move impl wf check so they occur earlier

Needed to keep coherence from freaking out.

Author: nikomatsakis

src/librustc_typeck/check/impl_item_duplicate.rs

@@ -143,8 +143,6 @@ mod closure;
 mod callee;
 mod compare_method;
 mod intrinsic;
-mod impl_item_duplicate;
-mod impl_parameters_used;
 mod op;
 
 /// closures defined within the function.  For example:
@@ -817,7 +815,7 @@ pub fn check_item_type<'a,'tcx>(ccx: &CrateCtxt<'a,'tcx>, it: &'tcx hir::Item) {
                             it.id);
       }
       hir::ItemFn(..) => {} // entirely within check_item_body
-      hir::ItemImpl(_, _, ref hir_generics, _, _, ref impl_item_refs) => {
+      hir::ItemImpl(.., ref impl_item_refs) => {
           debug!("ItemImpl {} with id {}", it.name, it.id);
           let impl_def_id = ccx.tcx.map.local_def_id(it.id);
           if let Some(impl_trait_ref) = ccx.tcx.impl_trait_ref(impl_def_id) {
@@ -829,14 +827,6 @@ pub fn check_item_type<'a,'tcx>(ccx: &CrateCtxt<'a,'tcx>, it: &'tcx hir::Item) {
               let trait_def_id = impl_trait_ref.def_id;
               check_on_unimplemented(ccx, trait_def_id, it);
           }
-
-          impl_parameters_used::enforce_impl_params_are_constrained(ccx,
-                                                                    hir_generics,
-                                                                    impl_def_id,
-                                                                    impl_item_refs);
-
-          impl_item_duplicate::enforce_impl_items_are_distinct(ccx,
-                                                               impl_item_refs);
       }
       hir::ItemTrait(..) => {
         let def_id = ccx.tcx.map.local_def_id(it.id);

src/librustc_typeck/check/mod.rs

@@ -8,11 +8,24 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+//! This pass enforces various "well-formedness constraints" on impls.
+//! Logically, it is part of wfcheck -- but we do it early so that we
+//! can stop compilation afterwards, since part of the trait matching
+//! infrastructure gets very grumpy if these conditions don't hold. In
+//! particular, if there are type parameters that are not part of the
+//! impl, then coherence will report strange inference ambiguity
+//! errors; if impls have duplicate items, we get misleading
+//! specialization errors. These things can (and probably should) be
+//! fixed, but for the moment it's easier to do these checks early.
+
 use constrained_type_params as ctp;
+use rustc::dep_graph::DepNode;
 use rustc::hir;
+use rustc::hir::itemlikevisit::ItemLikeVisitor;
 use rustc::hir::def_id::DefId;
 use rustc::ty;
-use rustc::util::nodemap::FxHashSet;
+use rustc::util::nodemap::{FxHashMap, FxHashSet};
+use std::collections::hash_map::Entry::{Occupied, Vacant};
 
 use syntax_pos::Span;
 
@@ -48,22 +61,52 @@ use CrateCtxt;
 /// impl<'a> Trait<Foo> for Bar { type X = &'a i32; }
 ///      ^ 'a is unused and appears in assoc type, error
 /// ```
-pub fn enforce_impl_params_are_constrained<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
-                                                     impl_hir_generics: &hir::Generics,
-                                                     impl_def_id: DefId,
-                                                     impl_item_refs: &[hir::ImplItemRef])
+pub fn impl_wf_check<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>) {
+    // We will tag this as part of the WF check -- logically, it is,
+    // but it's one that we must perform earlier than the rest of
+    // WfCheck.
+    ccx.tcx.visit_all_item_likes_in_krate(DepNode::WfCheck, &mut ImplWfCheck { ccx: ccx });
+}
+
+struct ImplWfCheck<'a, 'tcx: 'a> {
+    ccx: &'a CrateCtxt<'a, 'tcx>,
+}
+
+impl<'a, 'tcx> ItemLikeVisitor<'tcx> for ImplWfCheck<'a, 'tcx> {
+    fn visit_item(&mut self, item: &'tcx hir::Item) {
+        match item.node {
+            hir::ItemImpl(.., ref generics, _, _, ref impl_item_refs) => {
+                let impl_def_id = self.ccx.tcx.map.local_def_id(item.id);
+                enforce_impl_params_are_constrained(self.ccx,
+                                                    generics,
+                                                    impl_def_id,
+                                                    impl_item_refs);
+                enforce_impl_items_are_distinct(self.ccx, impl_item_refs);
+            }
+            _ => { }
+        }
+    }
+
+    fn visit_impl_item(&mut self, _impl_item: &'tcx hir::ImplItem) { }
+}
+
+fn enforce_impl_params_are_constrained<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
+                                                 impl_hir_generics: &hir::Generics,
+                                                 impl_def_id: DefId,
+                                                 impl_item_refs: &[hir::ImplItemRef])
 {
     // Every lifetime used in an associated type must be constrained.
-    let impl_scheme = ccx.tcx.lookup_item_type(impl_def_id);
-    let impl_predicates = ccx.tcx.lookup_predicates(impl_def_id);
+    let impl_self_ty = ccx.tcx.item_type(impl_def_id);
+    let impl_generics = ccx.tcx.item_generics(impl_def_id);
+    let impl_predicates = ccx.tcx.item_predicates(impl_def_id);
     let impl_trait_ref = ccx.tcx.impl_trait_ref(impl_def_id);
 
