stage2: fix switch on tagged union capture-by-pointer

 * AstGen: always use `typeof` and never `typeof_elem` on the
   `switch_cond`/`switch_cond_ref` instruction because both variants
   return a value and not a pointer.
   - Delete the `typeof_elem` ZIR instruction since it is no longer
     needed.
 * Sema: validateUnionInit now recognizes a comptime mutable value and
   no longer emits a compile error saying "cannot evaluate constant
   expression"
   - Still to-do is detecting comptime union values in a function that
     is not being executed at compile-time.
     - This is still to-do for structs too.
 * Sema: when emitting a call AIR instruction, call resolveTypeLayout on
   all the parameter types as well as the return type.
 * `Type.structFieldOffset` now works for unions in addition to structs.

2 files changed, 43 insertions, 42 deletions

diff --git a/test/behavior/switch.zig b/test/behavior/switch.zig
index 67cda60958..d5e4a40500 100644
--- a/test/behavior/switch.zig
+++ b/test/behavior/switch.zig
@@ -219,3 +219,46 @@ test "switch on global mutable var isn't constant-folded" {
         poll();
     }
 }
+
+const SwitchProngWithVarEnum = union(enum) {
+    One: i32,
+    Two: f32,
+    Meh: void,
+};
+
+test "switch prong with variable" {
+    try switchProngWithVarFn(SwitchProngWithVarEnum{ .One = 13 });
+    try switchProngWithVarFn(SwitchProngWithVarEnum{ .Two = 13.0 });
+    try switchProngWithVarFn(SwitchProngWithVarEnum{ .Meh = {} });
+}
+fn switchProngWithVarFn(a: SwitchProngWithVarEnum) !void {
+    switch (a) {
+        SwitchProngWithVarEnum.One => |x| {
+            try expect(x == 13);
+        },
+        SwitchProngWithVarEnum.Two => |x| {
+            try expect(x == 13.0);
+        },
+        SwitchProngWithVarEnum.Meh => |x| {
+            const v: void = x;
+            _ = v;
+        },
+    }
+}
+
+test "switch on enum using pointer capture" {
+    try testSwitchEnumPtrCapture();
+    comptime try testSwitchEnumPtrCapture();
+}
+
+fn testSwitchEnumPtrCapture() !void {
+    var value = SwitchProngWithVarEnum{ .One = 1234 };
+    switch (value) {
+        SwitchProngWithVarEnum.One => |*x| x.* += 1,
+        else => unreachable,
+    }
+    switch (value) {
+        SwitchProngWithVarEnum.One => |x| try expect(x == 1235),
+        else => unreachable,
+    }
+}
diff --git a/test/behavior/switch_stage1.zig b/test/behavior/switch_stage1.zig
index 5847acb7d2..c42a9b7894 100644
--- a/test/behavior/switch_stage1.zig
+++ b/test/behavior/switch_stage1.zig
@@ -3,48 +3,6 @@ const expect = std.testing.expect;
 const expectError = std.testing.expectError;
 const expectEqual = std.testing.expectEqual;
 
-test "switch prong with variable" {
-    try switchProngWithVarFn(SwitchProngWithVarEnum{ .One = 13 });
-    try switchProngWithVarFn(SwitchProngWithVarEnum{ .Two = 13.0 });
-    try switchProngWithVarFn(SwitchProngWithVarEnum{ .Meh = {} });
-}
-const SwitchProngWithVarEnum = union(enum) {
-    One: i32,
-    Two: f32,
-    Meh: void,
-};
-fn switchProngWithVarFn(a: SwitchProngWithVarEnum) !void {
-    switch (a) {
-        SwitchProngWithVarEnum.One => |x| {
-            try expect(x == 13);
-        },
-        SwitchProngWithVarEnum.Two => |x| {
-            try expect(x == 13.0);
-        },
-        SwitchProngWithVarEnum.Meh => |x| {
-            const v: void = x;
-            _ = v;
-        },
-    }
-}
-
-test "switch on enum using pointer capture" {
-    try testSwitchEnumPtrCapture();
-    comptime try testSwitchEnumPtrCapture();
-}
-
-fn testSwitchEnumPtrCapture() !void {
-    var value = SwitchProngWithVarEnum{ .One = 1234 };
-    switch (value) {
-        SwitchProngWithVarEnum.One => |*x| x.* += 1,
-        else => unreachable,
-    }
-    switch (value) {
-        SwitchProngWithVarEnum.One => |x| try expect(x == 1235),
-        else => unreachable,
-    }
-}
-
 test "switch handles all cases of number" {
     try testSwitchHandleAllCases();
     comptime try testSwitchHandleAllCases();