fix std.testing.expectEqual for comptime-only union

switch from `inline for` with `std.mem.eql`
to `inline else` and tag comparison;
expectEqualDeep(Inner) was already doing this.

add a previously-failing test case.

1 files changed, 14 insertions, 12 deletions

diff --git a/lib/std/testing.zig b/lib/std/testing.zig
index 051b6becee..341161a64b 100644
--- a/lib/std/testing.zig
+++ b/lib/std/testing.zig
@@ -147,18 +147,10 @@ fn expectEqualInner(comptime T: type, expected: T, actual: T) !void {
 
             try expectEqual(expectedTag, actualTag);
 
-            // we only reach this loop if the tags are equal
-            inline for (std.meta.fields(@TypeOf(actual))) |fld| {
-                if (std.mem.eql(u8, fld.name, @tagName(actualTag))) {
-                    try expectEqual(@field(expected, fld.name), @field(actual, fld.name));
-                    return;
-                }
+            // we only reach this switch if the tags are equal
+            switch (expected) {
+                inline else => |val, tag| try expectEqual(val, @field(actual, @tagName(tag))),
             }
-
-            // we iterate over *all* union fields
-            // => we should never get here as the loop above is
-            //    including all possible values.
-            unreachable;
         },
 
         .Optional => {
@@ -208,6 +200,16 @@ test "expectEqual.union(enum)" {
     try expectEqual(a10, a10);
 }
 
+test "expectEqual union with comptime-only field" {
+    const U = union(enum) {
+        a: void,
+        b: void,
+        c: comptime_int,
+    };
+
+    try expectEqual(U{ .a = {} }, .a);
+}
+
 /// This function is intended to be used only in tests. When the formatted result of the template
 /// and its arguments does not equal the expected text, it prints diagnostics to stderr to show how
 /// they are not equal, then returns an error. It depends on `expectEqualStrings()` for printing
@@ -809,7 +811,7 @@ fn expectEqualDeepInner(comptime T: type, expected: T, actual: T) error{TestExpe
 
             try expectEqual(expectedTag, actualTag);
 
-            // we only reach this loop if the tags are equal
+            // we only reach this switch if the tags are equal
             switch (expected) {
                 inline else => |val, tag| {
                     try expectEqualDeep(val, @field(actual, @tagName(tag)));