[PATCH wayland 0/3] "enum" and "bitfield" attributes for protocol XML files

Bill Spitzak spitzak at gmail.com
Fri Jun 26 10:25:46 PDT 2015

I am very much in favor of this, and posted earlier a further patch that
uses this information to produce better protocol documentation.

The above design is exactly correct (in particular the bitfield indicator
is on the enumeration, not the argument).

On Fri, Jun 26, 2015 at 8:04 AM, Auke Booij <auke at tulcod.com> wrote:

> On 26 June 2015 at 16:02, Auke Booij <auke at tulcod.com> wrote:
> > Although arguments can only refer to enums in specific cases (see the
> > scanner.c changes), this new protocol data should not break the C
> bindings.
> > It is thinkable that other bindings *do* use the data in a way that
> breaks
> > the protocol; however such usage will be considered nonstandard.
> In retrospect, I phrased this a bit poorly. Obviously this new code
> should not break any existing bindings: it merely introduces two new
> datums that no one is using so far. Instead, the three points I am
> making here are:
> - The scanner.c code checks whether arguments that have an enum
> attribute are of type (u)int, and if they refer to an enum with
> bitfield=true, then it checks they are of type uint (not int!).
> - In the discussion a few months ago, it emerged that whenever a
> protocol starts supplying such data, when it did not specify it
> before, this should not change the bindings API ("being more specific
> shouldn't break anything"). Indeed this is not the case for the C
> scanner, since it still doesn't use the data - these patches only
> block builds when the new attributes aren't consistent in the sense
> made by the previous point.
> - Other bindings, in theory, can use the data given by these new
> attributes, for example to strengthen the type safety of the generated
> API. However, this might introduce API breakages when the protocol is
> updated in a non-breaking way. While this is definitely not endorsed
> by this set of changes, these changes do provide a way to convey more
> type safety in strongly typed languages. My own (ab)use-case here is
> the Haskell bindings I wrote.
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