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

1 files changed, 776 insertions, 0 deletions

diff --git a/test/functional/ui/diff_spec.lua b/test/functional/ui/diff_spec.lua
new file mode 100644
index 0000000000..8f2b667b3c
--- /dev/null
+++ b/test/functional/ui/diff_spec.lua
@@ -0,0 +1,776 @@
+local helpers = require('test.functional.helpers')(after_each)
+local Screen = require('test.functional.ui.screen')
+
+local feed = helpers.feed
+local clear = helpers.clear
+local write_file = helpers.write_file
+
+describe('Diff mode screen', function()
+  local fname = 'Xtest-functional-diff-screen-1'
+  local fname_2 = fname .. '.2'
+  local screen
+
+  local reread = function()
+    feed(':e<cr><c-w>w:e<cr><c-w>w')
+  end
+
+  setup(function()
+    clear()
+    os.remove(fname)
+    os.remove(fname_2)
+  end)
+
+  teardown(function()
+    os.remove(fname)
+    os.remove(fname_2)
+  end)
+
+  before_each(function()
+    clear()
+    feed(':e ' .. fname_2 .. '<cr>')
+    feed(':vnew ' .. fname .. '<cr>')
+    feed(':diffthis<cr>')
+    feed('<c-w>w:diffthis<cr><c-w>w')
+
+    screen = Screen.new(40, 16)
+    screen:attach()
+    screen:set_default_attr_ids({
+      [1] = {foreground = Screen.colors.DarkBlue, background = Screen.colors.WebGray},
+      [2] = {background = Screen.colors.LightCyan1, bold = true, foreground = Screen.colors.Blue1},
+      [3] = {reverse = true},
+      [4] = {background = Screen.colors.LightBlue},
+      [5] = {foreground = Screen.colors.DarkBlue, background = Screen.colors.LightGrey},
+      [6] = {bold = true, foreground = Screen.colors.Blue1},
+      [7] = {bold = true, reverse = true},
+      [8] = {bold = true, background = Screen.colors.Red},
+      [9] = {background = Screen.colors.LightMagenta},
+    })
+  end)
+
+  it('Add a line in beginning of file 2', function()
+    write_file(fname, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n", false)
+    write_file(fname_2, "0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n", false)
+    reread()
+
+    feed(':set diffopt=filler<cr>')
+    screen:expect([[
+      {1:  }{2:------------------}{3:│}{1:  }{4:0                }|
+      {1:  }^1                 {3:│}{1:  }1                |
+      {1:  }2                 {3:│}{1:  }2                |
+      {1:  }3                 {3:│}{1:  }3                |
+      {1:  }4                 {3:│}{1:  }4                |
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:+ }{5:+--  4 lines: 7···}{3:│}{1:+ }{5:+--  4 lines: 7··}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt=filler                     |
+    ]])
+
+    feed(':set diffopt+=internal<cr>')
+    screen:expect([[
+      {1:  }{2:------------------}{3:│}{1:  }{4:0                }|
+      {1:  }^1                 {3:│}{1:  }1                |
+      {1:  }2                 {3:│}{1:  }2                |
+      {1:  }3                 {3:│}{1:  }3                |
+      {1:  }4                 {3:│}{1:  }4                |
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:+ }{5:+--  4 lines: 7···}{3:│}{1:+ }{5:+--  4 lines: 7··}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt+=internal                  |
+    ]])
+  end)
+
+  it('Add a line in beginning of file 1', function()
+    write_file(fname, "0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n", false)
+    write_file(fname_2, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n", false)
+    reread()
+
+    feed(":set diffopt=filler<cr>")
+    screen:expect([[
+      {1:  }{4:^0                 }{3:│}{1:  }{2:-----------------}|
+      {1:  }1                 {3:│}{1:  }1                |
+      {1:  }2                 {3:│}{1:  }2                |
+      {1:  }3                 {3:│}{1:  }3                |
+      {1:  }4                 {3:│}{1:  }4                |
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:+ }{5:+--  4 lines: 7···}{3:│}{1:+ }{5:+--  4 lines: 7··}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt=filler                     |
+    ]])
+
+    feed(":set diffopt+=internal<cr>")
+    screen:expect([[
+      {1:  }{4:^0                 }{3:│}{1:  }{2:-----------------}|
+      {1:  }1                 {3:│}{1:  }1                |
+      {1:  }2                 {3:│}{1:  }2                |
+      {1:  }3                 {3:│}{1:  }3                |
