Sema: implement struct init is_ref=true

Takes advantage of the pattern already established with
array_init_anon. Also upgrades array_init (non-anon) to the pattern.

Implements comptime struct value equality and pointer value hashing.

test/behavior/enum.zig

@@ -972,3 +972,116 @@ fn test3_2(f: Test3Foo) !void {
         else => unreachable,
     }
 }
+
+test "@tagName" {
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
+
+    try expect(mem.eql(u8, testEnumTagNameBare(BareNumber.Three), "Three"));
+    comptime try expect(mem.eql(u8, testEnumTagNameBare(BareNumber.Three), "Three"));
+}
+
+fn testEnumTagNameBare(n: anytype) []const u8 {
+    return @tagName(n);
+}
+
+const BareNumber = enum { One, Two, Three };
+
+test "@tagName non-exhaustive enum" {
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
+
+    try expect(mem.eql(u8, testEnumTagNameBare(NonExhaustive.B), "B"));
+    comptime try expect(mem.eql(u8, testEnumTagNameBare(NonExhaustive.B), "B"));
+}
+const NonExhaustive = enum(u8) { A, B, _ };
+
+test "@tagName is null-terminated" {
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
+
+    const S = struct {
+        fn doTheTest(n: BareNumber) !void {
+            try expect(@tagName(n)[3] == 0);
+        }
+    };
+    try S.doTheTest(.Two);
+    try comptime S.doTheTest(.Two);
+}
+
+test "tag name with assigned enum values" {
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
+
+    const LocalFoo = enum(u8) {
+        A = 1,
+        B = 0,
+    };
+    var b = LocalFoo.B;
+    try expect(mem.eql(u8, @tagName(b), "B"));
+}
+
+test "@tagName on enum literals" {
+    try expect(mem.eql(u8, @tagName(.FooBar), "FooBar"));
+    comptime try expect(mem.eql(u8, @tagName(.FooBar), "FooBar"));
+}
+
+test "enum literal casting to optional" {
+    var bar: ?Bar = undefined;
+    bar = .B;
+
+    try expect(bar.? == Bar.B);
+}
+
+const A = enum(u3) { One, Two, Three, Four, One2, Two2, Three2, Four2 };
+const B = enum(u3) { One3, Two3, Three3, Four3, One23, Two23, Three23, Four23 };
+const C = enum(u2) { One4, Two4, Three4, Four4 };
+
+const BitFieldOfEnums = packed struct {
+    a: A,
+    b: B,
+    c: C,
+};
+
+const bit_field_1 = BitFieldOfEnums{
+    .a = A.Two,
+    .b = B.Three3,
+    .c = C.Four4,
+};
+
+test "bit field access with enum fields" {
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
+
+    var data = bit_field_1;
+    try expect(getA(&data) == A.Two);
+    try expect(getB(&data) == B.Three3);
+    try expect(getC(&data) == C.Four4);
+    comptime try expect(@sizeOf(BitFieldOfEnums) == 1);
+
+    data.b = B.Four3;
+    try expect(data.b == B.Four3);
+
+    data.a = A.Three;
+    try expect(data.a == A.Three);
+    try expect(data.b == B.Four3);
+}
+
+fn getA(data: *const BitFieldOfEnums) A {
+    return data.a;
+}
+
+fn getB(data: *const BitFieldOfEnums) B {
+    return data.b;
+}
+
+fn getC(data: *const BitFieldOfEnums) C {
+    return data.c;
+}
+
+test "enum literal in array literal" {
+    const Items = enum { one, two };
+    const array = [_]Items{ .one, .two };
+
+    try expect(array[0] == .one);
+    try expect(array[1] == .two);
+}