Add deterministic ordering

backend/reconcile/src/operation_transformation/edited_text.rs

@@ -25,7 +25,7 @@ use crate::{
 #[derive(Debug, Clone, PartialEq, Default)]
 pub struct EditedText<'a, T>
 where
-    T: PartialEq + Clone,
+    T: PartialEq + Clone + std::fmt::Debug,
 {
     text: &'a str,
     operations: Vec<OrderedOperation<T>>,
@@ -46,7 +46,7 @@ impl<'a> EditedText<'a, String> {
 
 impl<'a, T> EditedText<'a, T>
 where
-    T: PartialEq + Clone,
+    T: PartialEq + Clone + std::fmt::Debug,
 {
     /// Create an `EditedText` from the given original (old) and updated (new)
     /// strings. The returned `EditedText` represents the changes from the
@@ -207,9 +207,12 @@ where
                     |(operation, _)| {
                         (
                             operation.order,
-                            // Operations on left and right must come in the same order so that
+                            // Operations on the left and right must come in the same order so that
                             // inserts can be merged with other inserts and deletes with deletes.
                             usize::from(matches!(operation.operation, Operation::Delete { .. })),
+                            // Make sure that the ordering is deterministic regardless which text
+                            // is left or right.
+                            operation.operation.get_hash(),
                         )
                     },
                 )
@@ -282,7 +285,7 @@ mod tests {
         let original = "hello world! ...";
         let left = "Hello world! I'm Andras.";
         let right = "Hello world! How are you?";
-        let expected = "Hello world! I'm Andras.How are you?";
+        let expected = "Hello world! How are you?I'm Andras.";
 
         let operations_1 = EditedText::from_strings(original, left);
         let operations_2 = EditedText::from_strings(original, right);

backend/reconcile/src/operation_transformation/operation.rs

@@ -2,18 +2,18 @@ use core::{
     fmt::{Debug, Display},
     ops::Range,
 };
-use std::cmp::min;
+use std::hash::{DefaultHasher, Hash, Hasher};
 
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
 use super::merge_context::MergeContext;
 use crate::{
+    Token,
     utils::{
         find_longest_prefix_contained_within::find_longest_prefix_contained_within,
         string_builder::StringBuilder,
     },
-    Token,
 };
 
 /// Represents a change that can be applied to a text document.
@@ -39,6 +39,28 @@ where
     },
 }
 
+impl<T> Hash for Operation<T>
+where
+    T: PartialEq + Clone + std::fmt::Debug,
+{
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        match self {
+            Operation::Insert { index, text } => {
+                index.hash(state);
+                text.iter().for_each(|token| token.original().hash(state));
+            }
+            Operation::Delete {
+                index,
+                deleted_character_count,
+                ..
+            } => {
+                index.hash(state);
+                deleted_character_count.hash(state);
+            }
+        };
+    }
+}
+
 impl<T> Operation<T>
 where
     T: PartialEq + Clone + std::fmt::Debug,
@@ -300,6 +322,13 @@ where
             }
         }
     }
+
+    /// Gets the hash of the operation based on the indexes and original text.
+    pub fn get_hash(&self) -> u64 {
+        let mut hasher = DefaultHasher::new();
+        self.hash(&mut hasher);
+        hasher.finish()
+    }
 }
 
 impl<T> Display for Operation<T>
@@ -362,9 +391,11 @@ mod tests {
     #[test]
     #[should_panic]
     fn test_shifting_error() {
-        insta::assert_debug_snapshot!(Operation::create_insert(1, vec!["hi".into()])
+        insta::assert_debug_snapshot!(
+            Operation::create_insert(1, vec!["hi".into()])
                 .unwrap()
-            .with_shifted_index(-2));
+                .with_shifted_index(-2)
+        );
     }
 
     #[test]