Nested functions are permitted for C but not C++ as extension.
They are also permitted for Fortran, which generates DECL_CONTEXT
== NAMESPACE_DECL for module variables.

That causes the gcc_assert (decl_function_context (decl) == info->context)
to fail in tree-nested.c's lookup_field_for_decl.

The call happens in convert_local_reference_stmt for:
2524        case GIMPLE_ASSIGN:
2525          if (gimple_clobber_p (stmt))
2528              if (DECL_P (lhs)
2529                  && !use_pointer_in_frame (lhs)
2530                  && lookup_field_for_decl (info, lhs, NO_INSERT))

The latter runs into the assert mentioned above. And the
'= {CLOBBER}' occurs in gfortran due to the intent(out).

As additional ingredient, a nested (internal) procedure involved,
obviously as otherwise tree-nested.c wouldn't be involved.

The patch fixes the assert and in terms of the assert it makes
sense, but I am not sure whether there are assumptions
elsewhere which are wrong for NAMESPACE_DECL.

OK for mainline? GCC 10?

Tobias

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