Original bug ID: 7436
Reporter: @Drup
Status: resolved (set by @xavierleroy on 2017-02-19T17:20:44Z)
Resolution: won't fix
Priority: normal
Severity: tweak
Version: 4.04.0
Category: typing
Monitored by: @Drup

Bug description

When encountering a with constraints, signatures are expanded in Types.module_type (indeed, there is no Mty_with ..). Same for "module type of".

This cause issues for libraries with a big API surface that is instantiated several time. Tyxml is such example. In the file 1 which can be found in eliom, the same (big) signature is copied 6 time. The size of the resulting cmi is 2.0Mo. The size is such that it slows compilation notably (See 2).

One solution, which we are probably going to adopt, is to factor the module type out and share it among the various instances. It's possible in this case since most constraints are the same.

It would be nice if the cmi format could be compact in this case, by storing the with constraints.

Steps to reproduce

An easy test case, using tyxml alone (compiled with ocamlfind ocamlc -package tyxml -c foo.ml).

module type Foo =
  Html_sigs.Make(Tyxml.Xml)(Tyxml.Svg).T

the cmi file is 622o

module type Foo =
  Html_sigs.Make(Tyxml.Xml)(Tyxml.Svg).T
  with type 'a wrap = 'a 

the cmi file is 199Ko