[XeTeX] Incorrect Bengali ZWJ behavior and v2 script spec

[Khaled Hosny]

On Mon, Mar 18, 2013 at 08:45:18PM +0200, Khaled Hosny wrote:
> On Mon, Mar 18, 2013 at 10:13:16AM -0500, Ian-Mathew Hornburg wrote:
> > Hello, and thanks to Khaled and contributors for their great work on this
> > project! I do work in Indic scripts, and XeTeX has been immensely helpful
> > in setting them.
> > 
> > I may have identified two possible bugs in 0.9999.0: the release notes
> > indicate that the version-2 OpenType Indic script tags are now supported,
> > and I’ve been testing various Bengali-script fonts with the git version of
> > XeTeX and a current install of TeX Live 2012 to check them for correct
> > shaping behavior. I’ve posted a MWE reproducing some examples from the
> > Microsoft standard here: [http://pastebin.com/mgAX8c7U].
> > 
> > Microsoft ships two Bengali fonts (Vrinda and Shonar Bangla; both v6.80)
> > with Windows 8 that support both the older (beng) and newer (bng2) Bengali
> > script specs. (Older versions of each are shipped with Windows 7 and other
> > Microsoft products.) The fonts behave correctly when using the beng script
> > feature, with the exception of a particular ZWJ sequence: the Microsoft
> > spec [https://www.microsoft.com/typography/OpenTypeDev/bengali/intro.htm]
> > says that the sequence of consonant-hasant-ZWJ-consonant should prevent a
> > ligature of the two consonants, then render a half-form of the first
> > consonant. XeTeX currently fails to suppress the ligature.
> 
> This looks like a HarfBuzz bug, I can reproduce it with its test tool
> and indeed Uniscribe gives a different result. If you can report this to
> HarfBuzz developers, you will be able to describe the issue better than
> me, else I’ll try to report it.

Actually it looks like a regression in 0.9.13 that we are using, 0.9.12
gives me the correct output. I’ll let HarfBuzz developers know about
this.

Regards,
Khaled