From 1639fcea43549853f1fded32aa1d711d21771e1c Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Thu, 3 Apr 2025 14:11:38 -0700
Subject: [PATCH 1/4] de-genericify SinglyLinkedList

by making it always intrusive, we make it a more broadly useful API, and
avoid binary bloat.
---
 CMakeLists.txt                   |   1 -
 lib/std/SinglyLinkedList.zig     | 166 ++++++++++++++++++++++++++++++
 lib/std/Thread/Pool.zig          |  31 +++---
 lib/std/heap/arena_allocator.zig |  41 +++++---
 lib/std/linked_list.zig          | 168 -------------------------------
 lib/std/std.zig                  |   2 +-
 6 files changed, 207 insertions(+), 202 deletions(-)
 create mode 100644 lib/std/SinglyLinkedList.zig

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ea25212fec..4292bc1b92 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -444,7 +444,6 @@ set(ZIG_STAGE2_SOURCES
     lib/std/json.zig
     lib/std/json/stringify.zig
     lib/std/leb128.zig
-    lib/std/linked_list.zig
     lib/std/log.zig
     lib/std/macho.zig
     lib/std/math.zig
diff --git a/lib/std/SinglyLinkedList.zig b/lib/std/SinglyLinkedList.zig
new file mode 100644
index 0000000000..d118ce0395
--- /dev/null
+++ b/lib/std/SinglyLinkedList.zig
@@ -0,0 +1,166 @@
+//! A singly-linked list is headed by a single forward pointer. The elements
+//! are singly-linked for minimum space and pointer manipulation overhead at
+//! the expense of O(n) removal for arbitrary elements. New elements can be
+//! added to the list after an existing element or at the head of the list.
+//!
+//! A singly-linked list may only be traversed in the forward direction.
+//!
+//! Singly-linked lists are useful under these conditions:
+//! * Ability to preallocate elements / requirement of infallibility for
+//!   insertion.
+//! * Ability to allocate elements intrusively along with other data.
+//! * Homogenous elements.
+
+const std = @import("std.zig");
+const debug = std.debug;
+const assert = debug.assert;
+const testing = std.testing;
+const SinglyLinkedList = @This();
+
+first: ?*Node = null,
+
+/// This struct contains only a next pointer and not any data payload. The
+/// intended usage is to embed it intrusively into another data structure and
+/// access the data with `@fieldParentPtr`.
+pub const Node = struct {
+    next: ?*Node = null,
+
+    pub fn insertAfter(node: *Node, new_node: *Node) void {
+        new_node.next = node.next;
+        node.next = new_node;
+    }
+
+    /// Remove the node after the one provided, returning it.
+    pub fn removeNext(node: *Node) ?*Node {
+        const next_node = node.next orelse return null;
+        node.next = next_node.next;
+        return next_node;
+    }
+
+    /// Iterate over the singly-linked list from this node, until the final
+    /// node is found.
+    ///
+    /// This operation is O(N). Instead of calling this function, consider
+    /// using a different data structure.
+    pub fn findLast(node: *Node) *Node {
+        var it = node;
+        while (true) {
+            it = it.next orelse return it;
+        }
+    }
+
+    /// Iterate over each next node, returning the count of all nodes except
+    /// the starting one.
+    ///
+    /// This operation is O(N). Instead of calling this function, consider
+    /// using a different data structure.
+    pub fn countChildren(node: *const Node) usize {
+        var count: usize = 0;
+        var it: ?*const Node = node.next;
+        while (it) |n| : (it = n.next) {
+            count += 1;
+        }
+        return count;
+    }
+
+    /// Reverse the list starting from this node in-place.
+    ///
+    /// This operation is O(N). Instead of calling this function, consider
+    /// using a different data structure.
+    pub fn reverse(indirect: *?*Node) void {
+        if (indirect.* == null) {
+            return;
+        }
+        var current: *Node = indirect.*.?;
+        while (current.next) |next| {
+            current.next = next.next;
+            next.next = indirect.*;
+            indirect.* = next;
+        }
+    }
+};
+
+pub fn prepend(list: *SinglyLinkedList, new_node: *Node) void {
+    new_node.next = list.first;
+    list.first = new_node;
+}
+
+pub fn remove(list: *SinglyLinkedList, node: *Node) void {
+    if (list.first == node) {
+        list.first = node.next;
+    } else {
+        var current_elm = list.first.?;
+        while (current_elm.next != node) {
+            current_elm = current_elm.next.?;
+        }
+        current_elm.next = node.next;
+    }
+}
+
+/// Remove and return the first node in the list.
+pub fn popFirst(list: *SinglyLinkedList) ?*Node {
+    const first = list.first orelse return null;
+    list.first = first.next;
+    return first;
+}
+
+/// Iterate over all nodes, returning the count.
+///
+/// This operation is O(N). Consider tracking the length separately rather than
+/// computing it.
+pub fn len(list: SinglyLinkedList) usize {
+    if (list.first) |n| {
+        return 1 + n.countChildren();
+    } else {
+        return 0;
+    }
+}
+
+test "basics" {
+    const L = struct {
+        data: u32,
+        node: SinglyLinkedList.Node = .{},
+    };
+    var list: SinglyLinkedList = .{};
+
+    try testing.expect(list.len() == 0);
+
+    var one: L = .{ .data = 1 };
+    var two: L = .{ .data = 2 };
+    var three: L = .{ .data = 3 };
+    var four: L = .{ .data = 4 };
+    var five: L = .{ .data = 5 };
+
+    list.prepend(&two.node); // {2}
+    two.node.insertAfter(&five.node); // {2, 5}
+    list.prepend(&one.node); // {1, 2, 5}
+    two.node.insertAfter(&three.node); // {1, 2, 3, 5}
+    three.node.insertAfter(&four.node); // {1, 2, 3, 4, 5}
+
+    try testing.expect(list.len() == 5);
+
+    // Traverse forwards.
+    {
+        var it = list.first;
+        var index: u32 = 1;
+        while (it) |node| : (it = node.next) {
+            const l: *L = @fieldParentPtr("node", node);
+            try testing.expect(l.data == index);
+            index += 1;
+        }
+    }
+
+    _ = list.popFirst(); // {2, 3, 4, 5}
+    _ = list.remove(&five.node); // {2, 3, 4}
+    _ = two.node.removeNext(); // {2, 4}
+
+    try testing.expect(@as(*L, @fieldParentPtr("node", list.first.?)).data == 2);
+    try testing.expect(@as(*L, @fieldParentPtr("node", list.first.?.next.?)).data == 4);
+    try testing.expect(list.first.?.next.?.next == null);
+
+    SinglyLinkedList.Node.reverse(&list.first);
+
+    try testing.expect(@as(*L, @fieldParentPtr("node", list.first.?)).data == 4);
+    try testing.expect(@as(*L, @fieldParentPtr("node", list.first.?.next.?)).data == 2);
+    try testing.expect(list.first.?.next.?.next == null);
+}
diff --git a/lib/std/Thread/Pool.zig b/lib/std/Thread/Pool.zig
index 874050a35f..e836665d70 100644
--- a/lib/std/Thread/Pool.zig
+++ b/lib/std/Thread/Pool.zig
@@ -5,7 +5,7 @@ const WaitGroup = @import("WaitGroup.zig");
 
 mutex: std.Thread.Mutex = .{},
 cond: std.Thread.Condition = .{},
-run_queue: RunQueue = .{},
+run_queue: std.SinglyLinkedList = .{},
 is_running: bool = true,
 allocator: std.mem.Allocator,
 threads: if (builtin.single_threaded) [0]std.Thread else []std.Thread,
@@ -16,9 +16,9 @@ ids: if (builtin.single_threaded) struct {
     }
 } else std.AutoArrayHashMapUnmanaged(std.Thread.Id, void),
 
