Auto merge of #48270 - leodasvacas:refactor-casts, r=<try>

Replace `structurally_resolved_type` in casts check.

The behaviour of `resolve_type_vars_if_possible` is simpler and infallible. Other minor refactorings.

I'm not sure if this is backwards compatible, in theory resolving obligations between two cast checks could solve a dependency between them, but I don't know if that's actually possible and it doesn't sound like something we'd want to support.

Author: bors

src/librustc/ty/cast.rs

@@ -20,7 +20,6 @@ use syntax::ast;
 pub enum IntTy {
     U(ast::UintTy),
     I,
-    Ivar,
     CEnum,
     Bool,
     Char
@@ -64,7 +63,7 @@ impl<'tcx> CastTy<'tcx> {
             ty::TyBool => Some(CastTy::Int(IntTy::Bool)),
             ty::TyChar => Some(CastTy::Int(IntTy::Char)),
             ty::TyInt(_) => Some(CastTy::Int(IntTy::I)),
-            ty::TyInfer(ty::InferTy::IntVar(_)) => Some(CastTy::Int(IntTy::Ivar)),
+            ty::TyInfer(ty::InferTy::IntVar(_)) => Some(CastTy::Int(IntTy::I)),
             ty::TyInfer(ty::InferTy::FloatVar(_)) => Some(CastTy::Float),
             ty::TyUint(u) => Some(CastTy::Int(IntTy::U(u))),
             ty::TyFloat(_) => Some(CastTy::Float),

src/librustc_typeck/check/cast.rs

@@ -392,8 +392,8 @@ impl<'a, 'gcx, 'tcx> CastCheck<'tcx> {
     }
 
     pub fn check(mut self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) {
-        self.expr_ty = fcx.structurally_resolved_type(self.span, self.expr_ty);
-        self.cast_ty = fcx.structurally_resolved_type(self.span, self.cast_ty);
+        self.expr_ty = fcx.resolve_type_vars_if_possible(&self.expr_ty);
+        self.cast_ty = fcx.resolve_type_vars_if_possible(&self.cast_ty);
 
         debug!("check_cast({}, {:?} as {:?})",
                self.expr.id,
@@ -488,11 +488,7 @@ impl<'a, 'gcx, 'tcx> CastCheck<'tcx> {
                     ty::TypeVariants::TyInfer(t) => {
                         match t {
                             ty::InferTy::IntVar(_) |
-                            ty::InferTy::FloatVar(_) |
-                            ty::InferTy::FreshIntTy(_) |
-                            ty::InferTy::FreshFloatTy(_) => {
-                                Err(CastError::NeedDeref)
-                            }
+                            ty::InferTy::FloatVar(_) => Err(CastError::NeedDeref),
                             _ => Err(CastError::NeedViaPtr),
                         }
                     }