stage2: fix AstGen for some struct syntaxes

 * AstGen: fix not emitting `struct_init_empty` when an explicit type is
   present in struct initialization syntax.
 * AstGen: these two syntaxes now lower to identical ZIR:
   - `var a = A{ .b = c };`
   - `var a = @as(A, .{ .b = c });`
 * Zir: clarify `auto_enum_tag` in the doc comments.
 * LLVM Backend: fix lowering of function return types when the type has
   0 bits.

1 files changed, 6 insertions, 926 deletions

diff --git a/test/behavior/struct.zig b/test/behavior/struct.zig
index d9e1c02aa1..6f00b71057 100644
--- a/test/behavior/struct.zig
+++ b/test/behavior/struct.zig
@@ -5,949 +5,29 @@ const expect = std.testing.expect;
 const expectEqual = std.testing.expectEqual;
 const expectEqualSlices = std.testing.expectEqualSlices;
 const maxInt = std.math.maxInt;
+
 const StructWithNoFields = struct {
     fn add(a: i32, b: i32) i32 {
         return a + b;
     }
 };
-const empty_global_instance = StructWithNoFields{};
-
-top_level_field: i32,
-
-test "top level fields" {
-    var instance = @This(){
-        .top_level_field = 1234,
-    };
-    instance.top_level_field += 1;
-    try expectEqual(@as(i32, 1235), instance.top_level_field);
-}
 
 test "call struct static method" {
     const result = StructWithNoFields.add(3, 4);
     try expect(result == 7);
 }
 
-test "return empty struct instance" {
-    _ = returnEmptyStructInstance();
-}
-fn returnEmptyStructInstance() StructWithNoFields {
-    return empty_global_instance;
-}
-
 const should_be_11 = StructWithNoFields.add(5, 6);
 
 test "invoke static method in global scope" {
     try expect(should_be_11 == 11);
 }
 
-test "void struct fields" {
-    const foo = VoidStructFieldsFoo{
-        .a = void{},
-        .b = 1,
-        .c = void{},
-    };
-    try expect(foo.b == 1);
-    try expect(@sizeOf(VoidStructFieldsFoo) == 4);
-}
-const VoidStructFieldsFoo = struct {
-    a: void,
-    b: i32,
-    c: void,
-};
-
-test "structs" {
-    var foo: StructFoo = undefined;
-    @memset(@ptrCast([*]u8, &foo), 0, @sizeOf(StructFoo));
-    foo.a += 1;
-    foo.b = foo.a == 1;
-    try testFoo(foo);
-    testMutation(&foo);
-    try expect(foo.c == 100);
-}
-const StructFoo = struct {
-    a: i32,
-    b: bool,
-    c: f32,
-};
-fn testFoo(foo: StructFoo) !void {
-    try expect(foo.b);
-}
-fn testMutation(foo: *StructFoo) void {
-    foo.c = 100;
-}
-
-const Node = struct {
-    val: Val,
-    next: *Node,
-};
-
-const Val = struct {
-    x: i32,
-};
-
-test "struct point to self" {
-    var root: Node = undefined;
-    root.val.x = 1;
-
-    var node: Node = undefined;
-    node.next = &root;
-    node.val.x = 2;
-
-    root.next = &node;
-
-    try expect(node.next.next.next.val.x == 1);
-}
-
-test "struct byval assign" {
-    var foo1: StructFoo = undefined;
-    var foo2: StructFoo = undefined;
-
-    foo1.a = 1234;
-    foo2.a = 0;
-    try expect(foo2.a == 0);
-    foo2 = foo1;
-    try expect(foo2.a == 1234);
-}
-
-fn structInitializer() void {
-    const val = Val{ .x = 42 };
-    try expect(val.x == 42);
-}
-
-test "fn call of struct field" {
-    const Foo = struct {
-        ptr: fn () i32,
-    };
-    const S = struct {
-        fn aFunc() i32 {
-            return 13;
-        }
-
-        fn callStructField(foo: Foo) i32 {
-            return foo.ptr();
