Refactor HIR item-like traversal (part 1)

- Create hir_crate_items query which traverses tcx.hir_crate(()).owners to return a hir::ModuleItems
- use tcx.hir_crate_items in tcx.hir().items() to return an iterator of hir::ItemId
- add par_items(impl Fn(hir::ItemId)) to traverse all items in parallel

Signed-off-by: Miguel Guarniz <mi9uel9@gmail.com>

Author: kckeiks

clippy_lints/src/same_name_method.rs

@@ -50,7 +50,8 @@ impl<'tcx> LateLintPass<'tcx> for SameNameMethod {
     fn check_crate_post(&mut self, cx: &LateContext<'tcx>) {
         let mut map = FxHashMap::<Res, ExistingName>::default();
 
-        for item in cx.tcx.hir().items() {
+        for id in cx.tcx.hir().items() {
+            let item = cx.tcx.hir().item(id);
             if let ItemKind::Impl(Impl {
                 items,
                 of_trait,

tests/ui/same_name_method.stderr

@@ -11,6 +11,19 @@ note: existing `foo` defined here
 LL |             fn foo() {}
    |             ^^^^^^^^^^^
 
+error: method's name is the same as an existing method in a trait
+  --> $DIR/same_name_method.rs:34:13
+   |
+LL |             fn clone() {}
+   |             ^^^^^^^^^^^^^
+   |
+note: existing `clone` defined here
+  --> $DIR/same_name_method.rs:30:18
+   |
+LL |         #[derive(Clone)]
+   |                  ^^^^^
+   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+
 error: method's name is the same as an existing method in a trait
   --> $DIR/same_name_method.rs:44:13
    |
@@ -47,18 +60,5 @@ note: existing `foo` defined here
 LL |         impl T1 for S {}
    |         ^^^^^^^^^^^^^^^^
 
-error: method's name is the same as an existing method in a trait
-  --> $DIR/same_name_method.rs:34:13
-   |
-LL |             fn clone() {}
-   |             ^^^^^^^^^^^^^
-   |
-note: existing `clone` defined here
-  --> $DIR/same_name_method.rs:30:18
-   |
-LL |         #[derive(Clone)]
-   |                  ^^^^^
-   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
-
 error: aborting due to 5 previous errors