Rollup merge of #102890 - camsteffen:adt-sized-representability, r=cjgillot

Check representability in adt_sized_constraint

Now that representability is a query, we can use it to preemptively avoid a cycle in `adt_sized_constraint`.

I moved the representability check into `check_mod_type_wf` to avoid a scenario where rustc quits before checking all the types for representability. This also removes the check from rustdoc, which is alright AFAIK.

r? ``@cjgillot``

Author: Dylan-DPC

compiler/rustc_hir_analysis/src/check/check.rs

@@ -380,7 +380,6 @@ fn check_struct(tcx: TyCtxt<'_>, def_id: LocalDefId) {
     let def = tcx.adt_def(def_id);
     let span = tcx.def_span(def_id);
     def.destructor(tcx); // force the destructor to be evaluated
-    let _ = tcx.representability(def_id);
 
     if def.repr().simd() {
         check_simd(tcx, span, def_id);
@@ -394,7 +393,6 @@ fn check_union(tcx: TyCtxt<'_>, def_id: LocalDefId) {
     let def = tcx.adt_def(def_id);
     let span = tcx.def_span(def_id);
     def.destructor(tcx); // force the destructor to be evaluated
-    let _ = tcx.representability(def_id);
     check_transparent(tcx, span, def);
     check_union_fields(tcx, span, def_id);
     check_packed(tcx, span, def);
@@ -1489,7 +1487,6 @@ fn check_enum<'tcx>(tcx: TyCtxt<'tcx>, vs: &'tcx [hir::Variant<'tcx>], def_id: L
 
     detect_discriminant_duplicate(tcx, def.discriminants(tcx).collect(), vs, sp);
 
-    let _ = tcx.representability(def_id);
     check_transparent(tcx, sp, def);
 }
 

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1041,6 +1041,8 @@ fn check_type_defn<'tcx, F>(
 ) where
     F: FnMut(&WfCheckingCtxt<'_, 'tcx>) -> Vec<AdtVariant<'tcx>>,
 {
+    let _ = tcx.representability(item.def_id.def_id);
+
     enter_wf_checking_ctxt(tcx, item.span, item.def_id.def_id, |wfcx| {
         let variants = lookup_fields(wfcx);
         let packed = tcx.adt_def(item.def_id).repr().packed();

compiler/rustc_middle/src/query/mod.rs

@@ -613,16 +613,8 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    // The cycle error here should be reported as an error by `check_representable`.
-    // We consider the type as Sized in the meanwhile to avoid
-    // further errors (done in impl Value for AdtSizedConstraint).
-    // Use `cycle_delay_bug` to delay the cycle error here to be emitted later
-    // in case we accidentally otherwise don't emit an error.
-    query adt_sized_constraint(
-        key: DefId
-    ) -> AdtSizedConstraint<'tcx> {
+    query adt_sized_constraint(key: DefId) -> &'tcx [Ty<'tcx>] {
         desc { |tcx| "computing `Sized` constraints for `{}`", tcx.def_path_str(key) }
-        cycle_delay_bug
     }
 
     query adt_dtorck_constraint(

compiler/rustc_middle/src/ty/adt.rs

@@ -26,9 +26,6 @@ use super::{
     Destructor, FieldDef, GenericPredicates, ReprOptions, Ty, TyCtxt, VariantDef, VariantDiscr,
 };
 
-#[derive(Copy, Clone, HashStable, Debug)]
-pub struct AdtSizedConstraint<'tcx>(pub &'tcx [Ty<'tcx>]);
-
 bitflags! {
     #[derive(HashStable, TyEncodable, TyDecodable)]
     pub struct AdtFlags: u32 {
@@ -563,7 +560,7 @@ impl<'tcx> AdtDef<'tcx> {
     /// Due to normalization being eager, this applies even if
     /// the associated type is behind a pointer (e.g., issue #31299).
     pub fn sized_constraint(self, tcx: TyCtxt<'tcx>) -> ty::EarlyBinder<&'tcx [Ty<'tcx>]> {
-        ty::EarlyBinder(tcx.adt_sized_constraint(self.did()).0)
+        ty::EarlyBinder(tcx.adt_sized_constraint(self.did()))
     }
 }
 

