With replacements, we can generate a use of a type w/ no definition for that type

[fitzgen]

creduce ftw! \o/

Flags: --whitelist-type Rooted -- --std=c++14

Input:

template <typename a> using MaybeWrapped = a;
class Rooted {
  MaybeWrapped<int> ptr;
};
/// <div rustbindgen replaces="MaybeWrapped"
template <typename a> using replaces_MaybeWrapped = a;

Output:

/* automatically generated by rust-bindgen */

#[repr(C)]
#[derive(Debug, Copy)]
pub struct Rooted {
    pub ptr: MaybeWrapped<a>,
}
#[test]
fn bindgen_test_layout_Rooted() {
    assert_eq!(::std::mem::size_of::<Rooted>() , 4usize);
    assert_eq!(::std::mem::align_of::<Rooted>() , 4usize);
}
impl Clone for Rooted {
    fn clone(&self) -> Self { *self }
}

Note how MaybeWrapped is used, but never defined. The <a> tells me we are probably treating it as a named template argument.

[fitzgen]

Hmmm.... somehow we end up with a field whose ty == ItemId(7), however we never BindgenContext::add_item(item) where item.id == ItemId(7). Looks like this is another dangling id issue...

[fitzgen]

Ah nevermind, it's just our logging that was incomplete. Looks like it is being added as a builtin type:

DEBUG:bindgen::ir::context: add_builtin_item: item = Item { id: ItemId(7), local_id: Cell { value: None }, next_child_local_id: Cell { value: 1 }, canonical_name_cache: RefCell { value: None }, comment: None, annotations: Annotations { opaque: false, hide: false, use_instead_of: None, disallow_copy: false, private_fields: None, accessor_kind: None }, parent_id: ItemId(6), kind: Type(Type { name: Some("MaybeWrapped<int>"), layout: Some(Layout { size: 4, align: 4, packed: false }), kind: ResolvedTypeRef(ItemId(4)), is_const: false }) }

[fitzgen]

• The field has ty: ItemId(7)
• ItemId(7) is a ResolvedTypeRef(ItemId(4))
• ItemId(4) is an Alias("MaybeWrapped", ItemId(5))
• ItemId(5) is a UnresolvedTypeRef(Type(a, kind: Unexposed, decl: Cursor( kind: NoDeclFound, loc: builtin definitions, usr: None), canon: Cursor( kind: NoDeclFound, loc: builtin definitions, usr: None)), Some(Cursor(MaybeWrapped kind: TypeAliasDecl, loc: RootingAPI.hpp:1:29, usr: Some("c:@MaybeWrapped"))), Some(ItemId(1)))

This last point seems to be where we go wrong. We should be creating a named type for ItemId(5) instead of an UnresolvedTypeRef.

[emilio]

Note that the unresolved types change before processing both replacements
and whitelisting, so you should probably take a look at the state of the
context after "resolve_typerefs".

Thanks for digging into this! :)

On Nov 15, 2016 1:04 AM, "Nick Fitzgerald" [email protected] wrote:

The field has ty: ItemId(7)

ItemId(7) is a ResolvedTypeRef(ItemId(4))

ItemId(4) is an Alias("MaybeWrapped", ItemId(5))

ItemId(5) is a UnresolvedTypeRef(Type(a, kind: Unexposed, decl:
Cursor( kind: NoDeclFound, loc: builtin definitions, usr: None), canon:
Cursor( kind: NoDeclFound, loc: builtin definitions, usr: None)),
Some(Cursor(MaybeWrapped kind: TypeAliasDecl, loc: RootingAPI.hpp:1:29,
usr: Some("c:@MaybeWrapped"))), Some(ItemId(1)))

This last point seems to be where we go wrong. We should be creating a
named type for ItemId(5) instead of an UnresolvedTypeRef.

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[fitzgen]

This is actually fixed -- thanks @emilio :)