add regression test for #48835

Fixes #48835.

The underlying issue was fixed in #51978.

src/test/ui/include-macros/mismatched-types.rs

@@ -0,0 +1,14 @@
+// Copyright 2018 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.
+
+fn main() {
+    let b: &[u8] = include_str!("file.txt");    //~ ERROR mismatched types
+    let s: &str = include_bytes!("file.txt");   //~ ERROR mismatched types
+}

src/test/ui/include-macros/mismatched-types.stderr

@@ -0,0 +1,21 @@
+error[E0308]: mismatched types
+  --> $DIR/mismatched-types.rs:12:20
+   |
+LL |     let b: &[u8] = include_str!("file.txt");    //~ ERROR mismatched types
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^ expected slice, found str
+   |
+   = note: expected type `&[u8]`
+              found type `&'static str`
+
+error[E0308]: mismatched types
+  --> $DIR/mismatched-types.rs:13:19
+   |
+LL |     let s: &str = include_bytes!("file.txt");   //~ ERROR mismatched types
+   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected str, found array of 0 elements
+   |
+   = note: expected type `&str`
+              found type `&'static [u8; 0]`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.