fixes #4115, #4029, #3898

[ahl]

Fixes #4115. Fixes #4029. Fixes #3898.

The new tests fail on master as follows:

Mismatch at tests/target/issue-4115.rs:1:
-#[derive(
-    A,
-    B,
-    C,
-    D,
-    // E,
-)]
+#[derive(A, B, C, D)]
 fn foo() {}

Mismatch at tests/target/issue-4029.rs:1:
 // issue #4029
-#[derive(Debug, Clone, Default Hash)]
+#[derive()]
 struct S;
 
 // issue #3898

Mismatch at tests/target/issue-4029.rs:6:
-#[derive(Debug, Clone, Default,, Hash)]
+#[derive()]
 struct T;

They (and all other tests) pass with the proposed fix.

At the root of all three issues is the use of ast::Attribute:: meta_item_list() which returns None if the derive is malformed. In addition no affordance was made for comments interspersed with derive components. This fix checks for errors from meta_item_list() and leans on existing mechanisms to deal with comments.

---

Although I handled this case, I would appreciate review feedback for the case where a derive doesn't fit quite fit on a single line and is formatted like this:

#[derive(this, would, be, too, long, for, a single, line, lets, say)]
// so you get this:
#[derive(
    this, would, be, too, long, for, a single, line, lets, say,
)]

To handle that case I use Always for the trailing separator with ListFormatting and then remove that final character if it all does fit on one line. I couldn't find an existing mechanism in ListFormatting that did what I wanted there.

See lines 143 and 177.

[topecongiro]

Awesome! LGTM, thank you!

---

Although I handled this case, I would appreciate review feedback for the case where a derive doesn't fit quite fit on a single line and is formatted like this:

I think we could use overflow::rewrite_with_parens for this with some refactoring, though I am not confident.

[karyon]

Backported in #4564