bug#259: delphi-mode does not properly format interface definitions

[Simon South <ssouth@slowcomputing.org>]

delphi-mode doesn't properly indent interface definition, things like
this:

type
   IHelloWorld = interface(IInvokable)
     ['{D613A992-AB12-0978-80D1-02B40DF72551}']
     function HelloWorld: String; stdcall;
   end;

This is because it doesn't distinguish between the "interface" keyword
used as a unit separator (i.e., as opposed to "implementation") and
used like a class declaration, as above.

As a result, delphi-mode will incorrectly indent the above code this
way:

type
   IHelloWorld = interface(IInvokable)
['{D613A992-AB12-0978-80D1-02B40DF72551}']
function HelloWorld: String; stdcall;
end;

I've taken a stab at updating delphi.el to distinguish between these
cases and support "dispinterface" properly as well (patch below) but I
don't understand the existing code well enough yet to finish it.  (I
suspect more changes need to be made to the delphi-enclosing-indent-of
function.)  Perhaps someone more familiar with this sort of thing
could help me complete it?

In GNU Emacs 22.1.1 (i386-mingw-nt5.1.2600)
  of 2007-06-02 on RELEASE
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4) --cflags -Ic:/gnuwin32/include'

*** delphi.el.orig	Thu May 15 17:57:29 2008
--- delphi.el	Fri May 16 12:07:37 2008
***************
*** 262,271 ****
   (defconst delphi-decl-sections '(type const var label resourcestring)
     "Denotes the start of a declaration section.")

   (defconst delphi-class-types '(class object)
     "Class types.")

! (defconst delphi-composite-types `(,@delphi-class-types record)
     "Types that contain declarations within them.")

   (defconst delphi-unit-sections
--- 262,275 ----
   (defconst delphi-decl-sections '(type const var label resourcestring)
     "Denotes the start of a declaration section.")

+ (defconst delphi-interface-types '(dispinterface interface)
+   "Interface types.")
+
   (defconst delphi-class-types '(class object)
     "Class types.")

! (defconst delphi-composite-types
!   `(,@delphi-class-types ,@delphi-interface-types record)
     "Types that contain declarations within them.")

   (defconst delphi-unit-sections
***************
*** 859,866 ****
         (delphi-stmt-line-indent-of token delphi-indent-level))))

   (defun delphi-composite-type-start (token last-token)
!   ;; Returns true (actually the last-token) if the pair equals (= 
class) or (=
!   ;; record), and nil otherwise.
     (if (and (eq 'equals (delphi-token-kind token))
              (delphi-is (delphi-token-kind last-token) 
delphi-composite-types))
         last-token))
--- 863,870 ----
         (delphi-stmt-line-indent-of token delphi-indent-level))))

   (defun delphi-composite-type-start (token last-token)
!   ;; Returns true (actually the last-token) if the pair equals (= 
class), (=
!   ;; interface), or (= record), and nil otherwise.
     (if (and (eq 'equals (delphi-token-kind token))
              (delphi-is (delphi-token-kind last-token) 
delphi-composite-types))
         last-token))
***************
*** 1252,1258 ****
             (throw 'done (delphi-line-indent-of token 0)))

            ;; Unit statements mean we indent right to the left.
!          ((delphi-is token-kind delphi-unit-statements) (throw 'done 0))
            )
           (unless (delphi-is token-kind delphi-whitespace)
              (setq last-token token))
--- 1256,1264 ----
             (throw 'done (delphi-line-indent-of token 0)))

            ;; Unit statements mean we indent right to the left.
!          ((and (delphi-is token-kind delphi-unit-statements)
!                (not (delphi-composite-type-start token last-token)))
!           (throw 'done 0))
            )
           (unless (delphi-is token-kind delphi-whitespace)
              (setq last-token token))
***************
*** 1351,1357 ****
                                            delphi-indent-level)))

            ;; In unit sections we indent right to the left.
!          ((delphi-is token-kind delphi-unit-sections) (throw 'done 0))

            ;; A previous terminator means we can stop.
            ((delphi-is token-kind delphi-previous-terminators)
--- 1357,1365 ----
                                            delphi-indent-level)))

            ;; In unit sections we indent right to the left.
!          ((and (delphi-is token-kind delphi-unit-sections)
!                (not (delphi-is token-kind delphi-interface-types)))
!           (throw 'done 0))

            ;; A previous terminator means we can stop.
            ((delphi-is token-kind delphi-previous-terminators)
***************
*** 1457,1463 ****
                      ;; Indent to the matching start ( or [.
                      (delphi-indent-of (delphi-group-start token)))

!                   ((delphi-is token-kind delphi-unit-statements) 0)

                     ((delphi-is token-kind delphi-comments)
                      ;; In a comment.
--- 1465,1475 ----
                      ;; Indent to the matching start ( or [.
                      (delphi-indent-of (delphi-group-start token)))

!                   ((and (delphi-is token-kind delphi-unit-statements)
!                         (not
!                          (delphi-is token-kind delphi-interface-types)))
!                         1)
!                    0)

                     ((delphi-is token-kind delphi-comments)
                      ;; In a comment.