-const RunQueue = std.SinglyLinkedList(Runnable);
 const Runnable = struct {
     runFn: RunProto,
+    node: std.SinglyLinkedList.Node = .{},
 };
 
 const RunProto = *const fn (*Runnable, id: ?usize) void;
@@ -110,12 +110,11 @@ pub fn spawnWg(pool: *Pool, wait_group: *WaitGroup, comptime func: anytype, args
     const Closure = struct {
         arguments: Args,
         pool: *Pool,
-        run_node: RunQueue.Node = .{ .data = .{ .runFn = runFn } },
+        runnable: Runnable = .{ .runFn = runFn },
         wait_group: *WaitGroup,
 
         fn runFn(runnable: *Runnable, _: ?usize) void {
-            const run_node: *RunQueue.Node = @fieldParentPtr("data", runnable);
-            const closure: *@This() = @alignCast(@fieldParentPtr("run_node", run_node));
+            const closure: *@This() = @alignCast(@fieldParentPtr("runnable", runnable));
             @call(.auto, func, closure.arguments);
             closure.wait_group.finish();
 
@@ -143,7 +142,7 @@ pub fn spawnWg(pool: *Pool, wait_group: *WaitGroup, comptime func: anytype, args
             .wait_group = wait_group,
         };
 
-        pool.run_queue.prepend(&closure.run_node);
+        pool.run_queue.prepend(&closure.runnable.node);
         pool.mutex.unlock();
     }
 
@@ -173,12 +172,11 @@ pub fn spawnWgId(pool: *Pool, wait_group: *WaitGroup, comptime func: anytype, ar
     const Closure = struct {
         arguments: Args,
         pool: *Pool,
-        run_node: RunQueue.Node = .{ .data = .{ .runFn = runFn } },
+        runnable: Runnable = .{ .runFn = runFn },
         wait_group: *WaitGroup,
 
         fn runFn(runnable: *Runnable, id: ?usize) void {
-            const run_node: *RunQueue.Node = @fieldParentPtr("data", runnable);
-            const closure: *@This() = @alignCast(@fieldParentPtr("run_node", run_node));
+            const closure: *@This() = @alignCast(@fieldParentPtr("runnable", runnable));
             @call(.auto, func, .{id.?} ++ closure.arguments);
             closure.wait_group.finish();
 
@@ -207,7 +205,7 @@ pub fn spawnWgId(pool: *Pool, wait_group: *WaitGroup, comptime func: anytype, ar
             .wait_group = wait_group,
         };
 
-        pool.run_queue.prepend(&closure.run_node);
+        pool.run_queue.prepend(&closure.runnable.node);
         pool.mutex.unlock();
     }
 
@@ -225,11 +223,10 @@ pub fn spawn(pool: *Pool, comptime func: anytype, args: anytype) !void {
     const Closure = struct {
         arguments: Args,
         pool: *Pool,
-        run_node: RunQueue.Node = .{ .data = .{ .runFn = runFn } },
+        runnable: Runnable = .{ .runFn = runFn },
 
         fn runFn(runnable: *Runnable, _: ?usize) void {
-            const run_node: *RunQueue.Node = @fieldParentPtr("data", runnable);
-            const closure: *@This() = @alignCast(@fieldParentPtr("run_node", run_node));
+            const closure: *@This() = @alignCast(@fieldParentPtr("runnable", runnable));
             @call(.auto, func, closure.arguments);
 
             // The thread pool's allocator is protected by the mutex.
@@ -251,7 +248,7 @@ pub fn spawn(pool: *Pool, comptime func: anytype, args: anytype) !void {
             .pool = pool,
         };
 
-        pool.run_queue.prepend(&closure.run_node);
+        pool.run_queue.prepend(&closure.runnable.node);
     }
 
     // Notify waiting threads outside the lock to try and keep the critical section small.
@@ -292,7 +289,8 @@ fn worker(pool: *Pool) void {
             pool.mutex.unlock();
             defer pool.mutex.lock();
 
-            run_node.data.runFn(&run_node.data, id);
+            const runnable: *Runnable = @fieldParentPtr("node", run_node);
+            runnable.runFn(runnable, id);
         }
 
         // Stop executing instead of waiting if the thread pool is no longer running.
@@ -312,7 +310,8 @@ pub fn waitAndWork(pool: *Pool, wait_group: *WaitGroup) void {
         if (pool.run_queue.popFirst()) |run_node| {
             id = id orelse pool.ids.getIndex(std.Thread.getCurrentId());
             pool.mutex.unlock();
-            run_node.data.runFn(&run_node.data, id);
+            const runnable: *Runnable = @fieldParentPtr("node", run_node);
+            runnable.runFn(runnable, id);
             continue;
         }
 
diff --git a/lib/std/heap/arena_allocator.zig b/lib/std/heap/arena_allocator.zig
index f88bb7de16..c472ae80c5 100644
--- a/lib/std/heap/arena_allocator.zig
+++ b/lib/std/heap/arena_allocator.zig
@@ -14,7 +14,7 @@ pub const ArenaAllocator = struct {
     /// Inner state of ArenaAllocator. Can be stored rather than the entire ArenaAllocator
     /// as a memory-saving optimization.
     pub const State = struct {
-        buffer_list: std.SinglyLinkedList(usize) = .{},
+        buffer_list: std.SinglyLinkedList = .{},
         end_index: usize = 0,
 
         pub fn promote(self: State, child_allocator: Allocator) ArenaAllocator {
@@ -37,7 +37,10 @@ pub const ArenaAllocator = struct {
         };
     }
 
-    const BufNode = std.SinglyLinkedList(usize).Node;
+    const BufNode = struct {
+        data: usize,
+        node: std.SinglyLinkedList.Node = .{},
+    };
     const BufNode_alignment: mem.Alignment = .fromByteUnits(@alignOf(BufNode));
 
     pub fn init(child_allocator: Allocator) ArenaAllocator {
@@ -51,7 +54,8 @@ pub const ArenaAllocator = struct {
         while (it) |node| {
             // this has to occur before the free because the free frees node
             const next_it = node.next;
-            const alloc_buf = @as([*]u8, @ptrCast(node))[0..node.data];
+            const buf_node: *BufNode = @fieldParentPtr("node", node);
+            const alloc_buf = @as([*]u8, @ptrCast(buf_node))[0..buf_node.data];
             self.child_allocator.rawFree(alloc_buf, BufNode_alignment, @returnAddress());
             it = next_it;
         }
@@ -78,7 +82,8 @@ pub const ArenaAllocator = struct {
         while (it) |node| : (it = node.next) {
             // Compute the actually allocated size excluding the
             // linked list node.
-            size += node.data - @sizeOf(BufNode);
+            const buf_node: *BufNode = @fieldParentPtr("node", node);
+            size += buf_node.data - @sizeOf(BufNode);
         }
         return size;
     }
@@ -130,7 +135,8 @@ pub const ArenaAllocator = struct {
             const next_it = node.next;
             if (next_it == null)
                 break node;
-            const alloc_buf = @as([*]u8, @ptrCast(node))[0..node.data];
+            const buf_node: *BufNode = @fieldParentPtr("node", node);
+            const alloc_buf = @as([*]u8, @ptrCast(buf_node))[0..buf_node.data];
             self.child_allocator.rawFree(alloc_buf, BufNode_alignment, @returnAddress());
             it = next_it;
         } else null;
@@ -140,12 +146,13 @@ pub const ArenaAllocator = struct {
         if (maybe_first_node) |first_node| {
             self.state.buffer_list.first = first_node;
             // perfect, no need to invoke the child_allocator
-            if (first_node.data == total_size)
+            const first_buf_node: *BufNode = @fieldParentPtr("node", first_node);
+            if (first_buf_node.data == total_size)
                 return true;
-            const first_alloc_buf = @as([*]u8, @ptrCast(first_node))[0..first_node.data];
+            const first_alloc_buf = @as([*]u8, @ptrCast(first_buf_node))[0..first_buf_node.data];
             if (self.child_allocator.rawResize(first_alloc_buf, BufNode_alignment, total_size, @returnAddress())) {
                 // successful resize
-                first_node.data = total_size;
+                first_buf_node.data = total_size;
             } else {
                 // manual realloc
                 const new_ptr = self.child_allocator.rawAlloc(total_size, BufNode_alignment, @returnAddress()) orelse {
@@ -153,9 +160,9 @@ pub const ArenaAllocator = struct {
                     return false;
                 };
                 self.child_allocator.rawFree(first_alloc_buf, BufNode_alignment, @returnAddress());
-                const node: *BufNode = @ptrCast(@alignCast(new_ptr));
-                node.* = .{ .data = total_size };
-                self.state.buffer_list.first = node;
+                const buf_node: *BufNode = @ptrCast(@alignCast(new_ptr));
+                buf_node.* = .{ .data = total_size };
+                self.state.buffer_list.first = &buf_node.node;
             }
         }
         return true;
@@ -169,7 +176,7 @@ pub const ArenaAllocator = struct {
             return null;
         const buf_node: *BufNode = @ptrCast(@alignCast(ptr));
         buf_node.* = .{ .data = len };
-        self.state.buffer_list.prepend(buf_node);
+        self.state.buffer_list.prepend(&buf_node.node);
         self.state.end_index = 0;
         return buf_node;
     }
@@ -179,8 +186,8 @@ pub const ArenaAllocator = struct {
         _ = ra;
 
