From 3ac8bc2dab8ccdbd777fa1a240c3d4ece6360c4f Mon Sep 17 00:00:00 2001
From: David Rubin <daviru007@icloud.com>
Date: Sun, 15 Dec 2024 01:48:56 -0800
Subject: [PATCH] disallow stores to element types with no comptime size

---
 src/Sema.zig                                      |  8 ++++++++
 .../compile_errors/store_no_comptime_size.zig     | 15 +++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 test/cases/compile_errors/store_no_comptime_size.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index f31e71047fa3..ccd124085291 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -31958,6 +31958,14 @@ fn storePtr2(
         });
     }
 
+    // Don't allow stores to element types that have no comptime size.
+    switch (elem_ty.zigTypeTag(zcu)) {
+        .@"fn",
+        .@"opaque",
+        => return sema.fail(block, ptr_src, "pointer element type must have a comptime-known size", .{}),
+        else => std.debug.print("{} {}", .{ elem_ty.fmt(pt), elem_ty.zigTypeTag(zcu) }),
+    }
+
     const store_inst = if (is_ret)
         try block.addBinOp(.store, ptr, operand)
     else
diff --git a/test/cases/compile_errors/store_no_comptime_size.zig b/test/cases/compile_errors/store_no_comptime_size.zig
new file mode 100644
index 000000000000..73b4bc51da08
--- /dev/null
+++ b/test/cases/compile_errors/store_no_comptime_size.zig
@@ -0,0 +1,15 @@
+export fn a() void {
+    const x: *fn () void = @ptrFromInt(4);
+    x.* = undefined;
+}
+
+export fn b(x: *anyopaque) void {
+    x.* = undefined;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:6: error: pointer element type must have a comptime-known size
+// :7:6: error: pointer element type must have a comptime-known size