compiler/rustc_middle/src/ty/query.rs

@@ -32,7 +32,7 @@ use crate::ty::layout::TyAndLayout;
 use crate::ty::subst::{GenericArg, SubstsRef};
 use crate::ty::util::AlwaysRequiresDrop;
 use crate::ty::GeneratorDiagnosticData;
-use crate::ty::{self, AdtSizedConstraint, CrateInherentImpls, ParamEnvAnd, Ty, TyCtxt};
+use crate::ty::{self, CrateInherentImpls, ParamEnvAnd, Ty, TyCtxt};
 use rustc_ast as ast;
 use rustc_ast::expand::allocator::AllocatorKind;
 use rustc_attr as attr;

compiler/rustc_middle/src/values.rs

@@ -3,7 +3,7 @@ use rustc_errors::{pluralize, struct_span_err, Applicability, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_middle::ty::Representability;
-use rustc_middle::ty::{self, AdtSizedConstraint, DefIdTree, Ty, TyCtxt};
+use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt};
 use rustc_query_system::query::QueryInfo;
 use rustc_query_system::Value;
 use rustc_span::def_id::LocalDefId;
@@ -31,18 +31,6 @@ impl<'tcx> Value<TyCtxt<'tcx>> for ty::SymbolName<'_> {
     }
 }
 
-impl<'tcx> Value<TyCtxt<'tcx>> for AdtSizedConstraint<'_> {
-    fn from_cycle_error(tcx: TyCtxt<'tcx>, _: &[QueryInfo]) -> Self {
-        // SAFETY: This is never called when `Self` is not `AdtSizedConstraint<'tcx>`.
-        // FIXME: Represent the above fact in the trait system somehow.
-        unsafe {
-            std::mem::transmute::<AdtSizedConstraint<'tcx>, AdtSizedConstraint<'_>>(
-                AdtSizedConstraint(tcx.intern_type_list(&[tcx.ty_error()])),
-            )
-        }
-    }
-}
-
 impl<'tcx> Value<TyCtxt<'tcx>> for ty::Binder<'_, ty::FnSig<'_>> {
     fn from_cycle_error(tcx: TyCtxt<'tcx>, _: &[QueryInfo]) -> Self {
         let err = tcx.ty_error();

compiler/rustc_ty_utils/src/ty.rs

@@ -85,9 +85,13 @@ fn impl_defaultness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::Defaultness {
 ///     - a type parameter or projection whose Sizedness can't be known
 ///     - a tuple of type parameters or projections, if there are multiple
 ///       such.
-///     - an Error, if a type contained itself. The representability
-///       check should catch this case.
-fn adt_sized_constraint(tcx: TyCtxt<'_>, def_id: DefId) -> ty::AdtSizedConstraint<'_> {
+///     - an Error, if a type is infinitely sized
+fn adt_sized_constraint(tcx: TyCtxt<'_>, def_id: DefId) -> &[Ty<'_>] {
+    if let Some(def_id) = def_id.as_local() {
+        if matches!(tcx.representability(def_id), ty::Representability::Infinite) {
+            return tcx.intern_type_list(&[tcx.ty_error()]);
+        }
+    }
     let def = tcx.adt_def(def_id);
 
     let result = tcx.mk_type_list(
@@ -99,7 +103,7 @@ fn adt_sized_constraint(tcx: TyCtxt<'_>, def_id: DefId) -> ty::AdtSizedConstrain
 
     debug!("adt_sized_constraint: {:?} => {:?}", def, result);
 
-    ty::AdtSizedConstraint(result)
+    result
 }
 
 /// See `ParamEnv` struct definition for details.

src/test/rustdoc-ui/infinite-recursive-type-impl-trait-return.rs

@@ -1,11 +1,12 @@
+// check-pass
 // normalize-stderr-test: "`.*`" -> "`DEF_ID`"
 // normalize-stdout-test: "`.*`" -> "`DEF_ID`"
 // edition:2018
 
 pub async fn f() -> impl std::fmt::Debug {
+    // rustdoc doesn't care that this is infinitely sized
     #[derive(Debug)]
     enum E {
-    //~^ ERROR recursive type `f::{closure#0}::E` has infinite size
         This(E),
         Unit,
     }

src/test/rustdoc-ui/infinite-recursive-type-impl-trait-return.stderr

@@ -1,6 +1,8 @@
+// check-pass
+
 fn f() -> impl Sized {
+    // rustdoc doesn't care that this is infinitely sized
     enum E {
-    //~^ ERROR recursive type `f::E` has infinite size
         V(E),
     }
     unimplemented!()