From 92915a42b55f2916f36ed6b1a2d51363331f47f8 Mon Sep 17 00:00:00 2001
From: Kendall Condon <goon.pri.low@gmail.com>
Date: Sun, 22 Mar 2026 17:39:43 -0400
Subject: [PATCH] zig fmt: do not reorder pointer casts with comments

This was especially bad as it could crash or duplicate them due to
them being moved around "zig fmt: on/off".

As a bonus this fixes a crash from reordering at the start of the file.
---
 lib/std/zig/Ast/Render.zig  | 37 +++++++++++++++++++++++++------------
 lib/std/zig/parser_test.zig | 21 +++++++++++++++++++++
 2 files changed, 46 insertions(+), 12 deletions(-)

diff --git a/lib/std/zig/Ast/Render.zig b/lib/std/zig/Ast/Render.zig
index 41cd1e2260e82a8b736ba3f173bee2eb1ac1f1f7..3a420cd3b204a0329040da5ecfee641562324890 100644
--- a/lib/std/zig/Ast/Render.zig
+++ b/lib/std/zig/Ast/Render.zig
@@ -800,34 +800,47 @@ fn renderExpression(r: *Render, node: Ast.Node.Index, space: Space) Error!void {
             canonicalize: {
                 if (params.len != 1) break :canonicalize;
 
-                const CastKind = enum {
+                const CastKind = enum(u8) {
                     ptrCast,
                     alignCast,
                     addrSpaceCast,
                     constCast,
                     volatileCast,
                 };
-                const kind = meta.stringToEnum(CastKind, tree.tokenSlice(builtin_token)[1..]) orelse break :canonicalize;
+                const kind = meta.stringToEnum(
+                    CastKind,
+                    tree.tokenSlice(builtin_token)[1..],
+                ) orelse break :canonicalize;
 
                 var cast_map = std.EnumMap(CastKind, Ast.TokenIndex).init(.{});
                 cast_map.put(kind, builtin_token);
 
                 var casts_before: usize = 0;
-                if (builtin_token >= 2) {
-                    var prev_builtin_token = builtin_token - 2;
-                    while (tree.tokenTag(prev_builtin_token) == .builtin) : (prev_builtin_token -= 2) {
-                        const prev_kind = meta.stringToEnum(CastKind, tree.tokenSlice(prev_builtin_token)[1..]) orelse break;
-                        if (cast_map.contains(prev_kind)) break :canonicalize;
-                        cast_map.put(prev_kind, prev_builtin_token);
-                        casts_before += 1;
-                    }
+                var prev_builtin_token = builtin_token;
+                while (prev_builtin_token >= 2) {
+                    prev_builtin_token -= 2;
+                    if (tree.tokenTag(prev_builtin_token) != .builtin) break;
+                    const builtin_name = tree.tokenSlice(prev_builtin_token)[1..];
+                    const prev_kind = meta.stringToEnum(CastKind, builtin_name) orelse break;
+                    if (cast_map.contains(prev_kind)) break :canonicalize;
+                    // This must be checked after so that cast builtins as arguments to other
+                    // builtins containing comments are reordered.
+                    if (hasComment(tree, prev_builtin_token, prev_builtin_token + 2))
+                        break :canonicalize;
+                    cast_map.put(prev_kind, prev_builtin_token);
+                    casts_before += 1;
                 }
 
                 var next_builtin_token = builtin_token + 2;
-                while (tree.tokenTag(next_builtin_token) == .builtin) : (next_builtin_token += 2) {
-                    const next_kind = meta.stringToEnum(CastKind, tree.tokenSlice(next_builtin_token)[1..]) orelse break;
+                while (true) {
+                    if (hasComment(tree, next_builtin_token - 2, next_builtin_token))
+                        break :canonicalize;
+                    if (tree.tokenTag(next_builtin_token) != .builtin) break;
+                    const builtin_name = tree.tokenSlice(next_builtin_token)[1..];
+                    const next_kind = meta.stringToEnum(CastKind, builtin_name) orelse break;
                     if (cast_map.contains(next_kind)) break :canonicalize;
                     cast_map.put(next_kind, next_builtin_token);
+                    next_builtin_token += 2;
                 }
 
                 var it = cast_map.iterator();
diff --git a/lib/std/zig/parser_test.zig b/lib/std/zig/parser_test.zig
index dd8b199dc29a7a9f1657f47602b3e65e2f4d3ec3..f44e9ae544b663ac7021c4bd115036cb065d693a 100644
--- a/lib/std/zig/parser_test.zig
+++ b/lib/std/zig/parser_test.zig
@@ -6133,6 +6133,16 @@ test "zig fmt: do not canonicalize invalid cast builtins" {
     );
 }
 
+test "zig fmt: canonicalize cast builtins at file start" {
+    try testTransform(
+        \\@alignCast(@ptrCast(a)),
+        \\
+    ,
+        \\@ptrCast(@alignCast(a)),
+        \\
+    );
+}
+
 test "zig fmt: extern addrspace in struct" {
     try testCanonical(
         \\const namespace = struct {
@@ -6909,6 +6919,17 @@ test "zig fmt: render extra colons with comments" {
     );
 }
 
+test "zig fmt: cast builtins are not reordered with comments" {
+    try testCanonical(
+        \\const a = @volatileCast(@constCast( // ...
+        \\    @alignCast(@ptrCast(a))));
+        \\
+        \\const b = @alignCast(@ptrCast( // zig fmt: off
+        \\    c));
+        \\
+    );
+}
+
 test "recovery: top level" {
     try testError(
         \\test "" {inline}
-- 
2.54.0