dialyzer: Duplicate named variables are not detected

[kikofernandez]

Dialyzer allows duplicate named variables with different types in the type specification.

Example

-module(test).

-export([repeated_annotated_variables_different_types_in_when1/1,
         repeated_annotated_variables_different_types_in_when2/1]).

-spec repeated_annotated_variables_different_types_in_when1(X) -> X :: atom() when X :: integer().
repeated_annotated_variables_different_types_in_when1(X) ->
    X.

-spec repeated_annotated_variables_different_types_in_when2(X :: integer()) -> X when X :: integer().
repeated_annotated_variables_different_types_in_when2(X) ->
    X.

Running dialyzer test.erl does not throw any error.

Expected behaviour
Variables can only be bound once to a single type, since multiple definitions do not make sense.
Which type is the expected one if Dialyzer / linter allows for multiple definitions of the same named type?

Affected versions
OTP-23+

[kikofernandez]

PR implementation:
#7582

[kikofernandez]

This was implemented in here: #7717

The issue is that it breaks existing code (backwards incompatible) since we forbid the repetition of type variables...
We also use some benchmarks mentioned in that PR that are broken with this change, so the benchmarks cannot be build and we are in a stalled position...