introduce verbosity levels

[hasufell]

We want verbosity for e.g. CI where:

• we don't see all the noisy debug output
• but we also don't have the wrapped screen output and no colors

[dfordivam]

If I understand correctly, we would like to see debug messages from ghcup, like these

[ Debug ] Decoding yaml at: /home/divam/.ghcup/cache/ghcup-0.0.8.yaml
[ Debug ] Running sh with arguments ["./configure","--prefix=/home/divam/.ghcup/ghc/9.6.6"]
[ Debug ] Running gmake with arguments ["DESTDIR=/home/divam/.ghcup/tmp/ghcup-82ee81a4336f1b13","install"]

without all the noisy output from ./configure and make. The output from these should be shown the same way it is shown without -v

[ulidtko]

FWIW, Github Actions CI does support console colors. (The classic escape sequences). Here's a quick sample:

But because GHA runner doesn't create a PTY (neither forwards it properly through all the containers) — the isatty(stdout) call returns false — thus virtually all classic tooling autodetects color support as absent — so it never works by default.

Must force-enable it explicitly, e.g. for stack call it with --color always.

[dfordivam]

These are the stats for the log generated by install ghc

Total lines: 16.5k
configure: 740
make: 430
merge tree log: 15.3k ("Recording installed file: ")

We can reduce a big amount of noise by removing merge tree logs from the default verbose output, and that would improve the situation a lot.

But there is another solution for GitHub as it has a way to group the log lines together and collapse them, so that viewing the file on the web will be much more easier.

To achieve this we need to wrap the log lines with these start/end "tags"

##[group][ Debug ] Log group header
...
...
##[endgroup]

One issue with this approach could be if there is interleaving of log lines from multiple places.