typeck: Support multiple expressions getting coerced at the same type.

src/librustc_typeck/check/callee.rs

@@ -82,7 +82,7 @@ pub fn check_call<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
         autoderef(fcx,
                   callee_expr.span,
                   original_callee_ty,
-                  Some(callee_expr),
+                  || Some(callee_expr),
                   UnresolvedTypeAction::Error,
                   LvaluePreference::NoPreference,
                   |adj_ty, idx| {

src/librustc_typeck/check/coercion.rs

@@ -87,6 +87,14 @@ struct Coerce<'a, 'tcx: 'a> {
 type CoerceResult<'tcx> = RelateResult<'tcx, Option<AutoAdjustment<'tcx>>>;
 
 impl<'f, 'tcx> Coerce<'f, 'tcx> {
+    fn new(fcx: &'a FnCtxt<'a, 'tcx>, origin: TypeOrigin) -> Self {
+        Coerce {
+            fcx: fcx,
+            origin: origin,
+            unsizing_obligations: RefCell::new(vec![])
+        }
+    }
+
     fn tcx(&self) -> &TyCtxt<'tcx> {
         self.fcx.tcx()
     }
@@ -96,16 +104,17 @@ fn subtype(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
         Ok(None) // No coercion required.
     }
 
-    fn coerce(&self,
-              expr_a: &hir::Expr,
+    fn coerce<'a, E, I>(&self,
+                        exprs: &E,
                         a: Ty<'tcx>,
                         b: Ty<'tcx>)
-              -> CoerceResult<'tcx> {
-        debug!("Coerce.tys({:?} => {:?})",
-               a,
-               b);
+                        -> CoerceResult<'tcx>
+        // FIXME(eddyb) use copyable iterators when that becomes ergonomic.
+        where E: Fn() -> I,
+              I: IntoIterator<Item=&'a hir::Expr> {
 
         let a = self.fcx.infcx().shallow_resolve(a);
+        debug!("Coerce.tys({:?} => {:?})", a, b);
 
         // Just ignore error types.
         if a.references_error() || b.references_error() {
@@ -156,15 +165,18 @@ fn coerce(&self,
     /// Reborrows `&mut A` to `&mut B` and `&(mut) A` to `&B`.
     /// To match `A` with `B`, autoderef will be performed,
     /// calling `deref`/`deref_mut` where necessary.
-    fn coerce_borrowed_pointer(&self,
-                               expr_a: &hir::Expr,
+    fn coerce_borrowed_pointer<'a, E, I>(&self,
+                                         span: Span,
+                                         exprs: &E,
                                          a: Ty<'tcx>,
                                          b: Ty<'tcx>,
                                          mutbl_b: hir::Mutability)
-                               -> CoerceResult<'tcx> {
-        debug!("coerce_borrowed_pointer(a={:?}, b={:?})",
-               a,
-               b);
+                                         -> CoerceResult<'tcx>
+        // FIXME(eddyb) use copyable iterators when that becomes ergonomic.
+        where E: Fn() -> I,
+              I: IntoIterator<Item=&'a hir::Expr> {
+
+        debug!("coerce_borrowed_pointer(a={:?}, b={:?})", a, b);
 
         // If we have a parameter of type `&M T_a` and the value
         // provided is `expr`, we will be adding an implicit borrow,
@@ -179,17 +191,15 @@ fn coerce_borrowed_pointer(&self,
             _ => return self.subtype(a, b)
         }
 
-        let coercion = Coercion(self.origin.span());
+        let span = self.origin.span();
+        let coercion = Coercion(span);
         let r_borrow = self.fcx.infcx().next_region_var(coercion);
         let r_borrow = self.tcx().mk_region(r_borrow);
         let autoref = Some(AutoPtr(r_borrow, mutbl_b));
 
         let lvalue_pref = LvaluePreference::from_mutbl(mutbl_b);
         let mut first_error = None;
-        let (_, autoderefs, success) = autoderef(self.fcx,
-                                                 expr_a.span,
-                                                 a,
-                                                 Some(expr_a),
+        let (_, autoderefs, success) = autoderef(self.fcx, span, a, exprs,
                                                  UnresolvedTypeAction::Ignore,
                                                  lvalue_pref,
                                                  |inner_ty, autoderef| {
@@ -323,9 +333,7 @@ fn coerce_unsized(&self,
             }
         }
 
