vim-patch:8.1.0360: using an external diff program is slow and inflexible

Problem:    Using an external diff program is slow and inflexible.
Solution:   Include the xdiff library. (Christian Brabandt)
            Use it by default.

https://github.com/vim/vim/commit/e828b7621cf9065a3582be0c4dd1e0e846e335bf

vim-patch:8.1.0360
vim-patch:8.1.0364
vim-patch:8.1.0366
vim-patch:8.1.0370
vim-patch:8.1.0377
vim-patch:8.1.0378
vim-patch:8.1.0381
vim-patch:8.1.0396
vim-patch:8.1.0432

2 files changed, 31 insertions, 8 deletions

diff --git a/runtime/doc/diff.txt b/runtime/doc/diff.txt
index 766240dfb0..ab002b4dcb 100644
--- a/runtime/doc/diff.txt
+++ b/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
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 29d9a60aa2..606e148a83 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -1859,8 +1859,8 @@ 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.
 
@@ -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.
+
+		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
 
-		:set diffopt=filler,context:4
+	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)