Fix offset conversion for end of file (#100)

crates/nil/src/vfs.rs

@@ -153,11 +153,11 @@ impl Vfs {
 #[derive(Debug, PartialEq, Eq)]
 pub struct LineMap {
  /// Invariant:
- /// - Have at least two elements.
+ /// - Have at least one element.
  /// - The first must be 0.
- /// - The last must be the length of original text.
  line_starts: Vec<u32>,
  char_diffs: HashMap<u32, Vec<(u32, CodeUnitsDiff)>>,
+ len: u32,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -169,12 +169,12 @@ enum CodeUnitsDiff {
 impl LineMap {
  fn normalize(mut text: String) -> (String, Self) {
  // Must be valid for `TextSize`.
- u32::try_from(text.len()).expect("Text too long");
+ let text_len = u32::try_from(text.len()).expect("Text too long");
 
  text.retain(|c| c != '\r');
  let bytes = text.as_bytes();
 
- let mut line_starts = Some(0)
+ let line_starts = Some(0)
  .into_iter()
  .chain(
  bytes
@@ -184,10 +184,12 @@ impl LineMap {
  .map(|(_, i)| i + 1),
  )
  .collect::<Vec<_>>();
- line_starts.push(text.len() as u32);
 
  let mut char_diffs = HashMap::new();
- for ((&start, &end), i) in line_starts.iter().zip(&line_starts[1..]).zip(0u32..) {
+
+ let start_pos_iter = line_starts.iter().copied();
+ let end_pos_iter = line_starts[1..].iter().copied().chain(Some(text_len));
+ for ((start, end), i) in start_pos_iter.zip(end_pos_iter).zip(0u32..) {
  let mut diffs = Vec::new();
  for (&b, pos) in bytes[start as usize..end as usize].iter().zip(0u32..) {
  let diff = match b {
@@ -207,12 +209,13 @@ impl LineMap {
  let this = Self {
  line_starts,
  char_diffs,
+ len: text_len,
  };
  (text, this)
  }
 
  pub fn last_line(&self) -> u32 {
- self.line_starts.len() as u32 - 2
+ self.line_starts.len() as u32 - 1
  }
 
  pub fn pos_for_line_col(&self, line: u32, mut col: u32) -> TextSize {
@@ -245,15 +248,16 @@ impl LineMap {
  }
 
  pub fn end_col_for_line(&self, line: u32) -> u32 {
- let mut len = self.line_starts[line as usize + 1] - self.line_starts[line as usize];
+ let mut len = if line + 1 >= self.line_starts.len() as u32 {
+ self.len - self.line_starts[line as usize]
+ } else {
+ // Minus the trailing `\n` for non-last-lines.
+ self.line_starts[line as usize + 1] - self.line_starts[line as usize] - 1
+ };
+
  if let Some(diffs) = self.char_diffs.get(&line) {
  len -= diffs.iter().map(|&(_, diff)| diff as u32).sum::<u32>();
  }
- // Lines except the last one has a trailing `\n`.
- // Note that `line_starts` has one element more than actual total lines.
- if line + 1 + 1 != self.line_starts.len() as u32 {
- len -= 1;
- }
  len
  }
 }
@@ -268,7 +272,7 @@ mod tests {
  let s = "hello\nworld\nend";
  let (norm, map) = LineMap::normalize(s.into());
  assert_eq!(norm, s);
- assert_eq!(&map.line_starts, &[0, 6, 12, 15]);
+ assert_eq!(&map.line_starts, &[0, 6, 12]);
 
  let mapping = [
  (0, 0, 0),
@@ -277,6 +281,7 @@ mod tests {
  (6, 1, 0),
  (11, 1, 5),
  (12, 2, 0),
+ (15, 2, 3),
  ];
  for (pos, line, col) in mapping {
  assert_eq!(map.line_col_for_pos(pos.into()), (line, col));
@@ -294,7 +299,7 @@ mod tests {
  let s = "_A_ß_ℝ_💣_";
  let (norm, map) = LineMap::normalize(s.into());
  assert_eq!(norm, s);
- assert_eq!(&map.line_starts, &[0, 15]);
+ assert_eq!(&map.line_starts, &[0]);
  assert_eq!(
  &map.char_diffs,
  &HashMap::from([(