-        }
-    };
-
-    try expect(S.callStructField(Foo{ .ptr = S.aFunc }) == 13);
-}
-
-test "store member function in variable" {
-    const instance = MemberFnTestFoo{ .x = 1234 };
-    const memberFn = MemberFnTestFoo.member;
-    const result = memberFn(instance);
-    try expect(result == 1234);
-}
-const MemberFnTestFoo = struct {
-    x: i32,
-    fn member(foo: MemberFnTestFoo) i32 {
-        return foo.x;
-    }
-};
-
-test "call member function directly" {
-    const instance = MemberFnTestFoo{ .x = 1234 };
-    const result = MemberFnTestFoo.member(instance);
-    try expect(result == 1234);
-}
-
-test "member functions" {
-    const r = MemberFnRand{ .seed = 1234 };
-    try expect(r.getSeed() == 1234);
-}
-const MemberFnRand = struct {
-    seed: u32,
-    pub fn getSeed(r: *const MemberFnRand) u32 {
-        return r.seed;
-    }
-};
-
-test "return struct byval from function" {
-    const bar = makeBar2(1234, 5678);
-    try expect(bar.y == 5678);
-}
-const Bar = struct {
-    x: i32,
-    y: i32,
-};
-fn makeBar2(x: i32, y: i32) Bar {
-    return Bar{
-        .x = x,
-        .y = y,
-    };
-}
-
-test "empty struct method call" {
-    const es = EmptyStruct{};
-    try expect(es.method() == 1234);
-}
-const EmptyStruct = struct {
-    fn method(es: *const EmptyStruct) i32 {
-        _ = es;
-        return 1234;
-    }
-};
-
-test "return empty struct from fn" {
-    _ = testReturnEmptyStructFromFn();
-}
-const EmptyStruct2 = struct {};
-fn testReturnEmptyStructFromFn() EmptyStruct2 {
-    return EmptyStruct2{};
-}
-
-test "pass slice of empty struct to fn" {
-    try expect(testPassSliceOfEmptyStructToFn(&[_]EmptyStruct2{EmptyStruct2{}}) == 1);
-}
-fn testPassSliceOfEmptyStructToFn(slice: []const EmptyStruct2) usize {
-    return slice.len;
-}
-
-const APackedStruct = packed struct {
-    x: u8,
-    y: u8,
-};
-
-test "packed struct" {
-    var foo = APackedStruct{
-        .x = 1,
-        .y = 2,
-    };
-    foo.y += 1;
-    const four = foo.x + foo.y;
-    try expect(four == 4);
-}
-
-const BitField1 = packed struct {
-    a: u3,
-    b: u3,
-    c: u2,
-};
-
-const bit_field_1 = BitField1{
-    .a = 1,
-    .b = 2,
-    .c = 3,
-};
-
-test "bit field access" {
-    var data = bit_field_1;
-    try expect(getA(&data) == 1);
-    try expect(getB(&data) == 2);
-    try expect(getC(&data) == 3);
-    comptime try expect(@sizeOf(BitField1) == 1);
-
-    data.b += 1;
-    try expect(data.b == 3);
-
-    data.a += 1;
-    try expect(data.a == 2);
-    try expect(data.b == 3);
-}
-
-fn getA(data: *const BitField1) u3 {
-    return data.a;
-}
-
-fn getB(data: *const BitField1) u3 {
-    return data.b;
-}
-
-fn getC(data: *const BitField1) u2 {
-    return data.c;
-}
-
-const Foo24Bits = packed struct {
-    field: u24,
-};
-const Foo96Bits = packed struct {
-    a: u24,
-    b: u24,
-    c: u24,
-    d: u24,
-};
-
-test "packed struct 24bits" {
-    comptime {
-        try expect(@sizeOf(Foo24Bits) == 4);
-        if (@sizeOf(usize) == 4) {
-            try expect(@sizeOf(Foo96Bits) == 12);
-        } else {
-            try expect(@sizeOf(Foo96Bits) == 16);
-        }
-    }
-
-    var value = Foo96Bits{
-        .a = 0,
-        .b = 0,
-        .c = 0,
-        .d = 0,
-    };
-    value.a += 1;
-    try expect(value.a == 1);
