type t = {foo: unit [@a]}

type t = {foo: < .. > [@a] }

The extra space after [@a] in the second case is added to avoid outputting >} which is a keyword. However, it's not necessary to add the protecting space if the object type has an annotation, as is the case here.

The same is also true of:

• inline record types in variants
• polymorphic variants (the token >] has the same problem)
• class parameter lists (weird, since parentheses are added in this case)

type t = A of {foo: unit [@a]}

type t = A of {foo: < .. > [@a] }

type t = [`Foo of unit]

type t = [`Foo of < .. >[@a] ]

let _ =
  object
    inherit [b, unit] foo

    inherit [b, (< f: unit >[@a]) ] foo
  end