Add simple --diff colour support

[gechr]

Happy to extend this to make diff output more smart/configurable in future, but wanted to get the ball rolling with hardcoded colours as this (in my opinion!) makes --diff output considerably easier to visually parse.

Since it uses stringc from ansible.utils.color, it naturally obeys the standard ANSIBLE_[NO|FORCE]COLOR constants.

I note there's currently another PR open (#14434) which modifies the surrounding code, so if you'd like me to rebase this on top of that to make things easier, let me know.

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Screenshot

[bcoca]

oohhh ... pretty ....

[mgedmin]

❤️

[mgedmin]

BTW have you checked whether it looks readable on terminals that use white background?

[gechr]

@mgedmin: I haven't, because, though configurable, the colours I chose are already in use by default (green=ok, red=failed, cyan=skipped). Colours can also be tweaked in the user's terminal preferences if they're using a non-black background.

With that said, I'll push a change to make the colours configurable in Ansible as well - variety is the spice of life!

[mgedmin]

I haven't, because, though configurable, the colours I chose are already in use by default (green=changed, red=failed, cyan=skipped).

Ah. In that case I can confirm that the colours are perfectly readable.

[towolf]

Thanks a lot for checking off an item from my personal whiteboard:

The second one today actually.

@bcoca, now that --diff is a "Major Change" on the CHANGELOG for 2.1.0, can you please get my PRs merged that add diff mode to apt: and lineinfile:?

ansible/ansible-modules-core/pull/2944
ansible/ansible-modules-core/pull/2896

[mgedmin]

@bcoca also my "No newline at EOF" --diff fix from #14434 ;)