-    try expect(value.b == 0);
-    try expect(value.c == 0);
-    try expect(value.d == 0);
-
-    value.b += 1;
-    try expect(value.a == 1);
-    try expect(value.b == 1);
-    try expect(value.c == 0);
-    try expect(value.d == 0);
-
-    value.c += 1;
-    try expect(value.a == 1);
-    try expect(value.b == 1);
-    try expect(value.c == 1);
-    try expect(value.d == 0);
-
-    value.d += 1;
-    try expect(value.a == 1);
-    try expect(value.b == 1);
-    try expect(value.c == 1);
-    try expect(value.d == 1);
-}
-
-const Foo32Bits = packed struct {
-    field: u24,
-    pad: u8,
-};
-
-const FooArray24Bits = packed struct {
-    a: u16,
-    b: [2]Foo32Bits,
-    c: u16,
-};
-
-// TODO revisit this test when doing https://github.com/ziglang/zig/issues/1512
-test "packed array 24bits" {
-    comptime {
-        try expect(@sizeOf([9]Foo32Bits) == 9 * 4);
-        try expect(@sizeOf(FooArray24Bits) == 2 + 2 * 4 + 2);
-    }
-
-    var bytes = [_]u8{0} ** (@sizeOf(FooArray24Bits) + 1);
-    bytes[bytes.len - 1] = 0xaa;
-    const ptr = &std.mem.bytesAsSlice(FooArray24Bits, bytes[0 .. bytes.len - 1])[0];
-    try expect(ptr.a == 0);
-    try expect(ptr.b[0].field == 0);
-    try expect(ptr.b[1].field == 0);
-    try expect(ptr.c == 0);
-
-    ptr.a = maxInt(u16);
-    try expect(ptr.a == maxInt(u16));
-    try expect(ptr.b[0].field == 0);
-    try expect(ptr.b[1].field == 0);
-    try expect(ptr.c == 0);
-
-    ptr.b[0].field = maxInt(u24);
-    try expect(ptr.a == maxInt(u16));
-    try expect(ptr.b[0].field == maxInt(u24));
-    try expect(ptr.b[1].field == 0);
-    try expect(ptr.c == 0);
-
-    ptr.b[1].field = maxInt(u24);
-    try expect(ptr.a == maxInt(u16));
-    try expect(ptr.b[0].field == maxInt(u24));
-    try expect(ptr.b[1].field == maxInt(u24));
-    try expect(ptr.c == 0);
-
-    ptr.c = maxInt(u16);
-    try expect(ptr.a == maxInt(u16));
-    try expect(ptr.b[0].field == maxInt(u24));
-    try expect(ptr.b[1].field == maxInt(u24));
-    try expect(ptr.c == maxInt(u16));
-
-    try expect(bytes[bytes.len - 1] == 0xaa);
-}
-
-const FooStructAligned = packed struct {
-    a: u8,
-    b: u8,
-};
-
-const FooArrayOfAligned = packed struct {
-    a: [2]FooStructAligned,
-};
-
-test "aligned array of packed struct" {
-    comptime {
-        try expect(@sizeOf(FooStructAligned) == 2);
-        try expect(@sizeOf(FooArrayOfAligned) == 2 * 2);
-    }
-
-    var bytes = [_]u8{0xbb} ** @sizeOf(FooArrayOfAligned);
-    const ptr = &std.mem.bytesAsSlice(FooArrayOfAligned, bytes[0..])[0];
-
-    try expect(ptr.a[0].a == 0xbb);
-    try expect(ptr.a[0].b == 0xbb);
-    try expect(ptr.a[1].a == 0xbb);
-    try expect(ptr.a[1].b == 0xbb);
-}
-
-test "runtime struct initialization of bitfield" {
-    const s1 = Nibbles{
-        .x = x1,
-        .y = x1,
-    };
-    const s2 = Nibbles{
-        .x = @intCast(u4, x2),
-        .y = @intCast(u4, x2),
-    };
-
-    try expect(s1.x == x1);
-    try expect(s1.y == x1);
-    try expect(s2.x == @intCast(u4, x2));
-    try expect(s2.y == @intCast(u4, x2));
-}
-
-var x1 = @as(u4, 1);
-var x2 = @as(u8, 2);
-
-const Nibbles = packed struct {
-    x: u4,
-    y: u4,
-};
-
-const Bitfields = packed struct {
-    f1: u16,
-    f2: u16,
-    f3: u8,
-    f4: u8,
-    f5: u4,
-    f6: u4,
-    f7: u8,
-};
-
