do not require a coloured Unicode terminal for opam-ci

[avsm]

The current dashboard display requires an ANSI and Unicode tty due to the use of colours. This is not optimal for several reasons:

• it makes it difficult to use with screen readers
• file redirection is messy
• it also fails to work on Windows due to Consolas not supporting the right format (via @dra27)

We should fallback to a more verbose rendering format in these situations instead of blasting escape codes to the screen unconditionally.

[samoht]

Also it doesn't help with copy/pasting code. Ideally the success and failure symbols should just be different, even if they have different colors. I advise to pick a consistent style, e.g. all successes are in circles and errors in square boxes or something like that.

[avsm]

Agreed, but the difficulty here is just finding a good Unicode symbol set that also renders on Windows. Suggestions very welcome -- the relevant code to be factored is in src/opam-ci/user.ml#L24

[trefis]

To go a bit further: I think a --ascii option is desirable (even though it makes the output less compact).

[samoht]

One idea could be to use a simple table instead of encoding the same information again and again on every line.

So instead of:

                     alcotest-async          0.8.2  ③ ④ ⑤ ⑥ ⑦ ⑧   🄳 🄰 🅄 🄵 🅂   ⓧ ⓐ ⓟ   ∬ fl ⚐
                            datakit         0.12.0  ③ ④ ⑤ ⑥ ⑦ ⑧   🄳 🄰 🅄 🄵 🅂   ⓧ ⓐ ⓟ   ∬ fl ⚐
              datakit-bridge-github         0.12.0  ③ ④ ⑤ ⑥ ⑦ ⑧   🄳 🄰 🅄 🄵 🅂   ⓧ ⓐ ⓟ   ∬ fl ⚐

Have something like that:

                               ③ ④ ⑤ ⑥ ⑦ ⑧   🄳 🄰 🅄 🄵 🅂   ⓧ ⓐ ⓟ   ∬ fl ⚐
alcotest-async        0.8.2    ✓  ✓  ✓  ✓ ✗  ✗   ✓  ✗  ✗  ✗  ✓   ✓  ✓  ✓   ✓ ✗ ✗
datakit               0.12.0   ✓  ✓  ✓  ✓ ✗  ✗   ✓  ✗  ✗  ✗  ✓   ✓  ✓  ✓   ✓ ✗ ✗
datakit-bridge-github 0.12.0   ✗  ✓  ✓  ✗ ✗  ✗   ✓  ✗  ✗  ✗  ✓   ✗  ✓  ✓   ✓ ✗ ✓

[samoht]

Also it would be nice if the columns to display should be customisable, for instance using a config file. Also maybe it's not worth showing the columns where everything is fine :-)

[dbuenzli]

Since you are already using Fmt, you might be interested in using Fmt_tty which has support for configuring conditional UTF-8 output and ANSI coloring in some kind of standard way.

Besides Fmt_cli has a cmdliner fragment to handle an explicit --color argument, possibly baked by a custom environment variable.

Here's a sample usage for the coloring bits.

[lpw25]

Could you also use other unicode for the symbols for debian, alpine etc.? I don't have any fonts that can display these letters in boxes symbols, and I imagine I am not alone.