Revert "language: Remove buffer fingerprinting (#9007)"

This reverts commit 6f2f61c9b1.

crates/rope/Cargo.toml

@@ -13,6 +13,7 @@ path = "src/rope.rs"
 
 [dependencies]
 arrayvec = "0.7.1"
+bromberg_sl2 = { git = "https://github.com/zed-industries/bromberg_sl2", rev = "950bc5482c216c395049ae33ae4501e08975f17f" }
 log.workspace = true
 smallvec.workspace = true
 sum_tree.workspace = true

crates/rope/src/rope.rs

@@ -4,6 +4,7 @@ mod point_utf16;
 mod unclipped;
 
 use arrayvec::ArrayString;
+use bromberg_sl2::HashMatrix;
 use smallvec::SmallVec;
 use std::{
     cmp, fmt, io, mem,
@@ -24,6 +25,12 @@ const CHUNK_BASE: usize = 6;
 #[cfg(not(test))]
 const CHUNK_BASE: usize = 16;
 
+/// Type alias to [`HashMatrix`], an implementation of a homomorphic hash function. Two [`Rope`] instances
+/// containing the same text will produce the same fingerprint. This hash function is special in that
+/// it allows us to hash individual chunks and aggregate them up the [`Rope`]'s tree, with the resulting
+/// hash being equivalent to hashing all the text contained in the [`Rope`] at once.
+pub type RopeFingerprint = HashMatrix;
+
 #[derive(Clone, Default)]
 pub struct Rope {
     chunks: SumTree<Chunk>,
@@ -34,6 +41,10 @@ impl Rope {
         Self::default()
     }
 
+    pub fn text_fingerprint(text: &str) -> RopeFingerprint {
+        bromberg_sl2::hash_strict(text.as_bytes())
+    }
+
     pub fn append(&mut self, rope: Rope) {
         let mut chunks = rope.chunks.cursor::<()>();
         chunks.next(&());
@@ -412,6 +423,10 @@ impl Rope {
         self.clip_point(Point::new(row, u32::MAX), Bias::Left)
             .column
     }
+
+    pub fn fingerprint(&self) -> RopeFingerprint {
+        self.chunks.summary().fingerprint
+    }
 }
 
 impl<'a> From<&'a str> for Rope {
@@ -962,12 +977,14 @@ impl sum_tree::Item for Chunk {
 #[derive(Clone, Debug, Default, Eq, PartialEq)]
 pub struct ChunkSummary {
     text: TextSummary,
+    fingerprint: RopeFingerprint,
 }
 
 impl<'a> From<&'a str> for ChunkSummary {
     fn from(text: &'a str) -> Self {
         Self {
             text: TextSummary::from(text),
+            fingerprint: Rope::text_fingerprint(text),
         }
     }
 }
@@ -977,6 +994,7 @@ impl sum_tree::Summary for ChunkSummary {
 
     fn add_summary(&mut self, summary: &Self, _: &()) {
         self.text += &summary.text;
+        self.fingerprint = self.fingerprint * summary.fingerprint;
     }
 }