Make fail message more presentable

[SiegeLord]

Given this code,

fn main()
{
    fail!("This is why you fail.")
}

the failure message looks like this

task '<main>' failed at 'This is why you fail.', test.rs:3

This is problematic as the useful information (the message passed to fail!)is buried inside the sentence. It'd be better if the failure message was on its own line, something akin to:

task '<main>' failed at test.rs:3, saying:

This is why you fail.

This format also allows for space to mention other useful information (e.g. issue #11704).

[jooert]

Is this still something we want to do? I have a small patch that implements something like this and would also fix #11704, but I'm not sure how many people really want another format for panic messages. Changing the format might also break existing tools (for example, there are several run-tests in this repo that expect a panic).

[SiegeLord]

I'd be all for it, I still find those messages hard to read even after all these years.

[steveklabnik]

@jooert you should submit it

[SiegeLord]

The pull request didn't really fix this bug... should I make another bug like this, or is this a wontfix now?

[jooert]

Oh sorry, that's because I didn't change the original pull request message. Perhaps @alexcrichton can comment on this?

[alexcrichton]

This is somewhat of a wontfix for now, the discussion of #30402 concluded that we likely don't want to radically change the format for now due to the concurrency/verbosity reasons mentioned. If this becomes extra onerous in the future, however, we can consider reformatting these messages.