Simplify changeset tracking.

2 files changed, 24 insertions, 7 deletions

diff --git a/helix-core/src/state.rs b/helix-core/src/state.rs
index d8aa3ed4..fde6a866 100644
--- a/helix-core/src/state.rs
+++ b/helix-core/src/state.rs
@@ -25,7 +25,8 @@ pub struct State {
 
     //
     pub syntax: Option<Syntax>,
-    pub changes: Option<ChangeSet>,
+    /// Pending changes since last history commit.
+    pub changes: ChangeSet,
     pub old_state: Option<(Rope, Selection)>,
 }
 
@@ -45,6 +46,8 @@ pub enum Granularity {
 impl State {
     #[must_use]
     pub fn new(doc: Rope) -> Self {
+        let changes = ChangeSet::new(&doc);
+
         Self {
             path: None,
             doc,
@@ -52,7 +55,7 @@ impl State {
             mode: Mode::Normal,
             restore_cursor: false,
             syntax: None,
-            changes: None,
+            changes,
             old_state: None,
         }
     }
diff --git a/helix-core/src/transaction.rs b/helix-core/src/transaction.rs
index dfb1bbe1..86fc0bc8 100644
--- a/helix-core/src/transaction.rs
+++ b/helix-core/src/transaction.rs
@@ -342,6 +342,22 @@ pub struct Transaction {
     // scroll_into_view
 }
 
+/// Like std::mem::replace() except it allows the replacement value to be mapped from the
+/// original value.
+pub fn take_with<T, F>(mut_ref: &mut T, closure: F)
+where
+    F: FnOnce(T) -> T,
+{
+    use std::{panic, ptr};
+
+    unsafe {
+        let old_t = ptr::read(mut_ref);
+        let new_t = panic::catch_unwind(panic::AssertUnwindSafe(|| closure(old_t)))
+            .unwrap_or_else(|_| ::std::process::abort());
+        ptr::write(mut_ref, new_t);
+    }
+}
+
 impl Transaction {
     /// Create a new, empty transaction.
     pub fn new(state: &mut State) -> Self {
@@ -364,11 +380,9 @@ impl Transaction {
             }
 
             // Compose this transaction with the previous one
-            let old_changes = state.changes.take();
-            state.changes = Some(old_changes.map_or_else(
-                || self.changes.clone(),
-                |changes| changes.compose(self.changes.clone()).unwrap(),
-            ));
+            take_with(&mut state.changes, |changes| {
+                changes.compose(self.changes.clone()).unwrap()
+            });
 
             if let Some(syntax) = &mut state.syntax {
                 // TODO: no unwrap