vim-patch:9.1.1243: diff mode is lacking for changes within lines

Problem:  Diff mode's inline highlighting is lackluster. It only
          performs a line-by-line comparison, and calculates a single
          shortest range within a line that could encompass all the
          changes. In lines with multiple changes, or those that span
          multiple lines, this approach tends to end up highlighting
          much more than necessary.

Solution: Implement new inline highlighting modes by doing per-character
          or per-word diff within the diff block, and highlight only the
          relevant parts, add "inline:simple" to the defaults (which is
          the old behaviour)

This change introduces a new diffopt option "inline:<type>". Setting to
"none" will disable all inline highlighting, "simple" (the default) will
use the old behavior, "char" / "word" will perform a character/word-wise
diff of the texts within each diff block and only highlight the
differences.

The new char/word inline diff only use the internal xdiff, and will
respect diff options such as algorithm choice, icase, and misc iwhite
options. indent-heuristics is always on to perform better sliding.

For character highlight, a post-process of the diff results is first
applied before we show the highlight. This is because a naive diff will
create a result with a lot of small diff chunks and gaps, due to the
repetitive nature of individual characters. The post-process is a
heuristic-based refinement that attempts to merge adjacent diff blocks
if they are separated by a short gap (1-3 characters), and can be
further tuned in the future for better results. This process results in
more characters than necessary being highlighted but overall less visual
noise.

For word highlight, always use first buffer's iskeyword definition.
Otherwise if each buffer has different iskeyword settings we would not
be able to group words properly.

The char/word diffing is always per-diff block, not per line, meaning
that changes that span multiple lines will show up correctly.
Added/removed newlines are not shown by default, but if the user has
'list' set (with "eol" listchar defined), the eol character will be be
highlighted correctly for the specific newline characters.

Also, add a new "DiffTextAdd" highlight group linked to "DiffText" by
default. It allows color schemes to use different colors for texts that
have been added within a line versus modified.

This doesn't interact with linematch perfectly currently. The linematch
feature splits up diff blocks into multiple smaller blocks for better
visual matching, which makes inline highlight less useful especially for
multi-line change (e.g. a line is broken into two lines). This could be
addressed in the future.

As a side change, this also removes the bounds checking introduced to
diff_read() as they were added to mask existing logic bugs that were
properly fixed in vim/vim#16768.

closes: vim/vim#16881

https://github.com/vim/vim/commit/9943d4790e42721a6777da9e12637aa595ba4965

Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

1 files changed, 533 insertions, 1 deletions

diff --git a/test/functional/ui/diff_spec.lua b/test/functional/ui/diff_spec.lua
index e0d88771d3..223622eb6b 100644
--- a/test/functional/ui/diff_spec.lua
+++ b/test/functional/ui/diff_spec.lua
@@ -1555,7 +1555,6 @@ it('diff mode overlapped diff blocks will be merged', function()
 
   local screen = Screen.new(35, 20)
   command('set winwidth=10 diffopt=filler,internal')
-
   command('args Xdifile1 Xdifile2 | vert all | windo diffthis')
 
