Fix a bug where layout would be printed the first time the user queried an abstract type, but only the second time that the user queried a locally-abstract type. This is an omission in flambda-backend, so I'm posting a corresponding PR there: oxcaml/oxcaml#2115. We need not merge this merlin-jst PR; we can just wait until we pick up the flambda-backend change in the normal merge process.

Old approach that we're no longer taking (we never show layouts when the user asks for the type of a value anymore):

Previously, when you asked for the type of a value (the second time), merlin wouldn't print a type declaration if the type was abstract. E.g. asking for the type of 4 will only ever print int, not type int. But this means that there isn't a sensible places to hang a layout annotation.

Now, merlin always prints a type declaration for Tconstrs when you ask for the type of a value the second time.

This is a bit weird for locally-abstract types, where we print type a : immediate. We could print a : immediate instead, but I think we should be consistent. That is, we should either:

• print int : immediate and a : value
• print type int : immediate and type a : value

I prefer the second because it's more uniform with how we handle non-abstract Tconstrs.