         const ptr_align = alignment.toByteUnits();
-        var cur_node = if (self.state.buffer_list.first) |first_node|
-            first_node
+        var cur_node: *BufNode = if (self.state.buffer_list.first) |first_node|
+            @fieldParentPtr("node", first_node)
         else
             (self.createNode(0, n + ptr_align) orelse return null);
         while (true) {
@@ -213,7 +220,8 @@ pub const ArenaAllocator = struct {
         _ = ret_addr;
 
         const cur_node = self.state.buffer_list.first orelse return false;
-        const cur_buf = @as([*]u8, @ptrCast(cur_node))[@sizeOf(BufNode)..cur_node.data];
+        const cur_buf_node: *BufNode = @fieldParentPtr("node", cur_node);
+        const cur_buf = @as([*]u8, @ptrCast(cur_buf_node))[@sizeOf(BufNode)..cur_buf_node.data];
         if (@intFromPtr(cur_buf.ptr) + self.state.end_index != @intFromPtr(buf.ptr) + buf.len) {
             // It's not the most recent allocation, so it cannot be expanded,
             // but it's fine if they want to make it smaller.
@@ -248,7 +256,8 @@ pub const ArenaAllocator = struct {
         const self: *ArenaAllocator = @ptrCast(@alignCast(ctx));
 
         const cur_node = self.state.buffer_list.first orelse return;
-        const cur_buf = @as([*]u8, @ptrCast(cur_node))[@sizeOf(BufNode)..cur_node.data];
+        const cur_buf_node: *BufNode = @fieldParentPtr("node", cur_node);
+        const cur_buf = @as([*]u8, @ptrCast(cur_buf_node))[@sizeOf(BufNode)..cur_buf_node.data];
 
         if (@intFromPtr(cur_buf.ptr) + self.state.end_index == @intFromPtr(buf.ptr) + buf.len) {
             self.state.end_index -= buf.len;
diff --git a/lib/std/linked_list.zig b/lib/std/linked_list.zig
index 07c5f5d4df..5b397a6ea7 100644
--- a/lib/std/linked_list.zig
+++ b/lib/std/linked_list.zig
@@ -3,174 +3,6 @@ const debug = std.debug;
 const assert = debug.assert;
 const testing = std.testing;
 
-/// A singly-linked list is headed by a single forward pointer. The elements
-/// are singly-linked for minimum space and pointer manipulation overhead at
-/// the expense of O(n) removal for arbitrary elements. New elements can be
-/// added to the list after an existing element or at the head of the list.
-/// A singly-linked list may only be traversed in the forward direction.
-/// Singly-linked lists are ideal for applications with large datasets and
-/// few or no removals or for implementing a LIFO queue.
-pub fn SinglyLinkedList(comptime T: type) type {
-    return struct {
-        const Self = @This();
-
-        /// Node inside the linked list wrapping the actual data.
-        pub const Node = struct {
-            next: ?*Node = null,
-            data: T,
-
-            pub const Data = T;
-
-            /// Insert a new node after the current one.
-            ///
-            /// Arguments:
-            ///     new_node: Pointer to the new node to insert.
-            pub fn insertAfter(node: *Node, new_node: *Node) void {
-                new_node.next = node.next;
-                node.next = new_node;
-            }
-
-            /// Remove a node from the list.
-            ///
-            /// Arguments:
-            ///     node: Pointer to the node to be removed.
-            /// Returns:
-            ///     node removed
-            pub fn removeNext(node: *Node) ?*Node {
-                const next_node = node.next orelse return null;
-                node.next = next_node.next;
-                return next_node;
-            }
-
-            /// Iterate over the singly-linked list from this node, until the final node is found.
-            /// This operation is O(N).
-            pub fn findLast(node: *Node) *Node {
-                var it = node;
-                while (true) {
-                    it = it.next orelse return it;
-                }
-            }
-
-            /// Iterate over each next node, returning the count of all nodes except the starting one.
-            /// This operation is O(N).
-            pub fn countChildren(node: *const Node) usize {
-                var count: usize = 0;
-                var it: ?*const Node = node.next;
-                while (it) |n| : (it = n.next) {
-                    count += 1;
-                }
-                return count;
-            }
-
-            /// Reverse the list starting from this node in-place.
-            /// This operation is O(N).
-            pub fn reverse(indirect: *?*Node) void {
-                if (indirect.* == null) {
-                    return;
-                }
-                var current: *Node = indirect.*.?;
-                while (current.next) |next| {
-                    current.next = next.next;
-                    next.next = indirect.*;
-                    indirect.* = next;
-                }
-            }
-        };
-
-        first: ?*Node = null,
-
-        /// Insert a new node at the head.
-        ///
-        /// Arguments:
-        ///     new_node: Pointer to the new node to insert.
-        pub fn prepend(list: *Self, new_node: *Node) void {
-            new_node.next = list.first;
-            list.first = new_node;
-        }
-
-        /// Remove a node from the list.
-        ///
-        /// Arguments:
-        ///     node: Pointer to the node to be removed.
-        pub fn remove(list: *Self, node: *Node) void {
-            if (list.first == node) {
-                list.first = node.next;
-            } else {
-                var current_elm = list.first.?;
-                while (current_elm.next != node) {
-                    current_elm = current_elm.next.?;
-                }
-                current_elm.next = node.next;
-            }
-        }
-
-        /// Remove and return the first node in the list.
-        ///
-        /// Returns:
-        ///     A pointer to the first node in the list.
-        pub fn popFirst(list: *Self) ?*Node {
-            const first = list.first orelse return null;
-            list.first = first.next;
-            return first;
-        }
-
-        /// Iterate over all nodes, returning the count.
-        /// This operation is O(N).
-        pub fn len(list: Self) usize {
-            if (list.first) |n| {
-                return 1 + n.countChildren();
-            } else {
-                return 0;
-            }
-        }
-    };
-}
-
-test "basic SinglyLinkedList test" {
-    const L = SinglyLinkedList(u32);
-    var list = L{};
-
-    try testing.expect(list.len() == 0);
-
-    var one = L.Node{ .data = 1 };
-    var two = L.Node{ .data = 2 };
-    var three = L.Node{ .data = 3 };
-    var four = L.Node{ .data = 4 };
-    var five = L.Node{ .data = 5 };
-
-    list.prepend(&two); // {2}
-    two.insertAfter(&five); // {2, 5}
-    list.prepend(&one); // {1, 2, 5}
-    two.insertAfter(&three); // {1, 2, 3, 5}
-    three.insertAfter(&four); // {1, 2, 3, 4, 5}
-
-    try testing.expect(list.len() == 5);
-
-    // Traverse forwards.
-    {
-        var it = list.first;
-        var index: u32 = 1;
-        while (it) |node| : (it = node.next) {
-            try testing.expect(node.data == index);
-            index += 1;
-        }
-    }
-
-    _ = list.popFirst(); // {2, 3, 4, 5}
-    _ = list.remove(&five); // {2, 3, 4}
-    _ = two.removeNext(); // {2, 4}
-
-    try testing.expect(list.first.?.data == 2);
-    try testing.expect(list.first.?.next.?.data == 4);
-    try testing.expect(list.first.?.next.?.next == null);
-
-    L.Node.reverse(&list.first);
-
-    try testing.expect(list.first.?.data == 4);
-    try testing.expect(list.first.?.next.?.data == 2);
-    try testing.expect(list.first.?.next.?.next == null);
-}
-
 /// A doubly-linked list has a pair of pointers to both the head and
 /// tail of the list. List elements have pointers to both the previous
 /// and next elements in the sequence. The list can be traversed both
diff --git a/lib/std/std.zig b/lib/std/std.zig
index 558710015c..b3c583f861 100644
--- a/lib/std/std.zig
+++ b/lib/std/std.zig
@@ -33,7 +33,7 @@ pub const Random = @import("Random.zig");
 pub const RingBuffer = @import("RingBuffer.zig");
 pub const SegmentedList = @import("segmented_list.zig").SegmentedList;
 pub const SemanticVersion = @import("SemanticVersion.zig");
-pub const SinglyLinkedList = @import("linked_list.zig").SinglyLinkedList;
+pub const SinglyLinkedList = @import("SinglyLinkedList.zig");
 pub const StaticBitSet = bit_set.StaticBitSet;
 pub const StringHashMap = hash_map.StringHashMap;
 pub const StringHashMapUnmanaged = hash_map.StringHashMapUnmanaged;

