added a suggestion to create a const item if the fn in the array repeat expression is a const fn

src/test/ui/consts/const-blocks/fn-call-in-non-const.stderr

@@ -7,6 +7,7 @@ LL |     let _: [Option<Bar>; 2] = [no_copy(); 2];
    = help: the following implementations were found:
              <Option<T> as Copy>
    = note: the `Copy` trait is required because the repeated element will be copied
+   = help: create an inline `const` block, see PR #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
 
 error: aborting due to previous error
 

src/test/ui/consts/const-fn-in-vec.rs

@@ -0,0 +1,7 @@
+fn main() {
+    // should hint to create an inline const block
+    // as all tests are on "nightly"
+    let strings: [String; 5] = [String::new(); 5];
+    //~^ ERROR the trait bound `String: Copy` is not satisfied
+    println!("{:?}", strings);
+}

src/test/ui/consts/const-fn-in-vec.stderr

@@ -0,0 +1,12 @@
+error[E0277]: the trait bound `String: Copy` is not satisfied
+  --> $DIR/const-fn-in-vec.rs:4:32
+   |
+LL |     let strings: [String; 5] = [String::new(); 5];
+   |                                ^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `String`
+   |
+   = note: the `Copy` trait is required because the repeated element will be copied
+   = help: create an inline `const` block, see PR #2920 <https://github.com/rust-lang/rfcs/pull/2920> for more information
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.