From 7453f56e678c80928ababa2868c69cfe41647fed Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Wed, 24 Aug 2022 20:27:11 -0700
Subject: stage2: explicitly tagged enums no longer have one possible value

Previously, Zig had inconsistent semantics for an enum like this:

`enum(u8){zero = 0}`

Although in theory this can only hold one possible value, the tag
`zero`, Zig no longer will treat the type this way. It will do loads and
stores, as if the type has runtime bits.

Closes #12619

Tests passed locally:
 * test-behavior
 * test-cases
---
 test/behavior/enum.zig | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

(limited to 'test/behavior/enum.zig')

diff --git a/test/behavior/enum.zig b/test/behavior/enum.zig
index 709d30af33..9e96163cc0 100644
--- a/test/behavior/enum.zig
+++ b/test/behavior/enum.zig
@@ -1,6 +1,7 @@
 const builtin = @import("builtin");
 const std = @import("std");
 const expect = std.testing.expect;
+const assert = std.debug.assert;
 const mem = std.mem;
 const Tag = std.meta.Tag;
 
@@ -1128,3 +1129,44 @@ test "tag name functions are unique" {
         _ = a;
     }
 }
+
+test "size of enum with only one tag which has explicit integer tag type" {
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
+
+    const E = enum(u8) { nope = 10 };
+    const S0 = struct { e: E };
+    const S1 = extern struct { e: E };
+    //const U = union(E) { nope: void };
+    comptime assert(@sizeOf(E) == 1);
+    comptime assert(@sizeOf(S0) == 1);
+    comptime assert(@sizeOf(S1) == 1);
+    //comptime assert(@sizeOf(U) == 1);
+
+    var s1: S1 = undefined;
+    s1.e = .nope;
+    try expect(s1.e == .nope);
+    const ptr = @ptrCast(*u8, &s1);
+    try expect(ptr.* == 10);
+
+    var s0: S0 = undefined;
+    s0.e = .nope;
+    try expect(s0.e == .nope);
+}
+
+test "switch on an extern enum with negative value" {
+    // TODO x86, wasm backends fail because they assume that enum tag types are unsigned
+    if (@import("builtin").zig_backend == .stage2_x86_64) return error.SkipZigTest;
+    if (@import("builtin").zig_backend == .stage2_wasm) return error.SkipZigTest;
+
+    const Foo = enum(c_int) {
+        Bar = -1,
+    };
+
+    const v = Foo.Bar;
+
+    switch (v) {
+        Foo.Bar => return,
+    }
+}
-- 
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