From 3b77a845f9a5409d19a9e330b82eece8af4ac18f Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Thu, 3 Apr 2025 15:35:21 -0700
Subject: [PATCH 2/4] de-genericify DoublyLinkedList

by making it always intrusive, we make it more broadly useful API, and
avoid binary bloat.
---
 lib/std/DoublyLinkedList.zig | 274 +++++++++++++++++++++++++++++++++
 lib/std/linked_list.zig      | 287 -----------------------------------
 lib/std/std.zig              |   2 +-
 3 files changed, 275 insertions(+), 288 deletions(-)
 create mode 100644 lib/std/DoublyLinkedList.zig
 delete mode 100644 lib/std/linked_list.zig

diff --git a/lib/std/DoublyLinkedList.zig b/lib/std/DoublyLinkedList.zig
new file mode 100644
index 0000000000..e0424b8252
--- /dev/null
+++ b/lib/std/DoublyLinkedList.zig
@@ -0,0 +1,274 @@
+//! A doubly-linked list has a pair of pointers to both the head and
+//! tail of the list. List elements have pointers to both the previous
+//! and next elements in the sequence. The list can be traversed both
+//! forward and backward. Some operations that take linear O(n) time
+//! with a singly-linked list can be done without traversal in constant
+//! O(1) time with a doubly-linked list:
+//!
+//! * Removing an element.
+//! * Inserting a new element before an existing element.
+//! * Pushing or popping an element from the end of the list.
+
+const std = @import("std.zig");
+const debug = std.debug;
+const assert = debug.assert;
+const testing = std.testing;
+const DoublyLinkedList = @This();
+
+first: ?*Node = null,
+last: ?*Node = null,
+len: usize = 0,
+
+/// This struct contains only the prev and next pointers and not any data
+/// payload. The intended usage is to embed it intrusively into another data
+/// structure and access the data with `@fieldParentPtr`.
+pub const Node = struct {
+    prev: ?*Node = null,
+    next: ?*Node = null,
+};
+
+pub fn insertAfter(list: *DoublyLinkedList, existing_node: *Node, new_node: *Node) void {
+    new_node.prev = existing_node;
+    if (existing_node.next) |next_node| {
+        // Intermediate node.
+        new_node.next = next_node;
+        next_node.prev = new_node;
+    } else {
+        // Last element of the list.
+        new_node.next = null;
+        list.last = new_node;
+    }
+    existing_node.next = new_node;
+
+    list.len += 1;
+}
+
+pub fn insertBefore(list: *DoublyLinkedList, existing_node: *Node, new_node: *Node) void {
+    new_node.next = existing_node;
+    if (existing_node.prev) |prev_node| {
+        // Intermediate node.
+        new_node.prev = prev_node;
+        prev_node.next = new_node;
+    } else {
+        // First element of the list.
+        new_node.prev = null;
+        list.first = new_node;
+    }
+    existing_node.prev = new_node;
+
+    list.len += 1;
+}
+
+/// Concatenate list2 onto the end of list1, removing all entries from the former.
+///
+/// Arguments:
+///     list1: the list to concatenate onto
+///     list2: the list to be concatenated
+pub fn concatByMoving(list1: *DoublyLinkedList, list2: *DoublyLinkedList) void {
+    const l2_first = list2.first orelse return;
+    if (list1.last) |l1_last| {
+        l1_last.next = list2.first;
+        l2_first.prev = list1.last;
+        list1.len += list2.len;
+    } else {
+        // list1 was empty
+        list1.first = list2.first;
+        list1.len = list2.len;
+    }
+    list1.last = list2.last;
+    list2.first = null;
+    list2.last = null;
+    list2.len = 0;
+}
+
+/// Insert a new node at the end of the list.
+///
+/// Arguments:
+///     new_node: Pointer to the new node to insert.
+pub fn append(list: *DoublyLinkedList, new_node: *Node) void {
+    if (list.last) |last| {
+        // Insert after last.
+        list.insertAfter(last, new_node);
+    } else {
+        // Empty list.
+        list.prepend(new_node);
+    }
+}
+
+/// Insert a new node at the beginning of the list.
+///
+/// Arguments:
+///     new_node: Pointer to the new node to insert.
+pub fn prepend(list: *DoublyLinkedList, new_node: *Node) void {
+    if (list.first) |first| {
+        // Insert before first.
+        list.insertBefore(first, new_node);
+    } else {
+        // Empty list.
+        list.first = new_node;
+        list.last = new_node;
+        new_node.prev = null;
+        new_node.next = null;
+
+        list.len = 1;
+    }
+}
+
+/// Remove a node from the list.
+///
+/// Arguments:
+///     node: Pointer to the node to be removed.
+pub fn remove(list: *DoublyLinkedList, node: *Node) void {
+    if (node.prev) |prev_node| {
+        // Intermediate node.
+        prev_node.next = node.next;
+    } else {
+        // First element of the list.
+        list.first = node.next;
+    }
+
+    if (node.next) |next_node| {
+        // Intermediate node.
+        next_node.prev = node.prev;
+    } else {
+        // Last element of the list.
+        list.last = node.prev;
+    }
+
+    list.len -= 1;
+    assert(list.len == 0 or (list.first != null and list.last != null));
+}
+
+/// Remove and return the last node in the list.
+///
+/// Returns:
+///     A pointer to the last node in the list.
+pub fn pop(list: *DoublyLinkedList) ?*Node {
+    const last = list.last orelse return null;
+    list.remove(last);
+    return last;
+}
+
+/// Remove and return the first node in the list.
+///
+/// Returns:
+///     A pointer to the first node in the list.
+pub fn popFirst(list: *DoublyLinkedList) ?*Node {
+    const first = list.first orelse return null;
+    list.remove(first);
+    return first;
+}
+
+test "basic DoublyLinkedList test" {
+    const L = DoublyLinkedList(u32);
+    var list = L{};
+
+    var one = L.Node{ .data = 1 };
+    var two = L.Node{ .data = 2 };
+    var three = L.Node{ .data = 3 };
+    var four = L.Node{ .data = 4 };
+    var five = L.Node{ .data = 5 };
+
+    list.append(&two); // {2}
+    list.append(&five); // {2, 5}
+    list.prepend(&one); // {1, 2, 5}
+    list.insertBefore(&five, &four); // {1, 2, 4, 5}
+    list.insertAfter(&two, &three); // {1, 2, 3, 4, 5}
+
+    // Traverse forwards.
+    {
+        var it = list.first;
+        var index: u32 = 1;
+        while (it) |node| : (it = node.next) {
+            try testing.expect(node.data == index);
+            index += 1;
+        }
+    }
+
+    // Traverse backwards.
+    {
+        var it = list.last;
+        var index: u32 = 1;
+        while (it) |node| : (it = node.prev) {
+            try testing.expect(node.data == (6 - index));
+            index += 1;
+        }
+    }
+
+    _ = list.popFirst(); // {2, 3, 4, 5}
+    _ = list.pop(); // {2, 3, 4}
+    list.remove(&three); // {2, 4}
+
+    try testing.expect(list.first.?.data == 2);
+    try testing.expect(list.last.?.data == 4);
+    try testing.expect(list.len == 2);
+}
+
+test "DoublyLinkedList concatenation" {
+    const L = DoublyLinkedList(u32);
+    var list1 = L{};
+    var list2 = L{};
+
+    var one = L.Node{ .data = 1 };
+    var two = L.Node{ .data = 2 };
+    var three = L.Node{ .data = 3 };
+    var four = L.Node{ .data = 4 };
+    var five = L.Node{ .data = 5 };
+
+    list1.append(&one);
+    list1.append(&two);
+    list2.append(&three);
+    list2.append(&four);
+    list2.append(&five);
+
+    list1.concatByMoving(&list2);
+
+    try testing.expect(list1.last == &five);
+    try testing.expect(list1.len == 5);
+    try testing.expect(list2.first == null);
+    try testing.expect(list2.last == null);
+    try testing.expect(list2.len == 0);
+
+    // Traverse forwards.
+    {
+        var it = list1.first;
+        var index: u32 = 1;
+        while (it) |node| : (it = node.next) {
+            try testing.expect(node.data == index);
+            index += 1;
+        }
+    }
+
+    // Traverse backwards.
+    {
+        var it = list1.last;
+        var index: u32 = 1;
+        while (it) |node| : (it = node.prev) {
+            try testing.expect(node.data == (6 - index));
+            index += 1;
+        }
+    }
+
+    // Swap them back, this verifies that concatenating to an empty list works.
+    list2.concatByMoving(&list1);
+
+    // Traverse forwards.
+    {
+        var it = list2.first;
+        var index: u32 = 1;
+        while (it) |node| : (it = node.next) {
+            try testing.expect(node.data == index);
+            index += 1;
+        }
+    }
+
+    // Traverse backwards.
+    {
+        var it = list2.last;
+        var index: u32 = 1;
+        while (it) |node| : (it = node.prev) {
+            try testing.expect(node.data == (6 - index));
+            index += 1;
+        }
+    }
+}
diff --git a/lib/std/linked_list.zig b/lib/std/linked_list.zig
deleted file mode 100644
index 5b397a6ea7..0000000000
--- a/lib/std/linked_list.zig
+++ /dev/null
@@ -1,287 +0,0 @@
-const std = @import("std.zig");
-const debug = std.debug;
-const assert = debug.assert;
-const testing = std.testing;
-
-/// A doubly-linked list has a pair of pointers to both the head and
-/// tail of the list. List elements have pointers to both the previous
-/// and next elements in the sequence. The list can be traversed both
-/// forward and backward. Some operations that take linear O(n) time
-/// with a singly-linked list can be done without traversal in constant
