Add new theme: base16-256

[mk12]

See #1033 for the discussion that led to this.

In summary, the base16 theme introduced in #543 works great for users who configure their terminals with the base16 system in which the 16 ANSI colors are repurposed as base16 palette slots. But it doesn't work for users of base16-shell, which aims to solve problems with base16-unaware software by leaving the bright colors (ANSI 8-15) alone, and instead using codes 16-21 for extra base16 palette slots (requiring a 256-color terminal, hence base16-256).

Here is how terminal themes for regular base16 and 256-color/base16-shell differ:

ANSI code	base16	base16-256
08	base03	base03
09	base09	base08
10	base01	base0B
11	base02	base0A
12	base04	base0D
13	base06	base0E
14	base0F	base0C
15	base07	base07
16		base09
17		base0F
18		base01
19		base02
20		base04
21		base06

Notice codes 08 (bright black) and 15 (bright white) stay the same. But 09 (bright red) through 14 (bright cyan) are replaced with their non-bright counterparts, and those base16 colors are moved to ANSI codes 16-21.

So the new base16-256 theme is just like base16, but makes the following replacements:

• base09 goes from ANSI 09 to 16: #09000000 → #10000000
• base01 goes from ANSI 10 to 18: #0a000000 → #12000000
• base02 goes from ANSI 11 to 19: #0b000000 → #13000000
• base04 goes from ANSI 12 to 20: #0c000000 → #14000000
• base06 goes from ANSI 13 to 21: #0d000000 → #15000000
• base0F goes from ANSI 14 to 17: #0e000000 → #11000000

terminal.rs already maps any #RR000000 to the 256-color code RR, so no code change is needed.

Here is what base16 and base16-256 look like on macOS, kitty terminal with https://github.com/kdrag0n/base16-kitty/blob/master/colors/base16-solarized-light-256.conf, and fish shell with base16-shell/profile_helper.fish sourced:

It's not so obvious in this example, but in this theme constants like 2.0 are supposed to be orange, not red. The base16 theme shows red because it's using ANSI bright red (which is just plain red in the 256-color terminal theme). The base16-256 theme correctly shows it as orange because it instead uses ANSI code 16.

Note: I have not regenerated themes.bin — I assume that will be done on release as before.

[antoineco]

Looks much better in 256-color terminal themes 👍

YAML example, to refer to the linked issue

before:

after:

[antoineco]

LGTM

[mk12]

@sharkdp Please take a look when you have time :)

I've also updated the README with a section on the 8-bit color themes (ansi-dark, ansi-light, base16, and base16-256) to help avoid confusion about them.

[sharkdp]

Thank you very much for your contribution and for the awesome documentation (and updating the README)!

I have only one minor request: Could you please add an entry to the "unreleased" section in the CHANGELOG.md? The format is:

- Description what has been changed, see #123 (@user)

where #123 links to the bug ticket and/or this PR and user is your username.

[sharkdp]

I rebased your branch on master in order to run the new CI pipelines. I am expecting one (new) test to fail, which regenerates the binary caches before running the unit tests. We simply have to add the theme to tests/assets.rs to make it pass.

Note: I have not regenerated themes.bin — I assume that will be done on release as before.

yes 👍

[mk12]

I have only one minor request: Could you please add an entry to the "unreleased" section in the CHANGELOG.md?

Done! (I amended the 1st commit and force pushed)

[sharkdp]

Thank you for the update.

My new testing mechanism catches the (future) error, but now the tests for the old binary theme set fail, of course. I'm adding the updated themes.bin to this branch for now and will further work on my test suite 😄

[sharkdp]

Added in v0.16.0.