From 80d84537f7c7002c29a39a429072f59303f7d0f7 Mon Sep 17 00:00:00 2001
From: Hila Friedman <red.black.liquorice@gmail.com>
Date: Thu, 12 Mar 2026 13:38:06 +0100
Subject: [PATCH] allow `packed union` comparisons in `std.meta.eql` (#31479)

#31464 implemented equality testing for `packed union`s - this PR updates `std.meta.eql`'s implementation to accept them.

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/31479
Co-authored-by: Hila Friedman <red.black.liquorice@gmail.com>
Co-committed-by: Hila Friedman <red.black.liquorice@gmail.com>
---
 lib/std/meta.zig | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/lib/std/meta.zig b/lib/std/meta.zig
index 632c65678f28107c8f20444c68a74d27cae02309..543157012a1ca18bad490280d7c35801273ac476 100644
--- a/lib/std/meta.zig
+++ b/lib/std/meta.zig
@@ -636,22 +636,22 @@ pub fn eql(a: anytype, b: @TypeOf(a)) bool {
             }
         },
         .@"union" => |info| {
-            if (info.tag_type) |UnionTag| {
-                const tag_a: UnionTag = a;
-                const tag_b: UnionTag = b;
-                if (tag_a != tag_b) return false;
+            if (info.layout == .@"packed") return a == b;
+            const UnionTag = info.tag_type orelse
+                @compileError("cannot compare untagged union type " ++ @typeName(T));
 
-                return switch (a) {
-                    inline else => |val, tag| return eql(val, @field(b, @tagName(tag))),
-                };
-            }
+            const tag_a: UnionTag = a;
+            const tag_b: UnionTag = b;
+            if (tag_a != tag_b) return false;
 
-            @compileError("cannot compare untagged union type " ++ @typeName(T));
+            return switch (a) {
+                inline else => |val, tag| return eql(val, @field(b, @tagName(tag))),
+            };
         },
         .array => {
-            if (a.len != b.len) return false;
-            for (a, 0..) |e, i|
-                if (!eql(e, b[i])) return false;
+            for (a, b) |x, y| {
+                if (!eql(x, y)) return false;
+            }
             return true;
         },
         .vector => return @reduce(.And, a == b),
@@ -662,9 +662,9 @@ pub fn eql(a: anytype, b: @TypeOf(a)) bool {
             };
         },
         .optional => {
-            if (a == null and b == null) return true;
-            if (a == null or b == null) return false;
-            return eql(a.?, b.?);
+            const some_a = a orelse return b == null;
+            const some_b = b orelse return false;
+            return eql(some_a, some_b);
         },
         else => return a == b,
     }
-- 
2.54.0