   WriteDiffFiles('a\nb', 'x\nx')
@@ -2252,3 +2251,536 @@ it('diff mode does not scroll with line("w0")', function()
     9                                            |
   ]])
 end)
+
+-- oldtest: Test_diff_inline()
+it('diff mode inline highlighting', function()
+  write_file('Xdifile1', '')
+  write_file('Xdifile2', '')
+  finally(function()
+    os.remove('Xdifile1')
+    os.remove('Xdifile2')
+  end)
+
+  local screen = Screen.new(37, 20)
+  screen:add_extra_attr_ids({
+    [100] = { background = Screen.colors.Blue1 },
+    [101] = { bold = true, background = Screen.colors.Red, foreground = Screen.colors.Blue1 },
+    [102] = { background = Screen.colors.LightMagenta, foreground = Screen.colors.Blue1 },
+    [103] = { bold = true, background = Screen.colors.Blue1, foreground = Screen.colors.Blue1 },
+    [104] = { bold = true, background = Screen.colors.LightBlue, foreground = Screen.colors.Blue1 },
+  })
+  command('set winwidth=10')
+  command('args Xdifile1 Xdifile2 | vert all | windo diffthis | 1wincmd w')
+
+  WriteDiffFiles('abcdef ghi jk n\nx\ny', 'aBcef gHi lm n\ny\nz')
+  command('set diffopt=internal,filler')
+  local s1 = [[
+    {7:  }{4:^a}{27:bcdef ghi jk}{4: n }│{7:  }{4:a}{27:Bcef gHi lm}{4: n  }|
+    {7:  }{22:x               }│{7:  }{23:----------------}|
+    {7:  }y               │{7:  }y               |
+    {7:  }{23:----------------}│{7:  }{22:z               }|
+    {1:~                 }│{1:~                 }|*14
+    {3:Xdifile1           }{2:Xdifile2          }|
+                                         |
+  ]]
+  screen:expect(s1)
+  command('set diffopt=internal,filler diffopt+=inline:none')
+  local s2 = [[
+    {7:  }{4:^abcdef ghi jk n }│{7:  }{4:aBcef gHi lm n  }|
+    {7:  }{22:x               }│{7:  }{23:----------------}|
+    {7:  }y               │{7:  }y               |
+    {7:  }{23:----------------}│{7:  }{22:z               }|
+    {1:~                 }│{1:~                 }|*14
+    {3:Xdifile1           }{2:Xdifile2          }|
+                                         |
+  ]]
+  screen:expect(s2)
+
+  -- inline:simple is the same as default
+  command('set diffopt=internal,filler diffopt+=inline:simple')
+  screen:expect(s1)
+
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  local s3 = [[
+    {7:  }{4:^a}{27:b}{4:c}{27:d}{4:ef g}{27:h}{4:i }{27:jk}{4: n }│{7:  }{4:a}{27:B}{4:cef g}{27:H}{4:i }{27:lm}{4: n  }|
+    {7:  }{22:x               }│{7:  }{23:----------------}|
+    {7:  }y               │{7:  }y               |
+    {7:  }{23:----------------}│{7:  }{22:z               }|
+    {1:~                 }│{1:~                 }|*14
+    {3:Xdifile1           }{2:Xdifile2          }|
+                                         |
+  ]]
+  screen:expect(s3)
+
+  command('set diffopt=internal,filler diffopt+=inline:word')
+  screen:expect([[
+    {7:  }{27:^abcdef}{4: }{27:ghi}{4: }{27:jk}{4: n }│{7:  }{27:aBcef}{4: }{27:gHi}{4: }{27:lm}{4: n  }|
+    {7:  }{22:x               }│{7:  }{23:----------------}|
+    {7:  }y               │{7:  }y               |
+    {7:  }{23:----------------}│{7:  }{22:z               }|
+    {1:~                 }│{1:~                 }|*14
+    {3:Xdifile1           }{2:Xdifile2          }|
+                                         |
+  ]])
+
+  -- multiple inline values will the last one
+  command('set diffopt=internal,filler diffopt+=inline:none,inline:char,inline:simple')
+  screen:expect(s1)
+  command('set diffopt=internal,filler diffopt+=inline:simple,inline:word,inline:none')
+  screen:expect(s2)
+  command('set diffopt=internal,filler diffopt+=inline:simple,inline:word,inline:char')
+  screen:expect(s3)
+
+  -- DiffTextAdd highlight
+  command('hi DiffTextAdd guibg=blue')
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  screen:expect([[
+    {7:  }{4:^a}{27:b}{4:c}{100:d}{4:ef g}{27:h}{4:i }{27:jk}{4: n }│{7:  }{4:a}{27:B}{4:cef g}{27:H}{4:i }{27:lm}{4: n  }|
+    {7:  }{22:x               }│{7:  }{23:----------------}|
+    {7:  }y               │{7:  }y               |
