Print 10 violations in normal mode

[mpickering]

Using --verbose on a large project prints out too much output (see haskell/cabal#10744)

Printing out all the violations if there are a lot of them is quite slow, printing out a lot to stdout is not that fast.

Therefore we reach a compromise where we print up to 10 reasons for failure and omit the rest. If you want all the failures you can use --verbose.

Fixes #48

---

What do you think @andreasabel ? The other solution I can think of was to add a flag which controlled whether violations were printed out.

[ulysses4ever]

Therefore we reach a compromise where we print up to 10 reasons for failure and omit the rest. If you want all the failures you can use --verbose.

Sounds good to me.

[ulysses4ever]

On the second thought... I think the issue in the past was that collecting violations slowed down the tool quite a bit. That's why it was hidden behind the --verbose flag:

• Print line violations only under --verbose flag #49

So, this patch probably gets back to square one?

Re-using the verbose flag was also a bad idea because on big projects just printing out file names (what verbose have been always doing) quickly becomes overwhelming. So, I think, more flags are necessary anyway. E.g. verbose should be unrelated to printing violations, and a new flag with a numeric value and a default would say whether to print violations and if yes, how many. For instance --violations with 0 as the default -- and --violations 10 to do what this patch does.

[mpickering]

@ulysses4ever I checked the profile and the slow part is printing the violations to stdout. Always collecting warnings is slightly slower, but not noticeable.

[ulysses4ever]

Oh, that’s good then. I still think decoupling violations printing from --verbose would be a good improvement but may be it can be done separately.

Just FYI, I can’t approve things here, just sticking around as a past contributor.

[mpickering]

Thanks Artem.

I don't mind splitting up the flag if that's what @andreasabel prefers. My goal is a solution which can run on CI and you can see what the violations are.

[andreasabel]

Sorry for the delay in looking into this.
How about the following refinement of --verbose?

• no flag: no error printed
• --verbose=all : all errors printed
• --verbose=N : at most N errors printed, defaults to 10, so
• --verbose : at most 10 errors printed

[andreasabel]

I pushed a commit to this extend. What do you think, @mpickering and @ulysses4ever ?

[ulysses4ever]

@andreasabel it's a fine interface but I don't think it solves the original problem. If you follow the link to the cabal ticket, you will see the crux of it well-put by Matt:

Either, the failures should be reported at the end, or run in non-verbose mode.

haskell/cabal#10744

Right now it's still hard to find one violation in a project with hundreds of modules, like Cabal, because of all the filenames that --verbose prints.