fix: store redo metadata along with undo metadata and restore it on redo

This commit refactors undo storage and handling significantly.

The undo/redo chaining in Buffer is much simpler and clearer.

The metadata generated by Editor now contains the pre and post change
states. The pre-state is restored on undo and the post-state is restored
on redo.

closes #348

src/buffer/Buffer.zig

@@ -46,9 +46,8 @@ auto_save: bool = false,
 meta: ?[]const u8 = null,
 lsp_version: usize = 1,
 
-undo_history: ?*UndoNode = null,
+undo_head: ?*UndoNode = null,
-redo_history: ?*UndoNode = null,
+redo_head: ?*UndoNode = null,
-curr_history: ?*UndoNode = null,
 
 mtime: i64,
 utime: i64,
@@ -62,14 +61,15 @@ pub const EolModeTag = @typeInfo(EolMode).@"enum".tag_type;
 
 const UndoNode = struct {
     root: Root,
-    next: ?*UndoNode = null,
+    next_undo: ?*UndoNode = null,
+    next_redo: ?*UndoNode = null,
     branches: ?*UndoBranch = null,
     meta: []const u8,
     file_eol_mode: EolMode,
 };
 
 const UndoBranch = struct {
-    redo: *UndoNode,
+    redo_head: *UndoNode,
     next: ?*UndoBranch,
 };
 
@@ -1511,9 +1511,8 @@ pub fn update(self: *Self, root: Root) void {
 }
 
 pub fn store_undo(self: *Self, meta: []const u8) error{OutOfMemory}!void {
-    self.push_undo(try self.create_undo(self.root, meta));
-    self.curr_history = null;
     try self.push_redo_branch();
+    self.push_undo(try self.create_undo(self.root, meta));
 }
 
 fn create_undo(self: *const Self, root: Root, meta_: []const u8) error{OutOfMemory}!*UndoNode {
@@ -1527,54 +1526,65 @@ fn create_undo(self: *const Self, root: Root, meta_: []const u8) error{OutOfMemo
     return h;
 }
 
-fn push_undo(self: *Self, h: *UndoNode) void {
+fn push_undo(self: *Self, node: *UndoNode) void {
-    const next = self.undo_history;
+    node.next_undo = self.undo_head;
-    self.undo_history = h;
+    self.undo_head = node;
-    h.next = next;
 }
 
-fn push_redo(self: *Self, h: *UndoNode) void {
+fn pop_undo(self: *Self) ?*UndoNode {
-    const next = self.redo_history;
+    const node = self.undo_head orelse return null;
-    self.redo_history = h;
+    self.undo_head = node.next_undo;
-    h.next = next;
+    return node;
+}
+
+fn push_redo(self: *Self, node: *UndoNode) void {
+    node.next_redo = self.redo_head;
+    self.redo_head = node;
+}
+
+fn pop_redo(self: *Self) ?*UndoNode {
+    const node = self.redo_head orelse return null;
+    self.redo_head = node.next_redo;
+    return node;
 }
 
 fn push_redo_branch(self: *Self) !void {
-    const r = self.redo_history orelse return;
+    const redo_head = self.redo_head orelse return;
-    const u = self.undo_history orelse return;
+    const undo_head = self.undo_head orelse return;
-    const next = u.branches;
+    const branch = try self.allocator.create(UndoBranch);
-    const b = try self.allocator.create(UndoBranch);
+    branch.* = .{
-    b.* = .{
+        .redo_head = redo_head,
-        .redo = r,
+        .next = undo_head.branches,
-        .next = next,
     };
-    u.branches = b;
+    undo_head.branches = branch;
-    self.redo_history = null;
+    self.redo_head = null;
 }
 
-pub fn undo(self: *Self, meta: []const u8) error{Stop}![]const u8 {
+pub fn undo(self: *Self) error{Stop}![]const u8 {
-    const r = self.curr_history orelse self.create_undo(self.root, meta) catch return error.Stop;
+    const node = self.pop_undo() orelse return error.Stop;
-    const h = self.undo_history orelse return error.Stop;
+    if (self.redo_head == null) blk: {
-    self.undo_history = h.next;
+        self.push_redo(self.create_undo(self.root, &.{}) catch break :blk);
-    self.curr_history = h;
+    }
-    self.root = h.root;
+    self.push_redo(node);
-    self.file_eol_mode = h.file_eol_mode;
+    self.root = node.root;
-    self.push_redo(r);
+    self.file_eol_mode = node.file_eol_mode;
     self.mtime = std.time.milliTimestamp();
-    return h.meta;
+    return node.meta;
 }
 
 pub fn redo(self: *Self) error{Stop}![]const u8 {
-    const u = self.curr_history orelse return error.Stop;
+    if (self.redo_head) |redo_head| if (self.root != redo_head.root)
-    const h = self.redo_history orelse return error.Stop;
+        return error.Stop;
-    if (u.root != self.root) return error.Stop;
+    const node = self.pop_redo() orelse return error.Stop;
-    self.redo_history = h.next;
+    self.push_undo(node);
-    self.curr_history = h;
+    if (self.redo_head) |head| {
-    self.root = h.root;
+        self.root = head.root;
-    self.file_eol_mode = h.file_eol_mode;
+        self.file_eol_mode = head.file_eol_mode;
-    self.push_undo(u);
+        if (head.next_redo == null)
+            self.redo_head = null;
+    }
     self.mtime = std.time.milliTimestamp();
-    return h.meta;
+    return node.meta;
 }
 
 pub fn write_state(self: *const Self, writer: *std.Io.Writer) error{ Stop, OutOfMemory, WriteFailed }!void {

src/tui/editor.zig

@@ -409,6 +409,22 @@ pub const Editor = struct {
         if (self.buffer) |p| p.set_meta(meta.written()) catch {};
     }
 
