1 files changed, 31 insertions, 3 deletions
diff --git a/src/string_joiner.zig b/src/string_joiner.zig
index 490989c9a..373d24633 100644
--- a/src/string_joiner.zig
+++ b/src/string_joiner.zig
@@ -1,7 +1,8 @@
 /// Rope-like data structure for joining many small strings into one big string.
 const std = @import("std");
-const default_allocator = @import("bun").default_allocator;
-const string = @import("string_types.zig").string;
+const default_allocator = bun.default_allocator;
+const bun = @import("bun");
+const string = bun.string;
 const Allocator = std.mem.Allocator;
 const ObjectPool = @import("./pool.zig").ObjectPool;
 const Joiner = @This();
@@ -15,7 +16,6 @@ const Joinable = struct {
     pub const Pool = ObjectPool(Joinable, null, true, 4);
 };
 
-last_byte: u8 = 0,
 len: usize = 0,
 use_pool: bool = true,
 node_allocator: Allocator = undefined,
@@ -23,6 +23,15 @@ node_allocator: Allocator = undefined,
 head: ?*Joinable.Pool.Node = null,
 tail: ?*Joinable.Pool.Node = null,
 
+/// Avoid an extra pass over the list when joining
+watcher: Watcher = .{},
+
+pub const Watcher = struct {
+    input: []const u8 = "",
+    estimated_count: u32 = 0,
+    needs_newline: bool = false,
+};
+
 pub fn done(this: *Joiner, allocator: Allocator) ![]u8 {
     if (this.head == null) {
         var out: []u8 = &[_]u8{};
@@ -60,6 +69,17 @@ pub fn lastByte(this: *const Joiner) u8 {
     return 0;
 }
 
+pub fn push(this: *Joiner, slice: string) void {
+    this.append(slice, 0, null);
+}
+
+pub fn ensureNewlineAtEnd(this: *Joiner) void {
+    if (this.watcher.needs_newline) {
+        this.watcher.needs_newline = false;
+        this.push("\n");
+    }
+}
+
 pub fn append(this: *Joiner, slice: string, offset: u32, allocator: ?Allocator) void {
     const data = slice[offset..];
     this.len += @truncate(u32, data.len);
@@ -69,6 +89,14 @@ pub fn append(this: *Joiner, slice: string, offset: u32, allocator: ?Allocator)
     else
         (this.node_allocator.create(Joinable.Pool.Node) catch unreachable);
 
+    this.watcher.estimated_count += @boolToInt(
+        this.watcher.input.len > 0 and
+            bun.strings.contains(data, this.watcher.input),
+    );
+
+    this.watcher.needs_newline = this.watcher.input.len > 0 and data.len > 0 and
+        data[data.len - 1] != '\n';
+
     new_tail.* = .{
         .allocator = default_allocator,
         .data = Joinable{