-/// O(1) time with a doubly-linked list:
-///
-/// - Removing an element.
-/// - Inserting a new element before an existing element.
-/// - Pushing or popping an element from the end of the list.
-pub fn DoublyLinkedList(comptime T: type) type {
-    return struct {
-        const Self = @This();
-
-        /// Node inside the linked list wrapping the actual data.
-        pub const Node = struct {
-            prev: ?*Node = null,
-            next: ?*Node = null,
-            data: T,
-        };
-
-        first: ?*Node = null,
-        last: ?*Node = null,
-        len: usize = 0,
-
-        /// Insert a new node after an existing one.
-        ///
-        /// Arguments:
-        ///     node: Pointer to a node in the list.
-        ///     new_node: Pointer to the new node to insert.
-        pub fn insertAfter(list: *Self, node: *Node, new_node: *Node) void {
-            new_node.prev = node;
-            if (node.next) |next_node| {
-                // Intermediate node.
-                new_node.next = next_node;
-                next_node.prev = new_node;
-            } else {
-                // Last element of the list.
-                new_node.next = null;
-                list.last = new_node;
-            }
-            node.next = new_node;
-
-            list.len += 1;
-        }
-
-        /// Insert a new node before an existing one.
-        ///
-        /// Arguments:
-        ///     node: Pointer to a node in the list.
-        ///     new_node: Pointer to the new node to insert.
-        pub fn insertBefore(list: *Self, node: *Node, new_node: *Node) void {
-            new_node.next = node;
-            if (node.prev) |prev_node| {
-                // Intermediate node.
-                new_node.prev = prev_node;
-                prev_node.next = new_node;
-            } else {
-                // First element of the list.
-                new_node.prev = null;
-                list.first = new_node;
-            }
-            node.prev = new_node;
-
-            list.len += 1;
-        }
-
-        /// Concatenate list2 onto the end of list1, removing all entries from the former.
-        ///
-        /// Arguments:
-        ///     list1: the list to concatenate onto
-        ///     list2: the list to be concatenated
-        pub fn concatByMoving(list1: *Self, list2: *Self) void {
-            const l2_first = list2.first orelse return;
-            if (list1.last) |l1_last| {
-                l1_last.next = list2.first;
-                l2_first.prev = list1.last;
-                list1.len += list2.len;
-            } else {
-                // list1 was empty
-                list1.first = list2.first;
-                list1.len = list2.len;
-            }
-            list1.last = list2.last;
-            list2.first = null;
-            list2.last = null;
-            list2.len = 0;
-        }
-
-        /// Insert a new node at the end of the list.
-        ///
-        /// Arguments:
-        ///     new_node: Pointer to the new node to insert.
-        pub fn append(list: *Self, new_node: *Node) void {
-            if (list.last) |last| {
-                // Insert after last.
-                list.insertAfter(last, new_node);
-            } else {
-                // Empty list.
-                list.prepend(new_node);
-            }
-        }
-
-        /// Insert a new node at the beginning of the list.
-        ///
-        /// Arguments:
-        ///     new_node: Pointer to the new node to insert.
-        pub fn prepend(list: *Self, new_node: *Node) void {
-            if (list.first) |first| {
-                // Insert before first.
-                list.insertBefore(first, new_node);
-            } else {
-                // Empty list.
-                list.first = new_node;
-                list.last = new_node;
-                new_node.prev = null;
-                new_node.next = null;
-
-                list.len = 1;
-            }
-        }
-
-        /// Remove a node from the list.
-        ///
-        /// Arguments:
-        ///     node: Pointer to the node to be removed.
-        pub fn remove(list: *Self, node: *Node) void {
-            if (node.prev) |prev_node| {
-                // Intermediate node.
-                prev_node.next = node.next;
-            } else {
-                // First element of the list.
-                list.first = node.next;
-            }
-
-            if (node.next) |next_node| {
-                // Intermediate node.
-                next_node.prev = node.prev;
-            } else {
-                // Last element of the list.
-                list.last = node.prev;
-            }
-
-            list.len -= 1;
-            assert(list.len == 0 or (list.first != null and list.last != null));
-        }
-
-        /// Remove and return the last node in the list.
-        ///
-        /// Returns:
-        ///     A pointer to the last node in the list.
-        pub fn pop(list: *Self) ?*Node {
-            const last = list.last orelse return null;
-            list.remove(last);
-            return last;
-        }
-
-        /// Remove and return the first node in the list.
-        ///
-        /// Returns:
-        ///     A pointer to the first node in the list.
-        pub fn popFirst(list: *Self) ?*Node {
-            const first = list.first orelse return null;
-            list.remove(first);
-            return first;
-        }
-    };
-}
-
-test "basic DoublyLinkedList test" {
-    const L = DoublyLinkedList(u32);
-    var list = L{};
-
-    var one = L.Node{ .data = 1 };
-    var two = L.Node{ .data = 2 };
-    var three = L.Node{ .data = 3 };
-    var four = L.Node{ .data = 4 };
-    var five = L.Node{ .data = 5 };
-
-    list.append(&two); // {2}
-    list.append(&five); // {2, 5}
-    list.prepend(&one); // {1, 2, 5}
-    list.insertBefore(&five, &four); // {1, 2, 4, 5}
-    list.insertAfter(&two, &three); // {1, 2, 3, 4, 5}
-
-    // Traverse forwards.
-    {
-        var it = list.first;
-        var index: u32 = 1;
-        while (it) |node| : (it = node.next) {
-            try testing.expect(node.data == index);
-            index += 1;
-        }
-    }
-
-    // Traverse backwards.
-    {
-        var it = list.last;
-        var index: u32 = 1;
-        while (it) |node| : (it = node.prev) {
-            try testing.expect(node.data == (6 - index));
-            index += 1;
-        }
-    }
-
-    _ = list.popFirst(); // {2, 3, 4, 5}
-    _ = list.pop(); // {2, 3, 4}
-    list.remove(&three); // {2, 4}
-
-    try testing.expect(list.first.?.data == 2);
-    try testing.expect(list.last.?.data == 4);
-    try testing.expect(list.len == 2);
-}
-
-test "DoublyLinkedList concatenation" {
-    const L = DoublyLinkedList(u32);
-    var list1 = L{};
-    var list2 = L{};
-
-    var one = L.Node{ .data = 1 };
-    var two = L.Node{ .data = 2 };
-    var three = L.Node{ .data = 3 };
-    var four = L.Node{ .data = 4 };
-    var five = L.Node{ .data = 5 };
-
-    list1.append(&one);
-    list1.append(&two);
-    list2.append(&three);
-    list2.append(&four);
-    list2.append(&five);
-
-    list1.concatByMoving(&list2);
-
-    try testing.expect(list1.last == &five);
-    try testing.expect(list1.len == 5);
-    try testing.expect(list2.first == null);
-    try testing.expect(list2.last == null);
-    try testing.expect(list2.len == 0);
-
-    // Traverse forwards.
-    {
-        var it = list1.first;
-        var index: u32 = 1;
-        while (it) |node| : (it = node.next) {
-            try testing.expect(node.data == index);
-            index += 1;
-        }
-    }
-
-    // Traverse backwards.
-    {
-        var it = list1.last;
-        var index: u32 = 1;
-        while (it) |node| : (it = node.prev) {
-            try testing.expect(node.data == (6 - index));
-            index += 1;
-        }
-    }
-
-    // Swap them back, this verifies that concatenating to an empty list works.
-    list2.concatByMoving(&list1);
-
-    // Traverse forwards.
-    {
-        var it = list2.first;
-        var index: u32 = 1;
-        while (it) |node| : (it = node.next) {
-            try testing.expect(node.data == index);
-            index += 1;
-        }
-    }
-
-    // Traverse backwards.
-    {
-        var it = list2.last;
-        var index: u32 = 1;
-        while (it) |node| : (it = node.prev) {
-            try testing.expect(node.data == (6 - index));
-            index += 1;
-        }
-    }
-}
diff --git a/lib/std/std.zig b/lib/std/std.zig
index b3c583f861..94851657a6 100644
--- a/lib/std/std.zig
+++ b/lib/std/std.zig
@@ -16,7 +16,7 @@ pub const BufMap = @import("buf_map.zig").BufMap;
 pub const BufSet = @import("buf_set.zig").BufSet;
 pub const StaticStringMap = static_string_map.StaticStringMap;
 pub const StaticStringMapWithEql = static_string_map.StaticStringMapWithEql;
-pub const DoublyLinkedList = @import("linked_list.zig").DoublyLinkedList;
+pub const DoublyLinkedList = @import("DoublyLinkedList.zig");
 pub const DynLib = @import("dynamic_library.zig").DynLib;
 pub const DynamicBitSet = bit_set.DynamicBitSet;
 pub const DynamicBitSetUnmanaged = bit_set.DynamicBitSetUnmanaged;

