minor: replace panics with types

Author: matklad

crates/mbe/src/syntax_bridge.rs

@@ -280,7 +280,7 @@ fn convert_tokens<C: TokenConvertor>(conv: &mut C) -> tt::Subtree {
  parent.subtree.token_trees.extend(entry.subtree.token_trees);
  }
 
- let subtree = stack.into_first().subtree;
+ let subtree = stack.into_last().subtree;
  if let [tt::TokenTree::Subtree(first)] = &*subtree.token_trees {
  first.clone()
  } else {

crates/stdx/src/non_empty_vec.rs

@@ -1,45 +1,39 @@
-//! A [`Vec`] that is guaranteed to at least contain one element.
+//! See [`NonEmptyVec`].
 
-pub struct NonEmptyVec<T>(Vec<T>);
+/// A [`Vec`] that is guaranteed to at least contain one element.
+pub struct NonEmptyVec<T> {
+ first: T,
+ rest: Vec<T>,
+}
 
 impl<T> NonEmptyVec<T> {
  #[inline]
- pub fn new(initial: T) -> Self {
- NonEmptyVec(vec![initial])
+ pub fn new(first: T) -> Self {
+ NonEmptyVec { first, rest: Vec::new() }
  }
 
  #[inline]
  pub fn last_mut(&mut self) -> &mut T {
- match self.0.last_mut() {
- Some(it) => it,
- None => unreachable!(),
- }
+ self.rest.last_mut().unwrap_or(&mut self.first)
  }
 
  #[inline]
  pub fn pop(&mut self) -> Option<T> {
- if self.0.len() <= 1 {
- None
- } else {
- self.0.pop()
- }
+ self.rest.pop()
  }
 
  #[inline]
  pub fn push(&mut self, value: T) {
- self.0.push(value)
+ self.rest.push(value)
  }
 
  #[inline]
  pub fn len(&self) -> usize {
- self.0.len()
+ 1 + self.rest.len()
  }
 
  #[inline]
- pub fn into_first(mut self) -> T {
- match self.0.pop() {
- Some(it) => it,
- None => unreachable!(),
- }
+ pub fn into_last(mut self) -> T {
+ self.rest.pop().unwrap_or(self.first)
  }
 }