From 6193470ceea89a986eb38a9abd7548118d18aab7 Mon Sep 17 00:00:00 2001
From: pentuppup <pentuppup@noreply.codeberg.org>
Date: Thu, 2 Apr 2026 14:57:33 -0400
Subject: [PATCH] error on tuples in extern contexts

---
 src/Sema.zig                                         |  4 ++++
 src/Type.zig                                         |  1 +
 .../cases/compile_errors/tuple_in_extern_context.zig | 12 ++++++++++++
 3 files changed, 17 insertions(+)
 create mode 100644 test/cases/compile_errors/tuple_in_extern_context.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index bda2659d8b1cdc0a2a81f0141017bfaff16fb0b6..a648a89e0c8f156d4260dd3cf3c0bc059159bf82 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -25262,6 +25262,10 @@ pub fn explainWhyTypeIsNotExtern(
             }
         },
         .@"struct" => {
+            if (ty.isTuple(zcu)) {
+                return sema.errNote(src_loc, msg, "tuples have no guaranteed in-memory representation", .{});
+            }
+
             const struct_obj = zcu.intern_pool.loadStructType(ty.toIntern());
             switch (struct_obj.layout) {
                 .auto => try sema.errNote(src_loc, msg, "struct with automatic layout has no guaranteed in-memory representation", .{}),
diff --git a/src/Type.zig b/src/Type.zig
index 7902788d1cbfcb1101485629012f369aa913cead..9aaf392dd63586f756e9de16801c5caca7c97146 100644
--- a/src/Type.zig
+++ b/src/Type.zig
@@ -3186,6 +3186,7 @@ pub fn validateExtern(ty: Type, position: ExternPosition, zcu: *const Zcu) bool
             };
         },
         .@"struct" => {
+            if (ty.isTuple(zcu)) return false;
             const struct_obj = zcu.intern_pool.loadStructType(ty.toIntern());
             return switch (struct_obj.layout) {
                 .auto => false,
diff --git a/test/cases/compile_errors/tuple_in_extern_context.zig b/test/cases/compile_errors/tuple_in_extern_context.zig
new file mode 100644
index 0000000000000000000000000000000000000000..5034fe8f87eff285382da300392659e6dc72484a
--- /dev/null
+++ b/test/cases/compile_errors/tuple_in_extern_context.zig
@@ -0,0 +1,12 @@
+const S = extern struct {
+    f: struct { u32 },
+};
+
+comptime {
+    _ = @sizeOf(S);
+}
+
+// error
+//
+// :2:8: error: extern structs cannot contain fields of type 'struct { u32 }'
+// :2:8: note: tuples have no guaranteed in-memory representation
-- 
2.54.0