Recent work on javac diagnostics have underlined the need for better diagnostics; the diagnostics to be improved, esp. those regarding the type-system area of the compiler, would hugely benefit from some kind of multiline/tabular support.

Examples:

1) Type-system diagnostic:

Test.java:3: method test in class Foo<T #0> cannot be applied to given types
   required: T #0
   found: T #1
      where T #0,T #1 are typevariables:
          T #0 extends String
              (declared in class Foo)
          T #1 extends Integer
              (declared in method <T>foo(T))
1 error

2) Method resolution diagnostics

Test.java:6: no suitable method m found for (String,String)
    method: <T>m(T,T) in Test
      (inferred type argument(s) String do not conform to bounds of type variable(s) T)
    method: m(Integer) in Test
1 error

All the above diagnostics suggests the need of a more structured way of representing the contents of a diagnostic sub-elements. In both examples we have that the diagnostic is composed of subparts (where clause in the first case, list of unapplicable method in the second case) that should displayed with the correct amount of indentation. This requires some sort of basic multiline support at the level of the javac diagnostic system.