}
find_opaque_ty_constraints_for_rpit(tcx, def_id, owner)
opaque::find_opaque_ty_constraints_for_rpit(tcx, def_id, owner)
}
ItemKind::Trait(..)
| ItemKind::TraitAlias(..)
Expand Down Expand Up @@ -502,304 +500,6 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
ty::EarlyBinder(output)
}

#[instrument(skip(tcx), level = "debug")]
/// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
/// laid for "higher-order pattern unification".
/// This ensures that inference is tractable.
/// In particular, definitions of opaque types can only use other generics as arguments,
/// and they cannot repeat an argument. Example:
///
/// ```ignore (illustrative)
/// type Foo<A, B> = impl Bar<A, B>;
///
/// // Okay -- `Foo` is applied to two distinct, generic types.
/// fn a<T, U>() -> Foo<T, U> { .. }
///
/// // Not okay -- `Foo` is applied to `T` twice.
/// fn b<T>() -> Foo<T, T> { .. }
///
/// // Not okay -- `Foo` is applied to a non-generic type.
/// fn b<T>() -> Foo<T, u32> { .. }
/// ```
///
fn find_opaque_ty_constraints_for_tait(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
use rustc_hir::{Expr, ImplItem, Item, TraitItem};

struct ConstraintLocator<'tcx> {
tcx: TyCtxt<'tcx>,

/// def_id of the opaque type whose defining uses are being checked
def_id: LocalDefId,

/// as we walk the defining uses, we are checking that all of them
/// define the same hidden type. This variable is set to `Some`
/// with the first type that we find, and then later types are
/// checked against it (we also carry the span of that first
/// type).
found: Option<ty::OpaqueHiddenType<'tcx>>,

/// In the presence of dead code, typeck may figure out a hidden type
/// while borrowck will not. We collect these cases here and check at
/// the end that we actually found a type that matches (modulo regions).
typeck_types: Vec<ty::OpaqueHiddenType<'tcx>>,
}

impl ConstraintLocator<'_> {
#[instrument(skip(self), level = "debug")]
fn check(&mut self, item_def_id: LocalDefId) {
// Don't try to check items that cannot possibly constrain the type.
if !self.tcx.has_typeck_results(item_def_id) {
debug!("no constraint: no typeck results");
return;
}
// Calling `mir_borrowck` can lead to cycle errors through
// const-checking, avoid calling it if we don't have to.
// ```rust
// type Foo = impl Fn() -> usize; // when computing type for this
// const fn bar() -> Foo {
// || 0usize
// }
// const BAZR: Foo = bar(); // we would mir-borrowck this, causing cycles
// // because we again need to reveal `Foo` so we can check whether the
// // constant does not contain interior mutability.
// ```
let tables = self.tcx.typeck(item_def_id);
if let Some(guar) = tables.tainted_by_errors {
self.found =
Some(ty::OpaqueHiddenType { span: DUMMY_SP, ty: self.tcx.ty_error(guar) });
return;
}
let Some(&typeck_hidden_ty) = tables.concrete_opaque_types.get(&self.def_id) else {
debug!("no constraints in typeck results");
return;
};
if self.typeck_types.iter().all(|prev| prev.ty != typeck_hidden_ty.ty) {
self.typeck_types.push(typeck_hidden_ty);
}

// Use borrowck to get the type with unerased regions.
let concrete_opaque_types = &self.tcx.mir_borrowck(item_def_id).concrete_opaque_types;
debug!(?concrete_opaque_types);
if let Some(&concrete_type) = concrete_opaque_types.get(&self.def_id) {
debug!(?concrete_type, "found constraint");
if let Some(prev) = &mut self.found {
if concrete_type.ty != prev.ty && !(concrete_type, prev.ty).references_error() {
let guar =
prev.report_mismatch(&concrete_type, self.def_id, self.tcx).emit();
prev.ty = self.tcx.ty_error(guar);
}
} else {
self.found = Some(concrete_type);
}
}
}
}

impl<'tcx> intravisit::Visitor<'tcx> for ConstraintLocator<'tcx> {
type NestedFilter = nested_filter::All;

fn nested_visit_map(&mut self) -> Self::Map {
self.tcx.hir()
}
fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
if let hir::ExprKind::Closure(closure) = ex.kind {
self.check(closure.def_id);
}
intravisit::walk_expr(self, ex);
}
fn visit_item(&mut self, it: &'tcx Item<'tcx>) {
trace!(?it.owner_id);
// The opaque type itself or its children are not within its reveal scope.
if it.owner_id.def_id != self.def_id {
self.check(it.owner_id.def_id);
intravisit::walk_item(self, it);
}
}
fn visit_impl_item(&mut self, it: &'tcx ImplItem<'tcx>) {
trace!(?it.owner_id);
// The opaque type itself or its children are not within its reveal scope.
if it.owner_id.def_id != self.def_id {
self.check(it.owner_id.def_id);
intravisit::walk_impl_item(self, it);
}
}
fn visit_trait_item(&mut self, it: &'tcx TraitItem<'tcx>) {
trace!(?it.owner_id);
self.check(it.owner_id.def_id);
intravisit::walk_trait_item(self, it);
}
}

let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
let scope = tcx.hir().get_defining_scope(hir_id);
let mut locator = ConstraintLocator { def_id, tcx, found: None, typeck_types: vec![] };

debug!(?scope);