+      {1:  }4                 {3:│}{1:  }4                |
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:+ }{5:+--  4 lines: 7···}{3:│}{1:+ }{5:+--  4 lines: 7··}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt+=internal                  |
+    ]])
+  end)
+
+  it('Add a line at the end of file 2', function()
+    write_file(fname, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n", false)
+    write_file(fname_2, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n", false)
+    reread()
+
+    feed(":set diffopt=filler<cr>")
+    screen:expect([[
+      {1:+ }{5:^+--  4 lines: 1···}{3:│}{1:+ }{5:+--  4 lines: 1··}|
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:  }7                 {3:│}{1:  }7                |
+      {1:  }8                 {3:│}{1:  }8                |
+      {1:  }9                 {3:│}{1:  }9                |
+      {1:  }10                {3:│}{1:  }10               |
+      {1:  }{2:------------------}{3:│}{1:  }{4:11               }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt=filler                     |
+    ]])
+
+    feed(":set diffopt+=internal<cr>")
+    screen:expect([[
+      {1:+ }{5:^+--  4 lines: 1···}{3:│}{1:+ }{5:+--  4 lines: 1··}|
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:  }7                 {3:│}{1:  }7                |
+      {1:  }8                 {3:│}{1:  }8                |
+      {1:  }9                 {3:│}{1:  }9                |
+      {1:  }10                {3:│}{1:  }10               |
+      {1:  }{2:------------------}{3:│}{1:  }{4:11               }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt+=internal                  |
+    ]])
+  end)
+
+  it('Add a line at the end of file 1', function()
+    write_file(fname, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n", false)
+    write_file(fname_2, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n", false)
+    reread()
+
+    feed(":set diffopt=filler<cr>")
+    screen:expect([[
+      {1:+ }{5:^+--  4 lines: 1···}{3:│}{1:+ }{5:+--  4 lines: 1··}|
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:  }7                 {3:│}{1:  }7                |
+      {1:  }8                 {3:│}{1:  }8                |
+      {1:  }9                 {3:│}{1:  }9                |
+      {1:  }10                {3:│}{1:  }10               |
+      {1:  }{4:11                }{3:│}{1:  }{2:-----------------}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt=filler                     |
+    ]])
+
+    feed(":set diffopt+=internal<cr>")
+    screen:expect([[
+      {1:+ }{5:^+--  4 lines: 1···}{3:│}{1:+ }{5:+--  4 lines: 1··}|
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:  }7                 {3:│}{1:  }7                |
+      {1:  }8                 {3:│}{1:  }8                |
+      {1:  }9                 {3:│}{1:  }9                |
+      {1:  }10                {3:│}{1:  }10               |
+      {1:  }{4:11                }{3:│}{1:  }{2:-----------------}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt+=internal                  |
+    ]])
+  end)
+
+  it('Add a line in the middle of file 2, remove on at the end of file 1', function()
+    write_file(fname, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n", false)
+    write_file(fname_2, "1\n2\n3\n4\n4\n5\n6\n7\n8\n9\n10\n", false)
+    reread()
+
+    feed(':set diffopt=filler<cr>')
+    screen:expect([[
+      {1:  }^1                 {3:│}{1:  }1                |
+      {1:  }2                 {3:│}{1:  }2                |
+      {1:  }3                 {3:│}{1:  }3                |
+      {1:  }4                 {3:│}{1:  }4                |
+      {1:  }{2:------------------}{3:│}{1:  }{4:4                }|
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:  }7                 {3:│}{1:  }7                |
+      {1:  }8                 {3:│}{1:  }8                |
+      {1:  }9                 {3:│}{1:  }9                |
+      {1:  }10                {3:│}{1:  }10               |
+      {1:  }{4:11                }{3:│}{1:  }{2:-----------------}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt=filler                     |
+    ]])
+
+    feed(':set diffopt+=internal<cr>')
+    screen:expect([[
+      {1:  }^1                 {3:│}{1:  }1                |