-        let mut obligations = self.unsizing_obligations.borrow_mut();
-        assert!(obligations.is_empty());
-        *obligations = leftover_predicates;
+        *self.unsizing_obligations.borrow_mut() = leftover_predicates;
 
         let adjustment = AutoDerefRef {
             autoderefs: if reborrow.is_some() { 1 } else { 0 },
@@ -425,39 +433,48 @@ fn coerce_unsafe_ptr(&self,
     }
 }
 
-pub fn try<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
-                     expr: &hir::Expr,
+fn apply<'a, 'b, 'tcx, E, I>(coerce: &mut Coerce<'a, 'tcx>,
+                             exprs: &E,
                              a: Ty<'tcx>,
                              b: Ty<'tcx>)
-                     -> RelateResult<'tcx, ()> {
-    debug!("coercion::try({:?} -> {:?})", a, b);
-    let mut unsizing_obligations = vec![];
-    let adjustment = try!(indent(|| {
-        fcx.infcx().commit_if_ok(|_| {
-            let coerce = Coerce {
-                fcx: fcx,
-                origin: TypeOrigin::ExprAssignable(expr.span),
-                unsizing_obligations: RefCell::new(vec![])
-            };
-            let adjustment = try!(coerce.coerce(expr, a, b));
-            unsizing_obligations = coerce.unsizing_obligations.into_inner();
-            Ok(adjustment)
-        })
-    }));
+                             -> RelateResult<'tcx, Ty<'tcx>>
+    where E: Fn() -> I,
+          I: IntoIterator<Item=&'b hir::Expr> {
+
+    let (ty, adjustment) = try!(indent(|| coerce.coerce(exprs, a, b)));
 
-    if let Some(AdjustDerefRef(auto)) = adjustment {
+    let fcx = coerce.fcx;
+    if let AdjustDerefRef(auto) = adjustment {
         if auto.unsize.is_some() {
-            for obligation in unsizing_obligations {
+            for obligation in coerce.unsizing_obligations.borrow_mut().drain() {
                 fcx.register_predicate(obligation);
             }
         }
     }
 
-    if let Some(adjustment) = adjustment {
+    if !adjustment.is_identity() {
         debug!("Success, coerced with {:?}", adjustment);
+        for expr in exprs() {
+            assert!(!fcx.inh.tables.borrow().adjustments.contains(&expr.id));
             fcx.write_adjustment(expr.id, adjustment);
         }
-    Ok(())
+    }
+    Ok(ty)
+}
+
+/// Attempt to coerce an expression from a type (a) to another type (b).
+/// Adjustments are only recorded if the coercion was successful.
+/// The expressions *must not* have any pre-existing adjustments.
+pub fn try<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
+                     expr: &hir::Expr,
+                     a: Ty<'tcx>,
+                     b: Ty<'tcx>)
+                     -> RelateResult<'tcx, ()> {
+    debug!("coercion::try({:?} -> {:?})", a, b);
+    let mut coerce = Coerce::new(fcx, TypeOrigin::ExprAssignable(expr.span));
+    fcx.infcx().commit_if_ok(|_| {
+        apply(&mut coerce, &|| Some(expr), a, b)
+    }).map(|_| ())
 }
 
