Debug info for packed structs should be a struct, but is a number

[Jarred-Sumner]

Zig Version

0.11.0-dev.1183+2b9478ce1

Steps to Reproduce and Observed Behavior

Code:

const std = @import("std");

const CacheConfig = packed struct(u16) {
    pending_cache: bool = false,
    entry_cache: bool = false,
    pos_in_pending: u5 = 0,
    name_len: u9 = 0,
};

pub fn main() anyerror!void {
    var config = CacheConfig{};
    config.pending_cache = true;
    std.mem.doNotOptimizeAway(&config);
    @breakpoint();
}

lldb:

❯ lldb repro
(lldb) target create "repro"
Current executable set to '/Users/jarred/Desktop/repro' (arm64).
(lldb) run
Process 2372 launched: '/Users/jarred/Desktop/repro' (arm64)
Process 2372 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BREAKPOINT (code=1, subcode=0x100000b74)
    frame #0: 0x0000000100000b78 repro`repro.main at repro.zig:14:5
   11       var config = CacheConfig{};
   12       config.pending_cache = true;
   13       std.mem.doNotOptimizeAway(&config);
-> 14       @breakpoint();
   15   }
(lldb) p config
(unsigned short) $0 = 1
(lldb) 

Expected Behavior

It should display as a struct so that you can see the fields without lots of extra work

❯ lldb repro
(lldb) target create "repro"
Current executable set to '/Users/jarred/Desktop/repro' (arm64).
(lldb) run
Process 2481 launched: '/Users/jarred/Desktop/repro' (arm64)
Process 2481 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BREAKPOINT (code=1, subcode=0x100000b84)
    frame #0: 0x0000000100000b88 repro`repro.main at repro.zig:14:5
   11       var config = CacheConfig{};
   12       config.pending_cache = true;
   13       std.mem.doNotOptimizeAway(&config);
-> 14       @breakpoint();
   15   }
(lldb) p config
(repro.CacheConfig) $0 = (pending_cache = true, entry_cache = false, pos_in_pending = '\0', name_len = 0)

[jcalabro]

Hi, I'm still seeing this in recent builds. Here's a bit more info on the debug symbols emitted by the compiler on Linux:

const std = @import("std");
const print = std.debug.print;

const BasicStruct = struct {
    A: u3 = 1,
    B: u5 = 2,
};

const PackedStruct = packed struct {
    A: u3 = 1,
    B: u5 = 2,
};

pub fn main() !void {
    const b = BasicStruct{};
    const p = PackedStruct{};

    print(
        "BasicStruct: {any} ({d} bytes)\nPackedStruct: {any} ({d} bytes)\n",
        .{
            b,
            @sizeOf(BasicStruct),
            p,
            @sizeOf(PackedStruct),
        },
    );
}

$ zig version
0.11.0-dev.3395+1e7dcaa3a

$ zig build-exe main.zig && ./main
BasicStruct: main.BasicStruct{ .A = 1, .B = 2 } (2 bytes)
PackedStruct: main.PackedStruct{ .A = 1, .B = 2 } (1 bytes)

Then via dwarfdump:

< 1><0x00016be9>    DW_TAG_base_type
                      DW_AT_name                  main.PackedStruct
                      DW_AT_encoding              DW_ATE_unsigned
                      DW_AT_byte_size             0x00000001
< 1><0x00016bf0>    DW_TAG_structure_type
                      DW_AT_name                  main.BasicStruct
                      DW_AT_byte_size             0x00000002
                      DW_AT_alignment             0x00000001
< 2><0x00016bf7>      DW_TAG_member
                        DW_AT_name                  A
                        DW_AT_type                  <0x0000197f>
                        DW_AT_alignment             0x00000001
                        DW_AT_data_member_location  0
< 2><0x00016c02>      DW_TAG_member
                        DW_AT_name                  B
                        DW_AT_type                  <0x000019a6>
                        DW_AT_alignment             0x00000001
                        DW_AT_data_member_location  1