+      {1:  }2                 {3:│}{1:  }2                |
+      {1:  }3                 {3:│}{1:  }3                |
+      {1:  }4                 {3:│}{1:  }4                |
+      {1:  }{2:------------------}{3:│}{1:  }{4:4                }|
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:  }7                 {3:│}{1:  }7                |
+      {1:  }8                 {3:│}{1:  }8                |
+      {1:  }9                 {3:│}{1:  }9                |
+      {1:  }10                {3:│}{1:  }10               |
+      {1:  }{4:11                }{3:│}{1:  }{2:-----------------}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt+=internal                  |
+    ]])
+  end)
+
+  it('Add a line in the middle of file 1, remove on at the end of file 2', function()
+    write_file(fname, "1\n2\n3\n4\n4\n5\n6\n7\n8\n9\n10\n", false)
+    write_file(fname_2, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n", false)
+    reread()
+
+    feed(':set diffopt=filler<cr>')
+    screen:expect([[
+      {1:  }^1                 {3:│}{1:  }1                |
+      {1:  }2                 {3:│}{1:  }2                |
+      {1:  }3                 {3:│}{1:  }3                |
+      {1:  }4                 {3:│}{1:  }4                |
+      {1:  }{4:4                 }{3:│}{1:  }{2:-----------------}|
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:  }7                 {3:│}{1:  }7                |
+      {1:  }8                 {3:│}{1:  }8                |
+      {1:  }9                 {3:│}{1:  }9                |
+      {1:  }10                {3:│}{1:  }10               |
+      {1:  }{2:------------------}{3:│}{1:  }{4:11               }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt=filler                     |
+    ]])
+
+    feed(':set diffopt+=internal<cr>')
+    screen:expect([[
+      {1:  }^1                 {3:│}{1:  }1                |
+      {1:  }2                 {3:│}{1:  }2                |
+      {1:  }3                 {3:│}{1:  }3                |
+      {1:  }4                 {3:│}{1:  }4                |
+      {1:  }{4:4                 }{3:│}{1:  }{2:-----------------}|
+      {1:  }5                 {3:│}{1:  }5                |
+      {1:  }6                 {3:│}{1:  }6                |
+      {1:  }7                 {3:│}{1:  }7                |
+      {1:  }8                 {3:│}{1:  }8                |
+      {1:  }9                 {3:│}{1:  }9                |
+      {1:  }10                {3:│}{1:  }10               |
+      {1:  }{2:------------------}{3:│}{1:  }{4:11               }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt+=internal                  |
+    ]])
+  end)
+
+  describe('normal/patience/histogram diff algorithm', function()
+    setup(function()
+      local f1 = [[#include <stdio.h>
+
+// Frobs foo heartily
+int frobnitz(int foo)
+{
+    int i;
+    for(i = 0; i < 10; i++)
+    {
+        printf("Your answer is: ");
+        printf("%d\n", foo);
+    }
+}
+
+int fact(int n)
+{
+    if(n > 1)
+    {
+        return fact(n-1) * n;
+    }
+    return 1;
+}
+
+int main(int argc, char **argv)
+{
+    frobnitz(fact(10));
+}]]
+      write_file(fname, f1, false)
+      local f2 = [[#include <stdio.h>
+
+int fib(int n)
+{
+    if(n > 2)
+    {
+        return fib(n-1) + fib(n-2);
+    }
+    return 1;
+}
+
+// Frobs foo heartily
+int frobnitz(int foo)
+{
+    int i;
+    for(i = 0; i < 10; i++)
+    {
+        printf("%d\n", foo);
+    }
+}
+
+int main(int argc, char **argv)
+{
+    frobnitz(fib(10));
+}]]
+      write_file(fname_2, f2, false)
+    end)
+
+    it('diffopt=+algorithm:myers', function()
+      reread()
+      feed(':set diffopt=internal,filler<cr>')
+      screen:expect([[
+        {1:  }^#include <stdio.h>{3:│}{1:  }#include <stdio.h|
+        {1:  }                  {3:│}{1:  }                 |
+        {1:  }{8:// Frobs foo heart}{3:│}{1:  }{8:int fib(int n)}{9:   }|
+        {1:  }{4:int frobnitz(int f}{3:│}{1:  }{2:-----------------}|
+        {1:  }{                 {3:│}{1:  }{                |
+        {1:  }{9:    i}{8:nt i;}{9:        }{3:│}{1:  }{9:    i}{8:f(n > 2)}{9:    }|
+        {1:  }{4:    for(i = 0; i <}{3:│}{1:  }{2:-----------------}|
+        {1:  }    {             {3:│}{1:  }    {            |
