From 7f82c31d40dedde6e8b709d07cc836d629e09021 Mon Sep 17 00:00:00 2001
From: Ali Cheraghi <alichraghi@proton.me>
Date: Mon, 29 Jun 2026 09:56:30 +0330
Subject: [PATCH] Sema: add compile error for using many-pointer in externs

---
 src/Sema.zig                                  | 15 +++++++++++
 src/codegen/spirv/CodeGen.zig                 |  2 ++
 ..._storage_buffer_must_be_single_pointer.zig | 25 +++++++++++++++++++
 3 files changed, 42 insertions(+)
 create mode 100644 test/cases/compile_errors/extern_spirv_storage_buffer_must_be_single_pointer.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index 10272d2a207a3b0b462df67c2a415141bf48d428..9e7e5b45885f9994ec96f33db8525233b2aaf1b3 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -24973,6 +24973,21 @@ fn zirBuiltinExtern(
         .location, .descriptor => {},
     };
 
+    switch (zcu.getTarget().os.tag) {
+        .vulkan, .opengl => switch (ptr_info.flags.address_space) {
+            .storage_buffer, .uniform, .push_constant => if (ptr_info.flags.size != .one) {
+                return sema.failWithOwnedErrorMsg(block, msg: {
+                    const msg = try sema.errMsg(ty_src, "extern in '{s}' address space must be a single-item pointer to a struct", .{@tagName(ptr_info.flags.address_space)});
+                    errdefer msg.destroy(sema.gpa);
+                    try sema.errNote(ty_src, msg, "wrap the element type in a struct containing a runtime-sized array", .{});
+                    break :msg msg;
+                });
+            },
+            else => {},
+        },
+        else => {},
+    }
+
     // TODO: error for threadlocal functions, non-const functions, etc
 
     const extern_val = try pt.getExtern(.{
diff --git a/src/codegen/spirv/CodeGen.zig b/src/codegen/spirv/CodeGen.zig
index b2ce676d4db04fcfb27a8e7f9e5b75683ea3e862..17cededf80410fa15a499d949d1376d4a83e7fd9 100644
--- a/src/codegen/spirv/CodeGen.zig
+++ b/src/codegen/spirv/CodeGen.zig
@@ -5503,6 +5503,8 @@ fn ptrAccessChain(
             });
         },
         .vulkan, .opengl => {
+            assert(target.cpu.has(.spirv, .variable_pointers) or
+                target.cpu.has(.spirv, .variable_pointers_storage_buffer));
             try cg.body.emit(gpa, .OpPtrAccessChain, .{
                 .id_result_type = result_ty_id,
                 .id_result = result_id,
diff --git a/test/cases/compile_errors/extern_spirv_storage_buffer_must_be_single_pointer.zig b/test/cases/compile_errors/extern_spirv_storage_buffer_must_be_single_pointer.zig
new file mode 100644
index 0000000000000000000000000000000000000000..3b8ac3c8338afff5ca93773f973d399fd6c51d1b
--- /dev/null
+++ b/test/cases/compile_errors/extern_spirv_storage_buffer_must_be_single_pointer.zig
@@ -0,0 +1,25 @@
+const a = @extern([*]addrspace(.storage_buffer) u32, .{
+    .name = "a",
+    .decoration = .{ .descriptor = .{ .set = 0, .binding = 0 } },
+});
+const b = @extern([]addrspace(.uniform) u32, .{
+    .name = "b",
+    .decoration = .{ .descriptor = .{ .set = 0, .binding = 1 } },
+});
+const c = @extern([*c]addrspace(.push_constant) u32, .{ .name = "c" });
+comptime {
+    _ = a;
+    _ = b;
+    _ = c;
+}
+
+// error
+// backend=selfhosted
+// target=spirv32-vulkan
+//
+// :1:19: error: extern in 'storage_buffer' address space must be a single-item pointer to a struct
+// :1:19: note: wrap the element type in a struct containing a runtime-sized array
+// :5:19: error: extern in 'uniform' address space must be a single-item pointer to a struct
+// :5:19: note: wrap the element type in a struct containing a runtime-sized array
+// :9:19: error: extern in 'push_constant' address space must be a single-item pointer to a struct
+// :9:19: note: wrap the element type in a struct containing a runtime-sized array
-- 
2.54.0