-test "native bit field understands endianness" {
-    var all: u64 = if (native_endian != .Little)
-        0x1111222233445677
-    else
-        0x7765443322221111;
-    var bytes: [8]u8 = undefined;
-    @memcpy(&bytes, @ptrCast([*]u8, &all), 8);
-    var bitfields = @ptrCast(*Bitfields, &bytes).*;
-
-    try expect(bitfields.f1 == 0x1111);
-    try expect(bitfields.f2 == 0x2222);
-    try expect(bitfields.f3 == 0x33);
-    try expect(bitfields.f4 == 0x44);
-    try expect(bitfields.f5 == 0x5);
-    try expect(bitfields.f6 == 0x6);
-    try expect(bitfields.f7 == 0x77);
-}
-
-test "align 1 field before self referential align 8 field as slice return type" {
-    const result = alloc(Expr);
-    try expect(result.len == 0);
-}
-
-const Expr = union(enum) {
-    Literal: u8,
-    Question: *Expr,
-};
-
-fn alloc(comptime T: type) []T {
-    return &[_]T{};
-}
-
-test "call method with mutable reference to struct with no fields" {
-    const S = struct {
-        fn doC(s: *const @This()) bool {
-            _ = s;
-            return true;
-        }
-        fn do(s: *@This()) bool {
-            _ = s;
-            return true;
-        }
-    };
-
-    var s = S{};
-    try expect(S.doC(&s));
-    try expect(s.doC());
-    try expect(S.do(&s));
-    try expect(s.do());
-}
-
-test "implicit cast packed struct field to const ptr" {
-    const LevelUpMove = packed struct {
-        move_id: u9,
-        level: u7,
-
-        fn toInt(value: u7) u7 {
-            return value;
-        }
-    };
-
-    var lup: LevelUpMove = undefined;
-    lup.level = 12;
-    const res = LevelUpMove.toInt(lup.level);
-    try expect(res == 12);
-}
-
-test "pointer to packed struct member in a stack variable" {
-    const S = packed struct {
-        a: u2,
-        b: u2,
-    };
-
-    var s = S{ .a = 2, .b = 0 };
-    var b_ptr = &s.b;
-    try expect(s.b == 0);
-    b_ptr.* = 2;
-    try expect(s.b == 2);
-}
-
-test "non-byte-aligned array inside packed struct" {
-    const Foo = packed struct {
-        a: bool,
-        b: [0x16]u8,
-    };
-    const S = struct {
-        fn bar(slice: []const u8) !void {
-            try expectEqualSlices(u8, slice, "abcdefghijklmnopqurstu");
-        }
-        fn doTheTest() !void {
-            var foo = Foo{
-                .a = true,
-                .b = "abcdefghijklmnopqurstu".*,
-            };
-            const value = foo.b;
-            try bar(&value);
-        }
-    };
-    try S.doTheTest();
-    comptime try S.doTheTest();
-}
-
-test "packed struct with u0 field access" {
-    const S = packed struct {
-        f0: u0,
-    };
-    var s = S{ .f0 = 0 };
-    comptime try expect(s.f0 == 0);
-}
-
-const S0 = struct {
-    bar: S1,
-
-    pub const S1 = struct {
-        value: u8,
-    };
-
-    fn init() @This() {
-        return S0{ .bar = S1{ .value = 123 } };
-    }
-};
-
-var g_foo: S0 = S0.init();
-
-test "access to global struct fields" {
-    g_foo.bar.value = 42;
-    try expect(g_foo.bar.value == 42);
-}
-
-test "packed struct with fp fields" {
-    const S = packed struct {
-        data: [3]f32,
-
-        pub fn frob(self: *@This()) void {
-            self.data[0] += self.data[1] + self.data[2];
-            self.data[1] += self.data[0] + self.data[2];
-            self.data[2] += self.data[0] + self.data[1];
-        }
