style: Improve logging for attribute changes.

And general Element logging. We now print all the attributes for comparison.

If this turns out to be too verbose we can change it to diff them or something.

Differential Revision: https://phabricator.services.mozilla.com/D2471

components/style/gecko/snapshot.rs

@@ -156,6 +156,15 @@ impl GeckoElementSnapshot {
 }
 
 impl ElementSnapshot for GeckoElementSnapshot {
+    fn debug_list_attributes(&self) -> String {
+        use nsstring::nsCString;
+        let mut string = nsCString::new();
+        unsafe {
+            bindings::Gecko_Snapshot_DebugListAttributes(self, &mut string);
+        }
+        String::from_utf8_lossy(&*string).into_owned()
+    }
+
     fn state(&self) -> Option<ElementState> {
         if self.has_any(Flags::State) {
             Some(ElementState::from_bits_truncate(self.mState))

components/style/gecko/wrapper.rs

@@ -562,28 +562,15 @@ pub struct GeckoElement<'le>(pub &'le RawGeckoElement);
 
 impl<'le> fmt::Debug for GeckoElement<'le> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use nsstring::nsCString;
+
         write!(f, "<{}", self.local_name())?;
-        if let Some(id) = self.id() {
-            write!(f, " id={}", id)?;
+
+        let mut attrs = nsCString::new();
+        unsafe {
+            bindings::Gecko_Element_DebugListAttributes(self.0, &mut attrs);
         }
-
-        let mut first = true;
-        let mut any = false;
-        self.each_class(|c| {
-            if first {
-                first = false;
-                any = true;
-                let _ = f.write_str(" class=\"");
-            } else {
-                let _ = f.write_str(" ");
-            }
-            let _ = write!(f, "{}", c);
-        });
-
-        if any {
-            f.write_str("\"")?;
-        }
-
+        write!(f, "{}", attrs)?;
         write!(f, "> ({:#x})", self.as_node().opaque().0)
     }
 }

components/style/invalidation/element/element_wrapper.rs

@@ -43,6 +43,11 @@ pub trait ElementSnapshot: Sized {
     /// If this snapshot contains attribute information.
     fn has_attrs(&self) -> bool;
 
+    /// Gets the attribute information of the snapshot as a string.
+    ///
+    /// Only for debugging purposes.
+    fn debug_list_attributes(&self) -> String { String::new() }
+
     /// The ID attribute per this snapshot. Should only be called if
     /// `has_attrs()` returns true.
     fn id_attr(&self) -> Option<&WeakAtom>;

components/style/invalidation/element/state_and_attributes.rs

@@ -208,20 +208,32 @@ where
             }
         }
 
-        debug!("Collecting changes for: {:?}", element);
-        debug!(" > state: {:?}", state_changes);
-        debug!(
-            " > id changed: {:?} -> +{:?} -{:?}",
-            snapshot.id_changed(),
-            id_added,
-            id_removed
-        );
-        debug!(
-            " > class changed: {:?} -> +{:?} -{:?}",
-            snapshot.class_changed(),
-            classes_added,
-            classes_removed
-        );
+        if log_enabled!(::log::Level::Debug) {
+            debug!("Collecting changes for: {:?}", element);
+            if !state_changes.is_empty() {
+                debug!(" > state: {:?}", state_changes);
+            }
+            if snapshot.id_changed() {
+                debug!(
+                    " > id changed: +{:?} -{:?}",
+                    id_added,
+                    id_removed
+                );
+            }
+            if snapshot.class_changed() {
+                debug!(
+                    " > class changed: +{:?} -{:?}",
+                    classes_added,
+                    classes_removed
+                );
+            }
+            if snapshot.other_attr_changed() {
+                debug!(
+                    " > attributes changed, old: {}",
+                    snapshot.debug_list_attributes()
+                )
+            }
+        }
 
         let lookup_element = if element.implemented_pseudo_element().is_some() {
             element.pseudo_element_originating_element().unwrap()