struct with field default initialized to size of the struct gives false positive 'depends on itself' error

[andrewrk]

Zig Version: 0.10.0-dev.2857+4e002dde6

const S = extern struct {
    size: u8 = @sizeOf(S),
    blah: u16,
};

test "struct default value initialize to size of itself" {
    var s: S = undefined;
    _ = s;
}

[nix-shell:~/dev/zig/build-release]$ stage2/bin/zig test test3.zig 
test3.zig:8:5: error: struct 'test3.S' depends on itself
    size: u8 = @sizeOf(S),
    ^

[endel]

I don't mean to generate noise, perhaps this report can collaborate to finding out a related problem:

---

I've tried to use io_mode = .evented on @Luukdegram's feilich example server, and also got "depends on itself" errors.

Without io_mode set no compiler errors appear.

./src/encryption.zig:139:13: error: '@Frame(.feilich.encryption.EncryptedReadWriter(std.io.reader.Reader(std.net.Stream,std.os.ReadError,std.net.Stream.read),std.io.writer.Writer(std.net.Stream,std.os.WriteError,std.net.Stream.write)).read)' depends on itself
        pub fn read(self: *Self, buf: []u8) ReadError!usize {
            ^
./src/encryption.zig:150:41: note: when analyzing type '@Frame(.feilich.encryption.EncryptedReadWriter(std.io.reader.Reader(std.net.Stream,std.os.ReadError,std.net.Stream.read),std.io.writer.Writer(std.net.Stream,std.os.WriteError,std.net.Stream.write)).read)' here
                        return self.read(buf);
                                        ^
/Users/endel/Projects/zig/zig/zig-dev/lib/zig/std/io/reader.zig:26:26: note: while checking if 'std.io.reader.Reader(*.feilich.encryption.EncryptedReadWriter(std.io.reader.Reader(std.net.Stream,std.os.ReadError,std.net.Stream.read),std.io.writer.Writer(std.net.Stream,std.os.WriteError,std.net.Stream.write)),.feilich.encryption.EncryptedReadWriter(std.io.reader.Reader(std.net.Stream,std.os.ReadError,std.net.Stream.read),std.io.writer.Writer(std.net.Stream,std.os.WriteError,std.net.Stream.write)).ReadError,.feilich.encryption.EncryptedReadWriter(std.io.reader.Reader(std.net.Stream,std.os.ReadError,std.net.Stream.read),std.io.writer.Writer(std.net.Stream,std.os.WriteError,std.net.Stream.write)).read).read' is async
            return readFn(self.context, buffer);
                         ^
./src/Server.zig:272:46: note: when analyzing type '@Frame(.feilich.Server.connect)' here
    var read_len = try decryption_reader.read(&decrypted_data);
                                             ^
./examples/server.zig:18:27: note: when analyzing type '@Frame(main)' here
        tls_server.connect(stream.reader(), stream.writer()) catch |err| {
                          ^
/Users/endel/Projects/zig/zig/zig-dev/lib/zig/std/start.zig:581:37: note: while checking if 'std.start.callMain' is async
            const result = root.main() catch |err| {
                                    ^
server...The following command exited with error code 1:

(MacOS, arm64)

[andrewrk]

Thanks for the data point. This issue is for stage2 while I believe your example is using stage1.

[andrewrk]

Problem

The field types and default values are generated as part of the same expression, which are then referenced later:

    %21 = extended(struct_decl(parent, Extern, {}, {
      %22 = decl_val("U8") token_offset:8:11
      %23 = decl_val("S") token_offset:8:24
      %24 = size_of(%23) node_offset:8:16
      %25 = as_node(%22, %24) node_offset:8:16
      %26 = decl_val("U16") token_offset:9:11
      %27 = break_inline(%21, @Zir.Inst.Ref.void_value)
    }, {
      size: %22 = %25,
      blah: %26,
    }) node_offset:7:18

Solution

Break this into two: one for the types; one for the values. The types go first, then the values. Something like this:

    %21 = extended(struct_decl(parent, Extern, {}, {
      %22 = decl_val("U8") token_offset:8:11
      %23 = decl_val("S") token_offset:8:24
      %26 = decl_val("U16") token_offset:9:11
      %27 = break_inline(%21, @Zir.Inst.Ref.void_value)
    }, {
      %24 = size_of(%23) node_offset:8:16
      %25 = as_node(%22, %24) node_offset:8:16
      %a = break_inline(%21, @Zir.Inst.Ref.void_value)
    }, {
      size: %22 = %25,
      blah: %26,
    }) node_offset:7:18

Alternate Solution

Do the coercion to the field type later:

      %25 = as_node(%22, %24) node_offset:8:16

If this part is omitted from the ZIR for the field initialization then everything works fine due to the lazy_sizeof Value Tag.

Edit: I think the main solution idea is better than the Alternate Solution because it handles more cases and is generally more straightforward.