G'day all,

I believe I've found a bug regarding how git-blame(1) colours its output
when invoked with both --color-lines and --ignore-rev.

== Summary ==
git-blame(1) has two options of interest.  '--color-lines' colours a
line (in cyan by default) if it has the same blame as the preceding
line.  And '--ignore-rev <rev>' prevents any line from being blamed on
<rev>, instead blaming such lines on the most recent commit prior to
<rev> that modified those lines.

When used in combination, it is possible for consecutive lines to have
the same blame without the latter lines being coloured correctly.  I
first observed this behaviour on Git 2.47.3, but have since compiled
the latest release candidate (Git 2.53.0.rc2) and have observed the same
behaviour.

== Reproducibility ==
I was able to construct a minimal working example as follows.

First create and cd(1) into a temporary directory.  Let's name it
'git-test'.

$ mkdir git-test
$ cd git-test

Make git(1) ignore the system and global config files.  This is mainly
to aid in reproducibility.

$ export GIT_CONFIG_SYSTEM=/dev/null
$ export GIT_CONFIG_GLOBAL=/dev/null

Initialise a Git repository.

$ git init --initial-branch main
Initialized empty Git repository in /.../git-test/.git/

Now set some default values.  In particular, set blame.coloring to
repeatedLines; equivalent to the --color-lines option for git-blame(1).

$ git config set user.name 'John Git'
$ git config set user.email 'johngit@for.real'
$ git config set blame.coloring repeatedLines
$ git config set blame.date short

Create a file (let's name it 'text'), give it some text, and commit it.

$ echo Why hello there how are you | xargs -n1 > text
$ git add text
$ git commit --message 'init'
[main (root-commit) xxxxxxx] init
 1 file changed, 6 insertions(+)
 create mode 100644 text

Then fixup some punctuation in the file and commit it.

$ sed -i -e '3s/$/!/' -e '4s/h/H/' -e '6s/$/?/' text
$ git add text
$ git commit --message 'fix'
[main yyyyyyy] fix
 1 file changed, 3 insertions(+), 3 deletions(-)

If we now blame the file, we get the following.

$ git blame text
^xxxxxxx (John Git YYYY-MM-DD 1) Why
^xxxxxxx (John Git YYYY-MM-DD 2) hello
yyyyyyyy (John Git YYYY-MM-DD 3) there!
yyyyyyyy (John Git YYYY-MM-DD 4) How
^xxxxxxx (John Git YYYY-MM-DD 5) are
yyyyyyyy (John Git YYYY-MM-DD 6) you?

Where lines 2 and 4 are coloured cyan.  This is expected, since their
listed commits are the same as that on lines 1 and 3, respectively.

Now consider the output of git-blame(1) if we ignore the second commit.

$ git blame --ignore-rev HEAD text
^xxxxxxx (John Git YYYY-MM-DD 1) Why
^xxxxxxx (John Git YYYY-MM-DD 2) hello
^xxxxxxx (John Git YYYY-MM-DD 3) there!
^xxxxxxx (John Git YYYY-MM-DD 4) How
^xxxxxxx (John Git YYYY-MM-DD 5) are
^xxxxxxx (John Git YYYY-MM-DD 6) you?

My expected behaviour of git-blame(1) is to colour lines 2-6 cyan.  This
is because lines 1-6 all blame the same commit, meaning lines 2-6 all
have the same blame as their respective preceding lines.  And as the man
page for git-blame(1) states:

$ MANWIDTH=72 man git-blame | sed -n '/--color-lines$/,/^$/p'
       --color-lines
           Color line annotations in the default format differently if
           they come from the same commit as the preceding line. This
           makes it easier to distinguish code blocks introduced by
           different commits. The color defaults to cyan and can be
           adjusted using the color.blame.repeatedLines config option.

However, the actual behaviour of git-blame(1) is to colour only lines 2
and 4 cyan.  That is, it colours the output as if the --ignore-rev
option was not given.

== Environment ==
The following info was added verbatim from git-bugreport(1).

[System Info]
git version:
git version 2.53.0.rc2
cpu: x86_64
built from commit: ab380cb80b0727f7f2d7f6b17592ae6783e9820c
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
rust: disabled
gettext: enabled
libcurl: 8.14.1
OpenSSL: OpenSSL 3.5.4 30 Sep 2025
zlib: 1.3.1
SHA-1: SHA1_DC
SHA-256: SHA256_BLK
default-ref-format: files
default-hash: sha1
uname: Linux 6.12.63+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.63-1 (2025-12-30) x86_64
compiler info: gnuc: 14.2
libc info: glibc: 2.41
$SHELL (typically, interactive shell): /bin/bash


[Enabled Hooks]


And here's some extra info, in case it helps:

OS: Debian GNU/Linux 13 (trixie)
Terminal: GNOME Terminal 3.56.2
bash: (GNU bash) 5.2.37(1)-release (x86_64-pc-linux-gnu)
sed: (GNU sed) 4.9
xargs: (GNU findutils) 4.10.0

I'd be happy to further elaborate or provide help if needed.

-- 
Take care,
	Seth McDonald.

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