 fn coerce_mutbls<'tcx>(from_mutbl: hir::Mutability,

src/librustc_typeck/check/method/confirm.rs

@@ -158,7 +158,7 @@ fn adjust_self_ty(&mut self,
         let (autoderefd_ty, n, result) = check::autoderef(self.fcx,
                                                           self.span,
                                                           unadjusted_self_ty,
-                                                          Some(self.self_expr),
+                                                          || Some(self.self_expr),
                                                           UnresolvedTypeAction::Error,
                                                           NoPreference,
                                                           |_, n| {
@@ -287,7 +287,7 @@ fn extract_trait_ref<R, F>(&mut self, self_ty: Ty<'tcx>, mut closure: F) -> R wh
         let (_, _, result) = check::autoderef(self.fcx,
                                               self.span,
                                               self_ty,
-                                              None,
+                                              || None,
                                               UnresolvedTypeAction::Error,
                                               NoPreference,
                                               |ty, _| {
@@ -509,7 +509,7 @@ fn fixup_derefs_on_method_receiver_if_necessary(&self,
                 check::autoderef(self.fcx,
                                  expr.span,
                                  self.fcx.expr_ty(expr),
-                                 Some(expr),
+                                 || Some(expr),
                                  UnresolvedTypeAction::Error,
                                  PreferMutLvalue,
                                  |_, autoderefs| {
@@ -522,7 +522,9 @@ fn fixup_derefs_on_method_receiver_if_necessary(&self,
             }
 
             // Don't retry the first one or we might infinite loop!
-            if i != 0 {
+            if i == 0 {
+                continue;
+            }
             match expr.node {
                 hir::ExprIndex(ref base_expr, ref index_expr) => {
                     // If this is an overloaded index, the
@@ -597,20 +599,20 @@ fn fixup_derefs_on_method_receiver_if_necessary(&self,
                     // a preference for mut
                     let method_call = ty::MethodCall::expr(expr.id);
                     if self.fcx.inh.tables.borrow().method_map.contains_key(&method_call) {
-                            check::try_overloaded_deref(
+                        let method = check::try_overloaded_deref(
                             self.fcx,
                             expr.span,
-                                Some(method_call),
                             Some(&base_expr),
                             self.fcx.expr_ty(&base_expr),
                             PreferMutLvalue);
+                        let method = method.expect("re-trying deref failed");
+                        self.fcx.inh.tables.borrow_mut().method_map.insert(method_call, method);
                     }
                 }
                 _ => {}
             }
         }
     }
-    }
 
     ///////////////////////////////////////////////////////////////////////////
     // MISCELLANY

src/librustc_typeck/check/method/probe.rs

@@ -200,7 +200,7 @@ fn create_steps<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     let (final_ty, dereferences, _) = check::autoderef(fcx,
                                                        span,
                                                        self_ty,
-                                                       None,
+                                                       || None,
                                                        UnresolvedTypeAction::Error,
                                                        NoPreference,
                                                        |t, d| {

src/librustc_typeck/check/method/suggest.rs

@@ -351,7 +351,7 @@ fn is_local(ty: Ty) -> bool {
         return is_local(fcx.resolve_type_vars_if_possible(rcvr_ty));
     }
 
-    check::autoderef(fcx, span, rcvr_ty, None,
+    check::autoderef(fcx, span, rcvr_ty, || None,
                      check::UnresolvedTypeAction::Ignore, ty::NoPreference,
                      |ty, _| {
         if is_local(ty) {

src/librustc_typeck/check/mod.rs

@@ -2053,20 +2053,21 @@ pub enum UnresolvedTypeAction {
 ///
 /// Note: this method does not modify the adjustments table. The caller is responsible for
 /// inserting an AutoAdjustment record into the `fcx` using one of the suitable methods.
-pub fn autoderef<'a, 'tcx, T, F>(fcx: &FnCtxt<'a, 'tcx>,
+pub fn autoderef<'a, 'b, 'tcx, E, I, T, F>(fcx: &FnCtxt<'a, 'tcx>,
                                            sp: Span,
                                            base_ty: Ty<'tcx>,
-                                 opt_expr: Option<&hir::Expr>,
+                                           maybe_exprs: E,
                                            unresolved_type_action: UnresolvedTypeAction,
                                            mut lvalue_pref: LvaluePreference,
                                            mut should_stop: F)
                                            -> (Ty<'tcx>, usize, Option<T>)
-    where F: FnMut(Ty<'tcx>, usize) -> Option<T>,
+    // FIXME(eddyb) use copyable iterators when that becomes ergonomic.
+    where E: Fn() -> I,
+          I: IntoIterator<Item=&'b hir::Expr>,
+          F: FnMut(Ty<'tcx>, usize) -> Option<T>,
 {
-    debug!("autoderef(base_ty={:?}, opt_expr={:?}, lvalue_pref={:?})",
-           base_ty,
-           opt_expr,
-           lvalue_pref);
+    debug!("autoderef(base_ty={:?}, lvalue_pref={:?})",
+           base_ty, lvalue_pref);
 
     let mut t = base_ty;
     for autoderefs in 0..fcx.tcx().sess.recursion_limit.get() {
@@ -2092,11 +2093,6 @@ pub fn autoderef<'a, 'tcx, T, F>(fcx: &FnCtxt<'a, 'tcx>,
         }
 
         // Otherwise, deref if type is derefable:
-        let mt = match resolved_t.builtin_deref(false, lvalue_pref) {
-            Some(mt) => Some(mt),
-            None => {
-                let method_call =
-                    opt_expr.map(|expr| MethodCall::autoderef(expr.id, autoderefs as u32));
 
         // Super subtle: it might seem as though we should
         // pass `opt_expr` to `try_overloaded_deref`, so that
@@ -2109,19 +2105,24 @@ pub fn autoderef<'a, 'tcx, T, F>(fcx: &FnCtxt<'a, 'tcx>,
         // when they encounter an overloaded autoderef, have
         // to do some reconstructive surgery. This is a pretty
         // complex mess that is begging for a proper MIR.
-                try_overloaded_deref(fcx, sp, method_call, None, resolved_t, lvalue_pref)
+        let mt = if let Some(mt) = resolved_t.builtin_deref(false, lvalue_pref) {
+            mt
+        } else if let Some(method) = try_overloaded_deref(fcx, sp, None,
+                                                          resolved_t, lvalue_pref) {
+            for expr in maybe_exprs() {
+                let method_call = MethodCall::autoderef(expr.id, autoderefs as u32);
+                fcx.inh.tables.borrow_mut().method_map.insert(method_call, method);
             }
+            make_overloaded_lvalue_return_type(fcx.tcx(), method)
+        } else {
+            return (resolved_t, autoderefs, None);
         };
-        match mt {
-            Some(mt) => {
+
         t = mt.ty;
         if mt.mutbl == hir::MutImmutable {
             lvalue_pref = NoPreference;
         }
     }
-            None => return (resolved_t, autoderefs, None)
-        }
-    }
 
     // We've reached the recursion limit, error gracefully.
     span_err!(fcx.tcx().sess, sp, E0055,
@@ -2132,11 +2133,10 @@ pub fn autoderef<'a, 'tcx, T, F>(fcx: &FnCtxt<'a, 'tcx>,
 
 fn try_overloaded_deref<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                                   span: Span,
-                                  method_call: Option<MethodCall>,
                                   base_expr: Option<&hir::Expr>,
                                   base_ty: Ty<'tcx>,
                                   lvalue_pref: LvaluePreference)
-                                  -> Option<ty::TypeAndMut<'tcx>>
+                                  -> Option<MethodCallee<'tcx>>
 {
     // Try DerefMut first, if preferred.
     let method = match (lvalue_pref, fcx.tcx().lang_items.deref_mut_trait()) {
@@ -2158,33 +2158,23 @@ fn try_overloaded_deref<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
         (method, _) => method
     };
 
-    make_overloaded_lvalue_return_type(fcx, method_call, method)
+    method
 }
 
 /// For the overloaded lvalue expressions (`*x`, `x[3]`), the trait returns a type of `&T`, but the
 /// actual type we assign to the *expression* is `T`. So this function just peels off the return
-/// type by one layer to yield `T`. It also inserts the `method-callee` into the method map.
-fn make_overloaded_lvalue_return_type<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
-                                                method_call: Option<MethodCall>,
-                                                method: Option<MethodCallee<'tcx>>)
-                                                -> Option<ty::TypeAndMut<'tcx>>
+/// type by one layer to yield `T`.
+fn make_overloaded_lvalue_return_type<'tcx>(tcx: &ty::ctxt<'tcx>,
+                                            method: MethodCallee<'tcx>)
+                                            -> ty::TypeAndMut<'tcx>
 {
-    match method {
-        Some(method) => {
     // extract method return type, which will be &T;
     // all LB regions should have been instantiated during method lookup
     let ret_ty = method.ty.fn_ret();
-            let ret_ty = fcx.tcx().no_late_bound_regions(&ret_ty).unwrap().unwrap();
-
-            if let Some(method_call) = method_call {
-                fcx.inh.tables.borrow_mut().method_map.insert(method_call, method);
-            }
+    let ret_ty = tcx.no_late_bound_regions(&ret_ty).unwrap().unwrap();
 
