Avoiding extra linebreaks when doc-comment added to enum

I've noticed what I consider to be an unfortunate decision in rustfmt: the moment a single doc-comment is added in an enum, the whole enum is laid out with a line per field, even when no fields are documented.

That is, the type:

enum MyType {
    A { field1: bool, field2: bool },
    B { field1: bool, field2: bool },
    /// OMG a comment
    C { field1: bool, field2: bool },
    D { field1: bool, field2: bool },
}

becomes

enum MyType {
    A {
        field1: bool,
        field2: bool,
    },
    B {
        field1: bool,
        field2: bool,
    },
    /// OMG a comment
    C {
        field1: bool,
        field2: bool,
    },
    D {
        field1: bool,
        field2: bool,
    },
}

The formatting policy I would like would leave the type unchanged. If a doc-comment is added to a single field of a variant, then only that variant should be broken up on multiple lines rather than the whole type.

is this something that could potentially be customizable as an option in rustfmt.toml? If so, I would be happy to implement this if someone can point be in the right direction.

Start by locating rustfmt’s enum-formatting logic and related formatting tests; the issue provides the enum example and desired output. Check whether the behavior belongs in a rustfmt.toml option or should be the default, then run the formatter tests. Done means coverage showing that a comment on one variant does not expand unrelated variants, while a documented field still expands its own variant.