coherence: move the builtin trait checks to their own module

no functional changes

Author: arielb1

src/librustc_typeck/coherence/builtin.rs

@@ -0,0 +1,357 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Check properties that are required by built-in traits and set
+//! up data structures required by type-checking/translation.
+
+use rustc::middle::free_region::FreeRegionMap;
+use rustc::middle::lang_items::UnsizeTraitLangItem;
+
+use rustc::traits::{self, ObligationCause, Reveal};
+use rustc::ty::{self, Ty, TyCtxt};
+use rustc::ty::ParameterEnvironment;
+use rustc::ty::TypeFoldable;
+use rustc::ty::subst::Subst;
+use rustc::ty::util::CopyImplementationError;
+use rustc::infer;
+
+use rustc::hir::map as hir_map;
+use rustc::hir::{self, ItemImpl};
+
+pub fn check<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
+    populate_destructors(tcx);
+    check_implementations_of_copy(tcx);
+    check_implementations_of_coerce_unsized(tcx);
+}
+
+fn populate_destructors<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
+    let drop_trait = match tcx.lang_items.drop_trait() {
+        Some(id) => id,
+        None => return,
+    };
+    tcx.populate_implementations_for_trait_if_necessary(drop_trait);
+    let drop_trait = tcx.lookup_trait_def(drop_trait);
+
+    drop_trait.for_each_impl(tcx, |impl_did| {
+        let items = tcx.associated_item_def_ids(impl_did);
+        if items.is_empty() {
+            // We'll error out later. For now, just don't ICE.
+            return;
+        }
+        let method_def_id = items[0];
+
+        let self_type = tcx.item_type(impl_did);
+        match self_type.sty {
+            ty::TyAdt(type_def, _) => {
+                type_def.set_destructor(method_def_id);
+            }
+            _ => {
+                // Destructors only work on nominal types.
+                if let Some(impl_node_id) = tcx.map.as_local_node_id(impl_did) {
+                    match tcx.map.find(impl_node_id) {
+                        Some(hir_map::NodeItem(item)) => {
+                            let span = match item.node {
+                                ItemImpl(.., ref ty, _) => ty.span,
+                                _ => item.span,
+                            };
+                            struct_span_err!(tcx.sess,
+                                             span,
+                                             E0120,
+                                             "the Drop trait may only be implemented on \
+                                              structures")
+                                    .span_label(span,
+                                                &format!("implementing Drop requires a struct"))
+                                .emit();
+                        }
+                        _ => {
+                            bug!("didn't find impl in ast map");
+                        }
+                    }
+                } else {
+                    bug!("found external impl of Drop trait on \
+                          something other than a struct");
+                }
+            }
+        }
+    });
+}
+
+fn check_implementations_of_copy<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
+    let copy_trait = match tcx.lang_items.copy_trait() {
+        Some(id) => id,
+        None => return,
+    };
+    tcx.populate_implementations_for_trait_if_necessary(copy_trait);
+    let copy_trait = tcx.lookup_trait_def(copy_trait);
+
+    copy_trait.for_each_impl(tcx, |impl_did| {
+        debug!("check_implementations_of_copy: impl_did={:?}", impl_did);
+
+        let impl_node_id = if let Some(n) = tcx.map.as_local_node_id(impl_did) {
+            n
+        } else {
+            debug!("check_implementations_of_copy(): impl not in this \
+                    crate");
+            return;
+        };
+
+        let self_type = tcx.item_type(impl_did);
+        debug!("check_implementations_of_copy: self_type={:?} (bound)",
+               self_type);
+
+        let span = tcx.map.span(impl_node_id);
+        let param_env = ParameterEnvironment::for_item(tcx, impl_node_id);
+        let self_type = self_type.subst(tcx, &param_env.free_substs);
+        assert!(!self_type.has_escaping_regions());
+
+        debug!("check_implementations_of_copy: self_type={:?} (free)",
+               self_type);
+
+        match param_env.can_type_implement_copy(tcx, self_type, span) {
+            Ok(()) => {}
+            Err(CopyImplementationError::InfrigingField(name)) => {
+                struct_span_err!(tcx.sess,
+                                 span,
+                                 E0204,
+                                 "the trait `Copy` may not be implemented for this type")
+                    .span_label(span, &format!("field `{}` does not implement `Copy`", name))
+                    .emit()
+            }
+            Err(CopyImplementationError::InfrigingVariant(name)) => {
+                let item = tcx.map.expect_item(impl_node_id);
+                let span = if let ItemImpl(.., Some(ref tr), _, _) = item.node {
+                    tr.path.span
+                } else {
+                    span
+                };
+
+                struct_span_err!(tcx.sess,
