Auto merge of #10848 - heycam:struct-accessor, r=bholley

Add Servo_GetStyleFoo functions to get style structs from GeckoComputedValues

r?@bholley

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ports/geckolib/glue.rs

@@ -92,29 +92,29 @@ pub extern "C" fn Servo_StylesheetFromUTF8Bytes(bytes: *const u8,
     }
 }
 
-struct ArcHelpers<GeckoType, ServoType> {
+pub struct ArcHelpers<GeckoType, ServoType> {
     phantom1: PhantomData<GeckoType>,
     phantom2: PhantomData<ServoType>,
 }
 
 impl<GeckoType, ServoType> ArcHelpers<GeckoType, ServoType> {
-    fn with<F, Output>(raw: *mut GeckoType, cb: F) -> Output
-                       where F: FnOnce(&Arc<ServoType>) -> Output {
+    pub fn with<F, Output>(raw: *mut GeckoType, cb: F) -> Output
+                           where F: FnOnce(&Arc<ServoType>) -> Output {
         let owned = unsafe { Self::into(raw) };
         let result = cb(&owned);
         forget(owned);
         result
     }
 
-    unsafe fn into(ptr: *mut GeckoType) -> Arc<ServoType> {
+    pub unsafe fn into(ptr: *mut GeckoType) -> Arc<ServoType> {
         transmute(ptr)
     }
 
-    unsafe fn addref(ptr: *mut GeckoType) {
+    pub unsafe fn addref(ptr: *mut GeckoType) {
         Self::with(ptr, |arc| forget(arc.clone()));
     }
 
-    unsafe fn release(ptr: *mut GeckoType) {
+    pub unsafe fn release(ptr: *mut GeckoType) {
         let _ = Self::into(ptr);
     }
 }

ports/geckolib/properties.mako.rs

@@ -11,14 +11,13 @@
 
 use app_units::Au;
 % for style_struct in data.style_structs:
-%if style_struct.gecko_ffi_name:
 use gecko_style_structs::${style_struct.gecko_ffi_name};
 use bindings::Gecko_Construct_${style_struct.gecko_ffi_name};
 use bindings::Gecko_CopyConstruct_${style_struct.gecko_ffi_name};
 use bindings::Gecko_Destroy_${style_struct.gecko_ffi_name};
-% endif
 % endfor
 use gecko_style_structs;
+use glue::ArcHelpers;
 use heapsize::HeapSizeOf;
 use std::fmt::{self, Debug};
 use std::mem::{transmute, zeroed};
@@ -103,13 +102,9 @@ impl ComputedValues for GeckoComputedValues {
 
 <%def name="declare_style_struct(style_struct)">
 #[derive(Clone, HeapSizeOf, Debug)]
-% if style_struct.gecko_ffi_name:
 pub struct ${style_struct.gecko_struct_name} {
     gecko: ${style_struct.gecko_ffi_name},
 }
-% else:
-pub struct ${style_struct.gecko_struct_name};
-% endif
 </%def>
 
 <%def name="impl_simple_copy(ident, gecko_ffi_name)">
@@ -192,8 +187,10 @@ impl ${style_struct.gecko_struct_name} {
         }
         result
     }
+    pub fn get_gecko(&self) -> &${style_struct.gecko_ffi_name} {
+        &self.gecko
+    }
 }
-%if style_struct.gecko_ffi_name:
 impl Drop for ${style_struct.gecko_struct_name} {
     fn drop(&mut self) {
         unsafe {
@@ -227,7 +224,6 @@ impl Debug for ${style_struct.gecko_ffi_name} {
     }
 }
 %endif
-%endif
 </%def>
 
 <%def name="raw_impl_trait(style_struct, skip_longhands='', skip_additionals='')">
@@ -406,12 +402,24 @@ for side in SIDES:
 
 </%self:impl_trait>
 
+<%def name="define_ffi_struct_accessor(style_struct)">
+#[no_mangle]
+#[allow(non_snake_case, unused_variables)]
+pub extern "C" fn Servo_GetStyle${style_struct.gecko_name}(computed_values: *mut ServoComputedValues)
+  -> *const ${style_struct.gecko_ffi_name} {
+    type Helpers = ArcHelpers<ServoComputedValues, GeckoComputedValues>;
+    Helpers::with(computed_values, |values| values.get_${style_struct.trait_name_lower}().get_gecko()
+                                                as *const ${style_struct.gecko_ffi_name})
+}
+</%def>
+
 % for style_struct in data.style_structs:
 ${declare_style_struct(style_struct)}
 ${impl_style_struct(style_struct)}
 % if not style_struct.trait_name in data.manual_style_structs:
 <%self:raw_impl_trait style_struct="${style_struct}"></%self:raw_impl_trait>
 % endif
+${define_ffi_struct_accessor(style_struct)}
 % endfor
 
 lazy_static! {