layout: Implement text-indent per CSS 2.1 § 16.1.

I had to use a somewhat unconventional method of computing text
indentation (propagating from blocks down to inlines) because of the way
containing blocks are handled in Servo.

(As a side note, neither Gecko nor WebKit correctly handles percentages
in `text-align`, at least incrementally -- i.e. when the percentages are
relative to the viewport and the viewport is resized.)

components/layout/block.rs

@@ -1256,6 +1256,7 @@ impl BlockFlow {
     #[inline(always)]
     pub fn propagate_assigned_inline_size_to_children(
             &mut self,
+            layout_context: &LayoutContext,
             inline_start_content_edge: Au,
             content_inline_size: Au,
             optional_column_computed_inline_sizes: Option<&[ColumnComputedInlineSize]>) {
@@ -1306,6 +1307,13 @@ impl BlockFlow {
             (LPA_Length(length), _) => Some(length),
         };
 
+        // Calculate containing block inline size.
+        let containing_block_size = if flags.contains(IS_ABSOLUTELY_POSITIONED) {
+            self.containing_block_size(layout_context.shared.screen_size).inline
+        } else {
+            content_inline_size
+        };
+
         for (i, kid) in self.base.child_iter().enumerate() {
             {
                 let kid_base = flow::mut_base(kid);
@@ -1383,7 +1391,16 @@ impl BlockFlow {
             // Per CSS 2.1 § 16.3.1, text alignment propagates to all children in flow.
             //
             // TODO(#2018, pcwalton): Do this in the cascade instead.
-            flow::mut_base(kid).flags.propagate_text_alignment_from_parent(flags.clone())
+            flow::mut_base(kid).flags.propagate_text_alignment_from_parent(flags.clone());
+
+            // Handle `text-indent` on behalf of any inline children that we have. This is
+            // necessary because any percentages are relative to the containing block, which only
+            // we know.
+            if kid.is_inline_flow() {
+                kid.as_inline().first_line_indentation =
+                    specified(self.fragment.style().get_inheritedtext().text_indent,
+                              containing_block_size);
+            }
         }
     }
 
@@ -1609,7 +1626,8 @@ impl Flow for BlockFlow {
         let padding_and_borders = self.fragment.border_padding.inline_start_end();
         let content_inline_size = self.fragment.border_box.size.inline - padding_and_borders;
 
-        self.propagate_assigned_inline_size_to_children(inline_start_content_edge,
+        self.propagate_assigned_inline_size_to_children(layout_context,
+                                                        inline_start_content_edge,
                                                         content_inline_size,
                                                         None);
     }

components/layout/inline.rs

@@ -177,11 +177,13 @@ struct LineBreaker {
     lines: Vec<Line>,
     /// The current position in the block direction.
     cur_b: Au,
+    /// The computed value of the indentation for the first line (`text-indent`, CSS 2.1 § 16.1).
+    first_line_indentation: Au,
 }
 
 impl LineBreaker {
-    /// Creates a new `LineBreaker` with a set of floats.
+    /// Creates a new `LineBreaker` with a set of floats and the indentation of the first line.
-    fn new(float_context: Floats) -> LineBreaker {
+    fn new(float_context: Floats, first_line_indentation: Au) -> LineBreaker {
         LineBreaker {
             new_fragments: Vec::new(),
             work_list: RingBuf::new(),
@@ -193,6 +195,7 @@ impl LineBreaker {
             floats: float_context,
             lines: Vec::new(),
             cur_b: Au(0),
+            first_line_indentation: first_line_indentation,
         }
     }
 
@@ -325,7 +328,7 @@ impl LineBreaker {
         let placement_inline_size = if first_fragment.can_split() {
             Au(0)
         } else {
-            first_fragment.border_box.size.inline
+            first_fragment.border_box.size.inline + self.indentation_for_pending_fragment()
         };
 
