FYI: New Fwd headers for Web IDL is there

[Kagami Rosylight]

As of bug 1957934 (30 April 2025, yes it's late...) we got new autogenerated forward declarations headers. From now on if you have an interface or dictionary like:

// foo.webidl

interface Foo {};

dictionary FooDict {};

Then you get forward declaration for Foo and FooDict in mozilla/dom/FooFwd.h.

And with typedefs:

// bar.webidl

typedef (Baz or Waz) BarUnion;

You get an alias named BarUnion in BarFwd.h instead of having to call it BarOrWaz.

Questions welcome, and happy software engineering.

(Thank you for the ping to post an actual announcement, unfortunately I lost the original notification that pinged me and don't remember who did it...)

[Gabriele Svelto]

On 31/07/2025 19:06, 'Kagami Rosylight' via dev-pl...@mozilla.org wrote:
> As of bug 1957934 <https://bugzilla.mozilla.org/show_bug.cgi?
> id=1957934> (30 April 2025, yes it's late...) we got new autogenerated

> forward declarations headers. From now on if you have an interface or
> dictionary like:
>
> // foo.webidl
> interface Foo {};
> dictionary FooDict {};
>
> Then you get forward declaration for Foo and FooDict in mozilla/dom/
> FooFwd.h.

this is great! I take this opportunity to remind everybody that we have
an `includehell` [1] bug where we gather all bugs about minimizing
unnecessary header inclusions. If you're touching code pulling in lots
of headers consider checking if you can prune some stuff or replace them
with forward declarations, the compilation time benefits are worth it.

Gabriele

[1] [Meta] Fix Gecko's #include dependencies
https://bugzilla.mozilla.org/show_bug.cgi?id=includehell

[Tom Ritter]

On the topic of compile time speedups, a long time ago we got a nice boost in 1443252 [0] by marking some central classes `final`. (Meta is 1332680 [1]) 

gcc supports the -Wsuggest-final-types but I don't think LLVM does - so if anyone happens to have a kind-of-working gcc build of Firefox, you could try this warning and see what it spits out today.

[0] https://bugzilla.mozilla.org/show_bug.cgi?id=1443252

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1332680

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