Add get_column_styles for getting column structure and styles for a table

components/layout/flow.rs

@@ -171,6 +171,12 @@ pub trait Flow: HasBaseFlow + fmt::Debug + Sync + Send + 'static {
         panic!("called as_mut_table_colgroup() on a non-tablecolgroup flow")
     }
 
+    /// If this is a table colgroup flow, returns the underlying object. Fails
+    /// otherwise.
+    fn as_table_colgroup(&self) -> &TableColGroupFlow {
+        panic!("called as_table_colgroup() on a non-tablecolgroup flow")
+    }
+
     /// If this is a table rowgroup flow, returns the underlying object, borrowed mutably. Fails
     /// otherwise.
     fn as_mut_table_rowgroup(&mut self) -> &mut TableRowGroupFlow {

components/layout/fragment.rs

@@ -1408,6 +1408,16 @@ impl Fragment {
         }
     }
 
+    /// If this is a Column fragment, get the col span
+    ///
+    /// Panics for non-column fragments
+    pub fn column_span(&self) -> u32 {
+        match self.specific {
+            SpecificFragmentInfo::TableColumn(col_fragment) => max(col_fragment.span, 1),
+            _ => panic!("non-table-column fragment inside table column?!"),
+        }
+    }
+
     /// Returns true if this element can be split. This is true for text fragments, unless
     /// `white-space: pre` or `white-space: nowrap` is set.
     pub fn can_split(&self) -> bool {

components/layout/table.rs

@@ -203,6 +203,34 @@ impl TableFlow {
         }
         self.spacing().horizontal() * (num_columns as i32 + 1)
     }
+
+    fn column_styles(&self) -> Vec<ColumnStyle> {
+        let mut styles = vec![];
+        for group in self.block_flow.base.child_iter()
+                       .filter(|kid| kid.is_table_colgroup()) {
+            // XXXManishearth these as_foo methods should return options
+            // so that we can filter_map
+            let group = group.as_table_colgroup();
+            let colgroup_style = group.fragment.as_ref().map(|f| f.style());
+
+            // The colgroup's span attribute is only relevant when
+            // it has no children
+            // https://html.spec.whatwg.org/multipage/#forming-a-table
+            if group.cols.is_empty() {
+                let span = group.fragment.as_ref().map(|f| f.column_span()).unwrap_or(1);
+                styles.push(ColumnStyle { span, colgroup_style, col_style: None });
+            } else {
+                for col in &group.cols {
+                    styles.push(ColumnStyle {
+                        span: col.column_span(),
+                        colgroup_style,
+                        col_style: Some(col.style()),
+                    })
+                }
+            }
+        }
+        styles
+    }
 }
 
 impl Flow for TableFlow {
@@ -529,6 +557,13 @@ impl Flow for TableFlow {
     }
 }
 
+#[derive(Debug, Copy, Clone)]
+struct ColumnStyle<'a> {
+    span: u32,
+    colgroup_style: Option<&'a ComputedValues>,
+    col_style: Option<&'a ComputedValues>,
+}
+
 impl fmt::Debug for TableFlow {
     /// Outputs a debugging string describing this table flow.
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

components/layout/table_colgroup.rs

@@ -11,9 +11,8 @@ use context::LayoutContext;
 use display_list::{DisplayListBuildState, StackingContextCollectionState};
 use euclid::Point2D;
 use flow::{BaseFlow, Flow, FlowClass, ForceNonfloatedFlag, OpaqueFlow};
-use fragment::{Fragment, FragmentBorderBoxIterator, Overflow, SpecificFragmentInfo};
+use fragment::{Fragment, FragmentBorderBoxIterator, Overflow};
 use layout_debug;
-use std::cmp::max;
 use std::fmt;
 use style::logical_geometry::LogicalSize;
 use style::properties::ComputedValues;
@@ -63,6 +62,10 @@ impl Flow for TableColGroupFlow {
         self
     }
 
+    fn as_table_colgroup(&self) -> &TableColGroupFlow {
+        self
+    }
+
     fn bubble_inline_sizes(&mut self) {
         let _scope = layout_debug_scope!("table_colgroup::bubble_inline_sizes {:x}",
                                             self.base.debug_id());
@@ -70,11 +73,7 @@ impl Flow for TableColGroupFlow {
         for fragment in &self.cols {
             // Retrieve the specified value from the appropriate CSS property.
             let inline_size = fragment.style().content_inline_size();
-            let span = match fragment.specific {
-                SpecificFragmentInfo::TableColumn(col_fragment) => max(col_fragment.span, 1),
-                _ => panic!("non-table-column fragment inside table column?!"),
-            };
-            for _ in 0..span {
+            for _ in 0..fragment.column_span() {
                 self.inline_sizes.push(inline_size)
             }
         }