Don't generate useless InheritTypes interfaces

[nox]

Interfaces with no descendant need neither a Base trait nor upcast functions, and interfaces with no ancestors neither a Derived trait nor downcast functions.

[nox]

I fixed the setting of hasProxyDescendant. This flag shouldn't be set on the proxy itself. This led to CSSStyleDeclaration's upcasts to be generated even though they are useless.

[Ms2ger]

Reviewed 1 of 1 files at r1.
Review status: 1 of 2 files reviewed at latest revision, 2 unresolved discussions, all commit checks successful.

---

^{components/script/dom/bindings/codegen/CodegenRust.py, line 5812 [r2] (raw file):}
I had issues wrapping my head around this, so I rewrote it:

        descriptors = config.getDescriptors(register=True, isCallback=False)
        allprotos = [CGGeneric("use dom::types::*;\n"),
                     CGGeneric("use dom::bindings::js::{JS, LayoutJS, Root};\n"),
                     CGGeneric("use dom::bindings::trace::JSTraceable;\n"),
                     CGGeneric("use dom::bindings::utils::Reflectable;\n"),
                     CGGeneric("use js::jsapi::JSTracer;\n\n"),
                     CGGeneric("use std::mem;\n\n")]

        allprotos.extend(CGGeneric(conversion)
                         for conversion in conversions(descriptor)
                         for descriptor in descriptors)

        curr = CGList(allprotos)
        curr = CGWrapper(curr, pre=AUTOGENERATED_WARNING_COMMENT)
        return curr


def conversions(descriptor):
    name = descriptor.name
    upcast = (descriptor.interface.getUserData("hasConcreteDescendant", False) or
              descriptor.interface.getUserData("hasProxyDescendant", False))

    downcast = len(descriptor.prototypeChain) > 1

    if upcast or downcast:
        yield "pub struct %sCast;\n" % name


    chain = descriptor.prototypeChain

    # Define a `FooBase` trait for subclasses to implement, as well as the
    # `FooCast::from_*` methods that use it.
    if upcast:
        yield string.Template("""\
/// Types which are derived from `${name}` and can be freely converted
/// to `${name}`
pub trait ${fromBound} : Sized {}

impl ${name}Cast {
    #[inline]
    /// Upcast an instance of a derived class of `${name}` to `${name}`
    pub fn from_ref<'a, T: ${fromBound}+Reflectable>(derived: &'a T) -> &'a ${name} {
        unsafe { mem::transmute(derived) }
    }
    #[inline]
    #[allow(unrooted_must_root)]
    pub fn from_layout_js<T: ${fromBound}+Reflectable>(derived: &LayoutJS<T>) -> LayoutJS<${name}> {
        unsafe { mem::transmute_copy(derived) }
    }
    #[inline]
    pub fn from_root<T: ${fromBound}+Reflectable>(derived: Root<T>) -> Root<${name}> {
        unsafe { mem::transmute(derived) }
    }
}
""").substitute({'name': name, 'fromBound': name + 'Base'})
    else:
        # The `FooBase` trait is not defined, so avoid implementing it by
        # removing `Foo` itself from the chain.
        chain = chain[:-1]

    # Implement `BarBase` for `Foo`, for all `Bar` that `Foo` inherits from.
    for proto in chain:
        yield 'impl %s for %s {}\n' % (proto + 'Base', descriptor.concreteType)


    # Define a `FooDerived` trait for superclasses to implement, as well as the
    # `FooCast::to_*` methods that use it.
    if downcast:
        yield string.Template("""\
/// Types which `${name}` derives from
pub trait ${toBound} : Sized { fn ${checkFn}(&self) -> bool; }