+    {7:  }{23:----------------}│{7:  }{22:z               }|
+    {1:~                 }│{1:~                 }|*14
+    {3:Xdifile1           }{2:Xdifile2          }|
+                                         |
+  ]])
+
+  -- Live update in insert mode
+  feed('isometext')
+  screen:expect([[
+    {7:  }{27:sometext^abcd}{4:ef g}│{7:  }{27:aBc}{4:ef g}{27:H}{4:i }{27:lm}{4: n  }|
+    {7:  }{22:x               }│{7:  }{23:----------------}|
+    {7:  }y               │{7:  }y               |
+    {7:  }{23:----------------}│{7:  }{22:z               }|
+    {1:~                 }│{1:~                 }|*14
+    {3:Xdifile1 [+]       }{2:Xdifile2          }|
+    {5:-- INSERT --}                         |
+  ]])
+  feed('<Esc>')
+  command('silent! undo')
+
+  -- icase simple scenarios
+  command('set diffopt=internal,filler diffopt+=inline:simple,icase')
+  screen:expect([[
+    {7:  }{4:^abc}{27:def ghi jk}{4: n }│{7:  }{4:aBc}{27:ef gHi lm}{4: n  }|
+    {7:  }{22:x               }│{7:  }{23:----------------}|
+    {7:  }y               │{7:  }y               |
+    {7:  }{23:----------------}│{7:  }{22:z               }|
+    {1:~                 }│{1:~                 }|*14
+    {3:Xdifile1           }{2:Xdifile2          }|
+                                         |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:char,icase')
+  screen:expect([[
+    {7:  }{4:^abc}{100:d}{4:ef ghi }{27:jk}{4: n }│{7:  }{4:aBcef gHi }{27:lm}{4: n  }|
+    {7:  }{22:x               }│{7:  }{23:----------------}|
+    {7:  }y               │{7:  }y               |
+    {7:  }{23:----------------}│{7:  }{22:z               }|
+    {1:~                 }│{1:~                 }|*14
+    {3:Xdifile1           }{2:Xdifile2          }|
+                                         |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:word,icase')
+  screen:expect([[
+    {7:  }{27:^abcdef}{4: ghi }{27:jk}{4: n }│{7:  }{27:aBcef}{4: gHi }{27:lm}{4: n  }|
+    {7:  }{22:x               }│{7:  }{23:----------------}|
+    {7:  }y               │{7:  }y               |
+    {7:  }{23:----------------}│{7:  }{22:z               }|
+    {1:~                 }│{1:~                 }|*14
+    {3:Xdifile1           }{2:Xdifile2          }|
+                                         |
+  ]])
+
+  screen:try_resize(45, 20)
+  command('wincmd =')
+  -- diff algorithms should affect highlight
+  WriteDiffFiles('apples and oranges', 'oranges and apples')
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  screen:expect([[
+    {7:  }{27:^appl}{4:es and }{27:orang}{4:es  }│{7:  }{27:orang}{4:es and }{27:appl}{4:es  }|
+    {1:~                     }│{1:~                     }|*17
+    {3:Xdifile1               }{2:Xdifile2              }|
+                                                 |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:char,algorithm:patience')
+  screen:expect([[
+    {7:  }{100:^apples and }{4:oranges  }│{7:  }{4:oranges}{100: and apples}{4:  }|
+    {1:~                     }│{1:~                     }|*17
+    {3:Xdifile1               }{2:Xdifile2              }|
+                                                 |
+  ]])
+
+  screen:try_resize(65, 20)
+  command('wincmd =')
+  -- icase: composing chars and Unicode fold case edge cases
+  WriteDiffFiles(
+    '1 - sigma in 6σ and Ὀδυσσεύς\n1 - angstrom in åå\n1 - composing: ii⃗I⃗',
+    '2 - Sigma in 6Σ and ὈΔΥΣΣΕΎΣ\n2 - Angstrom in ÅÅ\n2 - Composing: i⃗I⃗I⃗'
+  )
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  screen:expect([[
+    {7:  }{27:^1}{4: - }{27:s}{4:igma in 6}{27:σ}{4: and Ὀ}{27:δυσσεύς}{4:  }│{7:  }{27:2}{4: - }{27:S}{4:igma in 6}{27:Σ}{4: and Ὀ}{27:ΔΥΣΣΕΎΣ}{4:  }|
+    {7:  }{27:1}{4: - }{27:a}{4:ngstrom in }{27:åå}{4:            }│{7:  }{27:2}{4: - }{27:A}{4:ngstrom in }{27:ÅÅ}{4:            }|
+    {7:  }{27:1}{4: - }{27:c}{4:omposing: }{100:i}{4:i⃗I⃗            }│{7:  }{27:2}{4: - }{27:C}{4:omposing: i⃗I⃗}{100:I⃗}{4:            }|
+    {1:~                               }│{1:~                               }|*15