+        {1:  }{9:        }{8:printf("Yo}{3:│}{1:  }{9:        }{8:return fi}|
+        {1:  }{4:        printf("%d}{3:│}{1:  }{2:-----------------}|
+        {1:  }    }             {3:│}{1:  }    }            |
+        {1:  }{2:------------------}{3:│}{1:  }{4:    return 1;    }|
+        {1:  }}                 {3:│}{1:  }}                |
+        {1:  }                  {3:│}{1:  }                 |
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+        :set diffopt=internal,filler            |
+      ]])
+
+      feed('G')
+      screen:expect([[
+        {1:  }{2:------------------}{3:│}{1:  }{4:int frobnitz(int }|
+        {1:  }{                 {3:│}{1:  }{                |
+        {1:  }{9:    i}{8:f(n > 1)}{9:     }{3:│}{1:  }{9:    i}{8:nt i;}{9:       }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    for(i = 0; i }|
+        {1:  }    {             {3:│}{1:  }    {            |
+        {1:  }{9:        }{8:return fac}{3:│}{1:  }{9:        }{8:printf("%}|
+        {1:  }    }             {3:│}{1:  }    }            |
+        {1:  }{4:    return 1;     }{3:│}{1:  }{2:-----------------}|
+        {1:  }}                 {3:│}{1:  }}                |
+        {1:  }                  {3:│}{1:  }                 |
+        {1:  }int main(int argc,{3:│}{1:  }int main(int argc|
+        {1:  }{                 {3:│}{1:  }{                |
+        {1:  }{9:    frobnitz(f}{8:act}{9:(}{3:│}{1:  }{9:    frobnitz(f}{8:ib}{9:(}|
+        {1:  }^}                 {3:│}{1:  }}                |
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+        :set diffopt=internal,filler            |
+      ]])
+    end)
+
+    it('diffopt+=algorithm:patience', function()
+      reread()
+      feed(':set diffopt=internal,filler,algorithm:patience<cr>')
+      screen:expect([[
+        {1:  }^#include <stdio.h>{3:│}{1:  }#include <stdio.h|
+        {1:  }                  {3:│}{1:  }                 |
+        {1:  }{2:------------------}{3:│}{1:  }{4:int fib(int n)   }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:{                }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    if(n > 2)    }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    {            }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:        return fi}|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    }            }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    return 1;    }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:}                }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:                 }|
+        {1:  }// Frobs foo heart{3:│}{1:  }// Frobs foo hear|
+        {1:  }int frobnitz(int f{3:│}{1:  }int frobnitz(int |
+        {1:  }{                 {3:│}{1:  }{                |
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+                                                |
+      ]])
+
+      feed('G')
+      screen:expect([[
+        {1:  }                  {3:│}{1:  }                 |
+        {1:  }{4:int fact(int n)   }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:{                 }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:    if(n > 1)     }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:    {             }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:        return fac}{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:    }             }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:    return 1;     }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:}                 }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:                  }{3:│}{1:  }{2:-----------------}|
+        {1:  }int main(int argc,{3:│}{1:  }int main(int argc|
+        {1:  }{                 {3:│}{1:  }{                |
+        {1:  }{9:    frobnitz(f}{8:act}{9:(}{3:│}{1:  }{9:    frobnitz(f}{8:ib}{9:(}|
+        {1:  }^}                 {3:│}{1:  }}                |
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+                                                |
+      ]])
+    end)
+
+    it('diffopt+=algorithm:histogram', function()
+      reread()
+      feed(':set diffopt=internal,filler,algorithm:histogram<cr>')
+      screen:expect([[
+        {1:  }^#include <stdio.h>{3:│}{1:  }#include <stdio.h|
