implement Display for Tree

Author: LoZack19

.gitignore

@@ -1,2 +1,3 @@
 target
 Cargo.lock
+.vscode

src/lib.rs

@@ -35,7 +35,7 @@
     missing_copy_implementations
 )]
 
-use std::fmt::{self, Debug, Formatter};
+use std::fmt::{self, Debug, Display, Formatter};
 use std::num::NonZeroUsize;
 
 /// Vec-backed ID-tree.
@@ -718,3 +718,41 @@ impl<T: Debug> Debug for Tree<T> {
         }
     }
 }
+
+impl<T: Display> Display for Tree<T> {
+    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
+        use iter::Edge;
+
+        fn indent(f: &mut Formatter, level: usize) -> Result<(), fmt::Error> {
+            for _ in 0..level {
+                write!(f, "    ")?;
+            }
+            Ok(())
+        }
+
+        let mut level: usize = 0;
+
+        for edge in self.root().traverse() {
+            match edge {
+                Edge::Open(node) if node.has_children() => {
+                    indent(f, level)?;
+                    write!(f, "{}\n", node.value())?;
+                    level += 1;
+                }
+                Edge::Open(node) if node.next_sibling().is_some() => {
+                    indent(f, level)?;
+                    write!(f, "{}\n", node.value())?;
+                }
+                Edge::Open(node) => {
+                    indent(f, level)?;
+                    write!(f, "{}\n", node.value())?;
+                }
+                Edge::Close(node) if node.has_children() => {
+                    level -= 1;
+                }
+                _ => {}
+            }
+        }
+        Ok(())
+    }
+}

tests/tree.rs

@@ -156,3 +156,35 @@ fn insert_id_before() {
     );
     assert_eq!(3, tree.root().children().count());
 }
+
+#[test]
+fn test_display() {
+    let tree = tree! {
+        "root" => {
+            "a" => {
+                "child 1",
+            },
+            "b" => {
+                "child 2",
+            },
+        }
+    };
+
+    let repr = format!("{tree}");
+    let expected = "root\n    a\n        child 1\n    b\n        child 2\n";
+
+    assert_eq!(repr, expected);
+
+    let tree = tree! {
+        "root" => {
+            "a", "b" => {
+                "x", "y"
+            }, "c"
+        }
+    };
+
+    let repr = format!("{tree}");
+    let expected = "root\n    a\n    b\n        x\n        y\n    c\n";
+
+    assert_eq!(repr, expected);
+}