+    {3:Xdifile1                         }{2:Xdifile2                        }|
+                                                                     |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:char,icase')
+  screen:expect([[
+    {7:  }{27:^1}{4: - sigma in 6σ and Ὀδυσσεύς  }│{7:  }{27:2}{4: - Sigma in 6Σ and ὈΔΥΣΣΕΎΣ  }|
+    {7:  }{27:1}{4: - angstrom in åå            }│{7:  }{27:2}{4: - Angstrom in ÅÅ            }|
+    {7:  }{27:1}{4: - composing: }{27:i}{4:i⃗I⃗            }│{7:  }{27:2}{4: - Composing: }{27:i⃗}{4:I⃗I⃗            }|
+    {1:~                               }│{1:~                               }|*15
+    {3:Xdifile1                         }{2:Xdifile2                        }|
+                                                                     |
+  ]])
+
+  screen:try_resize(35, 20)
+  command('wincmd =')
+  -- wide chars
+  WriteDiffFiles('abc😅xde一\nf🚀g', 'abcy😢de\n二f🚀g')
+  command('set diffopt=internal,filler diffopt+=inline:char,icase')
+  screen:expect([[
+    {7:  }{4:^abc}{27:😅x}{4:de}{100:一}{4:     }│{7:  }{4:abc}{27:y😢}{4:de       }|
+    {7:  }{4:f🚀g           }│{7:  }{100:二}{4:f🚀g         }|
+    {1:~                }│{1:~                }|*16
+    {3:Xdifile1          }{2:Xdifile2         }|
+                                       |
+  ]])
+
+  -- NUL char
+  WriteDiffFiles('1\00034\0005\0006', '1234\0005\n6')
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  screen:expect([[
+    {7:  }{4:^1}{101:^@}{4:34}{102:^@}{4:5}{101:^@}{4:6    }│{7:  }{4:1}{27:2}{4:34}{102:^@}{4:5        }|
+    {7:  }{23:---------------}│{7:  }{4:6              }|
+    {1:~                }│{1:~                }|*16
+    {3:Xdifile1          }{2:Xdifile2         }|
+                                       |
+  ]])
+
+  -- word diff: always use first buffer's iskeyword and ignore others' for consistency
+  WriteDiffFiles('foo+bar test', 'foo+baz test')
+  command('set diffopt=internal,filler diffopt+=inline:word')
+  local sw1 = [[
+    {7:  }{4:^foo+}{27:bar}{4: test   }│{7:  }{4:foo+}{27:baz}{4: test   }|
+    {1:~                }│{1:~                }|*17
+    {3:Xdifile1          }{2:Xdifile2         }|
+                                       |
+  ]]
+  screen:expect(sw1)
+
+  command('set iskeyword+=+ | diffupdate')
+  screen:expect([[
+    {7:  }{27:^foo+bar}{4: test   }│{7:  }{27:foo+baz}{4: test   }|
+    {1:~                }│{1:~                }|*17
+    {3:Xdifile1          }{2:Xdifile2         }|
+                                       |
+  ]])
+
+  command('set iskeyword& | wincmd w')
+  command('set iskeyword+=+ | wincmd w | diffupdate')
+  -- Use the previous screen as 2nd buffer's iskeyword does not matter
+  screen:expect(sw1)
+
+  command('windo set iskeyword& | 1wincmd w')
+
+  screen:try_resize(69, 20)
+  command('wincmd =')
+  -- char diff: should slide highlight to whitespace boundary if possible for
+  -- better readability (by using forced indent-heuristics). A wrong result
+  -- would be if the highlight is "Bar, prefix". It should be "prefixBar, "
+  -- instead.
+  WriteDiffFiles('prefixFoo, prefixEnd', 'prefixFoo, prefixBar, prefixEnd')
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  screen:expect([[
+    {7:  }{4:^prefixFoo, prefixEnd            }│{7:  }{4:prefixFoo, }{100:prefixBar, }{4:prefixEnd }|
+    {1:~                                 }│{1:~                                 }|*17
+    {3:Xdifile1                           }{2:Xdifile2                          }|
+                                                                         |
+  ]])
+
+  screen:try_resize(39, 20)
+  command('wincmd =')
+  -- char diff: small gaps between inline diff blocks will be merged during refine step
+  -- - first segment: test that we iteratively merge small gaps after we merged
+  --   adjacent blocks, but only with limited number (set to 4) of iterations.
+  -- - second and third segments: show that we need a large enough adjacent block to
+  --   trigger a merge.
+  -- - fourth segment: small gaps are not merged when adjacent large block is