+        {1:  }                  {3:│}{1:  }                 |
+        {1:  }{2:------------------}{3:│}{1:  }{4:int fib(int n)   }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:{                }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    if(n > 2)    }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    {            }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:        return fi}|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    }            }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    return 1;    }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:}                }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:                 }|
+        {1:  }// Frobs foo heart{3:│}{1:  }// Frobs foo hear|
+        {1:  }int frobnitz(int f{3:│}{1:  }int frobnitz(int |
+        {1:  }{                 {3:│}{1:  }{                |
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+                                                |
+      ]])
+
+      feed('G')
+      screen:expect([[
+        {1:  }                  {3:│}{1:  }                 |
+        {1:  }{4:int fact(int n)   }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:{                 }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:    if(n > 1)     }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:    {             }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:        return fac}{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:    }             }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:    return 1;     }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:}                 }{3:│}{1:  }{2:-----------------}|
+        {1:  }{4:                  }{3:│}{1:  }{2:-----------------}|
+        {1:  }int main(int argc,{3:│}{1:  }int main(int argc|
+        {1:  }{                 {3:│}{1:  }{                |
+        {1:  }{9:    frobnitz(f}{8:act}{9:(}{3:│}{1:  }{9:    frobnitz(f}{8:ib}{9:(}|
+        {1:  }^}                 {3:│}{1:  }}                |
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+                                                |
+      ]])
+    end)
+  end)
+
+  describe('diffopt+=indent-heuristic', function()
+    setup(function()
+      local f1 = [[
+  def finalize(values)
+
+    values.each do |v|
+      v.finalize
+    end]]
+      write_file(fname, f1, false)
+      local f2 = [[
+  def finalize(values)
+
+    values.each do |v|
+      v.prepare
+    end
+
+    values.each do |v|
+      v.finalize
+    end]]
+      write_file(fname_2, f2, false)
+      feed(':diffupdate!<cr>')
+    end)
+
+    it('internal', function()
+      reread()
+      feed(":set diffopt=internal,filler<cr>")
+      screen:expect([[
+        {1:  }^def finalize(value{3:│}{1:  }def finalize(valu|
+        {1:  }                  {3:│}{1:  }                 |
+        {1:  }  values.each do |{3:│}{1:  }  values.each do |
+        {1:  }{2:------------------}{3:│}{1:  }{4:    v.prepare    }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:  end            }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:                 }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:  values.each do }|
+        {1:  }    v.finalize    {3:│}{1:  }    v.finalize   |
+        {1:  }  end             {3:│}{1:  }  end            |
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+        :set diffopt=internal,filler            |
+      ]])
+    end)
+
+    it('indent-heuristic', function()
+      reread()
+      feed(':set diffopt=internal,filler,indent-heuristic<cr>')
+      screen:expect([[
+        {1:  }^def finalize(value{3:│}{1:  }def finalize(valu|
+        {1:  }                  {3:│}{1:  }                 |
+        {1:  }{2:------------------}{3:│}{1:  }{4:  values.each do }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:    v.prepare    }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:  end            }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:                 }|
+        {1:  }  values.each do |{3:│}{1:  }  values.each do |
+        {1:  }    v.finalize    {3:│}{1:  }    v.finalize   |
+        {1:  }  end             {3:│}{1:  }  end            |
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+                                                |
