Compiler crash with incompatible type when doing reflection

[kuon]

Zig Version

0.11.0-dev.1796+c9e02d3e69 (llvm 15.0.6)

Steps to Reproduce and Observed Behavior

I have some code that convert elixir struct into zig struct in a NIF, and for this I have an approach a bit similar to the json lib in std.

I have found that having an optional slice triggers a compiler error, I was able to reduce the bug into a minimal example below.

In src/main.zig

const std = @import("std");
const meta = std.meta;
const mem = std.mem;

pub const Data = struct {
    foo: ?[]const u8 = null,
};

export fn do_something() void {
    var data: Data = mem.zeroes(Data);

    populate(&data) catch unreachable;
    std.debug.print("bug: {any}\n", .{data});
}

fn populate(dest: anytype) !void {
    const T = @TypeOf(dest.*);
    switch (@typeInfo(T)) {
        .Struct => {
            const key = "foo";

            inline for (comptime meta.fieldNames(T)) |n| {
                if (mem.eql(u8, n, key)) {
                    try populate(
                        &@field(dest, n),
                    );
                }
            }
        },
        .Optional => |O| {
            dest.* = mem.zeroes(O.child);
            try populate(&dest.*.?);
            return;
        },
        .Pointer => |ptr_info| {
            switch (ptr_info.size) {
                .Slice => {
                    if (ptr_info.child == u8) {
                        dest.* = "hello";
                    }
                    return;
                },
                else => return error.UnsupportedType,
            }
        },
        else => return error.UnsupportedType,
    }
}

in builg.zig

const std = @import("std");

pub fn build(b: *std.Build) void {
    const optimize = b.standardOptimizeOption(.{
        .preferred_optimize_mode = .ReleaseSafe,
    });

    const step = b.step("lib", "Compile library");

    const lib = b.addSharedLibrary(.{
        .name = "testlib",
        .root_source_file = .{ .path = "./src/main.zig" },
        .optimize = optimize,
        .target = .{},
    });

    lib.install();
    lib.linkLibC();
    step.dependOn(&lib.step);
}

Running zig build lib

$ zig build lib
LLVM Emit Object... invalid type ref
!1772 = distinct !DIGlobalVariable(name: "zeroes__anon_630__anon_858", linkageName: "mem.zeroes__anon_630__anon_858", scope: !1709, file: !1709, line: 236, type: zig: /home/kuon/Repos/aur/llvm15/src/llvm-project/llvm/include/llvm/Support/Casting.h:578: decltype(auto) llvm::cast(From*) [with To = ValueAsMetadata; From = const Metadata]: Assertion `isa<To>(Val) && "cast<Ty>() argument of incompatible type!"' failed.
error: testlib...
error: The following command terminated unexpectedly:
/usr/bin/zig build-lib /home/kuon/Playground/zig-bug/src/main.zig -lc --cache-dir /home/kuon/Playground/zig-bug/zig-cache --global-cache-dir /home/kuon/.cache/zig --name testlib -dynamic --enable-cache 
error: the following build command failed with exit code 6:
/home/kuon/Playground/zig-bug/zig-cache/o/9e2f65e31bd0e49cb1973579ed662e04/build /usr/bin/zig /home/kuon/Playground/zig-bug /home/kuon/Playground/zig-bug/zig-cache /home/kuon/.cache/zig lib

Expected Behavior

Code should compile.

[kuon]

Note, if I add:

pub fn main() !void {
    do_something();
}

and run the code with:

zig run src/main.zig 

it compiles and run

[kuon]

If I change fieldNames to fields like so, it compiles:

            inline for (comptime meta.field(T)) |n| {
                if (mem.eql(u8, n.name, key)) {
                    try populate(&@field(dest, n.name));
                }
            }

This workaround doesn't work in my actual codebase, only in the minimal example above.

[kuon]

Actually, the error in my code in a bit different:

LLVM Emit Object... invalid base type
!217 = !DIDerivedType(tag: DW_TAG_member, name: "account_name", scope: !207, baseType: zig: /home/kuon/Repos/aur/llvm15/src/llvm-project/llvm/include/llvm/Support/Casting.h:578: decltype(auto) llvm::cast(From*) [with To = ValueAsMetadata; From = const Metadata]: Assertion `isa<To>(Val) && "cast<Ty>() argument of incompatible type!"' failed.
error: zkfs_client_nif...
error: The following command terminated unexpectedly:
/usr/bin/zig build-lib /home/kuon/pbg/zkfs-sdk/elixir/nif/zkfs_client.zig -lc --cache-dir /home/kuon/pbg/zkfs-sdk/elixir/zig-cache --global-cache-dir /home/kuon/.cache/zig --name zkfs_client_nif -dynamic --mod zkfs::/home/kuon/pbg/zkfs-sdk/common/src/lib.zig --deps zkfs -I /usr/lib/erlang/usr/include --enable-cache 
error: the following build command failed with exit code 6:
/home/kuon/pbg/zkfs-sdk/elixir/zig-cache/o/05b171cf699d3838533760e258f04b59/build /usr/bin/zig /home/kuon/pbg/zkfs-sdk/elixir /home/kuon/pbg/zkfs-sdk/elixir/zig-cache /home/kuon/.cache/zig nif_lib

[kuon]

I was trying different work around, but I still get the same error. I made a repo to make it easier:

https://github.com/kuon/zig-issue-14715

[kuon]

I confirm that #14789 fix both my minimal example and my actual code. Thanks.