Bug 1519175 - Allow creating PrintTree instances with other sinks. r=kvark

This will let us print trees to files instead of stdout.

Differential Revision: https://phabricator.services.mozilla.com/D16228

--HG--
extra : moz-landing-system : lando

gfx/wr/webrender/src/print_tree.rs

@@ -2,15 +2,23 @@
  * 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::{stdout, Stdout, Write};
+
 /// A struct that makes it easier to print out a pretty tree of data, which
 /// can be visually scanned more easily.
-pub struct PrintTree {
+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>,
+
+    /// The sink to print to.
+    sink: W,
 }
 
 /// A trait that makes it easy to describe a pretty tree of data,
@@ -22,37 +30,50 @@ pub trait PrintTreePrinter {
     fn add_item(&mut self, text: String);
 }
 
-impl PrintTree {
+impl PrintTree<Stdout> {
-    pub fn new(title: &str) -> PrintTree {
+    pub fn new(title: &str) -> Self {
-        println!("\u{250c} {}", title);
+        PrintTree::new_with_sink(title, stdout())
+    }
+}
+
+impl<W> PrintTree<W>
+where
+    W: Write
+{
+    pub fn new_with_sink(title: &str, mut sink: W) -> Self {
+        writeln!(sink, "\u{250c} {}", title).unwrap();
         PrintTree {
             level: 1,
             queued_item: None,
+            sink,
         }
     }
 
-    fn print_level_prefix(&self) {
+    fn print_level_prefix(&mut self) {
         for _ in 0 .. self.level {
-            print!("\u{2502}  ");
+            write!(self.sink, "\u{2502}  ").unwrap();
         }
     }
 
     fn flush_queued_item(&mut self, prefix: &str) {
         if let Some(queued_item) = self.queued_item.take() {
             self.print_level_prefix();
-            println!("{} {}", prefix, queued_item);
+            writeln!(self.sink, "{} {}", prefix, queued_item).unwrap();
         }
     }
 }
 
 // The default `println!` based printer
-impl PrintTreePrinter for PrintTree {
+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();
-        println!("\u{251C}\u{2500} {}", title);
+        writeln!(self.sink, "\u{251C}\u{2500} {}", title).unwrap();
 
         self.level = self.level + 1;
     }
@@ -70,7 +91,10 @@ impl PrintTreePrinter for PrintTree {
     }
 }
 
-impl Drop for PrintTree {
+impl<W> Drop for PrintTree<W>
+where
+    W: Write
+{
     fn drop(&mut self) {
         self.flush_queued_item("\u{9492}\u{9472}");
     }