move duplicate checking into TypeCheck

This completes the effort to not touch the impl-items during
`Collect(Impl)`.

src/librustc_typeck/check/impl_item_duplicate.rs

@@ -0,0 +1,46 @@
+// Copyright 2012-2014 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.
+
+use rustc::hir;
+use rustc_data_structures::fx::FxHashMap;
+use std::collections::hash_map::Entry::{Occupied, Vacant};
+
+use CrateCtxt;
+
+/// Enforce that we do not have two items in an impl with the same name.
+pub fn enforce_impl_items_are_distinct<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
+                                                 impl_item_ids: &[hir::ImplItemId])
+{
+    let tcx = ccx.tcx;
+    let mut seen_type_items = FxHashMap();
+    let mut seen_value_items = FxHashMap();
+    for &impl_item_id in impl_item_ids {
+        let impl_item = tcx.map.impl_item(impl_item_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/mod.rs

@@ -143,6 +143,7 @@ mod closure;
 mod callee;
 mod compare_method;
 mod intrinsic;
+mod impl_item_duplicate;
 mod impl_parameters_used;
 mod op;
 
@@ -834,6 +835,8 @@ pub fn check_item_type<'a,'tcx>(ccx: &CrateCtxt<'a,'tcx>, it: &'tcx hir::Item) {
                                                                     impl_def_id,
                                                                     impl_item_ids);
 
+          impl_item_duplicate::enforce_impl_items_are_distinct(ccx,
+                                                               impl_item_ids);
       }
       hir::ItemTrait(..) => {
         let def_id = ccx.tcx.map.local_def_id(it.id);

src/librustc_typeck/collect.rs

@@ -77,7 +77,6 @@ use CrateCtxt;
 use rustc_const_math::ConstInt;
 
 use std::cell::RefCell;
-use std::collections::hash_map::Entry::{Occupied, Vacant};
 
 use syntax::{abi, ast, attr};
 use syntax::parse::token::{self, keywords};
@@ -732,7 +731,11 @@ fn convert_item(ccx: &CrateCtxt, it: &hir::Item) {
                       ref generics,
                       ref opt_trait_ref,
                       ref selfty,
-                      ref impl_item_ids) => {
+                      ref _impl_item_ids /* [1] */) => {
+            // [1]: We really don't want to be inspecting the details
+            // of impl-items here; it creates bad edges in the
+            // incr. comp. graph.
+
             // Create generics from the generics specified in the impl head.
             debug!("convert: ast_generics={:?}", generics);
             let def_id = ccx.tcx.map.local_def_id(it.id);
@@ -763,35 +766,6 @@ fn convert_item(ccx: &CrateCtxt, it: &hir::Item) {
                                                &mut ctp::parameters_for_impl(selfty, trait_ref));
 
             tcx.predicates.borrow_mut().insert(def_id, ty_predicates.clone());
-
-
-            // Convert all the associated consts.
-            // Also, check if there are any duplicate associated items
-            let mut seen_type_items = FxHashMap();
-            let mut seen_value_items = FxHashMap();
-
-            for &impl_item_id in impl_item_ids {
-                let impl_item = tcx.map.impl_item(impl_item_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);
-                    }
-                }
-            }
         },
         hir::ItemTrait(.., ref trait_items) => {
             let trait_def = trait_def_of_item(ccx, it);