Re: bison 2.4 breaks libIDL 0.8.11 build

[Joel E. Denny]

On Tue, 4 Nov 2008, Juergen Daubert wrote:

> > > ./parser.y:610.9-10: $$ for the midrule at $6 of `struct_type' has no 
> > > declared type
> > > ./parser.y:627.9-10: $$ for the midrule at $10 of `union_type' has no 
> > > declared type

These errors are legitimate.

>         struct_type:          z_props TOK_STRUCT
>                     { $<str>$ = "struct"; }
>                     z_new_scope_catch '{'             {
>             g_hash_table_insert (__IDL_structunion_ht, $4, $4);
> 610:        $$ = IDL_type_struct_new ($4, NULL);

It is a bug that Bison 2.3 accepts this line.  The user failed to specify 
the semantic type for the mid-rule value (referenced by $$ here but $6 in 
later actions).  Bison 2.3 accidentally uses the semantic type from the 
LHS (which would be referenced by $$ if this were not a mid-rule).  The 
user is lucky that this just happens to be the right semantic type.

Bison 2.3a and later correctly spot this as a user error and fail because 
they realize there's no logical way to proceed.  The line should be 
rewritten as:

  $<tree>$ = IDL_type_struct_new ($4, NULL); 

>         }                             member_list
>                     '}' pop_scope                     {
>             g_hash_table_remove (__IDL_structunion_ht, $4);
>             $$ = $<tree>6;

This line correctly specifies the type of that same mid-rule value.

>             __IDL_assign_up_node ($$, $7);
>             IDL_TYPE_STRUCT ($$).member_list = $7;
>             assign_props (IDL_TYPE_STRUCT ($$).ident, $1);
>         }
>             ;
> 
>         union_type:           z_props TOK_UNION
>                     { $<str>$ = "union"; }
>                     z_new_scope_catch TOK_SWITCH '('
>                         switch_type_spec
>                     ')' '{'                           {
>             g_hash_table_insert (__IDL_structunion_ht, $4, $4);
> 627:        $$ = IDL_type_union_new ($4, $7, NULL);

Same problem, different rule.

>         }                             switch_body
>                     '}' pop_scope                     {
>             g_hash_table_remove (__IDL_structunion_ht, $4);
>             $$ = $<tree>10;

But gets it right again.

>             __IDL_assign_up_node ($$, $11);
>             IDL_TYPE_UNION ($$).switch_body = $11;
>             assign_props (IDL_TYPE_UNION ($$).ident, $1);
>         }
>             ;

I suggest you report this bug to the maintainers of libIDL.