+                                 span,
+                                 E0205,
+                                 "the trait `Copy` may not be implemented for this type")
+                    .span_label(span,
+                                &format!("variant `{}` does not implement `Copy`", name))
+                    .emit()
+            }
+            Err(CopyImplementationError::NotAnAdt) => {
+                let item = tcx.map.expect_item(impl_node_id);
+                let span = if let ItemImpl(.., ref ty, _) = item.node {
+                    ty.span
+                } else {
+                    span
+                };
+
+                struct_span_err!(tcx.sess,
+                                 span,
+                                 E0206,
+                                 "the trait `Copy` may not be implemented for this type")
+                    .span_label(span, &format!("type is not a structure or enumeration"))
+                    .emit();
+            }
+            Err(CopyImplementationError::HasDestructor) => {
+                struct_span_err!(tcx.sess,
+                                 span,
+                                 E0184,
+                                 "the trait `Copy` may not be implemented for this type; the \
+                                  type has a destructor")
+                        .span_label(span, &format!("Copy not allowed on types with destructors"))
+                    .emit();
+            }
+        }
+    });
+}
+
+fn check_implementations_of_coerce_unsized<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
+    let coerce_unsized_trait = match tcx.lang_items.coerce_unsized_trait() {
+        Some(id) => id,
+        None => return,
+    };
+    let unsize_trait = match tcx.lang_items.require(UnsizeTraitLangItem) {
+        Ok(id) => id,
+        Err(err) => {
+            tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err));
+        }
+    };
+
+    let trait_def = tcx.lookup_trait_def(coerce_unsized_trait);
+
+    trait_def.for_each_impl(tcx, |impl_did| {
+        debug!("check_implementations_of_coerce_unsized: impl_did={:?}",
+               impl_did);
+
+        let impl_node_id = if let Some(n) = tcx.map.as_local_node_id(impl_did) {
+            n
+        } else {
+            debug!("check_implementations_of_coerce_unsized(): impl not \
+                    in this crate");
+            return;
+        };
+
+        let source = tcx.item_type(impl_did);
+        let trait_ref = tcx.impl_trait_ref(impl_did).unwrap();
+        let target = trait_ref.substs.type_at(1);
+        debug!("check_implementations_of_coerce_unsized: {:?} -> {:?} (bound)",
+               source,
+               target);
+
+        let span = tcx.map.span(impl_node_id);
+        let param_env = ParameterEnvironment::for_item(tcx, impl_node_id);
+        let source = source.subst(tcx, &param_env.free_substs);
+        let target = target.subst(tcx, &param_env.free_substs);
+        assert!(!source.has_escaping_regions());
+
+        debug!("check_implementations_of_coerce_unsized: {:?} -> {:?} (free)",
+               source,
+               target);
+
+        tcx.infer_ctxt(None, Some(param_env), Reveal::ExactMatch).enter(|infcx| {
+            let cause = ObligationCause::misc(span, impl_node_id);
+            let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>,
+                               mt_b: ty::TypeAndMut<'tcx>,
+                               mk_ptr: &Fn(Ty<'tcx>) -> Ty<'tcx>| {
+                if (mt_a.mutbl, mt_b.mutbl) == (hir::MutImmutable, hir::MutMutable) {
+                    infcx.report_mismatched_types(&cause,
+                                                  mk_ptr(mt_b.ty),
+                                                  target,
+                                                  ty::error::TypeError::Mutability)
+                         .emit();
+                }
+                (mt_a.ty, mt_b.ty, unsize_trait, None)
+            };
+            let (source, target, trait_def_id, kind) = match (&source.sty, &target.sty) {
+                (&ty::TyBox(a), &ty::TyBox(b)) => (a, b, unsize_trait, None),
+
+                (&ty::TyRef(r_a, mt_a), &ty::TyRef(r_b, mt_b)) => {
+                    infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a);
+                    check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty))
+                }
+
+                (&ty::TyRef(_, mt_a), &ty::TyRawPtr(mt_b)) |
+                (&ty::TyRawPtr(mt_a), &ty::TyRawPtr(mt_b)) => {
+                    check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
+                }
+
+                (&ty::TyAdt(def_a, substs_a), &ty::TyAdt(def_b, substs_b))
+                    if def_a.is_struct() && def_b.is_struct() => {
+                    if def_a != def_b {
+                        let source_path = tcx.item_path_str(def_a.did);
+                        let target_path = tcx.item_path_str(def_b.did);
+                        span_err!(tcx.sess,
+                                  span,
+                                  E0377,
+                                  "the trait `CoerceUnsized` may only be implemented \
+                                   for a coercion between structures with the same \