-    };
-
-    var s: S = undefined;
-    s.data[0] = 1.0;
-    s.data[1] = 2.0;
-    s.data[2] = 3.0;
-    s.frob();
-    try expectEqual(@as(f32, 6.0), s.data[0]);
-    try expectEqual(@as(f32, 11.0), s.data[1]);
-    try expectEqual(@as(f32, 20.0), s.data[2]);
-}
-
-test "use within struct scope" {
-    const S = struct {
-        usingnamespace struct {
-            pub fn inner() i32 {
-                return 42;
-            }
-        };
-    };
-    try expectEqual(@as(i32, 42), S.inner());
-}
-
-test "default struct initialization fields" {
-    const S = struct {
-        a: i32 = 1234,
-        b: i32,
-    };
-    const x = S{
-        .b = 5,
-    };
-    var five: i32 = 5;
-    const y = S{
-        .b = five,
-    };
-    if (x.a + x.b != 1239) {
-        @compileError("it should be comptime known");
-    }
-    try expectEqual(y, x);
-    try expectEqual(1239, x.a + x.b);
-}
-
-test "fn with C calling convention returns struct by value" {
-    const S = struct {
-        fn entry() !void {
-            var x = makeBar(10);
-            try expectEqual(@as(i32, 10), x.handle);
-        }
-
-        const ExternBar = extern struct {
-            handle: i32,
-        };
-
-        fn makeBar(t: i32) callconv(.C) ExternBar {
-            return ExternBar{
-                .handle = t,
-            };
-        }
-    };
-    try S.entry();
-    comptime try S.entry();
-}
-
-test "for loop over pointers to struct, getting field from struct pointer" {
-    const S = struct {
-        const Foo = struct {
-            name: []const u8,
-        };
-
-        var ok = true;
-
-        fn eql(a: []const u8) bool {
-            _ = a;
-            return true;
-        }
-
-        const ArrayList = struct {
-            fn toSlice(self: *ArrayList) []*Foo {
-                _ = self;
-                return @as([*]*Foo, undefined)[0..0];
-            }
-        };
-
-        fn doTheTest() !void {
-            var objects: ArrayList = undefined;
-
-            for (objects.toSlice()) |obj| {
-                if (eql(obj.name)) {
-                    ok = false;
-                }
-            }
-
-            try expect(ok);
-        }
-    };
-    try S.doTheTest();
-}
-
-test "zero-bit field in packed struct" {
-    const S = packed struct {
-        x: u10,
-        y: void,
-    };
-    var x: S = undefined;
-    _ = x;
-}
-
-test "struct field init with catch" {
-    const S = struct {
-        fn doTheTest() !void {
-            var x: anyerror!isize = 1;
-            var req = Foo{
-                .field = x catch undefined,
-            };
-            try expect(req.field == 1);
-        }
-
-        pub const Foo = extern struct {
-            field: isize,
-        };
-    };
-    try S.doTheTest();
-    comptime try S.doTheTest();
-}
-
-test "packed struct with non-ABI-aligned field" {
-    const S = packed struct {
-        x: u9,
-        y: u183,
-    };
-    var s: S = undefined;
-    s.x = 1;
-    s.y = 42;
-    try expect(s.x == 1);
-    try expect(s.y == 42);
-}
-
-test "non-packed struct with u128 entry in union" {
-    const U = union(enum) {
-        Num: u128,
-        Void,
-    };
-
-    const S = struct {
-        f1: U,
-        f2: U,
-    };
-
-    var sx: S = undefined;
-    var s = &sx;
