Displays the differences between successive proof steps in coqtop and CoqIDE.

Proof General requires minor changes to make the diffs visible, but this code
shouldn't break the existing version of PG.

Diffs are computed for the hypotheses and conclusion of the first goal between
the old and new proofs. Strings are split into tokens using the Coq lexer,
then the list of tokens are diffed using the Myers algorithm.  A fixup routine
(Pp_diff.shorten_diff_span) shortens the span of the diff result in some cases.

Diffs can be enabled with the Coq commmand "Set Diffs on|off|removed." or
"-diffs on|off|removed" on the OS command line.  The "on" option shows only the
new item with added text, while "removed" shows each modified item twice--once
with the old value showing removed text and once with the new value showing
added text.

The highlights use 4 tags to specify the color and underline/strikeout.
These are "diffs.added", "diffs.removed", "diffs.added.bg" and "diffs.removed.bg".
The first two are for added or removed text; the last two are for
unmodified parts of a modified item.

Diffs that span multiple strings in the Pp are tagged with "start.diff.*" and
"end.diff.*", but only on the first and last strings of the span.

1 files changed, 158 insertions, 0 deletions

diff --git a/clib/diff2.ml b/clib/diff2.ml
new file mode 100644
index 0000000000..42c4733fed
--- /dev/null
+++ b/clib/diff2.ml
@@ -0,0 +1,158 @@
+(* copied from https://github.com/leque/ocaml-diff.git and renamed from "diff.ml" *)
+
+(*
+ * Copyright (C) 2016 OOHASHI Daichi
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ *)
+
+type 'a common =
+  [ `Common of int * int * 'a ]
+
+type 'a edit =
+  [ `Added of int * 'a
+  | `Removed of int * 'a
+  | 'a common
+  ]
+
+module type SeqType = sig
+  type t
+  type elem
+  val get : t -> int -> elem
+  val length : t -> int
+end
+
+module type S = sig
+  type t
+  type elem
+
+  val lcs :
+      ?equal:(elem -> elem -> bool) ->
+      t -> t -> elem common list
+
+  val diff :
+      ?equal:(elem -> elem -> bool) ->
+      t -> t -> elem edit list
+
+  val fold_left :
+      ?equal:(elem -> elem -> bool) ->
+      f:('a -> elem edit -> 'a) ->
+      init:'a ->
+      t -> t -> 'a
+
+  val iter :
+      ?equal:(elem -> elem -> bool) ->
+      f:(elem edit -> unit) ->
+      t -> t -> unit
+end
+
+module Make(M : SeqType) : (S with type t = M.t and type elem = M.elem) = struct
+  type t = M.t
+  type elem = M.elem
+
+  let lcs ?(equal = (=)) a b =
+    let n = M.length a in
+    let m = M.length b in
+    let mn = m + n in
+    let sz = 2 * mn + 1 in
+    let vd = Array.make sz 0 in
+    let vl = Array.make sz 0 in
+    let vr = Array.make sz [] in
+    let get v i = Array.get v (i + mn) in
+    let set v i x = Array.set v (i + mn) x in
+    let finish () =
+      let rec loop i maxl r =
+        if i > mn then
+          List.rev r
+        else if get vl i > maxl then
+          loop (i + 1) (get vl i) (get vr i)
+        else
+          loop (i + 1) maxl r
+      in loop (- mn) 0 []
+    in
+    if mn = 0 then
+      []
+    else
+      (* For d <- 0 to mn Do *)
+      let rec dloop d =
+        assert (d <= mn);
+        (* For k <- -d to d in steps of 2 Do *)
+        let rec kloop k =
+          if k > d then
+            dloop @@ d + 1
+          else
+            let x, l, r =
+              if k = -d || (k <> d && get vd (k - 1) < get vd (k + 1)) then
+                get vd (k + 1), get vl (k + 1), get vr (k + 1)
+              else
+                get vd (k - 1) + 1, get vl (k - 1), get vr (k - 1)
+            in
+            let x, y, l, r =
+              let rec xyloop x y l r =
+                if x < n && y < m && equal (M.get a x) (M.get b y) then
+                  xyloop (x + 1) (y + 1) (l + 1) (`Common(x, y, M.get a x) :: r)
+                else
+                  x, y, l, r
+              in xyloop x (x - k) l r
+            in
+            set vd k x;
+            set vl k l;
+            set vr k r;
+            if x >= n && y >= m then
+              (* Stop *)
+              finish ()
+            else
+              kloop @@ k + 2
+        in kloop @@ -d
+      in dloop 0
+
+  let fold_left ?(equal = (=)) ~f ~init a b =
+    let ff x y = f y x in
+    let fold_map f g x from to_ init =
+      let rec loop i init =
+        if i >= to_ then
+          init
+        else
+          loop (i + 1) (f (g i @@ M.get x i) init)
+      in loop from init
+    in
+    let added i x = `Added (i, x) in
+    let removed i x = `Removed (i, x) in
+    let rec loop cs apos bpos init =
+      match cs with
+      | [] ->
+          init
+          |> fold_map ff removed a apos (M.length a)
+          |> fold_map ff added b bpos (M.length b)
+      | `Common (aoff, boff, _) as e :: rest ->
+          init
+          |> fold_map ff removed a apos aoff
+          |> fold_map ff added b bpos boff
+          |> ff e
+          |> loop rest (aoff + 1) (boff + 1)
+    in loop (lcs ~equal a b) 0 0 init
+
+  let diff ?(equal = (=)) a b =
+    fold_left ~equal ~f:(fun xs x -> x::xs) ~init:[] a b
+
+  let iter ?(equal = (=)) ~f a b =
+    fold_left a b
+      ~equal
+      ~f:(fun () x -> f x)
+      ~init:()
+end