Merge #9306 'vim-patch: integrate xdiff library'

closes #1466
closes #1007
closes #1391

runtime/doc/autocmd.txt

@@ -628,6 +628,11 @@ CursorMoved			After the cursor was moved in Normal or Visual
 CursorMovedI			After the cursor was moved in Insert mode.
 				Not triggered when the popup menu is visible.
 				Otherwise the same as CursorMoved.
+							*DiffUpdated*
+DiffUpdated			After diffs have been updated.  Depending on
+				what kind of diff is being used (internal or
+				external) this can be triggered on every
+				change or when doing |:diffupdate|.
 							*DirChanged*
 DirChanged			After the |current-directory| was changed.
 				Sets these |v:event| keys:

runtime/doc/diff.txt

@@ -27,7 +27,9 @@ The second and following arguments may also be a directory name.  Vim will
 then append the file name of the first argument to the directory name to find
 the file.
 
-This only works when a standard "diff" command is available.  See 'diffexpr'.
+By default an internal diff library will be used.  When 'diffopt' or
+'diffexpr' has been set an external "diff" command will be used.  This only
+works when such a diff program is available.
 
 Diffs are local to the current tab page |tab-page|.  You can't see diffs with
 a window in another tab page.  This does make it possible to have several
@@ -332,8 +334,9 @@ between file1 and file2: >
 
 The ">" is replaced with the value of 'shellredir'.
 
-The output of "diff" must be a normal "ed" style diff.  Do NOT use a context
-diff.  This example explains the format that Vim expects: >
+The output of "diff" must be a normal "ed" style diff or a unified diff.  Do
+NOT use a context diff.  This example explains the format that Vim expects for
+the "ed" style diff: >
 
 	1a2
 	> bbb

runtime/doc/options.txt

@@ -1859,13 +1859,13 @@ A jump table for the options with a short description can be found at |Q_op|.
 						*'dex'* *'diffexpr'*
 'diffexpr' 'dex'	string	(default "")
 			global
-	Expression which is evaluated to obtain an ed-style diff file from two
-	versions of a file.  See |diff-diffexpr|.
+	Expression which is evaluated to obtain a diff file (either ed-style
+	or unified-style) from two versions of a file.  See |diff-diffexpr|.
 	This option cannot be set from a |modeline| or in the |sandbox|, for
 	security reasons.
 
 						*'dip'* *'diffopt'*
-'diffopt' 'dip'		string	(default "filler")
+'diffopt' 'dip'		string	(default "internal,filler")
 			global
 	Option settings for diff mode.  It can consist of the following items.
 	All are optional.  Items must be separated by a comma.
@@ -1925,11 +1925,31 @@ A jump table for the options with a short description can be found at |Q_op|.
 		foldcolumn:{n}	Set the 'foldcolumn' option to {n} when
 				starting diff mode.  Without this 2 is used.
 
-	Examples: >
+		internal	Use the internal diff library.  This is
+				ignored when 'diffexpr' is set.  *E960*
+				When running out of memory when writing a
+				buffer this item will be ignored for diffs
+				involving that buffer.  Set the 'verbose'
+				option to see when this happens.
 
-		:set diffopt=filler,context:4
+		indent-heuristic
+				Use the indent heuristic for the internal
+				diff library.
+
+                algorithm:{text} Use the specified diff algorithm with the
+				internal diff engine. Currently supported 
+				algorithms are:
+				myers      the default algorithm
+				minimal    spend extra time to generate the
+					   smallest possible diff
+				patience   patience diff algorithm
+				histogram  histogram diff algorithm
+
+	Examples: >
+		:set diffopt=internal,filler,context:4
 		:set diffopt=
-		:set diffopt=filler,foldcolumn:3
+		:set diffopt=internal,filler,foldcolumn:3
+		:set diffopt-=internal  " do NOT use the internal diff parser
 <
 				     *'digraph'* *'dg'* *'nodigraph'* *'nodg'*
 'digraph' 'dg'		boolean	(default off)