The line position after "Move to parent" in tig blame.

[akr]

I found that "Move to parent" (',' key) in tig blame doesn't set the line position appropriately.

% git init
Initialized empty Git repository in /tmp/h/.git/
% print -l a a a b foo c d d d d d d d d d d d d d d > file
% cat file
a
a
a
b
foo
c
d
d
d
d
d
d
d
d
d
d
d
d
d
d
% git add file; git commit -m 'initial file'
[master (root-commit) 54a3b91] initial file
 1 file changed, 20 insertions(+)
 create mode 100644 file
% print -l a a a a a a a a a a a b bar c > file
% cat file
a
a
a
a
a
a
a
a
a
a
a
b
bar
c
% git add file ; git commit -m 'modified file'
[master e693734] modified file
 1 file changed, 9 insertions(+), 15 deletions(-)
% strace -s 2000 -f -o log /home/src/tig/bin/tig blame file

Then, tig shows following screen.

54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   1│ a
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   2│ a
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   3│ a
e693734 Tanaka Akira 2019-11-29 20:59 +0900   4│ a
e693734 Tanaka Akira 2019-11-29 20:59 +0900   5│ a
e693734 Tanaka Akira 2019-11-29 20:59 +0900   6│ a
e693734 Tanaka Akira 2019-11-29 20:59 +0900   7│ a
e693734 Tanaka Akira 2019-11-29 20:59 +0900   8│ a
e693734 Tanaka Akira 2019-11-29 20:59 +0900   9│ a
e693734 Tanaka Akira 2019-11-29 20:59 +0900  10│ a
e693734 Tanaka Akira 2019-11-29 20:59 +0900  11│ a
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  12│ b
e693734 Tanaka Akira 2019-11-29 20:59 +0900  13│ bar    <------ press "," here
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  14│ c

I pressed "," (Move to parent) at "bar" line as I noted as above.
Then tig shows follows.

54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   1│ a
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   2│ a
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   3│ a
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   4│ b
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   5│ foo
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   6│ c
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   7│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   8│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900   9│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  10│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  11│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  12│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  13│ d      <------- cursor here
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  14│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  15│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  16│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  17│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  18│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  19│ d
54a3b91 Tanaka Akira 2019-11-29 20:59 +0900  20│ d

The cursor line is set at the line 13 as I noted as above.

I intended to change the line "foo" to "bar",
the cursor should be positioned at the line 5.

It seems tig determine the line position in parent commit using git diff -U0
(The function setup_blame_parent_line in src/blame.c).

I checked git diff command invoked by tig.

% grep '"-U0"' log|tail -1                                                                                                                                           
23134 execve("/bin/git", ["git", "diff", "--encoding=UTF-8", "--no-textconv", "--no-ext-diff", "--no-color", "-U0", "54a3b91240752884232d471fae6db09a879fce29:file", "e693734891968f483446c17a7f5a7ffe1433c0dd:file", "--"], 0x7ffc49783b58 /* 61 vars */) = 0
% git diff --encoding=UTF-8 --no-textconv --no-ext-diff --no-color -U0 54a3b91240752884232d471fae6db09a879fce29:file e693734891968f483446c17a7f5a7ffe1433c0dd:file --|cat
diff --git a/file b/file
index dbb7301..45f4569 100644
--- a/file
+++ b/file
@@ -3,0 +4,8 @@ a
+a
+a
+a
+a
+a
+a
+a
+a
@@ -5 +13 @@ b
-foo
+bar
@@ -7,14 +14,0 @@ c
-d
-d
-d
-d
-d
-d
-d
-d
-d
-d
-d
-d
-d
-d

It seems git diff correctly found my intention, "foo" is changed to "bar".
So, I think the current behavior is not intentional.

I compiled tig today.

% /home/src/tig/bin/tig -v               
tig version 2.5.0-1-g6202c60
ncursesw version 6.1.20181013