+  --   on a different line.
+  WriteDiffFiles(
+    'abcdefghijklmno\nanchor1\n'
+      .. 'abcdefghijklmno\nanchor2\n'
+      .. 'abcdefghijklmno\nanchor3\n'
+      .. 'test\nmultiline',
+    'a?c?e?g?i?k???o\nanchor1\n'
+      .. 'a??de?????klmno\nanchor2\n'
+      .. 'a??de??????lmno\nanchor3\n'
+      .. 't?s?\n??????i?e'
+  )
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  screen:expect([[
+    {7:  }{4:^a}{27:b}{4:c}{27:defghijklmn}{4:o  }│{7:  }{4:a}{27:?}{4:c}{27:?e?g?i?k???}{4:o  }|
+    {7:  }anchor1          │{7:  }anchor1          |
+    {7:  }{4:a}{27:bc}{4:de}{27:fghij}{4:klmno  }│{7:  }{4:a}{27:??}{4:de}{27:?????}{4:klmno  }|
+    {7:  }anchor2          │{7:  }anchor2          |
+    {7:  }{4:a}{27:bcdefghijk}{4:lmno  }│{7:  }{4:a}{27:??de??????}{4:lmno  }|
+    {7:  }anchor3          │{7:  }anchor3          |
+    {7:  }{4:t}{27:e}{4:s}{27:t}{4:             }│{7:  }{4:t}{27:?}{4:s}{27:?}{4:             }|
+    {7:  }{27:multilin}{4:e        }│{7:  }{27:??????i?}{4:e        }|
+    {1:~                  }│{1:~                  }|*10
+    {3:Xdifile1            }{2:Xdifile2           }|
+                                           |
+  ]])
+
+  screen:try_resize(49, 20)
+  command('wincmd =')
+  -- Test multi-line blocks and whitespace
+  WriteDiffFiles(
+    'this   is   \nsometest text foo\nbaz abc def \none\nword another word\nadditional line',
+    'this is some test\ntexts\nfoo bar abX Yef     \noneword another word'
+  )
+  command('set diffopt=internal,filler diffopt+=inline:char,iwhite')
+  screen:expect([[
+    {7:  }{4:^this   is             }│{7:  }{4:this is some}{100: }{4:test     }|
+    {7:  }{4:sometest text foo     }│{7:  }{4:text}{100:s}{4:                 }|
+    {7:  }{4:ba}{27:z}{4: ab}{27:c}{4: }{27:d}{4:ef           }│{7:  }{4:foo ba}{27:r}{4: ab}{27:X}{4: }{27:Y}{4:ef       }|
+    {7:  }{4:one                   }│{7:  }{4:oneword another word  }|
+    {7:  }{4:word another word     }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line       }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {3:Xdifile1                 }{2:Xdifile2                }|
+                                                     |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:word,iwhite')
+  screen:expect([[
+    {7:  }{4:^this   is             }│{7:  }{4:this is }{27:some}{4: }{27:test}{4:     }|
+    {7:  }{27:sometest}{4: }{27:text}{4: }{27:foo}{4:     }│{7:  }{27:texts}{4:                 }|
+    {7:  }{27:baz}{4: }{27:abc}{4: }{27:def}{4:           }│{7:  }{27:foo}{4: }{27:bar}{4: }{27:abX}{4: }{27:Yef}{4:       }|
+    {7:  }{27:one}{4:                   }│{7:  }{27:oneword}{4: another word  }|
+    {7:  }{27:word}{4: another word     }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line       }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {3:Xdifile1                 }{2:Xdifile2                }|
+                                                     |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:char,iwhiteeol')
+  screen:expect([[
+    {7:  }{4:^this }{100:  }{4:is             }│{7:  }{4:this is some}{100: }{4:test     }|
+    {7:  }{4:sometest text foo     }│{7:  }{4:text}{100:s}{4:                 }|
+    {7:  }{4:ba}{27:z}{4: ab}{27:c}{4: }{27:d}{4:ef           }│{7:  }{4:foo ba}{27:r}{4: ab}{27:X}{4: }{27:Y}{4:ef       }|
+    {7:  }{4:one                   }│{7:  }{4:oneword another word  }|
+    {7:  }{4:word another word     }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line       }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {3:Xdifile1                 }{2:Xdifile2                }|
+                                                     |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:word,iwhiteeol')
+  screen:expect([[
+    {7:  }{4:^this }{100:  }{4:is             }│{7:  }{4:this is }{27:some}{4: }{27:test}{4:     }|
+    {7:  }{27:sometest}{4: }{27:text}{4: foo     }│{7:  }{27:texts}{4:                 }|
+    {7:  }{27:baz}{4: }{27:abc}{4: }{27:def}{4:           }│{7:  }{4:foo }{27:bar}{4: }{27:abX}{4: }{27:Yef}{4:       }|
+    {7:  }{27:one}{4:                   }│{7:  }{27:oneword}{4: another word  }|
+    {7:  }{27:word}{4: another word     }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line       }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {3:Xdifile1                 }{2:Xdifile2                }|
+                                                     |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:char,iwhiteall')
+  screen:expect([[
+    {7:  }{4:^this   is             }│{7:  }{4:this is some test     }|
+    {7:  }{4:sometest text foo     }│{7:  }{4:text}{100:s}{4:                 }|
+    {7:  }{4:ba}{27:z}{4: ab}{27:c d}{4:ef           }│{7:  }{4:foo ba}{27:r}{4: ab}{27:X Y}{4:ef       }|
+    {7:  }{4:one                   }│{7:  }{4:oneword another word  }|
+    {7:  }{4:word another word     }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line       }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {3:Xdifile1                 }{2:Xdifile2                }|
+                                                     |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:word,iwhiteall')
+  screen:expect([[
+    {7:  }{4:^this   is             }│{7:  }{4:this is }{27:some test}{4:     }|
+    {7:  }{27:sometest text}{4: foo     }│{7:  }{27:texts}{4:                 }|
+    {7:  }{27:baz abc def }{4:          }│{7:  }{4:foo }{27:bar abX Yef     }{4:  }|
+    {7:  }{27:one}{4:                   }│{7:  }{27:oneword}{4: another word  }|
+    {7:  }{27:word}{4: another word     }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line       }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {3:Xdifile1                 }{2:Xdifile2                }|
+                                                     |
+  ]])
+
+  -- newline should be highlighted too when 'list' is set
+  command('windo set list listchars=eol:$')
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  screen:expect([[
+    {7:  }{4:this }{100:  }{4:is }{100:  }{103:$}{4:         }│{7:  }{4:^this is some}{100: }{4:test}{101:$}{4:    }|
+    {7:  }{4:sometest}{27: }{4:text}{27: }{4:foo}{101:$}{4:    }│{7:  }{4:text}{27:s}{101:$}{4:                }|
+    {7:  }{4:ba}{27:z}{4: ab}{27:c}{4: }{27:d}{4:ef }{11:$}{4:         }│{7:  }{4:foo}{27: }{4:ba}{27:r}{4: ab}{27:X}{4: }{27:Y}{4:ef }{100:    }{11:$}{4: }|
+    {7:  }{4:one}{103:$}{4:                  }│{7:  }{4:oneword another word}{11:$}{4: }|
+    {7:  }{4:word another word}{11:$}{4:    }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line}{104:$}{22:      }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {2:Xdifile1                 }{3:Xdifile2                }|
+                                                     |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:char,iwhite')
+  screen:expect([[
+    {7:  }{4:this   is   }{11:$}{4:         }│{7:  }{4:^this is some}{100: }{4:test}{11:$}{4:    }|
+    {7:  }{4:sometest text foo}{11:$}{4:    }│{7:  }{4:text}{100:s}{11:$}{4:                }|
+    {7:  }{4:ba}{27:z}{4: ab}{27:c}{4: }{27:d}{4:ef }{11:$}{4:         }│{7:  }{4:foo ba}{27:r}{4: ab}{27:X}{4: }{27:Y}{4:ef     }{11:$}{4: }|
+    {7:  }{4:one}{103:$}{4:                  }│{7:  }{4:oneword another word}{11:$}{4: }|
+    {7:  }{4:word another word}{11:$}{4:    }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line}{104:$}{22:      }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {2:Xdifile1                 }{3:Xdifile2                }|
+                                                     |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:char,iwhiteeol')
+  screen:expect([[
+    {7:  }{4:this }{100:  }{4:is   }{11:$}{4:         }│{7:  }{4:^this is some}{100: }{4:test}{11:$}{4:    }|
+    {7:  }{4:sometest text foo}{11:$}{4:    }│{7:  }{4:text}{100:s}{11:$}{4:                }|
+    {7:  }{4:ba}{27:z}{4: ab}{27:c}{4: }{27:d}{4:ef }{11:$}{4:         }│{7:  }{4:foo ba}{27:r}{4: ab}{27:X}{4: }{27:Y}{4:ef     }{11:$}{4: }|
+    {7:  }{4:one}{103:$}{4:                  }│{7:  }{4:oneword another word}{11:$}{4: }|
