Rollup merge of #84613 - lcnr:recursive-types, r=jackh726

move representability checks to rustc_ty_utils

Author: Dylan-DPC

Cargo.lock

@@ -4590,6 +4590,7 @@ dependencies = [
  "rustc_span",
  "rustc_target",
  "rustc_trait_selection",
+ "rustc_ty_utils",
  "smallvec",
  "tracing",
 ]

compiler/rustc_middle/src/ty/util.rs

@@ -18,10 +18,10 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_macros::HashStable;
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::DUMMY_SP;
 use rustc_target::abi::{Integer, Size, TargetDataLayout};
 use smallvec::SmallVec;
-use std::{cmp, fmt, iter};
+use std::{fmt, iter};
 
 #[derive(Copy, Clone, Debug)]
 pub struct Discr<'tcx> {
@@ -135,21 +135,6 @@ impl IntTypeExt for attr::IntType {
     }
 }
 
-/// Describes whether a type is representable. For types that are not
-/// representable, 'SelfRecursive' and 'ContainsRecursive' are used to
-/// distinguish between types that are recursive with themselves and types that
-/// contain a different recursive type. These cases can therefore be treated
-/// differently when reporting errors.
-///
-/// The ordering of the cases is significant. They are sorted so that cmp::max
-/// will keep the "more erroneous" of two values.
-#[derive(Clone, PartialOrd, Ord, Eq, PartialEq, Debug)]
-pub enum Representability {
-    Representable,
-    ContainsRecursive,
-    SelfRecursive(Vec<Span>),
-}
-
 impl<'tcx> TyCtxt<'tcx> {
     /// Creates a hash of the type `Ty` which will be the same no matter what crate
     /// context it's calculated within. This is used by the `type_id` intrinsic.
@@ -870,178 +855,6 @@ impl<'tcx> ty::TyS<'tcx> {
         }
     }
 
