Add union with default field values case test

In particular, there should be no additional errors (default field
values for `union` fields are currently erroneously accepted).

Author: jieyouxu

tests/ui/structs/default-field-values/failures.rs

@@ -49,6 +49,12 @@ enum E {
     Variant {} //~ ERROR the `#[default]` attribute may only be used on unit enum variants
 }
 
+union U
+{
+    x: i32 = 1,
+    y: f32 = 2.,
+}
+
 fn main () {
     let _ = Foo { .. }; // ok
     let _ = Foo::default(); // ok

tests/ui/structs/default-field-values/failures.stderr

@@ -28,19 +28,19 @@ LL | pub struct S;
    |
 
 error: missing field `bar` in initializer
-  --> $DIR/failures.rs:55:19
+  --> $DIR/failures.rs:61:19
    |
 LL |     let _ = Bar { .. };
    |                   ^ fields that do not have a defaulted value must be provided explicitly
 
 error: missing field `bar` in initializer
-  --> $DIR/failures.rs:56:27
+  --> $DIR/failures.rs:62:27
    |
 LL |     let _ = Bar { baz: 0, .. };
    |                           ^ fields that do not have a defaulted value must be provided explicitly
 
 error[E0308]: mismatched types
-  --> $DIR/failures.rs:60:17
+  --> $DIR/failures.rs:66:17
    |
 LL |     let _ = Rak(..);
    |             --- ^^ expected `i32`, found `RangeFull`
@@ -53,19 +53,19 @@ note: tuple struct defined here
 LL | pub struct Rak(i32 = 42);
    |            ^^^
 help: you might have meant to use `..` to skip providing a value for expected fields, but this is only supported on non-tuple struct literals; it is instead interpreted as a `std::ops::RangeFull` literal
-  --> $DIR/failures.rs:60:17
+  --> $DIR/failures.rs:66:17
    |
 LL |     let _ = Rak(..);
    |                 ^^
 
 error[E0061]: this struct takes 1 argument but 2 arguments were supplied
-  --> $DIR/failures.rs:62:13
+  --> $DIR/failures.rs:68:13
    |
 LL |     let _ = Rak(0, ..);
    |             ^^^    -- unexpected argument #2 of type `RangeFull`
    |
 help: you might have meant to use `..` to skip providing a value for expected fields, but this is only supported on non-tuple struct literals; it is instead interpreted as a `std::ops::RangeFull` literal
-  --> $DIR/failures.rs:62:20
+  --> $DIR/failures.rs:68:20
    |
 LL |     let _ = Rak(0, ..);
    |                    ^^
@@ -81,13 +81,13 @@ LL +     let _ = Rak(0);
    |
 
 error[E0061]: this struct takes 1 argument but 2 arguments were supplied
-  --> $DIR/failures.rs:64:13
+  --> $DIR/failures.rs:70:13
    |
 LL |     let _ = Rak(.., 0);
    |             ^^^ -- unexpected argument #1 of type `RangeFull`
    |
 help: you might have meant to use `..` to skip providing a value for expected fields, but this is only supported on non-tuple struct literals; it is instead interpreted as a `std::ops::RangeFull` literal
-  --> $DIR/failures.rs:64:17
+  --> $DIR/failures.rs:70:17
    |
 LL |     let _ = Rak(.., 0);
    |                 ^^