Derive + blacklisted types

[fitzgen]

• document blacklisting + derive interaction
• derive Copy
• derive Debug
• --impl-debug
• derive Default
• derive Hash
• derive PartialEq

[highfive]

Warning

• These commits modify unsafe code. Please review it carefully!

[fitzgen]

r? @emilio

[upsuper]

Although bindgen shouldn't put any assumption on blacklisted type, it could potentially be a trouble to ban all the derivation on them as well. (I haven't tried, but Debug seems to be relied widely, so it might become a problem.)

Probably we can allow people to specify which blacklisted type can derive what trait.

Maybe I should try this patch first and see if it really becomes a problem.

[emilio]

This looks ok to me, but probably we should give it a try on mozjs / stylo.

[fitzgen]

This patch works fine with mozjs.

[fitzgen]

With Stylo, I get the following error:

error: this trait cannot be derived for unions
    --> /home/fitzgen/mozilla-central/obj-x86_64-pc-linux-gnu/toolkit/library/x86_64-unknown-linux-gnu/release/build/style-14c013fa10f9d775/out/gecko/structs_release.rs:3238:22
     |
3238 |             #[derive(Debug, Copy)]
     |                      ^^^^^

on this struct:

            #[repr(C)]
            #[derive(Debug, Copy)]
            pub union OwningNodeOrString_Value {
                pub _bindgen_opaque_blob: [u64; 2usize],
            }

But let me double check that against master and see whether or not that same error occurs.

[fitzgen]

Hm yeah with master I get tons of "copy could not be implemented for this type".

[fitzgen]

Here is a minimal test case:

// bindgen-flags: --opaque-type DoggoOrNull

class Doggo {};

class None {};

union DoggoOrNull {
    Doggo doggo;
    None none;
};

Testing if this is also a bug on master or not.

[fitzgen]

It kind of seems to me that we shouldn't be emitting unions for opaque unions -- just structs of the right size/align...

[upsuper]

You need to make bindgen target 1.0 for building stylo.

[fitzgen]

Ok, so I targeted 1.0 and still getting errors that seem unrelated to deriving:

error[E0432]: unresolved import `gecko_bindings::structs::ServoStyleSheet`
  --> /home/fitzgen/mozilla-central/servo/components/style/gecko/data.rs:10:77
   |
10 | use gecko_bindings::structs::{RawGeckoPresContextOwned, ServoStyleSetSizes, ServoStyleSheet};
   |                                                                             ^^^^^^^^^^^^^^^ no `ServoStyleSheet` in `gecko_bindings::structs`. Did you mean to use `ServoStyleContext`?

But I verified that root::mozilla::ServoStyleSheet is defined in the structs_*.rs bindings. Did it not used to be namespaced or something?

Anyways, I don't think these errors are related to this PR, and it fixes other errors that get hit when trying to build Stylo with master (the copy deriving) so I think we should land this.

[fitzgen]

@bors-servo r=emilio

[bors-servo]

📌 Commit 74e2aea has been approved by emilio

[bors-servo]

⌛ Testing commit 74e2aea with merge cb10597...

[bors-servo]

☀️ Test successful - status-travis
Approved by: emilio
Pushing cb10597 to master...