Default implementation for Reader_def.print_outcome using Oprint from compiler-libs

Generate an extension node that will be reported as a syntax error by Merlin.

Physical locations might be too precise for some features.

For instance in: let x = f in y ^1 ^2

Merlin cannot distinguish position ^1 from ^2 in the normal AST, because IN doesn't appear in abstract syntax. This is a problem when completing, because a different environment should be selected for both positions.

One can add relaxed_location attributes to make some locations closer to the concrete syntax.

Here is the same line annotated with physical and relaxed locations: let x = f in y -- physical locations for f and y nodes -- relaxed locations for f and y nodes

If some code should be ignored by merlin when reporting information to the user, put a hide_node attribute.

This is useful for generated/desugared code which doesn't correspond to anything in concrete syntax (example use-case: encoding of some js_of_ocaml constructs).

The converse: when merlin should focus on a specific node of the AST. The main use case is also for js_of_ocaml.

Assuming <code> is translated to:

let module M = struct let prolog = ... (* boilerplate *)

let code = <mapping-of-code>

let epilog = ... (* boilerplate *) end in M.boilerplate

To make merlin focus on M.code and ignore the boilerplate (M.prolog and M.epilog), add a focus_node attribute to the M.code item.