-    try std.testing.expect(@ptrToInt(&s.f2) - @ptrToInt(&s.f1) == @offsetOf(S, "f2"));
-    var v2 = U{ .Num = 123 };
-    s.f2 = v2;
-    try std.testing.expect(s.f2.Num == 123);
-}
-
-test "packed struct field passed to generic function" {
-    const S = struct {
-        const P = packed struct {
-            b: u5,
-            g: u5,
-            r: u5,
-            a: u1,
-        };
-
-        fn genericReadPackedField(ptr: anytype) u5 {
-            return ptr.*;
-        }
-    };
-
-    var p: S.P = undefined;
-    p.b = 29;
-    var loaded = S.genericReadPackedField(&p.b);
-    try expect(loaded == 29);
-}
-
-test "anonymous struct literal syntax" {
-    const S = struct {
-        const Point = struct {
-            x: i32,
-            y: i32,
-        };
-
-        fn doTheTest() !void {
-            var p: Point = .{
-                .x = 1,
-                .y = 2,
-            };
-            try expect(p.x == 1);
-            try expect(p.y == 2);
-        }
-    };
-    try S.doTheTest();
-    comptime try S.doTheTest();
-}
-
-test "fully anonymous struct" {
-    const S = struct {
-        fn doTheTest() !void {
-            try dump(.{
-                .int = @as(u32, 1234),
-                .float = @as(f64, 12.34),
-                .b = true,
-                .s = "hi",
-            });
-        }
-        fn dump(args: anytype) !void {
-            try expect(args.int == 1234);
-            try expect(args.float == 12.34);
-            try expect(args.b);
-            try expect(args.s[0] == 'h');
-            try expect(args.s[1] == 'i');
-        }
-    };
-    try S.doTheTest();
-    comptime try S.doTheTest();
-}
-
-test "fully anonymous list literal" {
-    const S = struct {
-        fn doTheTest() !void {
-            try dump(.{ @as(u32, 1234), @as(f64, 12.34), true, "hi" });
-        }
-        fn dump(args: anytype) !void {
-            try expect(args.@"0" == 1234);
-            try expect(args.@"1" == 12.34);
-            try expect(args.@"2");
-            try expect(args.@"3"[0] == 'h');
-            try expect(args.@"3"[1] == 'i');
-        }
-    };
-    try S.doTheTest();
-    comptime try S.doTheTest();
-}
-
-test "anonymous struct literal assigned to variable" {
-    var vec = .{ @as(i32, 22), @as(i32, 55), @as(i32, 99) };
-    try expect(vec.@"0" == 22);
-    try expect(vec.@"1" == 55);
-    try expect(vec.@"2" == 99);
-}
-
-test "struct with var field" {
-    const Point = struct {
-        x: anytype,
-        y: anytype,
-    };
-    const pt = Point{
-        .x = 1,
-        .y = 2,
-    };
-    try expect(pt.x == 1);
-    try expect(pt.y == 2);
-}
-
-test "comptime struct field" {
-    const T = struct {
-        a: i32,
-        comptime b: i32 = 1234,
-    };
-
-    var foo: T = undefined;
-    comptime try expect(foo.b == 1234);
-}
-
-test "anon struct literal field value initialized with fn call" {
-    const S = struct {
-        fn doTheTest() !void {
-            var x = .{foo()};
-            try expectEqualSlices(u8, x[0], "hi");
-        }
-        fn foo() []const u8 {
-            return "hi";
-        }
-    };
-    try S.doTheTest();
-    comptime try S.doTheTest();
-}
-
-test "self-referencing struct via array member" {
-    const T = struct {
-        children: [1]*@This(),
-    };
-    var x: T = undefined;
-    x = T{ .children = .{&x} };