+      ]])
+    end)
+  end)
+
+  it('Diff the same file', function()
+    write_file(fname, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n", false)
+    write_file(fname_2, "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n", false)
+    reread()
+
+    feed(':set diffopt=filler<cr>')
+    screen:expect([[
+      {1:+ }{5:^+-- 10 lines: 1···}{3:│}{1:+ }{5:+-- 10 lines: 1··}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt=filler                     |
+    ]])
+
+    feed(':set diffopt+=internal<cr>')
+    screen:expect([[
+      {1:+ }{5:^+-- 10 lines: 1···}{3:│}{1:+ }{5:+-- 10 lines: 1··}|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt+=internal                  |
+    ]])
+  end)
+
+  it('Diff an empty file', function()
+    write_file(fname, "", false)
+    write_file(fname_2, "", false)
+    reread()
+
+    feed(':set diffopt=filler<cr>')
+    screen:expect([[
+      {1:- }^                  {3:│}{1:- }                 |
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt=filler                     |
+    ]])
+
+    feed(':set diffopt+=internal<cr>')
+    screen:expect([[
+      {1:- }^                  {3:│}{1:- }                 |
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt+=internal                  |
+    ]])
+  end)
+
+  it('diffopt+=icase', function()
+    write_file(fname, "a\nb\ncd\n", false)
+    write_file(fname_2, "A\nb\ncDe\n", false)
+    reread()
+
+    feed(':set diffopt=filler,icase<cr>')
+    screen:expect([[
+      {1:  }^a                 {3:│}{1:  }A                |
+      {1:  }b                 {3:│}{1:  }b                |
+      {1:  }{9:cd                }{3:│}{1:  }{9:cD}{8:e}{9:              }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt=filler,icase               |
+    ]])
+
+    feed(':set diffopt+=internal<cr>')
+    screen:expect([[
+      {1:  }^a                 {3:│}{1:  }A                |
+      {1:  }b                 {3:│}{1:  }b                |
+      {1:  }{9:cd                }{3:│}{1:  }{9:cD}{8:e}{9:              }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+      {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+      :set diffopt+=internal                  |
+    ]])
+  end)
+
+  describe('diffopt+=iwhite', function()
+    setup(function()
+      local f1 = 'int main()\n{\n   printf("Hello, World!");\n   return 0;\n}\n'
+      write_file(fname, f1, false)
+      local f2 = 'int main()\n{\n   if (0)\n   {\n      printf("Hello, World!");\n      return 0;\n   }\n}\n'
+      write_file(fname_2, f2, false)
+      feed(':diffupdate!<cr>')
+    end)
+
+    it('external', function()
+      reread()
+      feed(':set diffopt=filler,iwhite<cr>')
+      screen:expect([[
+        {1:  }^int main()        {3:│}{1:  }int main()       |
+        {1:  }{                 {3:│}{1:  }{                |
+        {1:  }{2:------------------}{3:│}{1:  }{4:   if (0)        }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:   {             }|
+        {1:  }   printf("Hello, {3:│}{1:  }      printf("Hel|
+        {1:  }   return 0;      {3:│}{1:  }      return 0;  |
+        {1:  }{2:------------------}{3:│}{1:  }{4:   }             }|
+        {1:  }}                 {3:│}{1:  }}                |
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+        :set diffopt=filler,iwhite              |
+      ]])
+    end)
+
+    it('internal', function()
+      reread()
+      feed(':set diffopt=filler,iwhite,internal<cr>')
+      screen:expect([[
+        {1:  }^int main()        {3:│}{1:  }int main()       |
+        {1:  }{                 {3:│}{1:  }{                |
+        {1:  }{2:------------------}{3:│}{1:  }{4:   if (0)        }|
+        {1:  }{2:------------------}{3:│}{1:  }{4:   {             }|
+        {1:  }   printf("Hello, {3:│}{1:  }      printf("Hel|
+        {1:  }   return 0;      {3:│}{1:  }      return 0;  |
+        {1:  }{2:------------------}{3:│}{1:  }{4:   }             }|
+        {1:  }}                 {3:│}{1:  }}                |
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {1:  }{6:~                 }{3:│}{1:  }{6:~                }|
+        {7:<onal-diff-screen-1  }{3:<l-diff-screen-1.2 }|
+        :set diffopt=filler,iwhite,internal     |
+      ]])
+    end)
+  end)
+end)