impl %{name}Cast {
    #[inline]
    /// Downcast an instance of a base class of `${name}` to an instance of
    /// `${name}`, if it internally is an instance of `${name}`
    pub fn to_ref<'a, T: ${toBound}+Reflectable>(base: &'a T) -> Option<&'a ${name}> {
        match base.${checkFn}() {
            true => Some(unsafe { mem::transmute(base) }),
            false => None
        }
    }
    #[inline]
    #[allow(unrooted_must_root)]
    pub fn to_layout_js<T: ${toBound}+Reflectable>(base: &LayoutJS<T>) -> Option<LayoutJS<${name}>> {
        unsafe {
            match (*base.unsafe_get()).${checkFn}() {
                true => Some(mem::transmute_copy(base)),
                false => None
            }
        }
    }
    #[inline]
    pub fn to_root<T: ${toBound}+Reflectable>(base: Root<T>) -> Option<Root<${name}>> {
        match base.r().${checkFn}() {
            true => Some(unsafe { mem::transmute(base) }),
            false => None
        }
    }
}
""").substitute({'checkFn': 'is_' + name.lower(), 'name': name, 'toBound': name + 'Derived'})


    # Implement the `FooDerived` trait for non-root superclasses by deferring to
    # the direct superclass. This leaves the implementation of the `FooDerived`
    # trait for the root superclass to manual code. `FooDerived` is not
    # implemented for `Foo` itself. 
    for protoName in descriptor.prototypeChain[1:-1]:
        protoDescriptor = config.getDescriptor(protoName)
        yield string.Template("""\
impl ${name}Derived for ${baseName} {
    #[inline]
    fn ${fname}(&self) -> bool {
        let base: &${parentName} = ${parentName}Cast::from_ref(self);
        base.${fname}()
    }
}
""").substitute({'fname': 'is_' + name.lower(),
                 'name': name,
                 'baseName': protoDescriptor.concreteType,
                 'parentName': protoDescriptor.prototypeChain[-2]})

How would you feel about me rewriting the code in this fashion, and letting you rebase on top of it?

---

^{components/script/dom/bindings/codegen/CodegenRust.py, line 5904 [r2] (raw file):}
This doesn't use checkFn

---

Comments from the review on Reviewable.io

[nox]

Review status: 1 of 2 files reviewed at latest revision, 2 unresolved discussions, all commit checks successful.

---

^{components/script/dom/bindings/codegen/CodegenRust.py, line 5812 [r2] (raw file):}
Sure.

---

Comments from the review on Reviewable.io

[nox]

Review status: 1 of 2 files reviewed at latest revision, 2 unresolved discussions, all commit checks successful.

---

^{components/script/dom/bindings/codegen/CodegenRust.py, line 5812 [r2] (raw file):}

17:31 Ms2ger: Actually I have a problem with your rewrite, in my other patch I build a dictionary from interface names to their immediate descendants, to generate the TypeId enums,
17:31 Ms2ger: your generator rewrite forbids me to build this dictionary, AFAICT.

It forbids me to build this dictionary while generating the plain old conversions functions, I mean.

---

Comments from the review on Reviewable.io

[nox]

Review status: 1 of 2 files reviewed at latest revision, 2 unresolved discussions, all commit checks successful.

---

^{components/script/dom/bindings/codegen/CodegenRust.py, line 5812 [r2] (raw file):}
master...nox:codegen-typeid

---

Comments from the review on Reviewable.io

[Ms2ger]

@bors-servo r+

[bors-servo]

📌 Commit e24b8ab has been approved by Ms2ger

[bors-servo]

⌛ Testing commit e24b8ab with merge 8db54e4...

[bors-servo]

💔 Test failed - mac-dev-ref-unit

[nox]

@bors-servo retry p=1

#7785

[bors-servo]

⌛ Testing commit e24b8ab with merge 243647d...

[bors-servo]

💔 Test failed - linux-rel

[nox]

@bors-servo retry

#7870

[bors-servo]

⚡ Previous build results for android, gonk, linux-dev, mac-dev-ref-unit are reusable. Rebuilding only linux-rel, mac-rel-css, mac-rel-wpt...

[bors-servo]

☀️ Test successful - android, gonk, linux-dev, linux-rel, mac-dev-ref-unit, mac-rel-css, mac-rel-wpt