auto merge of #18121 : nikomatsakis/rust/method-call-use-trait-matching-infrastructure-2, r=pcwalton

Convert trait method dispatch to use new trait matching machinery.

This fixes about 90% of #17918. What remains to be done is to make inherent dispatch work with conditional dispatch as well. I plan to do this in a future patch by generalizing the "method match" code slightly to work for inherent impls as well (the basic algorithm is precisely the same).

Fixes #17178.

This is a [breaking-change] for two reasons:

1. The old code was a bit broken. I found various minor cases, particularly around operators, where the old code incorrectly matched, but an extra `*` or other change is now required. (See commit e8cef25 ("Correct case where the old version of method lookup...") for examples.)
2. The old code didn't type check calls against the method signature from the *trait* but rather the *impl*. The two can be different in subtle ways. This makes the new method dispatch both more liberal and more conservative than the original. (See commit 8308332 ("The new method lookup mechanism typechecks...") for examples.)

r? @pcwalton since he's been reviewing most of this series of changes
f? @nick29581 for commit 39df55f ("Permit DST types to unify like other types")
cc @aturon as this relates to library stabilization

Author: bors

src/libcore/num/mod.rs

@@ -1374,7 +1374,7 @@ macro_rules! checkeddiv_int_impl(
                 if *v == 0 || (*self == $min && *v == -1) {
                     None
                 } else {
-                    Some(self / *v)
+                    Some(*self / *v)
                 }
             }
         }
@@ -1395,7 +1395,7 @@ macro_rules! checkeddiv_uint_impl(
                 if *v == 0 {
                     None
                 } else {
-                    Some(self / *v)
+                    Some(*self / *v)
                 }
             }
         }

src/libcore/ops.rs

@@ -638,7 +638,7 @@ shr_impl!(uint u8 u16 u32 u64 int i8 i16 i32 i64)
  * ```
  */
 #[lang="index"]
-pub trait Index<Index, Result> {
+pub trait Index<Index, Sized? Result> {
     /// The method for the indexing (`Foo[Bar]`) operation
     fn index<'a>(&'a self, index: &Index) -> &'a Result;
 }

src/librustc/middle/borrowck/graphviz.rs

@@ -142,8 +142,8 @@ impl<'a, 'tcx> dot::Labeller<'a, Node<'a>, Edge<'a>> for DataflowLabeller<'a, 't
 }
 
 impl<'a, 'tcx> dot::GraphWalk<'a, Node<'a>, Edge<'a>> for DataflowLabeller<'a, 'tcx> {
-    fn nodes(&self) -> dot::Nodes<'a, Node<'a>> { self.inner.nodes() }
-    fn edges(&self) -> dot::Edges<'a, Edge<'a>> { self.inner.edges() }
-    fn source(&self, edge: &Edge<'a>) -> Node<'a> { self.inner.source(edge) }
-    fn target(&self, edge: &Edge<'a>) -> Node<'a> { self.inner.target(edge) }
+    fn nodes(&'a self) -> dot::Nodes<'a, Node<'a>> { self.inner.nodes() }
+    fn edges(&'a self) -> dot::Edges<'a, Edge<'a>> { self.inner.edges() }
+    fn source(&'a self, edge: &Edge<'a>) -> Node<'a> { self.inner.source(edge) }
+    fn target(&'a self, edge: &Edge<'a>) -> Node<'a> { self.inner.target(edge) }
 }

src/librustc/middle/cfg/graphviz.rs

@@ -91,29 +91,29 @@ impl<'a, 'ast> dot::Labeller<'a, Node<'a>, Edge<'a>> for LabelledCFG<'a, 'ast> {
 }
 
 impl<'a> dot::GraphWalk<'a, Node<'a>, Edge<'a>> for &'a cfg::CFG {
-    fn nodes(&self) -> dot::Nodes<'a, Node<'a>> {
+    fn nodes(&'a self) -> dot::Nodes<'a, Node<'a>> {
         let mut v = Vec::new();
         self.graph.each_node(|i, nd| { v.push((i, nd)); true });
         dot::maybe_owned_vec::Growable(v)
     }
-    fn edges(&self) -> dot::Edges<'a, Edge<'a>> {
+    fn edges(&'a self) -> dot::Edges<'a, Edge<'a>> {
         self.graph.all_edges().iter().collect()
     }
-    fn source(&self, edge: &Edge<'a>) -> Node<'a> {
+    fn source(&'a self, edge: &Edge<'a>) -> Node<'a> {
         let i = edge.source();
         (i, self.graph.node(i))
     }
-    fn target(&self, edge: &Edge<'a>) -> Node<'a> {
+    fn target(&'a self, edge: &Edge<'a>) -> Node<'a> {
         let i = edge.target();
         (i, self.graph.node(i))
     }
 }
 
 impl<'a, 'ast> dot::GraphWalk<'a, Node<'a>, Edge<'a>> for LabelledCFG<'a, 'ast>
 {
-    fn nodes(&self) -> dot::Nodes<'a, Node<'a>> { self.cfg.nodes() }
-    fn edges(&self) -> dot::Edges<'a, Edge<'a>> { self.cfg.edges() }
-    fn source(&self, edge: &Edge<'a>) -> Node<'a> { self.cfg.source(edge) }
-    fn target(&self, edge: &Edge<'a>) -> Node<'a> { self.cfg.target(edge) }
+    fn nodes(&'a self) -> dot::Nodes<'a, Node<'a>> { self.cfg.nodes() }
+    fn edges(&'a self) -> dot::Edges<'a, Edge<'a>> { self.cfg.edges() }
+    fn source(&'a self, edge: &Edge<'a>) -> Node<'a> { self.cfg.source(edge) }
+    fn target(&'a self, edge: &Edge<'a>) -> Node<'a> { self.cfg.target(edge) }
 }
 

src/librustc/middle/traits/doc.rs

@@ -272,4 +272,11 @@ nested obligation `int : Bar<U>` to find out that `U=uint`.
 It would be good to only do *just as much* nested resolution as
 necessary. Currently, though, we just do a full resolution.
 
+## Method matching
+
+Method dispach follows a slightly different path than normal trait
+selection. This is because it must account for the transformed self
+type of the receiver and various other complications. The procedure is
+described in `select.rs` in the "METHOD MATCHING" section.
+
 */

src/librustc/middle/traits/mod.rs

@@ -24,6 +24,8 @@ use syntax::codemap::{Span, DUMMY_SP};
 pub use self::fulfill::FulfillmentContext;
 pub use self::select::SelectionContext;
 pub use self::select::SelectionCache;
+pub use self::select::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch};
+pub use self::select::{MethodMatchedData}; // intentionally don't export variants
 pub use self::util::supertraits;
 pub use self::util::transitive_bounds;
 pub use self::util::Supertraits;
@@ -219,22 +221,6 @@ pub struct VtableParamData {
     pub bound: Rc<ty::TraitRef>,
 }
 
-pub fn evaluate_obligation<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
-                                    param_env: &ty::ParameterEnvironment,
-                                    obligation: &Obligation,
-                                    typer: &Typer<'tcx>)
-                                    -> bool
-{
-    /*!
-     * Attempts to resolve the obligation given. Returns `None` if
-     * we are unable to resolve, either because of ambiguity or
-     * due to insufficient inference.
-     */
-
-    let mut selcx = select::SelectionContext::new(infcx, param_env, typer);
-    selcx.evaluate_obligation(obligation)
-}
-
 pub fn select_inherent_impl<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
                                      param_env: &ty::ParameterEnvironment,
                                      typer: &Typer<'tcx>,