1 files changed, 122 insertions, 0 deletions
diff --git a/gfx/wr/webrender/src/print_tree.rs b/gfx/wr/webrender/src/print_tree.rs
new file mode 100644
index 0000000000..56d7852561
--- /dev/null
+++ b/gfx/wr/webrender/src/print_tree.rs
@@ -0,0 +1,122 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::io::Write;
+use std::fmt::Write as FmtWrite;
+
+/// A struct that makes it easier to print out a pretty tree of data, which
+/// can be visually scanned more easily.
+pub struct PrintTree<W>
+where
+    W: Write
+{
+    /// The current level of recursion.
+    level: u32,
+
+    /// An item which is queued up, so that we can determine if we need
+    /// a mid-tree prefix or a branch ending prefix.
+    queued_item: Option<String>,
+
+    // We hold lines until they are done, and then output them all at
+    // once
+    line_buffer: String,
+
+    /// The sink to print to.
+    sink: W,
+}
+
+/// A trait that makes it easy to describe a pretty tree of data,
+/// regardless of the printing destination, to either print it
+/// directly to stdout, or serialize it as in the debugger
+pub trait PrintTreePrinter {
+    fn new_level(&mut self, title: String);
+    fn end_level(&mut self);
+    fn add_item(&mut self, text: String);
+}
+
+// The default does nothing but log
+impl PrintTree<std::io::Sink> {
+    pub fn new(title: &str) -> Self {
+        PrintTree::new_with_sink(title, std::io::sink())
+    }
+}
+
+impl<W> PrintTree<W>
+where
+    W: Write
+{
+    pub fn new_with_sink(title: &str, sink: W) -> Self {
+        let mut result = PrintTree {
+            level: 1,
+            queued_item: None,
+            line_buffer: String::new(),
+            sink,
+        };
+
+        writeln!(result.line_buffer, "\u{250c} {}", title).unwrap();
+        result.flush_line();
+        result
+    }
+
+    fn print_level_prefix(&mut self) {
+        for _ in 0 .. self.level {
+            write!(self.line_buffer, "\u{2502}  ").unwrap();
+        }
+    }
+
+    fn flush_queued_item(&mut self, prefix: &str) {
+        if let Some(queued_item) = self.queued_item.take() {
+            self.print_level_prefix();
+            writeln!(self.line_buffer, "{} {}", prefix, queued_item).unwrap();
+            self.flush_line();
+        }
+    }
+
+    fn flush_line(&mut self) {
+        debug!("{}", self.line_buffer);
+        self.sink.write_all(self.line_buffer.as_bytes()).unwrap();
+        self.line_buffer.clear();
+    }
+}
+
+impl<W> PrintTreePrinter for PrintTree<W>
+where
+    W: Write
+{
+    /// Descend one level in the tree with the given title.
+    fn new_level(&mut self, title: String) {
+        self.flush_queued_item("\u{251C}\u{2500}");
+
+        self.print_level_prefix();
+        writeln!(self.line_buffer, "\u{251C}\u{2500} {}", title).unwrap();
+        self.flush_line();
+
+        self.level = self.level + 1;
+    }
+
+    /// Ascend one level in the tree.
+    fn end_level(&mut self) {
+        self.flush_queued_item("\u{2514}\u{2500}");
+        self.level = self.level - 1;
+    }
+
+    /// Add an item to the current level in the tree.
+    fn add_item(&mut self, text: String) {
+        self.flush_queued_item("\u{251C}\u{2500}");
+        self.queued_item = Some(text);
+    }
+}
+
+impl<W> Drop for PrintTree<W>
+where
+    W: Write
+{
+    fn drop(&mut self) {
+        self.flush_queued_item("\u{9492}\u{9472}");
+    }
+}
+
+pub trait PrintableTree {
+    fn print_with<T: PrintTreePrinter>(&self, pt: &mut T);
+}