stage2: panic when instantiating `@TypeOf` of anonymous struct

[topolarity]

Zig Version

0.10.0-dev.2855+aab1284e1

Steps to Reproduce

test {
    var x: u32 = 3;
    const T = @TypeOf(.{ .foo = x });
    const a: T = .{ .foo = 1 }; // Works on stage1, panics on stage2
    _ = a;

    const U = @TypeOf(.{ .foo = 2 });
    const b: U = .{}; // Fails on stage1 with "error: cannot assign to constant", panics on stage2
    _ = b;
}

Expected Behavior

Test should compile and pass

Actual Behavior

thread 1716 panic: attempt to use null value
Analyzing test.zig: test.zig:test_0
      %2 = dbg_block_begin())
      %3 = dbg_stmt(2, 5)
      %4 = alloc_mut(@Zir.Inst.Ref.u32_type) node_offset:2:5
      %5 = int(3)
      %6 = store_node(%4, %5) node_offset:2:18
      %7 = dbg_var_ptr(%4, "x")
      %8 = dbg_stmt(3, 5)
      %9 = typeof_builtin({
        %10 = load(%4) node_offset:3:33
        %11 = struct_init_anon([foo=%10]) node_offset:3:24
        %12 = break_inline(%9, %11)
      }) node_offset:3:15
      %13 = dbg_var_val(%9, "T")
      %14 = dbg_stmt(4, 5)
      %15 = alloc(%9) node_offset:4:5
      %16 = field_base_ptr(%15) node_offset:4:19
      %17 = field_ptr(%16, "foo") node_offset:4:28
      %18 = store_node(%17, @Zir.Inst.Ref.one) node_offset:4:28
    > %19 = validate_struct_init({
        %17 = field_ptr(%16, "foo") node_offset:4:28
      }) node_offset:4:19
      %20 = make_ptr_const(%15) node_offset:4:5
      %21 = dbg_var_ptr(%20, "a")
      %22 = dbg_stmt(5, 5)
      %23 = load(%20) node_offset:5:9
      %24 = ensure_result_non_error(%23) node_offset:5:9
      %25 = dbg_stmt(7, 5)
      %26 = typeof_builtin({
        %27 = int(2)
        %28 = struct_init_anon([foo=%27]) node_offset:7:24
        %29 = break_inline(%26, %28)
      }) node_offset:7:15
      %30 = dbg_var_val(%26, "U")
      %31 = dbg_stmt(8, 5)
      %34 = as(%26, @Zir.Inst.Ref.empty_struct)
      %35 = dbg_var_val(%34, "b")
      %36 = dbg_stmt(9, 5)
      %38 = dbg_block_end())
      %37 = ensure_result_non_error(%34) node_offset:9:9
      %39 = ret_tok(@Zir.Inst.Ref.void_value) token_offset:10:1
    For full context, use the command
      zig ast-check -t test.zig


/home/topolarity/repos/zig/src/Sema.zig:3318:39: 0x346cfb6 in Sema.zirValidateStructInit (zig)
            agg_ty.castTag(.@"struct").?.data,
                                      ^
/home/topolarity/repos/zig/src/Sema.zig:1064:47: 0x32841c1 in Sema.analyzeBodyInner (zig)
                try sema.zirValidateStructInit(block, inst, false);
                                              ^
/home/topolarity/repos/zig/src/Sema.zig:598:30: 0x326c60a in Sema.analyzeBody (zig)
    _ = sema.analyzeBodyInner(block, body) catch |err| switch (err) {
                             ^
/home/topolarity/repos/zig/src/Module.zig:5049:21: 0x309e306 in Module.analyzeFnBody (zig)
    sema.analyzeBody(&inner_block, fn_info.body) catch |err| switch (err) {
                    ^
/home/topolarity/repos/zig/src/Module.zig:3777:40: 0x30811e0 in Module.ensureFuncBodyAnalyzed (zig)
            var air = mod.analyzeFnBody(func, sema_arena) catch |err| switch (err) {
                                       ^
/home/topolarity/repos/zig/src/Compilation.zig:2937:42: 0x2dfe72a in Compilation.processOneJob (zig)
            module.ensureFuncBodyAnalyzed(func) catch |err| switch (err) {
                                         ^
/home/topolarity/repos/zig/src/Compilation.zig:2869:30: 0x2deb27d in Compilation.performAllTheWork (zig)
            try processOneJob(comp, work_item);
                             ^
/home/topolarity/repos/zig/src/Compilation.zig:2218:31: 0x2de3902 in Compilation.update (zig)
    try comp.performAllTheWork(main_progress_node);
                              ^
/home/topolarity/repos/zig/src/main.zig:3245:20: 0x2d4eebf in updateModule (zig)
    try comp.update();
                   ^
/home/topolarity/repos/zig/src/main.zig:2934:17: 0x2d1703a in buildOutputType (zig)
    updateModule(gpa, comp, hook) catch |err| switch (err) {
                ^
/home/topolarity/repos/zig/src/main.zig:225:31: 0x2cfb966 in mainArgs (zig)
        return buildOutputType(gpa, arena, args, .zig_test);
                              ^
/home/topolarity/repos/zig/src/main.zig:174:20: 0x2cfa9b4 in main (zig)
    return mainArgs(gpa, arena, args);
                   ^
/home/topolarity/repos/zig/lib/std/start.zig:581:37: 0x3220167 in std.start.callMain (zig)
            const result = root.main() catch |err| {
                                    ^
/home/topolarity/repos/zig/lib/std/start.zig:515:12: 0x2cfd407 in std.start.callMainWithArgs (zig)
    return @call(.{ .modifier = .always_inline }, callMain, .{});
           ^
/home/topolarity/repos/zig/lib/std/start.zig:480:12: 0x2cfd1b2 in std.start.main (zig)
    return @call(.{ .modifier = .always_inline }, callMainWithArgs, .{ @intCast(usize, c_argc), c_argv, envp });
           ^
???:?:?: 0x7faa7fb977fc in ??? (???)
[1]    1716 IOT instruction  ./stage2/bin/zig test test.zig

[topolarity]

Found two more pieces of functionality missing for .anon_struct types:

test {
    var x: u32 = 3;
    const anon_st = .{ .foo = x, .bar = x }; 
    _ = @fieldParentPtr(@TypeOf(anon_st), "foo", &anon_st.foo); // panic: attempt to use null value
}

test {
    var x: u32 = 3;
    const anon_st = .{ .foo = x, .bar = x }; 
    _ = @offsetOf(@TypeOf(anon_st), "foo");  // error: expected struct type, found 'struct{foo: u32, bar: u32}'
}

Both of these currently pass on stage 1

[topolarity]

Planning to work on this one at some point tomorrow