Drop dependency for failure crate, and make NodeId::remove() infallible

Cargo.toml

@@ -24,7 +24,6 @@ par_iter = ["rayon"]
 std = []
 
 [dependencies]
-failure = { version = "0.1.5", features = ["derive"] }
 rayon = { version = "1.0.3", optional = true }
 serde = { version = "1.0.90", features = ["derive"], optional = true }
 

examples/parallel_iteration.rs

@@ -1,8 +1,7 @@
-use failure::Fallible;
 use indextree::*;
 use rayon::prelude::*;
 
-pub fn main() -> Fallible<()> {
+pub fn main() -> Result<(), NodeError> {
     // Create a new arena
     let arena = &mut Arena::new();
 

src/arena.rs

@@ -82,9 +82,8 @@ impl<T> Arena<T> {
     /// let _bar = arena.new_node("bar");
     /// assert_eq!(arena.count(), 2);
     ///
-    /// let _ = foo.remove(&mut arena)?;
+    /// foo.remove(&mut arena);
     /// assert_eq!(arena.count(), 2);
-    /// # Ok::<(), failure::Error>(())
     /// ```
     pub fn count(&self) -> usize {
         self.nodes.len()
@@ -102,9 +101,8 @@ impl<T> Arena<T> {
     /// let foo = arena.new_node("foo");
     /// assert!(!arena.is_empty());
     ///
-    /// foo.remove(&mut arena)?;
+    /// foo.remove(&mut arena);
     /// assert!(!arena.is_empty());
-    /// # Ok::<(), failure::Error>(())
     /// ```
     pub fn is_empty(&self) -> bool {
         self.count() == 0
@@ -190,13 +188,12 @@ impl<T> Arena<T> {
     /// let mut arena = Arena::new();
     /// let _foo = arena.new_node("foo");
     /// let bar = arena.new_node("bar");
-    /// bar.remove(&mut arena)?;
+    /// bar.remove(&mut arena);
     ///
     /// let mut iter = arena.iter();
     /// assert_eq!(iter.next().map(|node| (node.data, node.is_removed())), Some(("foo", false)));
     /// assert_eq!(iter.next().map(|node| (node.data, node.is_removed())), Some(("bar", true)));
     /// assert_eq!(iter.next().map(|node| (node.data, node.is_removed())), None);
-    /// # Ok::<(), failure::Error>(())
     /// ```
     ///
     /// [`is_removed()`]: struct.Node.html#method.is_removed

src/error.rs

@@ -3,71 +3,46 @@
 #[cfg(not(feature = "std"))]
 use core::fmt;
 
-use failure::Fail;
-
 #[cfg(feature = "std")]
 use std::{error, fmt};
 
-#[derive(Debug, Fail)]
+#[derive(Debug, Clone, Copy)]
 /// Possible node failures.
 pub enum NodeError {
-    #[fail(display = "Can not append a node to itself")]
+    /// Attempt to append a node to itself.
     AppendSelf,
-
-    #[fail(display = "Can not prepend a node to itself")]
+    /// Attempt to prepend a node to itself.
     PrependSelf,
-
-    #[fail(display = "Can not insert a node before itself")]
+    /// Attempt to insert a node before itself.
     InsertBeforeSelf,
-
-    #[fail(display = "Can not insert a node after itself")]
+    /// Attempt to insert a node after itself.
     InsertAfterSelf,
+    // See <https://github.com/rust-lang/rfcs/blob/master/text/2008-non-exhaustive.md#how-we-do-this-today>.
+    #[doc(hidden)]
+    __Nonexhaustive,
+}
 
-    // Deprecated, no longer used.
-    #[fail(display = "First child is already set")]
-    FirstChildAlreadySet,
-
-    // Deprecated, no longer used.
-    #[fail(display = "Previous sibling is already set")]
-    PreviousSiblingAlreadySet,
-
-    // Deprecated, no longer used.
-    #[fail(display = "Next sibling is already set")]
-    NextSiblingAlreadySet,
-
-    // Deprecated, no longer used.
-    #[fail(display = "Previous sibling not equal current node")]
-    PreviousSiblingNotSelf,
-
-    // Deprecated, no longer used.
-    #[fail(display = "Next sibling not equal current node")]
-    NextSiblingNotSelf,
-
-    // Deprecated, no longer used.
-    #[fail(display = "First child not equal current node")]
-    FirstChildNotSelf,
-
-    // Deprecated, no longer used.
-    #[fail(display = "Last child not equal current node")]
-    LastChildNotSelf,
-
-    // Deprecated, no longer used.
-    #[fail(display = "Previous sibling is not set")]
-    PreviousSiblingNotSet,
-
-    // Deprecated, no longer used.
-    #[fail(display = "Next sibling is not set")]
-    NextSiblingNotSet,
-
-    // Deprecated, no longer used.
-    #[fail(display = "First child is not set")]
-    FirstChildNotSet,
+impl NodeError {
+    fn as_str(self) -> &'static str {
+        match self {
+            NodeError::AppendSelf => "Can not append a node to itself",
+            NodeError::PrependSelf => "Can not prepend a node to itself",
+            NodeError::InsertBeforeSelf => "Can not insert a node before itself",
+            NodeError::InsertAfterSelf => "Can not insert a node after itself",
+            NodeError::__Nonexhaustive => panic!("`__Nonexhaustive` should not be used"),
+        }
+    }
+}
 
-    // Deprecated, no longer used.
-    #[fail(display = "Last child is not set")]
-    LastChildNotSet,
+impl fmt::Display for NodeError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
 }
 
+#[cfg(feature = "std")]
+impl error::Error for NodeError {}
+
 /// An error type that represents the given structure or argument is
 /// inconsistent or invalid.
 // Intended for internal use.