1 files changed, 127 insertions, 0 deletions
diff --git a/third_party/rust/dwrote/src/com_helpers.rs b/third_party/rust/dwrote/src/com_helpers.rs
new file mode 100644
index 0000000000..b4bcf16641
--- /dev/null
+++ b/third_party/rust/dwrote/src/com_helpers.rs
@@ -0,0 +1,127 @@
+// This is only handy for implementing a single-interface-implementing IUnknown.
+
+macro_rules! implement_iunknown {
+    ($interface:ident, $typ:ident) => {
+        IUnknownVtbl {
+            QueryInterface: {
+                #[allow(non_snake_case)]
+                unsafe extern "system" fn QueryInterface(
+                    unknown_this: *mut IUnknown,
+                    riid: REFIID,
+                    ppv_object: *mut *mut c_void,
+                ) -> HRESULT {
+                    use $crate::winapi::Interface;
+                    let this = if $crate::winapi::shared::guiddef::IsEqualGUID(
+                        &*riid,
+                        &$interface::uuidof(),
+                    ) {
+                        mem::transmute(unknown_this)
+                    } else if $crate::winapi::shared::guiddef::IsEqualGUID(
+                        &*riid,
+                        &IUnknown::uuidof(),
+                    ) {
+                        mem::transmute(unknown_this)
+                    } else {
+                        return $crate::winapi::shared::winerror::E_NOINTERFACE;
+                    };
+
+                    (*unknown_this).AddRef();
+                    *ppv_object = this;
+                    return S_OK;
+                }
+                QueryInterface
+            },
+            AddRef: {
+                unsafe extern "system" fn AddRef(unknown_this: *mut IUnknown) -> ULONG {
+                    let this = $typ::from_interface(unknown_this);
+                    let count = this.refcount.fetch_add(1, atomic::Ordering::Relaxed) + 1;
+                    count as ULONG
+                }
+                AddRef
+            },
+            Release: {
+                unsafe extern "system" fn Release(unknown_this: *mut IUnknown) -> ULONG {
+                    let this = $typ::from_interface(unknown_this);
+                    let count = this.refcount.fetch_sub(1, atomic::Ordering::Release) - 1;
+                    if count == 0 {
+                        <$typ as Com<$interface>>::destroy(unknown_this as *mut $interface);
+                    }
+                    count as ULONG
+                }
+                Release
+            },
+        }
+    };
+    (static $interface:ident, $typ:ident) => {
+        IUnknownVtbl {
+            QueryInterface: {
+                #[allow(non_snake_case)]
+                unsafe extern "system" fn QueryInterface(
+                    unknown_this: *mut IUnknown,
+                    riid: REFIID,
+                    ppvObject: *mut *mut $crate::winapi::ctypes::c_void,
+                ) -> HRESULT {
+                    use $crate::winapi::Interface;
+                    let this = if $crate::winapi::shared::guiddef::IsEqualGUID(
+                        &*riid,
+                        &$interface::uuidof(),
+                    ) {
+                        mem::transmute(unknown_this)
+                    } else if $crate::winapi::shared::guiddef::IsEqualGUID(
+                        &*riid,
+                        &IUnknown::uuidof(),
+                    ) {
+                        mem::transmute(unknown_this)
+                    } else {
+                        return $crate::winapi::shared::winerror::E_NOINTERFACE;
+                    };
+
+                    (*unknown_this).AddRef();
+                    *ppvObject = this;
+                    return S_OK;
+                }
+                QueryInterface
+            },
+            AddRef: {
+                // FIXME(pcwalton): Uh? Maybe we should actually reference count?
+                #[allow(non_snake_case)]
+                unsafe extern "system" fn AddRef(_: *mut IUnknown) -> ULONG {
+                    1
+                }
+                AddRef
+            },
+            Release: {
+                #[allow(non_snake_case)]
+                unsafe extern "system" fn Release(_: *mut IUnknown) -> ULONG {
+                    1
+                }
+                Release
+            },
+        }
+    };
+}
+
+#[repr(C)]
+pub struct ComRepr<Type, Vtbl>(*const Vtbl, Type);
+
+pub trait Com<Interface>
+where
+    Self: Sized,
+{
+    type Vtbl: 'static;
+
+    fn vtbl() -> &'static Self::Vtbl;
+
+    fn into_interface(self) -> *mut Interface {
+        let com = Box::new(ComRepr(Self::vtbl(), self));
+        Box::into_raw(com) as *mut Interface
+    }
+
+    unsafe fn from_interface<'a>(thing: *mut Interface) -> &'a mut Self {
+        &mut (*(thing as *mut ComRepr<Self, Self::Vtbl>)).1
+    }
+
+    unsafe fn destroy(thing: *mut Interface) {
+        Box::from_raw(thing as *mut ComRepr<Self, Self::Vtbl>);
+    }
+}