Auto merge of #21351 - eddyb:x-coerce--a-new-hope, r=nikomatsakis

Coercions will now attempt to autoderef as needed before reborrowing.
This includes overloaded `Deref`, e.g. `&Rc<T>` coerces to `&T`, and
`DerefMut`, e.g. `&mut Vec<T>` coerces to `&mut [T]` (in addition to `&[T]`).
Closes #21432.

Author: bors

src/librustc/middle/infer/mod.rs

@@ -33,12 +33,10 @@ use std::rc::Rc;
 use syntax::ast;
 use syntax::codemap;
 use syntax::codemap::Span;
-use util::common::indent;
 use util::nodemap::FnvHashMap;
 use util::ppaux::{ty_to_string};
 use util::ppaux::{Repr, UserString};
 
-use self::coercion::Coerce;
 use self::combine::{Combine, Combineable, CombineFields};
 use self::region_inference::{RegionVarBindings, RegionSnapshot};
 use self::equate::Equate;
@@ -47,7 +45,6 @@ use self::lub::Lub;
 use self::unify::{UnificationTable, InferCtxtMethodsForSimplyUnifiableTypes};
 use self::error_reporting::ErrorReporting;
 
-pub mod coercion;
 pub mod combine;
 pub mod doc;
 pub mod equate;
@@ -68,7 +65,6 @@ pub type Bound<T> = Option<T>;
 pub type cres<'tcx, T> = Result<T,ty::type_err<'tcx>>; // "combine result"
 pub type ures<'tcx> = cres<'tcx, ()>; // "unify result"
 pub type fres<T> = Result<T, fixup_err>; // "fixup result"
-pub type CoerceResult<'tcx> = cres<'tcx, Option<ty::AutoAdjustment<'tcx>>>;
 
 pub struct InferCtxt<'a, 'tcx: 'a> {
     pub tcx: &'a ty::ctxt<'tcx>,
@@ -409,24 +405,6 @@ fn expected_found<T>(a_is_expected: bool,
     }
 }
 
-pub fn mk_coercety<'a, 'tcx>(cx: &InferCtxt<'a, 'tcx>,
-                             a_is_expected: bool,
-                             origin: TypeOrigin,
-                             a: Ty<'tcx>,
-                             b: Ty<'tcx>)
-                             -> CoerceResult<'tcx> {
-    debug!("mk_coercety({} -> {})", a.repr(cx.tcx), b.repr(cx.tcx));
-    indent(|| {
-        cx.commit_if_ok(|| {
-            let trace = TypeTrace {
-                origin: origin,
-                values: Types(expected_found(a_is_expected, a, b))
-            };
-            Coerce(cx.combine_fields(a_is_expected, trace)).tys(a, b)
-        })
-    })
-}
-
 trait then<'tcx> {
     fn then<T, F>(&self, f: F) -> Result<T, ty::type_err<'tcx>> where
         T: Clone,
@@ -689,10 +667,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     {
         debug!("sub_types({} <: {})", a.repr(self.tcx), b.repr(self.tcx));
         self.commit_if_ok(|| {
-            let trace = TypeTrace {
-                origin: origin,
-                values: Types(expected_found(a_is_expected, a, b))
-            };
+            let trace = TypeTrace::types(origin, a_is_expected, a, b);
             self.sub(a_is_expected, trace).tys(a, b).to_ures()
         })
     }
@@ -705,10 +680,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     -> ures<'tcx>
     {
         self.commit_if_ok(|| {
-            let trace = TypeTrace {
-                origin: origin,
-                values: Types(expected_found(a_is_expected, a, b))
-            };
+            let trace = TypeTrace::types(origin, a_is_expected, a, b);
             self.equate(a_is_expected, trace).tys(a, b).to_ures()
         })
     }
@@ -1118,6 +1090,17 @@ impl<'tcx> TypeTrace<'tcx> {
         self.origin.span()
     }
 
+    pub fn types(origin: TypeOrigin,
+                 a_is_expected: bool,
+                 a: Ty<'tcx>,
+                 b: Ty<'tcx>)
+                 -> TypeTrace<'tcx> {
+        TypeTrace {
+            origin: origin,
+            values: Types(expected_found(a_is_expected, a, b))
+        }
+    }
+
     pub fn dummy(tcx: &ty::ctxt<'tcx>) -> TypeTrace<'tcx> {
         TypeTrace {
             origin: Misc(codemap::DUMMY_SP),

src/librustc_typeck/check/callee.rs

@@ -21,6 +21,7 @@ use super::LvaluePreference;
 use super::method;
 use super::structurally_resolved_type;
 use super::TupleArgumentsFlag;
+use super::UnresolvedTypeAction;
 use super::write_call;
 
 use middle::infer;
@@ -77,6 +78,7 @@ pub fn check_call<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                   callee_expr.span,
                   original_callee_ty,
                   Some(callee_expr),
+                  UnresolvedTypeAction::Error,
                   LvaluePreference::NoPreference,
                   |adj_ty, idx| {
                       let autoderefref = ty::AutoDerefRef { autoderefs: idx, autoref: None };