No fallback in `structurally_resolve_types`. Further refactoring.

Put all fallback in `apply_fallback_if_possible`.

src/librustc_typeck/check/cast.rs

@@ -393,7 +393,7 @@ fn trivial_cast_lint(&self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) {
 
     pub fn check(mut self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) {
         self.expr_ty = fcx.resolved_type(self.span, self.expr_ty);
-        self.cast_ty = fcx.resolved_type(self.span, self.cast_ty);
+        self.cast_ty = fcx.structurally_resolved_type(self.span, self.cast_ty);
 
         debug!("check_cast({}, {:?} as {:?})",
                self.expr.id,

src/librustc_typeck/check/mod.rs

@@ -2127,23 +2127,23 @@ fn resolve_generator_interiors(&self, def_id: DefId) {
         }
     }
 
-    fn apply_diverging_fallback_to_type(&self, ty: Ty<'tcx>) {
-        assert!(ty.is_ty_infer());
-        if self.type_var_diverges(ty) {
-            debug!("default_type_parameters: defaulting `{:?}` to `!` because it diverges", ty);
-            self.demand_eqtype(syntax_pos::DUMMY_SP, ty, self.tcx.mk_diverging_default());
-        }
-    }
-
-    fn apply_numeric_fallback_to_type(&self, ty: Ty<'tcx>) {
+    // Tries to apply a fallback to `ty` if it is an unsolved variable.
+    // Non-numerics get replaced with ! or () (depending on whether
+    // feature(never_type) is enabled), unconstrained ints with i32,
+    // unconstrained floats with f64.
+    // Defaulting inference variables becomes very dubious if we have
+    // encountered type-checking errors. In that case, fallback to TyError.
+    fn apply_fallback_if_possible(&self, ty: Ty<'tcx>) {
         use rustc::ty::error::UnconstrainedNumeric::Neither;
         use rustc::ty::error::UnconstrainedNumeric::{UnconstrainedInt, UnconstrainedFloat};
 
         assert!(ty.is_ty_infer());
         let fallback = match self.type_is_unconstrained_numeric(ty) {
+            _ if self.is_tainted_by_errors() => self.tcx().types.err,
             UnconstrainedInt => self.tcx.types.i32,
             UnconstrainedFloat => self.tcx.types.f64,
-            Neither => return,
+            Neither if self.type_var_diverges(ty) => self.tcx.mk_diverging_default(),
+            Neither => return
         };
         debug!("default_type_parameters: defaulting `{:?}` to `{:?}`", ty, fallback);
         self.demand_eqtype(syntax_pos::DUMMY_SP, ty, fallback);
@@ -2158,21 +2158,8 @@ fn select_all_obligations_or_error(&self) {
 
         self.select_obligations_where_possible();
 
-        // Apply fallbacks to unsolved variables.
-        // Non-numerics get replaced with ! or () (depending on whether
-        // feature(never_type) is enabled), unconstrained ints with i32,
-        // unconstrained floats with f64.
         for ty in &self.unsolved_variables() {
-            if self.is_tainted_by_errors() {
-                // Defaulting inference variables becomes very dubious if we have
-                // encountered type-checking errors. In that case,
-                // just resolve all uninstanted type variables to TyError.
-                debug!("default_type_parameters: defaulting `{:?}` to error", ty);
-                self.demand_eqtype(syntax_pos::DUMMY_SP, *ty, self.tcx().types.err);
-            } else {
-                self.apply_diverging_fallback_to_type(ty);
-                self.apply_numeric_fallback_to_type(ty);
-            }
+            self.apply_fallback_if_possible(ty);
         }
 
         let mut fulfillment_cx = self.fulfillment_cx.borrow_mut();
@@ -4942,18 +4929,11 @@ fn check_impl_trait(&self,
     // If no resolution is possible, then an error is reported.
     // Numeric inference variables may be left unresolved.
     pub fn structurally_resolved_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
-        let mut ty = self.resolve_type_vars_with_obligations(ty);
+        let ty = self.resolve_type_vars_with_obligations(ty);
         if !ty.is_ty_var() {
             ty
         } else {
-            // Try divering fallback.
-            self.apply_diverging_fallback_to_type(ty);
-            ty = self.resolve_type_vars_with_obligations(ty);
-            if !ty.is_ty_var() {
-                ty
-            } else { // Fallback failed, error.
-                self.must_be_known_in_context(sp, ty)
-            }
+            self.must_be_known_in_context(sp, ty)
         }
     }
 
@@ -4963,9 +4943,7 @@ pub fn resolved_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
         if !ty.is_ty_infer() {
             return ty;
         } else {
-            // Try diverging or numeric fallback.
-            self.apply_diverging_fallback_to_type(ty);
-            self.apply_numeric_fallback_to_type(ty);
+            self.apply_fallback_if_possible(ty);
             ty = self.resolve_type_vars_with_obligations(ty);
             if !ty.is_ty_infer() {
                 ty

src/test/ui/mismatched_types/issue-26480.rs → src/test/ui/mismatched_types/issue-26480-1.rs

@@ -7,6 +7,7 @@
 // <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.
+// compile-flags: --error-format=human
 
 extern {
     fn write(fildes: i32, buf: *const i8, nbyte: u64) -> i64;
@@ -28,12 +29,7 @@ fn size_of<T>(_: T) -> usize {
     }}
 }
 
-macro_rules! cast {
-    ($x:expr) => ($x as ()) //~ ERROR non-primitive cast
-}
-
 fn main() {
     let hello = ['H', 'e', 'y'];
     write!(hello);
-    cast!(2);
 }

src/test/ui/mismatched_types/issue-26480-1.stderr

+error[E0308]: mismatched types
+  --> $DIR/issue-26480-1.rs:27:19
+   |
+27 |                   $arr.len() * size_of($arr[0])); //~ ERROR mismatched types
+   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected u64, found usize
+...
+34 |     write!(hello);
+   |     -------------- in this macro invocation
+
+error: aborting due to previous error
+

src/test/ui/mismatched_types/issue-26480-2.rs

+// Copyright 2016 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.
+// compile-flags: --error-format=human
+
+macro_rules! cast {
+    ($x:expr) => ($x as ()) //~ ERROR non-primitive cast
+}
+
+fn main() {
+    cast!(2);
+}

src/test/ui/mismatched_types/issue-26480-2.stderr

+error[E0605]: non-primitive cast: `i32` as `()`
+  --> $DIR/issue-26480-2.rs:13:19
+   |
+13 |     ($x:expr) => ($x as ()) //~ ERROR non-primitive cast
+   |                   ^^^^^^^^
+...
+17 |     cast!(2);
+   |     --------- in this macro invocation
+   |
+   = note: an `as` expression can only be used to convert between primitive types. Consider using the `From` trait
+
+error: aborting due to previous error
+

src/test/ui/mismatched_types/issue-26480.stderr

@@ -7,16 +7,5 @@ error[E0308]: mismatched types
 37 |     write!(hello);
    |     -------------- in this macro invocation
 
-error[E0605]: non-primitive cast: `i32` as `()`
-  --> $DIR/issue-26480.rs:32:19
-   |
-32 |     ($x:expr) => ($x as ()) //~ ERROR non-primitive cast
-   |                   ^^^^^^^^
-...
-38 |     cast!(2);
-   |     --------- in this macro invocation
-   |
-   = note: an `as` expression can only be used to convert between primitive types. Consider using the `From` trait
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error