Sema: fix issues in `@errorCast` with error unions

1 files changed, 14 insertions, 7 deletions

diff --git a/src/Sema.zig b/src/Sema.zig
index 096ebb0589..27dd7221fc 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -21771,10 +21771,10 @@ fn zirErrorCast(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData
     // operand must be defined since it can be an invalid error value
     const maybe_operand_val = try sema.resolveDefinedValue(block, operand_src, operand);
 
-    if (disjoint: {
+    const disjoint = disjoint: {
         // Try avoiding resolving inferred error sets if we can
-        if (!dest_ty.isAnyError(mod) and dest_ty.errorSetNames(mod).len == 0) break :disjoint true;
-        if (!operand_ty.isAnyError(mod) and operand_ty.errorSetNames(mod).len == 0) break :disjoint true;
+        if (!dest_ty.isAnyError(mod) and dest_ty.errorSetIsEmpty(mod)) break :disjoint true;
+        if (!operand_ty.isAnyError(mod) and operand_ty.errorSetIsEmpty(mod)) break :disjoint true;
         if (dest_ty.isAnyError(mod)) break :disjoint false;
         if (operand_ty.isAnyError(mod)) break :disjoint false;
         for (dest_ty.errorSetNames(mod)) |dest_err_name| {
@@ -21796,7 +21796,8 @@ fn zirErrorCast(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData
         }
 
         break :disjoint true;
-    }) {
+    };
+    if (disjoint and dest_tag != .ErrorUnion) {
         const msg = msg: {
             const msg = try sema.errMsg(
                 block,
@@ -21850,10 +21851,16 @@ fn zirErrorCast(sema: *Sema, block: *Block, extended: Zir.Inst.Extended.InstData
                 .int = .{ .ty = .u16_type, .storage = .{ .u64 = 0 } },
             }));
 
-            const has_value = try block.addTyOp(.error_set_has_value, dest_ty, err_code);
             const is_zero = try block.addBinOp(.cmp_eq, err_int, zero_u16);
-            const ok = try block.addBinOp(.bit_or, has_value, is_zero);
-            try sema.addSafetyCheck(block, src, ok, .invalid_error_code);
+            if (disjoint) {
+                // Error must be zero.
+                try sema.addSafetyCheck(block, src, is_zero, .invalid_error_code);
+            } else {
+                // Error must be in destination set or zero.
+                const has_value = try block.addTyOp(.error_set_has_value, dest_ty, err_code);
+                const ok = try block.addBinOp(.bit_or, has_value, is_zero);
+                try sema.addSafetyCheck(block, src, ok, .invalid_error_code);
+            }
         } else {
             const err_int_inst = try block.addBitCast(Type.err_int, operand);
             const ok = try block.addTyOp(.error_set_has_value, dest_ty, err_int_inst);