Sema: more union fixes

 * `Module.Union.getLayout`: fixes to support components of the union
   being 0 bits.
 * Implement `@typeInfo` for unions.
 * Add missing calls to `resolveTypeFields`.
 * Fix explicitly-provided union tag types passing a `Zir.Inst.Ref`
   where an `Air.Inst.Ref` was expected. We don't have any type safety
   for this; these typess are aliases.
 * Fix explicitly-provided `union(enum)` tag Values allocated to the
   wrong arena.

1 files changed, 13 insertions, 0 deletions

diff --git a/test/behavior/switch.zig b/test/behavior/switch.zig
index 16bb890c9e..caec804ec2 100644
--- a/test/behavior/switch.zig
+++ b/test/behavior/switch.zig
@@ -313,3 +313,16 @@ fn returnsFalse() bool {
 test "switch on const enum with var" {
     try expect(!returnsFalse());
 }
+
+test "anon enum literal used in switch on union enum" {
+    const Foo = union(enum) {
+        a: i32,
+    };
+
+    var foo = Foo{ .a = 1234 };
+    switch (foo) {
+        .a => |x| {
+            try expect(x == 1234);
+        },
+    }
+}