Move magic traits queries to rustc::traits::drop.

Author: cjgillot

src/librustc/traits/drop.rs

@@ -0,0 +1,202 @@
+//! Miscellaneous type-system utilities that are too small to deserve their own modules.
+
+use crate::middle::lang_items;
+use crate::traits::{self, ObligationCause};
+use crate::ty::util::NeedsDrop;
+use crate::ty::{self, Ty, TyCtxt, TypeFoldable};
+
+use rustc_hir as hir;
+use rustc_span::DUMMY_SP;
+
+#[derive(Clone)]
+pub enum CopyImplementationError<'tcx> {
+    InfrigingFields(Vec<&'tcx ty::FieldDef>),
+    NotAnAdt,
+    HasDestructor,
+}
+
+pub fn can_type_implement_copy(
+    tcx: TyCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    self_type: Ty<'tcx>,
+) -> Result<(), CopyImplementationError<'tcx>> {
+    // FIXME: (@jroesch) float this code up
+    tcx.infer_ctxt().enter(|infcx| {
+        let (adt, substs) = match self_type.kind {
+            // These types used to have a builtin impl.
+            // Now libcore provides that impl.
+            ty::Uint(_)
+            | ty::Int(_)
+            | ty::Bool
+            | ty::Float(_)
+            | ty::Char
+            | ty::RawPtr(..)
+            | ty::Never
+            | ty::Ref(_, _, hir::Mutability::Not) => return Ok(()),
+
+            ty::Adt(adt, substs) => (adt, substs),
+
+            _ => return Err(CopyImplementationError::NotAnAdt),
+        };
+
+        let mut infringing = Vec::new();
+        for variant in &adt.variants {
+            for field in &variant.fields {
+                let ty = field.ty(tcx, substs);
+                if ty.references_error() {
+                    continue;
+                }
+                let span = tcx.def_span(field.did);
+                let cause = ObligationCause { span, ..ObligationCause::dummy() };
+                let ctx = traits::FulfillmentContext::new();
+                match traits::fully_normalize(&infcx, ctx, cause, param_env, &ty) {
+                    Ok(ty) => {
+                        if !infcx.type_is_copy_modulo_regions(param_env, ty, span) {
+                            infringing.push(field);
+                        }
+                    }
+                    Err(errors) => {
+                        infcx.report_fulfillment_errors(&errors, None, false);
+                    }
+                };
+            }
+        }
+        if !infringing.is_empty() {
+            return Err(CopyImplementationError::InfrigingFields(infringing));
+        }
+        if adt.has_dtor(tcx) {
+            return Err(CopyImplementationError::HasDestructor);
+        }
+
+        Ok(())
+    })
+}
+
+fn is_copy_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
+    is_item_raw(tcx, query, lang_items::CopyTraitLangItem)
+}
+
+fn is_sized_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
+    is_item_raw(tcx, query, lang_items::SizedTraitLangItem)
+}
+
+fn is_freeze_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
+    is_item_raw(tcx, query, lang_items::FreezeTraitLangItem)
+}
+
+fn is_item_raw<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
+    item: lang_items::LangItem,
+) -> bool {
+    let (param_env, ty) = query.into_parts();
+    let trait_def_id = tcx.require_lang_item(item, None);
+    tcx.infer_ctxt().enter(|infcx| {
+        traits::type_known_to_meet_bound_modulo_regions(
+            &infcx,
+            param_env,
+            ty,
+            trait_def_id,
+            DUMMY_SP,
+        )
+    })
+}
+
+fn needs_drop_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> NeedsDrop {
+    let (param_env, ty) = query.into_parts();
+
+    let needs_drop = |ty: Ty<'tcx>| -> bool { tcx.needs_drop_raw(param_env.and(ty)).0 };
+
+    assert!(!ty.needs_infer());
+
+    NeedsDrop(match ty.kind {
+        // Fast-path for primitive types
+        ty::Infer(ty::FreshIntTy(_))
+        | ty::Infer(ty::FreshFloatTy(_))
+        | ty::Bool
+        | ty::Int(_)
+        | ty::Uint(_)
+        | ty::Float(_)
+        | ty::Never