From 337e1109f5c2894aad9519ee9f7ff1f1f4c65b56 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Thu, 3 Apr 2025 15:57:35 -0700
Subject: [PATCH 3/4] std.DoublyLinkedList: remove length tracking

this is trivial to tack on, and in my experience it is rarely wanted.
---
 lib/std/DoublyLinkedList.zig | 116 +++++++++++++++++++----------------
 lib/std/http/Client.zig      |  87 +++++++++++++-------------
 2 files changed, 107 insertions(+), 96 deletions(-)

diff --git a/lib/std/DoublyLinkedList.zig b/lib/std/DoublyLinkedList.zig
index e0424b8252..dcc656bf43 100644
--- a/lib/std/DoublyLinkedList.zig
+++ b/lib/std/DoublyLinkedList.zig
@@ -17,7 +17,6 @@ const DoublyLinkedList = @This();
 
 first: ?*Node = null,
 last: ?*Node = null,
-len: usize = 0,
 
 /// This struct contains only the prev and next pointers and not any data
 /// payload. The intended usage is to embed it intrusively into another data
@@ -39,8 +38,6 @@ pub fn insertAfter(list: *DoublyLinkedList, existing_node: *Node, new_node: *Nod
         list.last = new_node;
     }
     existing_node.next = new_node;
-
-    list.len += 1;
 }
 
 pub fn insertBefore(list: *DoublyLinkedList, existing_node: *Node, new_node: *Node) void {
@@ -55,8 +52,6 @@ pub fn insertBefore(list: *DoublyLinkedList, existing_node: *Node, new_node: *No
         list.first = new_node;
     }
     existing_node.prev = new_node;
-
-    list.len += 1;
 }
 
 /// Concatenate list2 onto the end of list1, removing all entries from the former.
@@ -69,16 +64,13 @@ pub fn concatByMoving(list1: *DoublyLinkedList, list2: *DoublyLinkedList) void {
     if (list1.last) |l1_last| {
         l1_last.next = list2.first;
         l2_first.prev = list1.last;
-        list1.len += list2.len;
     } else {
         // list1 was empty
         list1.first = list2.first;
-        list1.len = list2.len;
     }
     list1.last = list2.last;
     list2.first = null;
     list2.last = null;
-    list2.len = 0;
 }
 
 /// Insert a new node at the end of the list.
@@ -109,8 +101,6 @@ pub fn prepend(list: *DoublyLinkedList, new_node: *Node) void {
         list.last = new_node;
         new_node.prev = null;
         new_node.next = null;
-
-        list.len = 1;
     }
 }
 
@@ -134,9 +124,6 @@ pub fn remove(list: *DoublyLinkedList, node: *Node) void {
         // Last element of the list.
         list.last = node.prev;
     }
-
-    list.len -= 1;
-    assert(list.len == 0 or (list.first != null and list.last != null));
 }
 
 /// Remove and return the last node in the list.
@@ -159,28 +146,43 @@ pub fn popFirst(list: *DoublyLinkedList) ?*Node {
     return first;
 }
 
-test "basic DoublyLinkedList test" {
-    const L = DoublyLinkedList(u32);
-    var list = L{};
+/// Iterate over all nodes, returning the count.
+///
+/// This operation is O(N). Consider tracking the length separately rather than
+/// computing it.
+pub fn len(list: DoublyLinkedList) usize {
+    var count: usize = 0;
+    var it: ?*const Node = list.first;
+    while (it) |n| : (it = n.next) count += 1;
+    return count;
+}
 
-    var one = L.Node{ .data = 1 };
-    var two = L.Node{ .data = 2 };
-    var three = L.Node{ .data = 3 };
-    var four = L.Node{ .data = 4 };
-    var five = L.Node{ .data = 5 };
+test "basics" {
+    const L = struct {
+        data: u32,
+        node: DoublyLinkedList.Node = .{},
+    };
+    var list: DoublyLinkedList = .{};
 
-    list.append(&two); // {2}
-    list.append(&five); // {2, 5}
-    list.prepend(&one); // {1, 2, 5}
-    list.insertBefore(&five, &four); // {1, 2, 4, 5}
-    list.insertAfter(&two, &three); // {1, 2, 3, 4, 5}
+    var one: L = .{ .data = 1 };
+    var two: L = .{ .data = 2 };
+    var three: L = .{ .data = 3 };
+    var four: L = .{ .data = 4 };
+    var five: L = .{ .data = 5 };
+
+    list.append(&two.node); // {2}
+    list.append(&five.node); // {2, 5}
+    list.prepend(&one.node); // {1, 2, 5}
+    list.insertBefore(&five.node, &four.node); // {1, 2, 4, 5}
+    list.insertAfter(&two.node, &three.node); // {1, 2, 3, 4, 5}
 
     // Traverse forwards.
     {
         var it = list.first;
         var index: u32 = 1;
         while (it) |node| : (it = node.next) {
-            try testing.expect(node.data == index);
+            const l: *L = @fieldParentPtr("node", node);
+            try testing.expect(l.data == index);
             index += 1;
         }
     }
@@ -190,51 +192,56 @@ test "basic DoublyLinkedList test" {
         var it = list.last;
         var index: u32 = 1;
         while (it) |node| : (it = node.prev) {
-            try testing.expect(node.data == (6 - index));
+            const l: *L = @fieldParentPtr("node", node);
+            try testing.expect(l.data == (6 - index));
             index += 1;
         }
     }
 
