This is currently marked TODO in interface.c:gfc_expand_expr/gfc_expand_assign. When looking for a matching interface or type-bound operator, we could always continue looking through all possibilities and see if more than one option is found, in which case we should emit an error (or at least warn about that one of those will be chosen "arbitrarily").
-- Summary: Ambiguity checks for type-bound and interface operator calls Product: gcc Version: unknown Status: UNCONFIRMED Keywords: diagnostic Severity: normal Priority: P3 Component: fortran AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: domob at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41178