+        | ty::FnDef(..)
+        | ty::FnPtr(_)
+        | ty::Char
+        | ty::GeneratorWitness(..)
+        | ty::RawPtr(_)
+        | ty::Ref(..)
+        | ty::Str => false,
+
+        // Foreign types can never have destructors
+        ty::Foreign(..) => false,
+
+        // `ManuallyDrop` doesn't have a destructor regardless of field types.
+        ty::Adt(def, _) if Some(def.did) == tcx.lang_items().manually_drop() => false,
+
+        // Issue #22536: We first query `is_copy_modulo_regions`.  It sees a
+        // normalized version of the type, and therefore will definitely
+        // know whether the type implements Copy (and thus needs no
+        // cleanup/drop/zeroing) ...
+        _ if ty.is_copy_modulo_regions(tcx, param_env, DUMMY_SP) => false,
+
+        // ... (issue #22536 continued) but as an optimization, still use
+        // prior logic of asking for the structural "may drop".
+
+        // FIXME(#22815): Note that this is a conservative heuristic;
+        // it may report that the type "may drop" when actual type does
+        // not actually have a destructor associated with it. But since
+        // the type absolutely did not have the `Copy` bound attached
+        // (see above), it is sound to treat it as having a destructor.
+
+        // User destructors are the only way to have concrete drop types.
+        ty::Adt(def, _) if def.has_dtor(tcx) => true,
+
+        // Can refer to a type which may drop.
+        // FIXME(eddyb) check this against a ParamEnv.
+        ty::Dynamic(..)
+        | ty::Projection(..)
+        | ty::Param(_)
+        | ty::Bound(..)
+        | ty::Placeholder(..)
+        | ty::Opaque(..)
+        | ty::Infer(_)
+        | ty::Error => true,
+
+        ty::UnnormalizedProjection(..) => bug!("only used with chalk-engine"),
+
+        // Zero-length arrays never contain anything to drop.
+        ty::Array(_, len) if len.try_eval_usize(tcx, param_env) == Some(0) => false,
+
+        // Structural recursion.
+        ty::Array(ty, _) | ty::Slice(ty) => needs_drop(ty),
+
+        ty::Closure(def_id, ref substs) => {
+            substs.as_closure().upvar_tys(def_id, tcx).any(needs_drop)
+        }
+
+        // Pessimistically assume that all generators will require destructors
+        // as we don't know if a destructor is a noop or not until after the MIR
+        // state transformation pass
+        ty::Generator(..) => true,
+
+        ty::Tuple(..) => ty.tuple_fields().any(needs_drop),
+
+        // unions don't have destructors because of the child types,
+        // only if they manually implement `Drop` (handled above).
+        ty::Adt(def, _) if def.is_union() => false,
+
+        ty::Adt(def, substs) => def
+            .variants
+            .iter()
+            .any(|variant| variant.fields.iter().any(|field| needs_drop(field.ty(tcx, substs)))),
+    })
+}
+
+pub fn provide(providers: &mut ty::query::Providers<'_>) {
+    *providers = ty::query::Providers {
+        is_copy_raw,
+        is_sized_raw,
+        is_freeze_raw,
+        needs_drop_raw,
+        ..*providers
+    };
+}

src/librustc/traits/mod.rs

@@ -7,6 +7,7 @@ pub mod auto_trait;
 mod chalk_fulfill;
 pub mod codegen;
 mod coherence;
+pub mod drop;
 mod engine;
 pub mod error_reporting;
 mod fulfill;
@@ -1243,6 +1244,7 @@ impl<'tcx> TraitObligation<'tcx> {
 }
 
 pub fn provide(providers: &mut ty::query::Providers<'_>) {
+    drop::provide(providers);
     *providers = ty::query::Providers {
         is_object_safe: object_safety::is_object_safe_provider,
         specialization_graph_of: specialize::specialization_graph_provider,

src/librustc/ty/mod.rs

@@ -3318,7 +3318,6 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
     context::provide(providers);
     erase_regions::provide(providers);
     layout::provide(providers);
-    util::provide(providers);
     constness::provide(providers);
     *providers = ty::query::Providers {
         asyncness,