Show custom error message in prompt with hide_input=True

[doiken]

fixes #2809

prompt() with hide_input=True always showed a generic error message, even for custom types.

This change masks the input value using repr(value) matching
(consistent with built-in types' {value!r} pattern) and shows
custom messages that don't contain the input value as-is.

[kdeldycke]

So exactly what I was thinking @AndreasBackx : this fix is way too naive. See the number of failing edge-cases I was able to add.

So now: either I try to fix it locally on top of that PR, or I can implement a better long-term solution. Maybe by modifying how UsageError manage the raw value. But I have not studied the consequences and impact yet.

[AndreasBackx]

I've got two thoughts as well. We could instead of a ValueError do a custom error like you say, but require the message to be a literal meaning you cannot interpolate the input value in it.

Or... we wrap the input value in a wrapper that has its own str and repr implementation that would obfuscate the real value. The real value would be some subfield perhaps. Though this would be a breaking change and I don't think it's very pretty.

[kdeldycke]

I've got two thoughts as well. We could instead of a ValueError do a custom error like you say, but require the message to be a literal meaning you cannot interpolate the input value in it.

Or... we wrap the input value in a wrapper that has its own str and repr implementation that would obfuscate the real value. The real value would be some subfield perhaps. Though this would be a breaking change and I don't think it's very pretty.

I think the subfield looks like the ultimate, realiable solution. But it would introduce too much changes in my opinion. And I am not sure if it will look clean or not. I propose to defer that exploration in another PR.

In the mean time, I implemented a solution based on regexp so the hidden heuristic is more robust and cover all cases. You can see the edge-cases I handle with this regexp in the associated unittests. Just pushed that on top of the PR.

So this PR is ready to be reviewed and merged unless someone has feedbacks.

[doiken]

Thanks so much for taking the time to push the regex-based solution and the extra test coverage!