     _ = list.popFirst(); // {2, 3, 4, 5}
     _ = list.pop(); // {2, 3, 4}
-    list.remove(&three); // {2, 4}
+    list.remove(&three.node); // {2, 4}
 
-    try testing.expect(list.first.?.data == 2);
-    try testing.expect(list.last.?.data == 4);
-    try testing.expect(list.len == 2);
+    try testing.expect(@as(*L, @fieldParentPtr("node", list.first.?)).data == 2);
+    try testing.expect(@as(*L, @fieldParentPtr("node", list.last.?)).data == 4);
+    try testing.expect(list.len() == 2);
 }
 
-test "DoublyLinkedList concatenation" {
-    const L = DoublyLinkedList(u32);
-    var list1 = L{};
-    var list2 = L{};
+test "concatenation" {
+    const L = struct {
+        data: u32,
+        node: DoublyLinkedList.Node = .{},
+    };
+    var list1: DoublyLinkedList = .{};
+    var list2: DoublyLinkedList = .{};
 
-    var one = L.Node{ .data = 1 };
-    var two = L.Node{ .data = 2 };
-    var three = L.Node{ .data = 3 };
-    var four = L.Node{ .data = 4 };
-    var five = L.Node{ .data = 5 };
+    var one: L = .{ .data = 1 };
+    var two: L = .{ .data = 2 };
+    var three: L = .{ .data = 3 };
+    var four: L = .{ .data = 4 };
+    var five: L = .{ .data = 5 };
 
-    list1.append(&one);
-    list1.append(&two);
-    list2.append(&three);
-    list2.append(&four);
-    list2.append(&five);
+    list1.append(&one.node);
+    list1.append(&two.node);
+    list2.append(&three.node);
+    list2.append(&four.node);
+    list2.append(&five.node);
 
     list1.concatByMoving(&list2);
 
-    try testing.expect(list1.last == &five);
-    try testing.expect(list1.len == 5);
+    try testing.expect(list1.last == &five.node);
+    try testing.expect(list1.len() == 5);
     try testing.expect(list2.first == null);
     try testing.expect(list2.last == null);
-    try testing.expect(list2.len == 0);
+    try testing.expect(list2.len() == 0);
 
     // Traverse forwards.
     {
         var it = list1.first;
         var index: u32 = 1;
         while (it) |node| : (it = node.next) {
-            try testing.expect(node.data == index);
+            const l: *L = @fieldParentPtr("node", node);
+            try testing.expect(l.data == index);
             index += 1;
         }
     }
@@ -244,7 +251,8 @@ test "DoublyLinkedList concatenation" {
         var it = list1.last;
         var index: u32 = 1;
         while (it) |node| : (it = node.prev) {
-            try testing.expect(node.data == (6 - index));
+            const l: *L = @fieldParentPtr("node", node);
+            try testing.expect(l.data == (6 - index));
             index += 1;
         }
     }
@@ -257,7 +265,8 @@ test "DoublyLinkedList concatenation" {
         var it = list2.first;
         var index: u32 = 1;
         while (it) |node| : (it = node.next) {
-            try testing.expect(node.data == index);
+            const l: *L = @fieldParentPtr("node", node);
+            try testing.expect(l.data == index);
             index += 1;
         }
     }
@@ -267,7 +276,8 @@ test "DoublyLinkedList concatenation" {
         var it = list2.last;
         var index: u32 = 1;
         while (it) |node| : (it = node.prev) {
-            try testing.expect(node.data == (6 - index));
+            const l: *L = @fieldParentPtr("node", node);
+            try testing.expect(l.data == (6 - index));
             index += 1;
         }
     }
diff --git a/lib/std/http/Client.zig b/lib/std/http/Client.zig
index ecc1893194..d3041619b0 100644
--- a/lib/std/http/Client.zig
+++ b/lib/std/http/Client.zig
@@ -46,9 +46,9 @@ https_proxy: ?*Proxy = null,
 pub const ConnectionPool = struct {
     mutex: std.Thread.Mutex = .{},
     /// Open connections that are currently in use.
-    used: Queue = .{},
+    used: std.DoublyLinkedList = .{},
     /// Open connections that are not currently in use.
-    free: Queue = .{},
+    free: std.DoublyLinkedList = .{},
     free_len: usize = 0,
     free_size: usize = 32,
 
@@ -59,9 +59,6 @@ pub const ConnectionPool = struct {
         protocol: Connection.Protocol,
     };
 
-    const Queue = std.DoublyLinkedList(Connection);
-    pub const Node = Queue.Node;
-
     /// Finds and acquires a connection from the connection pool matching the criteria. This function is threadsafe.
     /// If no connection is found, null is returned.
     pub fn findConnection(pool: *ConnectionPool, criteria: Criteria) ?*Connection {
@@ -70,33 +67,34 @@ pub const ConnectionPool = struct {
 
         var next = pool.free.last;
         while (next) |node| : (next = node.prev) {
-            if (node.data.protocol != criteria.protocol) continue;
-            if (node.data.port != criteria.port) continue;
+            const connection: *Connection = @fieldParentPtr("pool_node", node);
+            if (connection.protocol != criteria.protocol) continue;
+            if (connection.port != criteria.port) continue;
 
             // Domain names are case-insensitive (RFC 5890, Section 2.3.2.4)
-            if (!std.ascii.eqlIgnoreCase(node.data.host, criteria.host)) continue;
+            if (!std.ascii.eqlIgnoreCase(connection.host, criteria.host)) continue;
 
-            pool.acquireUnsafe(node);
-            return &node.data;
+            pool.acquireUnsafe(connection);
+            return connection;
         }
 
         return null;
     }
 
     /// Acquires an existing connection from the connection pool. This function is not threadsafe.
-    pub fn acquireUnsafe(pool: *ConnectionPool, node: *Node) void {
-        pool.free.remove(node);
+    pub fn acquireUnsafe(pool: *ConnectionPool, connection: *Connection) void {
+        pool.free.remove(&connection.pool_node);
         pool.free_len -= 1;
 
-        pool.used.append(node);
+        pool.used.append(&connection.pool_node);
     }
 
     /// Acquires an existing connection from the connection pool. This function is threadsafe.
-    pub fn acquire(pool: *ConnectionPool, node: *Node) void {
+    pub fn acquire(pool: *ConnectionPool, connection: *Connection) void {
         pool.mutex.lock();
         defer pool.mutex.unlock();
 
-        return pool.acquireUnsafe(node);
+        return pool.acquireUnsafe(connection);
     }
 
     /// Tries to release a connection back to the connection pool. This function is threadsafe.
@@ -108,38 +106,37 @@ pub const ConnectionPool = struct {
         pool.mutex.lock();
         defer pool.mutex.unlock();
 
-        const node: *Node = @fieldParentPtr("data", connection);
+        pool.used.remove(&connection.pool_node);
 
-        pool.used.remove(node);
-
-        if (node.data.closing or pool.free_size == 0) {
-            node.data.close(allocator);
-            return allocator.destroy(node);
+        if (connection.closing or pool.free_size == 0) {
+            connection.close(allocator);
+            return allocator.destroy(connection);
         }
 
         if (pool.free_len >= pool.free_size) {
-            const popped = pool.free.popFirst() orelse unreachable;
+            const popped: *Connection = @fieldParentPtr("pool_node", pool.free.popFirst().?);
             pool.free_len -= 1;
 
-            popped.data.close(allocator);
+            popped.close(allocator);
             allocator.destroy(popped);
         }
 
-        if (node.data.proxied) {
-            pool.free.prepend(node); // proxied connections go to the end of the queue, always try direct connections first
+        if (connection.proxied) {
+            // proxied connections go to the end of the queue, always try direct connections first
+            pool.free.prepend(&connection.pool_node);
         } else {
-            pool.free.append(node);
+            pool.free.append(&connection.pool_node);
         }
 
         pool.free_len += 1;
     }
 
     /// Adds a newly created node to the pool of used connections. This function is threadsafe.
-    pub fn addUsed(pool: *ConnectionPool, node: *Node) void {
+    pub fn addUsed(pool: *ConnectionPool, connection: *Connection) void {
         pool.mutex.lock();
         defer pool.mutex.unlock();
 
