Potential bug in --color-words output

Hello,

Given an initial file with the contents "not to be", which I then change to "to be", the output of 'git diff --color-words', is

   notto be

with the first three letters colored red. To me this seems incorrect as it implies, or at least misleadingly suggests, that there was no space between "not" and "to" in the original file. (Even though in that case the output is actually "nottoto be" with the "notto" in red and "to" in green.)

If instead I start with a file with contents "to be", which I then change to "not to be", then the output is as expected:

   not to be

(First three letters colored green.)

Am I correct in seeing this as a bug? If so, any tips on what parts of diff.c to look at when starting a patch?

Thanks,

Simeon

Am 28.10.22 um 23:08 schrieb Simeon Krastnikov:

Well, not really. When you have a file with

   Line one.
   Line two.

then change it to

   Line ONE.
   Line TWO.

then --color-words currently prints it as

   Line one.ONE.
   Line two.TWO.

because it does not print the whitespace after[*] a sequence of deleted words. But if it were printed, we would see

   Line one.
   ONE.
   Line two.
   TWO.

That is considered inferior; hence, it isn't printed.

The current algorithm produces sensible output in the vast majority of cases while also being fairly straight-forward. To make it work "better" (for some definition of that word) in the borderline cases, the algorithm would have to be made considerably more sophisticated.

[*] It might be whitespace before a sequence of words, but that does not change the gist of the argument.

-- Hannes

Hi Simeon,

On Fri, 28 Oct 2022, Simeon Krastnikov wrote:

This seems to be a limitation of the original `--color-words` design.

FWIW I find myself using these three aliases all the time now, i.e. using a different word-coloring mode that works much better for me:

	[alias]
		cwdiff = diff --color-words=\"[A-Za-z0-9_]+|.\"
	        cwlog = log --color-words=\"[A-Za-z0-9_]+|.\"
		cwshow = show --color-words=\"[A-Za-z0-9_]+|.\"

Explanation: the regex `[A-Za-z0-9_]+|.` treats runs of alphanumerical
characters (including the underscore) as words, and also treats any
individual characters that do not fall into that category as "words".

The only downside of this is that the coloring does not help identifying white-space differences because only the foreground color is changed (which does not result in any visible difference for white-space characters).

Maybe these aliases help you, too?

Ciao, Johannes

Hi,

in my copy of git there is:

---- git % git grep --line-number --no-color color-words

Documentation/RelNotes/1.5.4.txt:377: * "git diff --color-words" colored context lines in a wrong color.

Documentation/RelNotes/1.6.2.txt:100:* The definition of what constitutes a word for "git diff --color-words"

Documentation/RelNotes/1.6.5.3.txt:23: * "git diff --color-words -U0" didn't work correctly.

Documentation/RelNotes/1.7.2.txt:64: * "git diff --word-diff=<mode>" extends the existing "--color-words"

Documentation/RelNotes/1.7.2.txt:141: * "git diff --graph" works better with "--color-words" and other options

Documentation/diff-options.txt:475:--color-words[=<regex>]::

contrib/completion/git-completion.bash:1718: --no-color --color-words --no-renames --check

contrib/diff-highlight/README:9:You can use "--color-words" to highlight only the changed portions of

diff.c:1914: * '--color-words' algorithm can be described as:

diff.c:1929: * For '--graph' to work with '--color-words', we need to output the graph prefix

diff.c:2138:/* In "color-words" mode, show word-diff of words accumulated in the buffer */

diff.c:5566:            OPT_CALLBACK_F(0, "color-words", options, N_("<regex>"),

gitk-git/gitk:207:            "--color-words*" - "--word-diff=color" {

t/t4034-diff-words.sh:70:               word_diff --color-words

t/t4034-diff-words.sh:100:      word_diff --color-words &&

t/t4034-diff-words.sh:180:      word_diff --color-words --unified=0

t/t4034-diff-words.sh:185:      word_diff --color-words="[a-z]+"

t/t4034-diff-words.sh:190:      word_diff --color-words="[a-z${LF}]*"

t/t4034-diff-words.sh:203:      word_diff --color-words="[a-z]+"

t/t4034-diff-words.sh:208:      word_diff --color-words

t/t4034-diff-words.sh:217:      word_diff --color-words="[a-z]+"

t/t4034-diff-words.sh:240:      word_diff --color-words

t/t4034-diff-words.sh:262:      word_diff --color-words

t/t4034-diff-words.sh:278:      word_diff --color-words="a+"

t/t4034-diff-words.sh:294: word_diff --color-words=. ----

So there are tests in t/t4034-diff-words.sh and probably around diff.c:1914- diff.c:2138

Best, Stefan

Am Mo., 7. Nov. 2022 um 12:43 Uhr schrieb Simeon Krastnikov <skrastnikov@gmail.com>: