Tracking issue for --explain expansion

[alexcrichton]

Tracking issue for the --explain related portions of rust-lang/rfcs#1644

Current open questions are:

• Let's look at an implementation! Does it end up being reasonable?
• Is there a way to deprecate --explain <CODE> and instead use --explain to activate these errors?
• Is it easy to template these longer explanations for authors?

cc @jonathandturner (feel free to fill out more)

[GuillaumeGomez]

Some error explanations are (I think) very easy to update to this new RFC. Some others (the longest or most "general" ones) are almost impossible as is. Some rework on these last ones is needed first (split them in smaller errors for example).

[Dylan-DPC-zz]

#61137

[GuillaumeGomez]

Closing this one then.