Tool to find TODO/FIXME only added in current branch

[bew]

Brainstorm

git grep TODO main | sed 's/^[^:]\+://' > main_todos
git grep TODO HEAD | sed 's/^[^:]\+://' > head_todoes
combine head_todoes xor main_todos

That looks like it works, but I don't get the line numbers...
(also: I also get TODOs that are in main but not my branch... I don't actually want them!)
And if I add -n to git grep to have the line numbers, the combination might not work as the lines content don't match anymore ><

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I could use git diff -U0 main.. to get a diff of all changes in the branch
There might be some options to avoid doing work, give better output, like --no-relative, --no-renames..
Also, it should skip leading indents, a TODO is a TODO, whereever it's placed!

Could use some git diff parsing code from delta ?

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(Thinking far: Could become a generic grep over changes in the branch?)
Stackoverflow already saw that question, WITHOUT conclusive / acceptable results..

• https://stackoverflow.com/questions/52617314/git-grep-across-all-new-and-modified-files-before-commit
• https://stackoverflow.com/questions/24212372/script-to-find-all-todo-comments-created-on-a-git-branch
  There IS a solution here: https://stackoverflow.com/a/51263327 BUT that requires searching twice, once to get the matching strings, another one (slow?) to get full file locations+matching string..

=> It would be better to just use git diff output and fill in line numbers!