No fallback in structurally_resolve_types. Further refactoring.

Put all fallback in `apply_fallback_if_possible`.

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 @@ macro_rules! write {
     }}
 }
 
-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

@@ -0,0 +1,11 @@
+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

@@ -0,0 +1,18 @@
+// 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

@@ -0,0 +1,13 @@
+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