From 2a1ba2f1ac45f6bf48e55be4db5e8d1965fccaf8 Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Mon, 5 Jan 2015 16:01:04 -0500
Subject: [PATCH] Permit method calls based on where clauses.

---
 src/librustc_typeck/check/callee.rs       |  2 +-
 src/librustc_typeck/check/method/probe.rs | 37 ++++++++++++++++++--
 src/test/run-pass/method-where-clause.rs  | 42 +++++++++++++++++++++++
 3 files changed, 78 insertions(+), 3 deletions(-)
 create mode 100644 src/test/run-pass/method-where-clause.rs

diff --git a/src/librustc_typeck/check/callee.rs b/src/librustc_typeck/check/callee.rs
index 98a826355a7..b1dc033b567 100644
--- a/src/librustc_typeck/check/callee.rs
+++ b/src/librustc_typeck/check/callee.rs
@@ -22,7 +22,7 @@ use super::TupleArgumentsFlag;
 use super::write_call;
 
 use middle::infer;
-use middle::ty::{mod, Ty};
+use middle::ty::{self, Ty};
 use syntax::ast;
 use syntax::codemap::Span;
 use syntax::parse::token;
diff --git a/src/librustc_typeck/check/method/probe.rs b/src/librustc_typeck/check/method/probe.rs
index beb51590b41..94e535cf2ef 100644
--- a/src/librustc_typeck/check/method/probe.rs
+++ b/src/librustc_typeck/check/method/probe.rs
@@ -442,7 +442,7 @@ impl<'a,'tcx> ProbeContext<'a,'tcx> {
 
     fn assemble_extension_candidates_for_trait(&mut self,
                                                trait_def_id: ast::DefId) {
-        debug!("assemble_extension_candidates_for_trait: trait_def_id={}",
+        debug!("assemble_extension_candidates_for_trait(trait_def_id={})",
                trait_def_id.repr(self.tcx()));
 
         // Check whether `trait_def_id` defines a method with suitable name:
@@ -471,8 +471,12 @@ impl<'a,'tcx> ProbeContext<'a,'tcx> {
                                                            matching_index);
 
         self.assemble_unboxed_closure_candidates(trait_def_id,
-                                                 method,
+                                                 method.clone(),
                                                  matching_index);
+
+        self.assemble_where_clause_candidates(trait_def_id,
+                                              method,
+                                              matching_index);
     }
 
     fn assemble_extension_candidates_for_trait_impls(&mut self,
@@ -599,6 +603,35 @@ impl<'a,'tcx> ProbeContext<'a,'tcx> {
         }
     }
 
+    fn assemble_where_clause_candidates(&mut self,
+                                        trait_def_id: ast::DefId,
+                                        method_ty: Rc<ty::Method<'tcx>>,
+                                        method_index: uint)
+    {
+        debug!("assemble_where_clause_candidates(trait_def_id={})",
+               trait_def_id.repr(self.tcx()));
+
+        // Check whether there are any where-clauses pertaining to this trait.
+        let caller_predicates =
+            self.fcx.inh.param_env.caller_bounds.predicates.as_slice().to_vec();
+        for bound in traits::elaborate_predicates(self.tcx(), caller_predicates)
+                     .filter_map(|p| p.to_opt_poly_trait_ref())
+                     .filter(|b| b.def_id() == trait_def_id)
+        {
+            let xform_self_ty = self.xform_self_ty(&method_ty, bound.substs());
+
+            debug!("assemble_where_clause_candidates: bound={} xform_self_ty={}",
+                   bound.repr(self.tcx()),
+                   xform_self_ty.repr(self.tcx()));
+
+            self.extension_candidates.push(Candidate {
+                xform_self_ty: xform_self_ty,
+                method_ty: method_ty.clone(),
+                kind: WhereClauseCandidate(bound, method_index)
+            });
+        }
+    }
+
     ///////////////////////////////////////////////////////////////////////////
     // THE ACTUAL SEARCH
 
diff --git a/src/test/run-pass/method-where-clause.rs b/src/test/run-pass/method-where-clause.rs
new file mode 100644
index 00000000000..4361c22f55a
--- /dev/null
+++ b/src/test/run-pass/method-where-clause.rs
@@ -0,0 +1,42 @@
+// Copyright 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.
+
+// Test that we can use method notation to call methods based on a
+// where clause type, and not only type parameters.
+
+trait Foo {
+    fn foo(&self) -> int;
+}
+
+impl Foo for Option<int>
+{
+    fn foo(&self) -> int {
+        self.unwrap_or(22)
+    }
+}
+
+impl Foo for Option<uint>
+{
+    fn foo(&self) -> int {
+        self.unwrap_or(22) as int
+    }
+}
+
+fn check<T>(x: Option<T>) -> (int, int)
+    where Option<T> : Foo
+{
+    let y: Option<T> = None;
+    (x.foo(), y.foo())
+}
+
+fn main() {
+    assert_eq!(check(Some(23u)), (23i, 22i));
+    assert_eq!(check(Some(23i)), (23i, 22i));
+}