1 files changed, 70 insertions, 0 deletions
diff --git a/third_party/rust/serde_json/src/iter.rs b/third_party/rust/serde_json/src/iter.rs
new file mode 100644
index 0000000000..9792916dcc
--- /dev/null
+++ b/third_party/rust/serde_json/src/iter.rs
@@ -0,0 +1,70 @@
+use crate::io;
+
+pub struct LineColIterator<I> {
+    iter: I,
+
+    /// Index of the current line. Characters in the first line of the input
+    /// (before the first newline character) are in line 1.
+    line: usize,
+
+    /// Index of the current column. The first character in the input and any
+    /// characters immediately following a newline character are in column 1.
+    /// The column is 0 immediately after a newline character has been read.
+    col: usize,
+
+    /// Byte offset of the start of the current line. This is the sum of lengths
+    /// of all previous lines. Keeping track of things this way allows efficient
+    /// computation of the current line, column, and byte offset while only
+    /// updating one of the counters in `next()` in the common case.
+    start_of_line: usize,
+}
+
+impl<I> LineColIterator<I>
+where
+    I: Iterator<Item = io::Result<u8>>,
+{
+    pub fn new(iter: I) -> LineColIterator<I> {
+        LineColIterator {
+            iter,
+            line: 1,
+            col: 0,
+            start_of_line: 0,
+        }
+    }
+
+    pub fn line(&self) -> usize {
+        self.line
+    }
+
+    pub fn col(&self) -> usize {
+        self.col
+    }
+
+    pub fn byte_offset(&self) -> usize {
+        self.start_of_line + self.col
+    }
+}
+
+impl<I> Iterator for LineColIterator<I>
+where
+    I: Iterator<Item = io::Result<u8>>,
+{
+    type Item = io::Result<u8>;
+
+    fn next(&mut self) -> Option<io::Result<u8>> {
+        match self.iter.next() {
+            None => None,
+            Some(Ok(b'\n')) => {
+                self.start_of_line += self.col + 1;
+                self.line += 1;
+                self.col = 0;
+                Some(Ok(b'\n'))
+            }
+            Some(Ok(c)) => {
+                self.col += 1;
+                Some(Ok(c))
+            }
+            Some(Err(e)) => Some(Err(e)),
+        }
+    }
+}