+    {7:  }{4:word another word}{11:$}{4:    }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line}{104:$}{22:      }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {2:Xdifile1                 }{3:Xdifile2                }|
+                                                     |
+  ]])
+  command('set diffopt=internal,filler diffopt+=inline:char,iwhiteall')
+  screen:expect([[
+    {7:  }{4:this   is   }{11:$}{4:         }│{7:  }{4:^this is some test}{11:$}{4:    }|
+    {7:  }{4:sometest text foo}{11:$}{4:    }│{7:  }{4:text}{100:s}{11:$}{4:                }|
+    {7:  }{4:ba}{27:z}{4: ab}{27:c d}{4:ef }{11:$}{4:         }│{7:  }{4:foo ba}{27:r}{4: ab}{27:X Y}{4:ef     }{11:$}{4: }|
+    {7:  }{4:one}{11:$}{4:                  }│{7:  }{4:oneword another word}{11:$}{4: }|
+    {7:  }{4:word another word}{11:$}{4:    }│{7:  }{23:----------------------}|
+    {7:  }{22:additional line}{104:$}{22:      }│{7:  }{23:----------------------}|
+    {1:~                       }│{1:~                       }|*12
+    {2:Xdifile1                 }{3:Xdifile2                }|
+                                                     |
+  ]])
+  command('windo set nolist')
+end)
+
+-- oldtest: Test_diff_inline_multibuffer()
+it('diff mode inline highlighting with 3 buffers', function()
+  write_file('Xdifile1', '')
+  write_file('Xdifile2', '')
+  write_file('Xdifile3', '')
+  finally(function()
+    os.remove('Xdifile1')
+    os.remove('Xdifile2')
+    os.remove('Xdifile3')
+  end)
+
+  local screen = Screen.new(75, 20)
+  screen:add_extra_attr_ids({
+    [100] = { background = Screen.colors.Blue1 },
+  })
+  command('args Xdifile1 Xdifile2 Xdifile3 | vert all | windo diffthis | 1wincmd w')
+  command('wincmd =')
+  command('hi DiffTextAdd guibg=Blue')
+
+  WriteDiffFiles3(
+    'That is buffer1.\nanchor\nSome random text\nanchor',
+    'This is buffer2.\nanchor\nSome text\nanchor\nbuffer2/3',
+    'This is buffer3. Last.\nanchor\nSome more\ntext here.\nanchor\nonly in buffer2/3\nnot in buffer1'
+  )
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  local s1 = [[
+    {7:  }{4:^Th}{27:at}{4: is buffer}{27:1}{4:.       }│{7:  }{4:Th}{27:is}{4: is buffer}{27:2}{4:.      }│{7:  }{4:Th}{27:is}{4: is buffer}{27:3. Last}{4:.}|
+    {7:  }anchor                 │{7:  }anchor                │{7:  }anchor                |
+    {7:  }{4:Some }{27:random }{4:text       }│{7:  }{4:Some text             }│{7:  }{4:Some }{27:more}{4:             }|
+    {7:  }{23:-----------------------}│{7:  }{23:----------------------}│{7:  }{4:text}{100: here.}{4:            }|
+    {7:  }anchor                 │{7:  }anchor                │{7:  }anchor                |
+    {7:  }{23:-----------------------}│{7:  }{4:buffer2/3             }│{7:  }{100:only in }{4:buffer2/3     }|
+    {7:  }{23:-----------------------}│{7:  }{23:----------------------}│{7:  }{22:not in buffer1        }|
+    {1:~                        }│{1:~                       }│{1:~                       }|*11
+    {3:Xdifile1                  }{2:Xdifile2                 Xdifile3                }|
+                                                                               |
+  ]]
+  screen:expect(s1)
+
+  -- Close one of the buffers and make sure it updates correctly
+  command('diffoff')
+  screen:expect([[
+    ^That is buffer1.         │{7:  }{4:This is buffer}{27:2}{4:.      }│{7:  }{4:This is buffer}{27:3. Last}{4:.}|
+    anchor                   │{7:  }anchor                │{7:  }anchor                |
+    Some random text         │{7:  }{4:Some text             }│{7:  }{4:Some }{100:more}{4:             }|
+    anchor                   │{7:  }{23:----------------------}│{7:  }{4:text}{100: here.}{4:            }|
+    {1:~                        }│{7:  }anchor                │{7:  }anchor                |
+    {1:~                        }│{7:  }{4:buffer2/3             }│{7:  }{100:only in }{4:buffer2/3     }|
+    {1:~                        }│{7:  }{23:----------------------}│{7:  }{22:not in buffer1        }|
