From eefaa867502859e7e0ea16926c478a14eedd286b Mon Sep 17 00:00:00 2001
From: Antonio Scandurra <me@as-cii.com>
Date: Fri, 25 Mar 2022 14:28:38 +0100
Subject: [PATCH] Introduce `Patch::transform_old`

---
 crates/text/src/patch.rs | 66 ++++++++++++++++++++++++++++------------
 1 file changed, 46 insertions(+), 20 deletions(-)

diff --git a/crates/text/src/patch.rs b/crates/text/src/patch.rs
index 8e68b2545c..080e5f131e 100644
--- a/crates/text/src/patch.rs
+++ b/crates/text/src/patch.rs
@@ -199,6 +199,28 @@ where
             self.0.push(edit);
         }
     }
+
+    pub fn transform_old(&self, old: T) -> T {
+        let ix = match self.0.binary_search_by(|probe| probe.old.start.cmp(&old)) {
+            Ok(ix) => ix,
+            Err(ix) => {
+                if ix == 0 {
+                    return old;
+                } else {
+                    ix - 1
+                }
+            }
+        };
+        if let Some(edit) = self.0.get(ix) {
+            if old >= edit.old.end {
+                edit.new.end + (old - edit.old.end)
+            } else {
+                edit.new.start
+            }
+        } else {
+            old
+        }
+    }
 }
 
 impl<T: Clone> IntoIterator for Patch<T> {
@@ -399,26 +421,6 @@ mod tests {
         );
     }
 
-    // #[test]
-    // fn test_compose_edits() {
-    //     assert_eq!(
-    //         compose_edits(
-    //             &Edit {
-    //                 old: 3..3,
-    //                 new: 3..6,
-    //             },
-    //             &Edit {
-    //                 old: 2..7,
-    //                 new: 2..4,
-    //             },
-    //         ),
-    //         Edit {
-    //             old: 2..4,
-    //             new: 2..4
-    //         }
-    //     );
-    // }
-
     #[gpui::test]
     fn test_two_new_edits_touching_one_old_edit() {
         assert_patch_composition(
@@ -455,6 +457,30 @@ mod tests {
         );
     }
 
+    #[gpui::test]
+    fn test_transform_old() {
+        let patch = Patch(vec![
+            Edit {
+                old: 2..4,
+                new: 2..4,
+            },
+            Edit {
+                old: 7..8,
+                new: 7..11,
+            },
+        ]);
+        assert_eq!(patch.transform_old(0), 0);
+        assert_eq!(patch.transform_old(1), 1);
+        assert_eq!(patch.transform_old(2), 2);
+        assert_eq!(patch.transform_old(3), 2);
+        assert_eq!(patch.transform_old(4), 4);
+        assert_eq!(patch.transform_old(5), 5);
+        assert_eq!(patch.transform_old(6), 6);
+        assert_eq!(patch.transform_old(7), 7);
+        assert_eq!(patch.transform_old(8), 11);
+        assert_eq!(patch.transform_old(9), 12);
+    }
+
     #[gpui::test(iterations = 100)]
     fn test_random_patch_compositions(mut rng: StdRng) {
         let operations = env::var("OPERATIONS")