         // Try to place the fragment between floats.
@@ -486,9 +489,9 @@ impl LineBreaker {
         // If we're not going to overflow the green zone vertically, we might still do so
         // horizontally. We'll try to place the whole fragment on this line and break somewhere if
         // it doesn't fit.
-
+        let indentation = self.indentation_for_pending_fragment();
         let new_inline_size = self.pending_line.bounds.size.inline +
-            fragment.border_box.size.inline;
+            fragment.border_box.size.inline + indentation;
         if new_inline_size <= green_zone.inline {
             debug!("LineBreaker: fragment fits without splitting");
             self.push_fragment_to_line(fragment);
@@ -506,7 +509,8 @@ impl LineBreaker {
         }
 
         // Split it up!
-        let available_inline_size = green_zone.inline - self.pending_line.bounds.size.inline;
+        let available_inline_size = green_zone.inline - self.pending_line.bounds.size.inline -
+            indentation;
         let (inline_start_fragment, inline_end_fragment) =
             match fragment.find_split_info_for_inline_size(CharIndex(0),
                                                            available_inline_size,
@@ -551,6 +555,7 @@ impl LineBreaker {
 
     /// Pushes a fragment to the current line unconditionally.
     fn push_fragment_to_line(&mut self, fragment: Fragment) {
+        let indentation = self.indentation_for_pending_fragment();
         if self.pending_line_is_empty() {
             assert!(self.new_fragments.len() <= (u16::MAX as uint));
             self.pending_line.range.reset(FragmentIndex(self.new_fragments.len() as int),
@@ -559,12 +564,22 @@ impl LineBreaker {
 
         self.pending_line.range.extend_by(FragmentIndex(1));
         self.pending_line.bounds.size.inline = self.pending_line.bounds.size.inline +
-            fragment.border_box.size.inline;
+            fragment.border_box.size.inline +
+            indentation;
         self.pending_line.bounds.size.block = max(self.pending_line.bounds.size.block,
                                                   fragment.border_box.size.block);
         self.new_fragments.push(fragment);
     }
 
+    /// Returns the indentation that needs to be applied before the fragment we're reflowing.
+    fn indentation_for_pending_fragment(&self) -> Au {
+        if self.pending_line_is_empty() && self.lines.is_empty() {
+            self.first_line_indentation
+        } else {
+            Au(0)
+        }
+    }
+
     /// Returns true if the pending line is empty and false otherwise.
     fn pending_line_is_empty(&self) -> bool {
         self.pending_line.range.length() == num::zero()
@@ -698,6 +713,11 @@ pub struct InlineFlow {
     /// The minimum depth below the baseline for each line, as specified by the line block-size and
     /// font style.
     pub minimum_depth_below_baseline: Au,
+
+    /// The amount of indentation to use on the first line. This is determined by our block parent
+    /// (because percentages are relative to the containing block, and we aren't in a position to
+    /// compute things relative to our parent's containing block).
+    pub first_line_indentation: Au,
 }
 
 impl InlineFlow {
@@ -708,6 +728,7 @@ impl InlineFlow {
             lines: Vec::new(),
             minimum_block_size_above_baseline: Au(0),
             minimum_depth_below_baseline: Au(0),
+            first_line_indentation: Au(0),
         }
     }
 
@@ -787,21 +808,22 @@ impl InlineFlow {
     /// Sets fragment positions in the inline direction based on alignment for one line.
     fn set_inline_fragment_positions(fragments: &mut InlineFragments,
                                      line: &Line,
-                                     line_align: text_align::T) {
+                                     line_align: text_align::T,
+                                     indentation: Au) {
         // Figure out how much inline-size we have.
         let slack_inline_size = max(Au(0), line.green_zone.inline - line.bounds.size.inline);
 
         // Set the fragment inline positions based on that alignment.
-        let mut offset = line.bounds.start.i;
+        let mut inline_start_position_for_fragment = line.bounds.start.i + indentation +
-        offset = offset + match line_align {
+                match line_align {
-            // So sorry, but justified text is more complicated than shuffling line
+                // So sorry, but justified text is more complicated than shuffling line
-            // coordinates.
+                // coordinates.
-            //
+                //
-            // TODO(burg, issue #213): Implement `text-align: justify`.
+                // TODO(burg, issue #213): Implement `text-align: justify`.
-            text_align::left | text_align::justify => Au(0),
+                text_align::left | text_align::justify => Au(0),
-            text_align::center => slack_inline_size.scale_by(0.5),
+                text_align::center => slack_inline_size.scale_by(0.5),
-            text_align::right => slack_inline_size,
+                text_align::right => slack_inline_size,
-        };
+            };
 
         for fragment_index in range(line.range.begin(), line.range.end()) {
             let fragment = fragments.get_mut(fragment_index.to_uint());
@@ -999,9 +1021,15 @@ impl Flow for InlineFlow {
         self.fragments.merge_broken_lines();
         self.lines = Vec::new();
 