+                                   definition; expected {}, found {}",
+                                  source_path,
+                                  target_path);
+                        return;
+                    }
+
+                    let fields = &def_a.struct_variant().fields;
+                    let diff_fields = fields.iter()
+                        .enumerate()
+                        .filter_map(|(i, f)| {
+                            let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b));
+
+                            if tcx.item_type(f.did).is_phantom_data() {
+                                // Ignore PhantomData fields
+                                return None;
+                            }
+
+                            // Ignore fields that aren't significantly changed
+                            if let Ok(ok) = infcx.sub_types(false, &cause, b, a) {
+                                if ok.obligations.is_empty() {
+                                    return None;
+                                }
+                            }
+
+                            // Collect up all fields that were significantly changed
+                            // i.e. those that contain T in coerce_unsized T -> U
+                            Some((i, a, b))
+                        })
+                        .collect::<Vec<_>>();
+
+                    if diff_fields.is_empty() {
+                        span_err!(tcx.sess,
+                                  span,
+                                  E0374,
+                                  "the trait `CoerceUnsized` may only be implemented \
+                                   for a coercion between structures with one field \
+                                   being coerced, none found");
+                        return;
+                    } else if diff_fields.len() > 1 {
+                        let item = tcx.map.expect_item(impl_node_id);
+                        let span = if let ItemImpl(.., Some(ref t), _, _) = item.node {
+                            t.path.span
+                        } else {
+                            tcx.map.span(impl_node_id)
+                        };
+
+                        let mut err = struct_span_err!(tcx.sess,
+                                                       span,
+                                                       E0375,
+                                                       "implementing the trait \
+                                                        `CoerceUnsized` requires multiple \
+                                                        coercions");
+                        err.note("`CoerceUnsized` may only be implemented for \
+                                  a coercion between structures with one field being coerced");
+                        err.note(&format!("currently, {} fields need coercions: {}",
+                                          diff_fields.len(),
+                                          diff_fields.iter()
+                                          .map(|&(i, a, b)| {
+                                              format!("{} ({} to {})", fields[i].name, a, b)
+                                          })
+                                          .collect::<Vec<_>>()
+                                          .join(", ")));
+                        err.span_label(span, &format!("requires multiple coercions"));
+                        err.emit();
+                        return;
+                    }
+
+                    let (i, a, b) = diff_fields[0];
+                    let kind = ty::adjustment::CustomCoerceUnsized::Struct(i);
+                    (a, b, coerce_unsized_trait, Some(kind))
+                }
+
+                _ => {
+                    span_err!(tcx.sess,
+                              span,
+                              E0376,
+                              "the trait `CoerceUnsized` may only be implemented \
+                               for a coercion between structures");
+                    return;
+                }
+            };
+
+            let mut fulfill_cx = traits::FulfillmentContext::new();
+
+            // Register an obligation for `A: Trait<B>`.
+            let cause = traits::ObligationCause::misc(span, impl_node_id);
+            let predicate =
+                tcx.predicate_for_trait_def(cause, trait_def_id, 0, source, &[target]);
+            fulfill_cx.register_predicate_obligation(&infcx, predicate);
+
+            // Check that all transitive obligations are satisfied.
+            if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) {
+                infcx.report_fulfillment_errors(&errors);
+            }
+
+            // Finally, resolve all regions.
+            let mut free_regions = FreeRegionMap::new();
+            free_regions.relate_free_regions_from_predicates(&infcx.parameter_environment
+                                                             .caller_bounds);
+            infcx.resolve_regions_and_report_errors(&free_regions, impl_node_id);
+
+            if let Some(kind) = kind {
+                tcx.custom_coerce_unsized_kinds.borrow_mut().insert(impl_did, kind);
+            }
+        });
+    });
+}