[ft-devel] ABI breakage in 2.3.8 (bad bad bad !!)

[David Turner]

Hello,

I'm currently updating the Android FreeType sources to the latest CVS. In doing so, I noticed something that unfortunately
escaped me before that: we added a new field to a publicly declared structure, thus breaking the ABI.

More specifically, the declaration of PS_FontInfoRec in include/freetype/t1tables.h is now:

typedef struct  PS_FontInfoRec_
  {
    FT_String*  version;
    FT_String*  notice;
    FT_String*  full_name;
    FT_String*  family_name;
    FT_String*  weight;
    FT_Long     italic_angle;
    FT_Bool     is_fixed_pitch;
    FT_Short    underline_position;
    FT_UShort   underline_thickness;

    /* since 2.3.8 */

    FT_UShort   fs_type;

  } PS_FontInfoRec;

the problem is that this structure can be allocated by the user (either in the heap or the stack), e.g. when calling
a function like FT_Get_PS_Font_Info declared as:

FT_EXPORT( FT_Error )
FT_Get_PS_Font_Info( FT_Face      face,
                     PS_FontInfo  afont_info );

This is very bad !!.

It means that any client code that was built against 2.3.7 or older will now experience a nice
silent stack or heap memory corruption whenever it calls this function in 2.3.8.

I suggest that we do the following instead:

• remove the field from the definition
• provide a new function to retrieve the corresponding information, as in FT_Get_PS_FsType() or whatever, that will not break the ABI
• release 2.3.9 ASAP explaining why.
  

I really hope that there isn't any code that relies on this new field out there.

Generalyl speaking, we should *NOT* add fields to public structures, except a very few instances where we know that the
corresponding object should never be stack or heap allocated by the user (FT_Face or FT_GlyphSlot for example). Even
in these cases, I'd really prefer that we discuss such changes on the development mailing list before hand.

- David