+        // Determine how much indentation the first line wants.
+        let mut indentation = if self.fragments.is_empty() {
+            Au(0)
+        } else {
+            self.first_line_indentation
+        };
 
         // Perform line breaking.
-        let mut scanner = LineBreaker::new(self.base.floats.clone());
+        let mut scanner = LineBreaker::new(self.base.floats.clone(), indentation);
         scanner.scan_for_lines(self, layout_context);
 
         // Now, go through each line and lay out the fragments inside.
@@ -1010,7 +1038,8 @@ impl Flow for InlineFlow {
             // Lay out fragments in the inline direction.
             InlineFlow::set_inline_fragment_positions(&mut self.fragments,
                                                       line,
-                                                      self.base.flags.text_align());
+                                                      self.base.flags.text_align(),
+                                                      indentation);
 
             // Set the block-start position of the current line.
             // `line_height_offset` is updated at the end of the previous loop.
@@ -1110,6 +1139,9 @@ impl Flow for InlineFlow {
                 largest_depth_below_baseline;
             line_distance_from_flow_block_start = line_distance_from_flow_block_start +
                 line.bounds.size.block;
+
+            // We're no longer on the first line, so set indentation to zero.
+            indentation = Au(0)
         } // End of `lines.iter_mut()` loop.
 
         // Assign block sizes for any inline-block descendants.

components/layout/table.rs

@@ -315,6 +315,7 @@ impl Flow for TableFlow {
         self.block_flow.base.flags.remove(IMPACTED_BY_RIGHT_FLOATS);
 
         self.block_flow.propagate_assigned_inline_size_to_children(
+            layout_context,
             inline_start_content_edge,
             content_inline_size,
             Some(self.column_computed_inline_sizes.as_slice()));

components/layout/table_cell.rs

@@ -96,7 +96,7 @@ impl Flow for TableCellFlow {
     /// Recursively (top-down) determines the actual inline-size of child contexts and fragments.
     /// When called on this context, the context has had its inline-size set by the parent table
     /// row.
-    fn assign_inline_sizes(&mut self, ctx: &LayoutContext) {
+    fn assign_inline_sizes(&mut self, layout_context: &LayoutContext) {
         let _scope = layout_debug_scope!("table_cell::assign_inline_sizes {:x}",
                                             self.block_flow.base.debug_id());
         debug!("assign_inline_sizes({}): assigning inline_size for flow", "table_cell");
@@ -107,7 +107,7 @@ impl Flow for TableCellFlow {
         let inline_size_computer = InternalTable;
 
         inline_size_computer.compute_used_inline_size(&mut self.block_flow,
-                                                      ctx,
+                                                      layout_context,
                                                       containing_block_inline_size);
 
         let inline_start_content_edge =
@@ -117,7 +117,8 @@ impl Flow for TableCellFlow {
         let content_inline_size =
             self.block_flow.fragment.border_box.size.inline - padding_and_borders;
 
-        self.block_flow.propagate_assigned_inline_size_to_children(inline_start_content_edge,
+        self.block_flow.propagate_assigned_inline_size_to_children(layout_context,
+                                                                   inline_start_content_edge,
                                                                    content_inline_size,
                                                                    None);
     }

components/layout/table_row.rs

@@ -234,6 +234,7 @@ impl Flow for TableRowFlow {
                                                       containing_block_inline_size);
 
         self.block_flow.propagate_assigned_inline_size_to_children(
+            layout_context,
             inline_start_content_edge,
             containing_block_inline_size,
             Some(self.column_computed_inline_sizes.as_slice()));