-        pool.used.append(node);
+        pool.used.append(&connection.pool_node);
     }
 
     /// Resizes the connection pool. This function is threadsafe.
@@ -170,18 +167,18 @@ pub const ConnectionPool = struct {
 
         var next = pool.free.first;
         while (next) |node| {
-            defer allocator.destroy(node);
+            const connection: *Connection = @fieldParentPtr("pool_node", node);
             next = node.next;
-
-            node.data.close(allocator);
+            connection.close(allocator);
+            allocator.destroy(connection);
         }
 
         next = pool.used.first;
         while (next) |node| {
-            defer allocator.destroy(node);
+            const connection: *Connection = @fieldParentPtr("pool_node", node);
             next = node.next;
-
-            node.data.close(allocator);
+            connection.close(allocator);
+            allocator.destroy(node);
         }
 
         pool.* = undefined;
@@ -194,6 +191,9 @@ pub const Connection = struct {
     /// undefined unless protocol is tls.
     tls_client: if (!disable_tls) *std.crypto.tls.Client else void,
 
+    /// Entry in `ConnectionPool.used` or `ConnectionPool.free`.
+    pool_node: std.DoublyLinkedList.Node,
+
     /// The protocol that this connection is using.
     protocol: Protocol,
 
@@ -1326,9 +1326,8 @@ pub fn connectTcp(client: *Client, host: []const u8, port: u16, protocol: Connec
     if (disable_tls and protocol == .tls)
         return error.TlsInitializationFailed;
 
-    const conn = try client.allocator.create(ConnectionPool.Node);
+    const conn = try client.allocator.create(Connection);
     errdefer client.allocator.destroy(conn);
-    conn.* = .{ .data = undefined };
 
     const stream = net.tcpConnectToHost(client.allocator, host, port) catch |err| switch (err) {
         error.ConnectionRefused => return error.ConnectionRefused,
@@ -1343,21 +1342,23 @@ pub fn connectTcp(client: *Client, host: []const u8, port: u16, protocol: Connec
     };
     errdefer stream.close();
 
-    conn.data = .{
+    conn.* = .{
         .stream = stream,
         .tls_client = undefined,
 
         .protocol = protocol,
         .host = try client.allocator.dupe(u8, host),
         .port = port,
+
+        .pool_node = .{},
     };
-    errdefer client.allocator.free(conn.data.host);
+    errdefer client.allocator.free(conn.host);
 
     if (protocol == .tls) {
         if (disable_tls) unreachable;
 
-        conn.data.tls_client = try client.allocator.create(std.crypto.tls.Client);
-        errdefer client.allocator.destroy(conn.data.tls_client);
+        conn.tls_client = try client.allocator.create(std.crypto.tls.Client);
+        errdefer client.allocator.destroy(conn.tls_client);
 
         const ssl_key_log_file: ?std.fs.File = if (std.options.http_enable_ssl_key_log_file) ssl_key_log_file: {
             const ssl_key_log_path = std.process.getEnvVarOwned(client.allocator, "SSLKEYLOGFILE") catch |err| switch (err) {
@@ -1375,19 +1376,19 @@ pub fn connectTcp(client: *Client, host: []const u8, port: u16, protocol: Connec
         } else null;
         errdefer if (ssl_key_log_file) |key_log_file| key_log_file.close();
 
-        conn.data.tls_client.* = std.crypto.tls.Client.init(stream, .{
+        conn.tls_client.* = std.crypto.tls.Client.init(stream, .{
             .host = .{ .explicit = host },
             .ca = .{ .bundle = client.ca_bundle },
             .ssl_key_log_file = ssl_key_log_file,
         }) catch return error.TlsInitializationFailed;
         // This is appropriate for HTTPS because the HTTP headers contain
         // the content length which is used to detect truncation attacks.
-        conn.data.tls_client.allow_truncation_attacks = true;
+        conn.tls_client.allow_truncation_attacks = true;
     }
 
     client.connection_pool.addUsed(conn);
 
-    return &conn.data;
+    return conn;
 }
 
 pub const ConnectUnixError = Allocator.Error || std.posix.SocketError || error{NameTooLong} || std.posix.ConnectError;

From 810f70ef42fa013dc31b13445dd2910a43f8a0f7 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Thu, 3 Apr 2025 16:02:55 -0700
Subject: [PATCH 4/4] update compiler usage of DoublyLinkedList API

---
 src/Package/Fetch/git.zig | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/src/Package/Fetch/git.zig b/src/Package/Fetch/git.zig
index f6e3dc1615..d74e83d8c3 100644
--- a/src/Package/Fetch/git.zig
+++ b/src/Package/Fetch/git.zig
@@ -473,14 +473,18 @@ const Object = struct {
 /// objects remaining in the cache will be freed when the cache itself is freed.
 const ObjectCache = struct {
     objects: std.AutoHashMapUnmanaged(u64, CacheEntry) = .empty,
-    lru_nodes: LruList = .{},
+    lru_nodes: std.DoublyLinkedList = .{},
+    lru_nodes_len: usize = 0,
     byte_size: usize = 0,
 
     const max_byte_size = 128 * 1024 * 1024; // 128MiB
     /// A list of offsets stored in the cache, with the most recently used
     /// entries at the end.
-    const LruList = std.DoublyLinkedList(u64);
-    const CacheEntry = struct { object: Object, lru_node: *LruList.Node };
+    const LruListNode = struct {
+        data: u64,
+        node: std.DoublyLinkedList.Node,
+    };
+    const CacheEntry = struct { object: Object, lru_node: *LruListNode };
 
     fn deinit(cache: *ObjectCache, allocator: Allocator) void {
         var object_iterator = cache.objects.iterator();
@@ -496,8 +500,8 @@ const ObjectCache = struct {
     /// position if it is present.
     fn get(cache: *ObjectCache, offset: u64) ?Object {
         if (cache.objects.get(offset)) |entry| {
-            cache.lru_nodes.remove(entry.lru_node);
-            cache.lru_nodes.append(entry.lru_node);
+            cache.lru_nodes.remove(&entry.lru_node.node);
+            cache.lru_nodes.append(&entry.lru_node.node);
             return entry.object;
         } else {
             return null;
@@ -510,26 +514,29 @@ const ObjectCache = struct {
     /// will not be evicted before the next call to `put` or `deinit` even if
     /// it exceeds the maximum cache size.
     fn put(cache: *ObjectCache, allocator: Allocator, offset: u64, object: Object) !void {
-        const lru_node = try allocator.create(LruList.Node);
+        const lru_node = try allocator.create(LruListNode);
         errdefer allocator.destroy(lru_node);
         lru_node.data = offset;
 
         const gop = try cache.objects.getOrPut(allocator, offset);
         if (gop.found_existing) {
             cache.byte_size -= gop.value_ptr.object.data.len;
-            cache.lru_nodes.remove(gop.value_ptr.lru_node);
+            cache.lru_nodes.remove(&gop.value_ptr.lru_node.node);
+            cache.lru_nodes_len -= 1;
             allocator.destroy(gop.value_ptr.lru_node);
             allocator.free(gop.value_ptr.object.data);
         }
         gop.value_ptr.* = .{ .object = object, .lru_node = lru_node };
         cache.byte_size += object.data.len;
-        cache.lru_nodes.append(lru_node);
+        cache.lru_nodes.append(&lru_node.node);
+        cache.lru_nodes_len += 1;
 
-        while (cache.byte_size > max_byte_size and cache.lru_nodes.len > 1) {
+        while (cache.byte_size > max_byte_size and cache.lru_nodes_len > 1) {
             // The > 1 check is to make sure that we don't evict the most
             // recently added node, even if it by itself happens to exceed the
             // maximum size of the cache.
-            const evict_node = cache.lru_nodes.popFirst().?;
+            const evict_node: *LruListNode = @alignCast(@fieldParentPtr("node", cache.lru_nodes.popFirst().?));
+            cache.lru_nodes_len -= 1;
             const evict_offset = evict_node.data;
             allocator.destroy(evict_node);
             const evict_object = cache.objects.get(evict_offset).?.object;