     // method returns &T, but the type as visible to user is T, so deref
-            ret_ty.builtin_deref(true, NoPreference)
-        }
-        None => None,
-    }
+    ret_ty.builtin_deref(true, NoPreference).unwrap()
 }
 
 fn lookup_indexing<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
@@ -2202,7 +2192,7 @@ fn lookup_indexing<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     let (ty, autoderefs, final_mt) = autoderef(fcx,
                                                base_expr.span,
                                                base_ty,
-                                               Some(base_expr),
+                                               || Some(base_expr),
                                                UnresolvedTypeAction::Error,
                                                lvalue_pref,
                                                |adj_ty, idx| {
@@ -2299,10 +2289,10 @@ fn try_index_step<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     // If some lookup succeeds, write callee into table and extract index/element
     // type from the method signature.
     // If some lookup succeeded, install method in table
-    method.and_then(|method| {
+    method.map(|method| {
         debug!("try_index_step: success, using overloaded indexing");
-        make_overloaded_lvalue_return_type(fcx, Some(method_call), Some(method)).
-            map(|ret| (input_ty, ret.ty))
+        fcx.inh.tables.borrow_mut().method_map.insert(method_call, method);
+        (input_ty, make_overloaded_lvalue_return_type(fcx.tcx(), method).ty)
     })
 }
 
@@ -2907,7 +2897,7 @@ fn check_field<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
         let (_, autoderefs, field_ty) = autoderef(fcx,
                                                   expr.span,
                                                   expr_t,
-                                                  Some(base),
+                                                  || Some(base),
                                                   UnresolvedTypeAction::Error,
                                                   lvalue_pref,
                                                   |base_t, _| {
@@ -3005,7 +2995,7 @@ fn check_tup_field<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
         let (_, autoderefs, field_ty) = autoderef(fcx,
                                                   expr.span,
                                                   expr_t,
-                                                  Some(base),
+                                                  || Some(base),
                                                   UnresolvedTypeAction::Error,
                                                   lvalue_pref,
                                                   |base_t, _| {
@@ -3253,22 +3243,22 @@ fn check_expr_struct<'a, 'tcx>(fcx: &FnCtxt<'a,'tcx>,
             match unop {
                 hir::UnDeref => {
                     oprnd_t = structurally_resolved_type(fcx, expr.span, oprnd_t);
-                    oprnd_t = match oprnd_t.builtin_deref(true, NoPreference) {
-                        Some(mt) => mt.ty,
-                        None => match try_overloaded_deref(fcx, expr.span,
-                                                           Some(MethodCall::expr(expr.id)),
-                                                           Some(&oprnd), oprnd_t, lvalue_pref) {
-                            Some(mt) => mt.ty,
-                            None => {
+
+                    if let Some(mt) = oprnd_t.builtin_deref(true, NoPreference) {
+                        oprnd_t = mt.ty;
+                    } else if let Some(method) = try_overloaded_deref(
+                            fcx, expr.span, Some(&oprnd), oprnd_t, lvalue_pref) {
+                        oprnd_t = make_overloaded_lvalue_return_type(tcx, method).ty;
+                        fcx.inh.tables.borrow_mut().method_map.insert(MethodCall::expr(expr.id),
+                                                                      method);
+                    } else {
                         fcx.type_error_message(expr.span, |actual| {
                             format!("type `{}` cannot be \
                                     dereferenced", actual)
                         }, oprnd_t, None);
-                                tcx.types.err
+                        oprnd_t = tcx.types.err;
                     }
                 }
-                    };
-                }
                 hir::UnNot => {
                     oprnd_t = structurally_resolved_type(fcx, oprnd.span,
                                                          oprnd_t);