-    try expect(x.children[0] == &x);
-}
-
-test "struct with union field" {
-    const Value = struct {
-        ref: u32 = 2,
-        kind: union(enum) {
-            None: usize,
-            Bool: bool,
-        },
-    };
-
-    var True = Value{
-        .kind = .{ .Bool = true },
-    };
-    try expectEqual(@as(u32, 2), True.ref);
-    try expectEqual(true, True.kind.Bool);
-}
-
-test "type coercion of anon struct literal to struct" {
-    const S = struct {
-        const S2 = struct {
-            A: u32,
-            B: []const u8,
-            C: void,
-            D: Foo = .{},
-        };
-
-        const Foo = struct {
-            field: i32 = 1234,
-        };
-
-        fn doTheTest() !void {
-            var y: u32 = 42;
-            const t0 = .{ .A = 123, .B = "foo", .C = {} };
-            const t1 = .{ .A = y, .B = "foo", .C = {} };
-            const y0: S2 = t0;
-            var y1: S2 = t1;
-            try expect(y0.A == 123);
-            try expect(std.mem.eql(u8, y0.B, "foo"));
-            try expect(y0.C == {});
-            try expect(y0.D.field == 1234);
-            try expect(y1.A == y);
-            try expect(std.mem.eql(u8, y1.B, "foo"));
-            try expect(y1.C == {});
-            try expect(y1.D.field == 1234);
-        }
-    };
-    try S.doTheTest();
-    comptime try S.doTheTest();
-}
-
-test "type coercion of pointer to anon struct literal to pointer to struct" {
-    const S = struct {
-        const S2 = struct {
-            A: u32,
-            B: []const u8,
-            C: void,
-            D: Foo = .{},
-        };
-
-        const Foo = struct {
-            field: i32 = 1234,
-        };
+const empty_global_instance = StructWithNoFields{};
 
-        fn doTheTest() !void {
-            var y: u32 = 42;
-            const t0 = &.{ .A = 123, .B = "foo", .C = {} };
-            const t1 = &.{ .A = y, .B = "foo", .C = {} };
-            const y0: *const S2 = t0;
-            var y1: *const S2 = t1;
-            try expect(y0.A == 123);
-            try expect(std.mem.eql(u8, y0.B, "foo"));
-            try expect(y0.C == {});
-            try expect(y0.D.field == 1234);
-            try expect(y1.A == y);
-            try expect(std.mem.eql(u8, y1.B, "foo"));
-            try expect(y1.C == {});
-            try expect(y1.D.field == 1234);
-        }
-    };
-    try S.doTheTest();
-    comptime try S.doTheTest();
+test "return empty struct instance" {
+    _ = returnEmptyStructInstance();
 }
-
-test "packed struct with undefined initializers" {
-    const S = struct {
-        const P = packed struct {
-            a: u3,
-            _a: u3 = undefined,
-            b: u3,
-            _b: u3 = undefined,
-            c: u3,
-            _c: u3 = undefined,
-        };
-
-        fn doTheTest() !void {
-            var p: P = undefined;
-            p = P{ .a = 2, .b = 4, .c = 6 };
-            // Make sure the compiler doesn't touch the unprefixed fields.
-            // Use expect since i386-linux doesn't like expectEqual
-            try expect(p.a == 2);
-            try expect(p.b == 4);
-            try expect(p.c == 6);
-        }
-    };
-
-    try S.doTheTest();
-    comptime try S.doTheTest();
+fn returnEmptyStructInstance() StructWithNoFields {
+    return empty_global_instance;
 }