+    fn count_cursels(self: *const Self) usize {
+        var count: usize = 0;
+        for (self.cursels.items) |*cursel_| if (cursel_.*) |_| {
+            count += 1;
+        };
+        return count;
+    }
+
+    fn count_cursels_saved(self: *const Self) usize {
+        var count: usize = 0;
+        for (self.cursels_saved.items) |*cursel_| if (cursel_.*) |_| {
+            count += 1;
+        };
+        return count;
+    }
+
     pub fn write_state(self: *const Self, writer: *std.Io.Writer) !void {
         try cbor.writeArrayHeader(writer, 10);
         try cbor.writeValue(writer, self.file_path orelse "");
@@ -427,11 +443,7 @@ pub const Editor = struct {
         }
         try self.view.write(writer);
 
-        var count_cursels: usize = 0;
+        try cbor.writeArrayHeader(writer, self.count_cursels());
-        for (self.cursels.items) |*cursel_| if (cursel_.*) |_| {
-            count_cursels += 1;
-        };
-        try cbor.writeArrayHeader(writer, count_cursels);
         for (self.cursels.items) |*cursel_| if (cursel_.*) |*cursel| {
             try cursel.write(writer);
         };
@@ -806,16 +818,17 @@ pub const Editor = struct {
     fn store_undo_meta(self: *Self, allocator: Allocator) ![]u8 {
         var meta: std.Io.Writer.Allocating = .init(allocator);
         defer meta.deinit();
+
+        try cbor.writeArrayHeader(&meta.writer, 2);
+
+        try cbor.writeArrayHeader(&meta.writer, self.count_cursels_saved());
         for (self.cursels_saved.items) |*cursel_| if (cursel_.*) |*cursel|
             try cursel.write(&meta.writer);
-        return meta.toOwnedSlice();
-    }
 
-    fn store_current_undo_meta(self: *Self, allocator: Allocator) ![]u8 {
+        try cbor.writeArrayHeader(&meta.writer, self.count_cursels());
-        var meta: std.Io.Writer.Allocating = .init(allocator);
-        defer meta.deinit();
         for (self.cursels.items) |*cursel_| if (cursel_.*) |*cursel|
             try cursel.write(&meta.writer);
+
         return meta.toOwnedSlice();
     }
 
@@ -839,15 +852,30 @@ pub const Editor = struct {
         try self.send_editor_modified();
     }
 
-    fn restore_undo_redo_meta(self: *Self, meta: []const u8) !void {
+    fn restore_cursels_array(self: *Self, iter: *[]const u8) !void {
+        var len = cbor.decodeArrayHeader(iter) catch return error.UndoMetaSyntaxCurSelsError;
+        while (len > 0) : (len -= 1) {
+            var cursel: CurSel = .{};
+            if (!try cursel.extract(iter)) return error.UndoMetaSyntaxCurSelError;
+            (try self.cursels.addOne(self.allocator)).* = cursel;
+        }
+    }
+
+    fn restore_undo_meta(self: *Self, meta: []const u8) !void {
         if (meta.len > 0)
             self.clear_all_cursors();
         var iter = meta;
-        while (iter.len > 0) {
+        if ((cbor.decodeArrayHeader(&iter) catch return error.UndoMetaSyntaxError) != 2) return error.UndoMetaSyntaxError;
-            var cursel: CurSel = .{};
+        return self.restore_cursels_array(&iter);
-            if (!try cursel.extract(&iter)) return error.SyntaxError;
-            (try self.cursels.addOne(self.allocator)).* = cursel;
     }
+
+    fn restore_redo_meta(self: *Self, meta: []const u8) !void {
+        if (meta.len > 0)
+            self.clear_all_cursors();
+        var iter = meta;
+        if ((cbor.decodeArrayHeader(&iter) catch return error.UndoMetaSyntaxError) != 2) return error.UndoMetaSyntaxError;
+        try cbor.skipValue(&iter); // first array is pre-operation cursels
+        return self.restore_cursels_array(&iter); // second array is post-operation cursels
     }
 
     fn restore_undo(self: *Self) !void {
@@ -856,18 +884,14 @@ pub const Editor = struct {
         if (self.buffer) |b_mut| {
             try self.send_editor_jump_source();
             self.cancel_all_matches();
-            var sfa = std.heap.stackFallback(512, self.allocator);
+            const meta = b_mut.undo() catch |e| switch (e) {
-            const sfa_allocator = sfa.get();
-            const redo_metadata = try self.store_current_undo_meta(sfa_allocator);
-            defer sfa_allocator.free(redo_metadata);
-            const meta = b_mut.undo(redo_metadata) catch |e| switch (e) {
                 error.Stop => {
                     self.logger.print("nothing to undo", .{});
                     return;
                 },
                 else => return e,
             };
-            try self.restore_undo_redo_meta(meta);
+            try self.restore_undo_meta(meta);
             try self.send_editor_jump_destination();
         }
     }
@@ -883,7 +907,7 @@ pub const Editor = struct {
                 },
                 else => return e,
             };
-            try self.restore_undo_redo_meta(meta);
+            try self.restore_redo_meta(meta);
             try self.send_editor_jump_destination();
         }
     }