+    {1:~                        }│{1:~                       }│{1:~                       }|*11
+    {3:Xdifile1                  }{2:Xdifile2                 Xdifile3                }|
+                                                                               |
+  ]])
+
+  -- Update text in the non-diff buffer and nothing should be changed
+  feed('isometext')
+  screen:expect([[
+    sometext^That is buffer1. │{7:  }{4:This is buffer}{27:2}{4:.      }│{7:  }{4:This is buffer}{27:3. Last}{4:.}|
+    anchor                   │{7:  }anchor                │{7:  }anchor                |
+    Some random text         │{7:  }{4:Some text             }│{7:  }{4:Some }{100:more}{4:             }|
+    anchor                   │{7:  }{23:----------------------}│{7:  }{4:text}{100: here.}{4:            }|
+    {1:~                        }│{7:  }anchor                │{7:  }anchor                |
+    {1:~                        }│{7:  }{4:buffer2/3             }│{7:  }{100:only in }{4:buffer2/3     }|
+    {1:~                        }│{7:  }{23:----------------------}│{7:  }{22:not in buffer1        }|
+    {1:~                        }│{1:~                       }│{1:~                       }|*11
+    {3:Xdifile1 [+]              }{2:Xdifile2                 Xdifile3                }|
+    {5:-- INSERT --}                                                               |
+  ]])
+  feed('<Esc>')
+  command('silent! undo')
+
+  command('diffthis')
+  screen:expect(s1)
+
+  -- Test that removing first buffer from diff will in turn use the next
+  -- earliest buffer's iskeyword during word diff.
+  WriteDiffFiles3('This+is=a-setence', 'This+is=another-setence', 'That+is=a-setence')
+  command('set iskeyword+=+ | 2wincmd w | set iskeyword+=- | 1wincmd w')
+  command('set diffopt=internal,filler diffopt+=inline:word')
+  local s4 = [[
+    {7:  }{27:^This+is}{4:=}{27:a}{4:-setence      }│{7:  }{27:This+is}{4:=}{27:another}{4:-setenc}│{7:  }{27:That+is}{4:=}{27:a}{4:-setence     }|
+    {1:~                        }│{1:~                       }│{1:~                       }|*17
+    {3:Xdifile1                  }{2:Xdifile2                 Xdifile3                }|
+                                                                               |
+  ]]
+  screen:expect(s4)
+  command('diffoff')
+  screen:expect([[
+    ^This+is=a-setence        │{7:  }{27:This}{4:+is=}{27:another-setenc}│{7:  }{27:That}{4:+is=}{27:a-setence}{4:     }|
+    {1:~                        }│{1:~                       }│{1:~                       }|*17
+    {3:Xdifile1                  }{2:Xdifile2                 Xdifile3                }|
+                                                                               |
+  ]])
+  command('diffthis')
+  screen:expect(s4)
+
+  -- Test multi-buffer char diff refinement, and that removing a buffer from
+  -- diff will update the others properly.
+  WriteDiffFiles3('abcdefghijkYmYYY', 'aXXdXXghijklmnop', 'abcdefghijkYmYop')
+  command('set diffopt=internal,filler diffopt+=inline:char')
+  local s6 = [[
+    {7:  }{4:^a}{27:bcdef}{4:ghijk}{27:YmYYY}{4:       }│{7:  }{4:a}{27:XXdXX}{4:ghijk}{27:lmnop}{4:      }│{7:  }{4:a}{27:bcdef}{4:ghijk}{27:YmYop}{4:      }|
+    {1:~                        }│{1:~                       }│{1:~                       }|*17
+    {3:Xdifile1                  }{2:Xdifile2                 Xdifile3                }|
+                                                                               |
+  ]]
+  screen:expect(s6)
+  command('diffoff')
+  screen:expect([[
+    ^abcdefghijkYmYYY         │{7:  }{4:a}{27:XXdXX}{4:ghijk}{27:l}{4:m}{27:n}{4:op      }│{7:  }{4:a}{27:bcdef}{4:ghijk}{27:Y}{4:m}{27:Y}{4:op      }|
+    {1:~                        }│{1:~                       }│{1:~                       }|*17
+    {3:Xdifile1                  }{2:Xdifile2                 Xdifile3                }|
+                                                                               |
+  ]])
+  command('diffthis')
+  screen:expect(s6)
+end)