Add incremental parsing unit tests

cli/src/tests/helpers/edits.rs

@@ -1,4 +1,6 @@
 use super::random::Rand;
+use std::ops::Range;
+use std::str;
 use tree_sitter::{InputEdit, Point, Tree};
 
 pub struct Edit {
@@ -7,6 +9,53 @@ pub struct Edit {
     pub inserted_text: Vec<u8>,
 }
 
+#[derive(Debug)]
+pub struct ReadRecorder<'a> {
+    content: &'a Vec<u8>,
+    indices_read: Vec<usize>,
+}
+
+impl<'a> ReadRecorder<'a> {
+    pub fn new(content: &'a Vec<u8>) -> Self {
+        Self {
+            content,
+            indices_read: Vec::new(),
+        }
+    }
+
+    pub fn read(&mut self, offset: usize) -> &'a [u8] {
+        if offset < self.content.len() {
+            if let Err(i) = self.indices_read.binary_search(&offset) {
+                self.indices_read.insert(i, offset);
+            }
+            &self.content[offset..(offset + 1)]
+        } else {
+            &[]
+        }
+    }
+
+    pub fn strings_read(&self) -> Vec<&'a str> {
+        let mut result = Vec::new();
+        let mut last_range: Option<Range<usize>> = None;
+        for index in self.indices_read.iter() {
+            if let Some(ref mut range) = &mut last_range {
+                if range.end == *index {
+                    range.end += 1;
+                } else {
+                    result.push(str::from_utf8(&self.content[range.clone()]).unwrap());
+                    last_range = None;
+                }
+            } else {
+                last_range = Some(*index..(*index + 1));
+            }
+        }
+        if let Some(range) = last_range {
+            result.push(str::from_utf8(&self.content[range.clone()]).unwrap());
+        }
+        result
+    }
+}
+
 pub fn perform_edit(tree: &mut Tree, input: &mut Vec<u8>, edit: &Edit) {
     let start_byte = edit.position;
     let old_end_byte = edit.position + edit.deleted_length;