-    /// Check whether a type is representable. This means it cannot contain unboxed
-    /// structural recursion. This check is needed for structs and enums.
-    pub fn is_representable(&'tcx self, tcx: TyCtxt<'tcx>, sp: Span) -> Representability {
-        // Iterate until something non-representable is found
-        fn fold_repr<It: Iterator<Item = Representability>>(iter: It) -> Representability {
-            iter.fold(Representability::Representable, |r1, r2| match (r1, r2) {
-                (Representability::SelfRecursive(v1), Representability::SelfRecursive(v2)) => {
-                    Representability::SelfRecursive(v1.into_iter().chain(v2).collect())
-                }
-                (r1, r2) => cmp::max(r1, r2),
-            })
-        }
-
-        fn are_inner_types_recursive<'tcx>(
-            tcx: TyCtxt<'tcx>,
-            sp: Span,
-            seen: &mut Vec<Ty<'tcx>>,
-            representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
-            ty: Ty<'tcx>,
-        ) -> Representability {
-            match ty.kind() {
-                Tuple(..) => {
-                    // Find non representable
-                    fold_repr(ty.tuple_fields().map(|ty| {
-                        is_type_structurally_recursive(tcx, sp, seen, representable_cache, ty)
-                    }))
-                }
-                // Fixed-length vectors.
-                // FIXME(#11924) Behavior undecided for zero-length vectors.
-                Array(ty, _) => {
-                    is_type_structurally_recursive(tcx, sp, seen, representable_cache, ty)
-                }
-                Adt(def, substs) => {
-                    // Find non representable fields with their spans
-                    fold_repr(def.all_fields().map(|field| {
-                        let ty = field.ty(tcx, substs);
-                        let span = match field
-                            .did
-                            .as_local()
-                            .map(|id| tcx.hir().local_def_id_to_hir_id(id))
-                            .and_then(|id| tcx.hir().find(id))
-                        {
-                            Some(hir::Node::Field(field)) => field.ty.span,
-                            _ => sp,
-                        };
-                        match is_type_structurally_recursive(
-                            tcx,
-                            span,
-                            seen,
-                            representable_cache,
-                            ty,
-                        ) {
-                            Representability::SelfRecursive(_) => {
-                                Representability::SelfRecursive(vec![span])
-                            }
-                            x => x,
-                        }
-                    }))
-                }
-                Closure(..) => {
-                    // this check is run on type definitions, so we don't expect
-                    // to see closure types
-                    bug!("requires check invoked on inapplicable type: {:?}", ty)
-                }
-                _ => Representability::Representable,
-            }
-        }
-
-        fn same_struct_or_enum<'tcx>(ty: Ty<'tcx>, def: &'tcx ty::AdtDef) -> bool {
-            match *ty.kind() {
-                Adt(ty_def, _) => ty_def == def,
-                _ => false,
-            }
-        }
-
-        // Does the type `ty` directly (without indirection through a pointer)
-        // contain any types on stack `seen`?
-        fn is_type_structurally_recursive<'tcx>(
-            tcx: TyCtxt<'tcx>,
-            sp: Span,
-            seen: &mut Vec<Ty<'tcx>>,
-            representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
-            ty: Ty<'tcx>,
-        ) -> Representability {
-            debug!("is_type_structurally_recursive: {:?} {:?}", ty, sp);
-            if let Some(representability) = representable_cache.get(ty) {
-                debug!(
-                    "is_type_structurally_recursive: {:?} {:?} - (cached) {:?}",
-                    ty, sp, representability
-                );
-                return representability.clone();
-            }
-
-            let representability =
-                is_type_structurally_recursive_inner(tcx, sp, seen, representable_cache, ty);
-
-            representable_cache.insert(ty, representability.clone());
-            representability
-        }
-
-        fn is_type_structurally_recursive_inner<'tcx>(
-            tcx: TyCtxt<'tcx>,
-            sp: Span,
-            seen: &mut Vec<Ty<'tcx>>,
-            representable_cache: &mut FxHashMap<Ty<'tcx>, Representability>,
-            ty: Ty<'tcx>,
-        ) -> Representability {
-            match ty.kind() {
-                Adt(def, _) => {
-                    {
-                        // Iterate through stack of previously seen types.
-                        let mut iter = seen.iter();
-
-                        // The first item in `seen` is the type we are actually curious about.
-                        // We want to return SelfRecursive if this type contains itself.
-                        // It is important that we DON'T take generic parameters into account
-                        // for this check, so that Bar<T> in this example counts as SelfRecursive:
-                        //
-                        // struct Foo;
-                        // struct Bar<T> { x: Bar<Foo> }
-
-                        if let Some(&seen_type) = iter.next() {
-                            if same_struct_or_enum(seen_type, *def) {
-                                debug!("SelfRecursive: {:?} contains {:?}", seen_type, ty);
-                                return Representability::SelfRecursive(vec![sp]);
-                            }
-                        }
-
-                        // We also need to know whether the first item contains other types
-                        // that are structurally recursive. If we don't catch this case, we
-                        // will recurse infinitely for some inputs.
-                        //
-                        // It is important that we DO take generic parameters into account
-                        // here, so that code like this is considered SelfRecursive, not
-                        // ContainsRecursive:
-                        //
-                        // struct Foo { Option<Option<Foo>> }
-
-                        for &seen_type in iter {
-                            if ty::TyS::same_type(ty, seen_type) {
-                                debug!("ContainsRecursive: {:?} contains {:?}", seen_type, ty);
-                                return Representability::ContainsRecursive;
-                            }
-                        }
-                    }
-
-                    // For structs and enums, track all previously seen types by pushing them
-                    // onto the 'seen' stack.
-                    seen.push(ty);
-                    let out = are_inner_types_recursive(tcx, sp, seen, representable_cache, ty);
-                    seen.pop();
-                    out
-                }
-                _ => {
-                    // No need to push in other cases.
-                    are_inner_types_recursive(tcx, sp, seen, representable_cache, ty)
-                }
-            }
-        }
-
-        debug!("is_type_representable: {:?}", self);
-
-        // To avoid a stack overflow when checking an enum variant or struct that
-        // contains a different, structurally recursive type, maintain a stack
-        // of seen types and check recursion for each of them (issues #3008, #3779).
-        let mut seen: Vec<Ty<'_>> = Vec::new();
-        let mut representable_cache = FxHashMap::default();
-        let r = is_type_structurally_recursive(tcx, sp, &mut seen, &mut representable_cache, self);
-        debug!("is_type_representable: {:?} is {:?}", self, r);
-        r
-    }
-
     /// Peel off all reference types in this type until there are none left.
     ///
     /// This method is idempotent, i.e. `ty.peel_refs().peel_refs() == ty.peel_refs()`.

compiler/rustc_ty_utils/src/lib.rs

@@ -20,6 +20,7 @@ use rustc_middle::ty::query::Providers;
 mod common_traits;
 pub mod instance;
 mod needs_drop;
+pub mod representability;
 mod ty;
 
 pub fn provide(providers: &mut Providers) {