components/layout/table_rowgroup.rs

@@ -143,7 +143,7 @@ impl Flow for TableRowGroupFlow {
 
     /// Recursively (top-down) determines the actual inline-size of child contexts and fragments.
     /// When called on this context, the context has had its inline-size set by the parent context.
-    fn assign_inline_sizes(&mut self, ctx: &LayoutContext) {
+    fn assign_inline_sizes(&mut self, layout_context: &LayoutContext) {
         let _scope = layout_debug_scope!("table_rowgroup::assign_inline_sizes {:x}",
                                             self.block_flow.base.debug_id());
         debug!("assign_inline_sizes({}): assigning inline_size for flow", "table_rowgroup");
@@ -157,10 +157,11 @@ impl Flow for TableRowGroupFlow {
 
         let inline_size_computer = InternalTable;
         inline_size_computer.compute_used_inline_size(&mut self.block_flow,
-                                                      ctx,
+                                                      layout_context,
                                                       containing_block_inline_size);
 
         self.block_flow.propagate_assigned_inline_size_to_children(
+            layout_context,
             inline_start_content_edge,
             content_inline_size,
             Some(self.column_computed_inline_sizes.as_slice()));

components/layout/table_wrapper.rs

@@ -299,12 +299,14 @@ impl Flow for TableWrapperFlow {
         match assigned_column_inline_sizes {
             None => {
                 self.block_flow.propagate_assigned_inline_size_to_children(
+                    layout_context,
                     inline_start_content_edge,
                     content_inline_size,
                     None)
             }
             Some(ref assigned_column_inline_sizes) => {
                 self.block_flow.propagate_assigned_inline_size_to_children(
+                    layout_context,
                     inline_start_content_edge,
                     content_inline_size,
                     Some(assigned_column_inline_sizes.as_slice()));

components/style/properties/mod.rs.mako

@@ -1111,6 +1111,8 @@ pub mod longhands {
         }
     </%self:single_component_value>
 
+    ${predefined_type("text-indent", "LengthOrPercentage", "computed::LP_Length(Au(0))")}
+
     ${new_style_struct("Text", is_inherited=False)}
 
     <%self:longhand name="text-decoration">

tests/ref/basic.list

@@ -197,3 +197,4 @@ fragment=top != ../html/acid2.html acid2_ref.html
 != border_black_groove.html border_black_solid.html
 != border_black_ridge.html border_black_solid.html
 != border_black_ridge.html border_black_groove.html
+== text_indent_a.html text_indent_ref.html

tests/ref/text_indent_a.html

@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<html>
+<!-- Tests that `text-indent` works, in particular when combined with `text-align`. -->
+<head>
+<link rel="stylesheet" type="text/css" href="css/ahem.css">
+<style>
+section {
+    color: blue;
+    position: absolute;
+    width: 200px;
+    height: 200px;
+}
+#a {
+    left: 0;
+    top: 0;
+    text-indent: 100px;
+}
+#b {
+    left: 0;
+    top: 200px;
+    text-indent: 50%;
+}
+#b2 {
+    left: 0;
+    top: 0;
+}
+#c {
+    left: 200px;
+    top: 0;
+    text-align: right;
+    text-indent: 100px;
+}
+</style>
+</head>
+<body>
+<section id=a>X X</section>
+<section id=b><section id=b2>X X</section></section>
+<section id=c>X X</section>
+</body>
+</html>

tests/ref/text_indent_ref.html

@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<html>
+<!-- Tests that `text-indent` works, in particular when combined with `text-align`. -->
+<head>
+<link rel="stylesheet" type="text/css" href="css/ahem.css">
+<style>
+section {
+    background: blue;
+    position: absolute;
+    width: 100px;
+}
+#a {
+    top: 0;
+    left: 100px;
+    height: 100px;
+}
+#b {
+    top: 100px;
+    left: 0;
+    height: 100px;
+}
+#c {
+    top: 200px;
+    left: 100px;
+    height: 100px;
+}
+#d {
+    top: 300px;
+    left: 0;
+    height: 100px;
+}
+#e {
+    top: 0;
+    left: 300px;
+    height: 200px;
+}
+</style>
+</head>
+<body>
+<section id=a></section>
+<section id=b></section>
+<section id=c></section>
+<section id=d></section>
+<section id=e></section>
+</body>
+</html>