-    let mut input_parameters = ctp::parameters_for_impl(impl_scheme.ty, impl_trait_ref);
+    let mut input_parameters = ctp::parameters_for_impl(impl_self_ty, impl_trait_ref);
     ctp::identify_constrained_type_params(
         &impl_predicates.predicates.as_slice(), impl_trait_ref, &mut input_parameters);
 
     // Disallow ANY unconstrained type parameters.
-    for (ty_param, param) in impl_scheme.generics.types.iter().zip(&impl_hir_generics.ty_params) {
+    for (ty_param, param) in impl_generics.types.iter().zip(&impl_hir_generics.ty_params) {
         let param_ty = ty::ParamTy::for_def(ty_param);
         if !input_parameters.contains(&ctp::Parameter::from(param_ty)) {
             report_unused_parameter(ccx, param.span, "type", &param_ty.to_string());
@@ -78,9 +121,9 @@ pub fn enforce_impl_params_are_constrained<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
             item.kind == ty::AssociatedKind::Type && item.has_value
         })
         .flat_map(|def_id| {
-            ctp::parameters_for(&ccx.tcx.lookup_item_type(def_id).ty, true)
+            ctp::parameters_for(&ccx.tcx.item_type(def_id), true)
         }).collect();
-    for (ty_lifetime, lifetime) in impl_scheme.generics.regions.iter()
+    for (ty_lifetime, lifetime) in impl_generics.regions.iter()
         .zip(&impl_hir_generics.lifetimes)
     {
         let param = ctp::Parameter::from(ty_lifetime.to_early_bound_region_data());
@@ -127,3 +170,34 @@ fn report_unused_parameter(ccx: &CrateCtxt,
         .span_label(span, &format!("unconstrained {} parameter", kind))
         .emit();
 }
+
+/// Enforce that we do not have two items in an impl with the same name.
+fn enforce_impl_items_are_distinct<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
+                                             impl_item_refs: &[hir::ImplItemRef])
+{
+    let tcx = ccx.tcx;
+    let mut seen_type_items = FxHashMap();
+    let mut seen_value_items = FxHashMap();
+    for impl_item_ref in impl_item_refs {
+        let impl_item = tcx.map.impl_item(impl_item_ref.id);
+        let seen_items = match impl_item.node {
+            hir::ImplItemKind::Type(_) => &mut seen_type_items,
+            _                    => &mut seen_value_items,
+        };
+        match seen_items.entry(impl_item.name) {
+            Occupied(entry) => {
+                let mut err = struct_span_err!(tcx.sess, impl_item.span, E0201,
+                                               "duplicate definitions with name `{}`:",
+                                               impl_item.name);
+                err.span_label(*entry.get(),
+                               &format!("previous definition of `{}` here",
+                                        impl_item.name));
+                err.span_label(impl_item.span, &format!("duplicate definition"));
+                err.emit();
+            }
+            Vacant(entry) => {
+                entry.insert(impl_item.span);
+            }
+        }
+    }
+}

src/librustc_typeck/check/impl_parameters_used.rs renamed to src/librustc_typeck/impl_wf_check.rs

@@ -131,6 +131,7 @@ mod rscope;
 mod astconv;
 pub mod collect;
 mod constrained_type_params;
+mod impl_wf_check;
 pub mod coherence;
 pub mod variance;
 
@@ -334,6 +335,11 @@ pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>)
     time(time_passes, "variance inference", ||
          variance::infer_variance(tcx));
 
+    tcx.sess.track_errors(|| {
+        time(time_passes, "impl wf inference", ||
+             impl_wf_check::impl_wf_check(&ccx));
+    })?;
+
     tcx.sess.track_errors(|| {
       time(time_passes, "coherence checking", ||
           coherence::check_coherence(&ccx));

src/librustc_typeck/lib.rs

@@ -15,7 +15,6 @@ fn foo<T>() {
 
     impl<T> Drop for foo<T> {
         //~^ ERROR wrong number of type arguments
-        //~^^ ERROR the type parameter `T` is not constrained
         fn drop(&mut self) {}
     }
 }