Original bug ID: 7318
Reporter: kosik
Status: acknowledged (set by @damiendoligez on 2016-11-08T10:49:30Z)
Resolution: open
Priority: low
Severity: feature
Version: 4.03.0
Target version: 4.05.0 +dev/beta1/beta2/beta3/rc1
Category: typing

Bug description

When I type:

  module M1 =
  struct
    type t = V0 | V1
  end

  (* M1 and M2 are equivalent *)
  module M2 =
  struct
    type t = M1.t = V0 | V1
  end

  (* M1 and M3 are not equivalent *)
  module M3 =
  struct
    type t = V0 | V1
  end

  module M4 =
  struct
    type t = {f0 : unit * unit * unit * M1.t * unit * unit * unit;
              f1 : unit * unit * unit * M1.t * unit * unit * unit}
  end

  (* A failed attempt to define a module equivalent to M4 *)
  module M5 =
  struct
    type t = M4.t = {f0 : unit * unit * unit * M2.t * unit * unit * unit;
                     f1 : unit * unit * unit * M3.t * unit * unit * unit}
  end

then the compiler (correctly) complains that:

  Error: This variant or record definition does not match that of type M4.t
         The types for field f1 are not equal.

The compiler marks the whole record definition.

Couldn't compiler mark the location of the particular field of the record whose type breaks the desired equality? (in this case "f1 : unit * unit * unit * M3.t * unit * unit * unit")

Or, even better, would it be possible to mark the location of the specific type-sub-term that breaks the equality? (in this case "M3.t")?