Recover from invalid `struct` item syntax

Parse unsupported "default field const values":

```rust
struct S {
    field: Type = const_val,
}
```

Recover from small `:` typo and provide suggestion:

```rust
struct S {
    field; Type,
    field2= Type,
}
```

3 files changed, 162 insertions, 0 deletions

diff --git a/src/test/ui/parser/struct-default-values-and-missing-field-separator.fixed b/src/test/ui/parser/struct-default-values-and-missing-field-separator.fixed
new file mode 100644
index 00000000000..28191b82621
--- /dev/null
+++ b/src/test/ui/parser/struct-default-values-and-missing-field-separator.fixed
@@ -0,0 +1,35 @@
+// run-rustfix
+#![allow(dead_code)]
+
+enum E {
+    A,
+}
+
+struct S {
+    field1: i32, //~ ERROR default values on `struct` fields aren't supported
+    field2: E, //~ ERROR default values on `struct` fields aren't supported
+    field3: i32, //~ ERROR default values on `struct` fields aren't supported
+    field4: i32, //~ ERROR default values on `struct` fields aren't supported
+    field5: E, //~ ERROR default values on `struct` fields aren't supported
+    field6: E, //~ ERROR default values on `struct` fields aren't supported
+}
+
+struct S1 {
+    field1: i32, //~ ERROR expected `,`, or `}`, found `field2`
+    field2: E, //~ ERROR expected `,`, or `}`, found `field3`
+    field3: i32, //~ ERROR default values on `struct` fields aren't supported
+    field4: i32, //~ ERROR default values on `struct` fields aren't supported
+    field5: E, //~ ERROR default values on `struct` fields aren't supported
+    field6: E, //~ ERROR default values on `struct` fields aren't supported
+}
+
+struct S2 {
+    field1 : i32, //~ ERROR expected `:`, found `=`
+    field2: E, //~ ERROR expected `:`, found `;`
+}
+
+const fn foo(_: i32) -> E {
+    E::A
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/struct-default-values-and-missing-field-separator.rs b/src/test/ui/parser/struct-default-values-and-missing-field-separator.rs
new file mode 100644
index 00000000000..924cb08a990
--- /dev/null
+++ b/src/test/ui/parser/struct-default-values-and-missing-field-separator.rs
@@ -0,0 +1,35 @@
+// run-rustfix
+#![allow(dead_code)]
+
+enum E {
+    A,
+}
+
+struct S {
+    field1: i32 = 42, //~ ERROR default values on `struct` fields aren't supported
+    field2: E = E::A, //~ ERROR default values on `struct` fields aren't supported
+    field3: i32 = 1 + 2, //~ ERROR default values on `struct` fields aren't supported
+    field4: i32 = { 1 + 2 }, //~ ERROR default values on `struct` fields aren't supported
+    field5: E = foo(42), //~ ERROR default values on `struct` fields aren't supported
+    field6: E = { foo(42) }, //~ ERROR default values on `struct` fields aren't supported
+}
+
+struct S1 {
+    field1: i32 //~ ERROR expected `,`, or `}`, found `field2`
+    field2: E //~ ERROR expected `,`, or `}`, found `field3`
+    field3: i32 = 1 + 2, //~ ERROR default values on `struct` fields aren't supported
+    field4: i32 = { 1 + 2 }, //~ ERROR default values on `struct` fields aren't supported
+    field5: E = foo(42), //~ ERROR default values on `struct` fields aren't supported
+    field6: E = { foo(42) }, //~ ERROR default values on `struct` fields aren't supported
+}
+
+struct S2 {
+    field1 = i32, //~ ERROR expected `:`, found `=`
+    field2; E, //~ ERROR expected `:`, found `;`
+}
+
+const fn foo(_: i32) -> E {
+    E::A
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/struct-default-values-and-missing-field-separator.stderr b/src/test/ui/parser/struct-default-values-and-missing-field-separator.stderr
new file mode 100644
index 00000000000..7f16ebcfc3a
--- /dev/null
+++ b/src/test/ui/parser/struct-default-values-and-missing-field-separator.stderr
@@ -0,0 +1,92 @@
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:9:16
+   |
+LL |     field1: i32 = 42,
+   |                ^^^^^ help: remove this unsupported default value
+
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:10:14
+   |
+LL |     field2: E = E::A,
+   |              ^^^^^^^ help: remove this unsupported default value
+
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:11:16
+   |
+LL |     field3: i32 = 1 + 2,
+   |                ^^^^^^^^ help: remove this unsupported default value
+
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:12:16
+   |
+LL |     field4: i32 = { 1 + 2 },
+   |                ^^^^^^^^^^^^ help: remove this unsupported default value
+
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:13:14
+   |
+LL |     field5: E = foo(42),
+   |              ^^^^^^^^^^ help: remove this unsupported default value
+
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:14:14
+   |
+LL |     field6: E = { foo(42) },
+   |              ^^^^^^^^^^^^^^ help: remove this unsupported default value
+
+error: expected `,`, or `}`, found `field2`
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:18:16
+   |
+LL |     field1: i32
+   |                ^ help: try adding a comma: `,`
+
+error: expected `,`, or `}`, found `field3`
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:19:14
+   |
+LL |     field2: E
+   |              ^ help: try adding a comma: `,`
+
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:20:16
+   |
+LL |     field3: i32 = 1 + 2,
+   |                ^^^^^^^^ help: remove this unsupported default value
+
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:21:16
+   |
+LL |     field4: i32 = { 1 + 2 },
+   |                ^^^^^^^^^^^^ help: remove this unsupported default value
+
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:22:14
+   |
+LL |     field5: E = foo(42),
+   |              ^^^^^^^^^^ help: remove this unsupported default value
+
+error: default values on `struct` fields aren't supported
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:23:14
+   |
+LL |     field6: E = { foo(42) },
+   |              ^^^^^^^^^^^^^^ help: remove this unsupported default value
+
+error: expected `:`, found `=`
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:27:12
+   |
+LL |     field1 = i32,
+   |            ^
+   |            |
+   |            expected `:`
+   |            help: field names and their types are separated with `:`
+
+error: expected `:`, found `;`
+  --> $DIR/struct-default-values-and-missing-field-separator.rs:28:11
+   |
+LL |     field2; E,
+   |           ^
+   |           |
+   |           expected `:`
+   |           help: field names and their types are separated with `:`
+
+error: aborting due to 14 previous errors
+