From d60ad49f841444b0984aed52f909afd7df0fdf7f Mon Sep 17 00:00:00 2001
From: CJ van den Berg <cj@vdbonline.com>
Date: Tue, 29 Oct 2024 21:30:19 +0100
Subject: [PATCH] feat: improve did_change performance with an arena

---
 src/Project.zig | 42 +++++++++++++++++++++---------------------
 1 file changed, 21 insertions(+), 21 deletions(-)

diff --git a/src/Project.zig b/src/Project.zig
index 5e98a95..8e42a13 100644
--- a/src/Project.zig
+++ b/src/Project.zig
@@ -315,27 +315,28 @@ pub fn did_open(self: *Self, file_path: []const u8, file_type: []const u8, langu
 pub fn did_change(self: *Self, file_path: []const u8, version: usize, root_dst_addr: usize, root_src_addr: usize, eol_mode: Buffer.EolMode) LspError!void {
     const lsp = try self.get_language_server(file_path);
     const uri = try self.make_URI(file_path);
-    defer self.allocator.free(uri);
+
+    var arena_ = std.heap.ArenaAllocator.init(self.allocator);
+    const arena = arena_.allocator();
+    var scratch_alloc: ?[]u32 = null;
+    defer {
+        const frame = tracy.initZone(@src(), .{ .name = "deinit" });
+        self.allocator.free(uri);
+        arena_.deinit();
+        frame.deinit();
+        if (scratch_alloc) |scratch|
+            self.allocator.free(scratch);
+    }
 
     const root_dst: Buffer.Root = if (root_dst_addr == 0) return else @ptrFromInt(root_dst_addr);
     const root_src: Buffer.Root = if (root_src_addr == 0) return else @ptrFromInt(root_src_addr);
 
     var dizzy_edits = std.ArrayListUnmanaged(dizzy.Edit){};
-    var dst = std.ArrayList(u8).init(self.allocator);
-    var src = std.ArrayList(u8).init(self.allocator);
-    var scratch = std.ArrayListUnmanaged(u32){};
-    var edits_cb = std.ArrayList(u8).init(self.allocator);
+    var dst = std.ArrayList(u8).init(arena);
+    var src = std.ArrayList(u8).init(arena);
+    var edits_cb = std.ArrayList(u8).init(arena);
     const writer = edits_cb.writer();
 
-    defer {
-        const frame = tracy.initZone(@src(), .{ .name = "deinit" });
-        edits_cb.deinit();
-        dst.deinit();
-        src.deinit();
-        scratch.deinit(self.allocator);
-        dizzy_edits.deinit(self.allocator);
-        frame.deinit();
-    }
     {
         const frame = tracy.initZone(@src(), .{ .name = "store" });
         defer frame.deinit();
@@ -343,17 +344,17 @@ pub fn did_change(self: *Self, file_path: []const u8, version: usize, root_dst_a
         try root_src.store(src.writer(), eol_mode);
     }
     const scratch_len = 4 * (dst.items.len + src.items.len) + 2;
-    {
+    const scratch = blk: {
         const frame = tracy.initZone(@src(), .{ .name = "scratch" });
         defer frame.deinit();
-        try scratch.ensureTotalCapacity(self.allocator, scratch_len);
-    }
-    scratch.items.len = scratch_len;
+        break :blk try self.allocator.alloc(u32, scratch_len);
+    };
+    scratch_alloc = scratch;
 
     {
         const frame = tracy.initZone(@src(), .{ .name = "diff" });
         defer frame.deinit();
-        try dizzy.PrimitiveSliceDiffer(u8).diff(self.allocator, &dizzy_edits, src.items, dst.items, scratch.items);
+        try dizzy.PrimitiveSliceDiffer(u8).diff(arena, &dizzy_edits, src.items, dst.items, scratch);
     }
     var lines_dst: usize = 0;
     var last_offset: usize = 0;
@@ -398,8 +399,7 @@ pub fn did_change(self: *Self, file_path: []const u8, version: usize, root_dst_a
     {
         const frame = tracy.initZone(@src(), .{ .name = "send" });
         defer frame.deinit();
-        var msg = std.ArrayList(u8).init(self.allocator);
-        defer msg.deinit();
+        var msg = std.ArrayList(u8).init(arena);
         const msg_writer = msg.writer();
         try cbor.writeMapHeader(msg_writer, 2);
         try cbor.writeValue(msg_writer, "textDocument");