------- Comment #2 from ian_harvey at bigpond dot com 2010-01-11 01:56 ------- Some primitive debugging: As directed by parse_contained, parsing and subsequent processing of the use statement in other_proc (parse_progunit) occurs prior to parsing of the add_b function and hence determination of the characteristics of the add_b symbol. This use statement processing includes ambiguous interface checking (gfc_compare_interfaces), which doesn't deal with the case when the symbol associated with argument s2 is of unknown type (BT_UNKNOWN) and no name is provided for type resolution.
A source code workaround is to move the USE statement to the specification part of the module or to reorder the module procedures such that add_b occurs before other_proc. The internal error is also generated if the module procedure name given in the INTERFACE OPERATOR block doesn't exist as a module procedure. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42684