if scope == hir::CRATE_HIR_ID {
tcx.hir().walk_toplevel_module(&mut locator);
} else {
trace!("scope={:#?}", tcx.hir().get(scope));
match tcx.hir().get(scope) {
// We explicitly call `visit_*` methods, instead of using `intravisit::walk_*` methods
// This allows our visitor to process the defining item itself, causing
// it to pick up any 'sibling' defining uses.
//
// For example, this code:
// ```
// fn foo() {
// type Blah = impl Debug;
// let my_closure = || -> Blah { true };
// }
// ```
//
// requires us to explicitly process `foo()` in order
// to notice the defining usage of `Blah`.
Node::Item(it) => locator.visit_item(it),
Node::ImplItem(it) => locator.visit_impl_item(it),
Node::TraitItem(it) => locator.visit_trait_item(it),
other => bug!("{:?} is not a valid scope for an opaque type item", other),
}
}

let Some(hidden) = locator.found else {
let reported = tcx.sess.emit_err(UnconstrainedOpaqueType {
span: tcx.def_span(def_id),
name: tcx.item_name(tcx.local_parent(def_id).to_def_id()),
what: match tcx.hir().get(scope) {
_ if scope == hir::CRATE_HIR_ID => "module",
Node::Item(hir::Item { kind: hir::ItemKind::Mod(_), .. }) => "module",
Node::Item(hir::Item { kind: hir::ItemKind::Impl(_), .. }) => "impl",
_ => "item",
},
});
return tcx.ty_error(reported);
};

// Only check against typeck if we didn't already error
if !hidden.ty.references_error() {
for concrete_type in locator.typeck_types {
if concrete_type.ty != tcx.erase_regions(hidden.ty)
&& !(concrete_type, hidden).references_error()
{
hidden.report_mismatch(&concrete_type, def_id, tcx).emit();
}
}
}

hidden.ty
}

fn find_opaque_ty_constraints_for_rpit(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
owner_def_id: LocalDefId,
) -> Ty<'_> {
use rustc_hir::{Expr, ImplItem, Item, TraitItem};

struct ConstraintChecker<'tcx> {
tcx: TyCtxt<'tcx>,

/// def_id of the opaque type whose defining uses are being checked
def_id: LocalDefId,

found: ty::OpaqueHiddenType<'tcx>,
}

impl ConstraintChecker<'_> {
#[instrument(skip(self), level = "debug")]
fn check(&self, def_id: LocalDefId) {
// Use borrowck to get the type with unerased regions.
let concrete_opaque_types = &self.tcx.mir_borrowck(def_id).concrete_opaque_types;
debug!(?concrete_opaque_types);
for (&def_id, &concrete_type) in concrete_opaque_types {
if def_id != self.def_id {
// Ignore constraints for other opaque types.
continue;
}

debug!(?concrete_type, "found constraint");

if concrete_type.ty != self.found.ty
&& !(concrete_type, self.found).references_error()
{
self.found.report_mismatch(&concrete_type, self.def_id, self.tcx).emit();
}
}
}
}

impl<'tcx> intravisit::Visitor<'tcx> for ConstraintChecker<'tcx> {
type NestedFilter = nested_filter::OnlyBodies;

fn nested_visit_map(&mut self) -> Self::Map {
self.tcx.hir()
}
fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
if let hir::ExprKind::Closure(closure) = ex.kind {
self.check(closure.def_id);
}
intravisit::walk_expr(self, ex);
}
fn visit_item(&mut self, it: &'tcx Item<'tcx>) {
trace!(?it.owner_id);
// The opaque type itself or its children are not within its reveal scope.
if it.owner_id.def_id != self.def_id {
self.check(it.owner_id.def_id);
intravisit::walk_item(self, it);
}
}
fn visit_impl_item(&mut self, it: &'tcx ImplItem<'tcx>) {
trace!(?it.owner_id);
// The opaque type itself or its children are not within its reveal scope.
if it.owner_id.def_id != self.def_id {
self.check(it.owner_id.def_id);
intravisit::walk_impl_item(self, it);
}
}
fn visit_trait_item(&mut self, it: &'tcx TraitItem<'tcx>) {
trace!(?it.owner_id);
self.check(it.owner_id.def_id);
intravisit::walk_trait_item(self, it);
}
}

let concrete = tcx.mir_borrowck(owner_def_id).concrete_opaque_types.get(&def_id).copied();

if let Some(concrete) = concrete {
let scope = tcx.hir().local_def_id_to_hir_id(owner_def_id);
debug!(?scope);
let mut locator = ConstraintChecker { def_id, tcx, found: concrete };

match tcx.hir().get(scope) {
Node::Item(it) => intravisit::walk_item(&mut locator, it),
Node::ImplItem(it) => intravisit::walk_impl_item(&mut locator, it),
Node::TraitItem(it) => intravisit::walk_trait_item(&mut locator, it),
other => bug!("{:?} is not a valid scope for an opaque type item", other),
}
}

concrete.map(|concrete| concrete.ty).unwrap_or_else(|| {
let table = tcx.typeck(owner_def_id);
if let Some(guar) = table.tainted_by_errors {
// Some error in the
// owner fn prevented us from populating
// the `concrete_opaque_types` table.
tcx.ty_error(guar)
} else {
table.concrete_opaque_types.get(&def_id).map(|ty| ty.ty).unwrap_or_else(|| {
// We failed to resolve the opaque type or it
// resolves to itself. We interpret this as the
// no values of the hidden type ever being constructed,
// so we can just make the hidden type be `!`.
// For backwards compatibility reasons, we fall back to
// `()` until we the diverging default is changed.
tcx.mk_diverging_default()
})
}
})
}

fn infer_placeholder_type<'a>(
tcx: TyCtxt<'a>,
def_id: LocalDefId,
Expand Down
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