Comment author: @xavierleroy

With CVS trunk, this definition is accepted at toplevel, but causes the following problem if put in .ml without .mli and compiled with ocamlc:

File "foo.ml", line 1, characters 0-1:
Error: The implementation foo.ml
does not match the interface (inferred signature):
Modules do not match:
sig type 'a t = 'a M.t constraint 'a = [< A ] end is not included in sig type 'a t = private 'a s constraint 'a = [< A ] end
Type declarations do not match:
type 'a t = 'a M.t constraint 'a = [< A ] is not included in type 'a t = private 'a s constraint 'a = [< A ]

Comment author: @garrigue

The second problem (reported by Xavier) is similar to PR4623, and was fixed for 3.11 in includecore.ml. (Looks like I missed the 1st report with my holidays..)

The first bug is specific to 3.10 (doesn't occur in 3.11).
With the CVS version it no longer causes a stack overflow... just a non-terminating computation. Should look into it.
Note that it is fundamentally different: it is a private row in 3.10, but a private abbreviation in 3.11. While the 3.11 semantics makes sense (use a private abbreviation to hide the representation of t), the 3.10 semantics does not make sense in this example: it should just be equivalent to writing "type 'a t = private [< `A]", which works ok. So this is really only about making the compiler terminate even on meaningless code.

Comment author: @garrigue

I was only keeping this one around because of 3.10, but since it went out of support a while ago, it seems ok to close this issue.