From 20befa4e64f1654fa3c69a0e7b0b194193c2ab27 Mon Sep 17 00:00:00 2001
From: Rue04 <iokg04@gmail.com>
Date: Wed, 15 Jul 2026 23:04:54 +0200
Subject: [PATCH] Sema: fix crash on invalid coercion from error union or
 optional

It seems the destination and source types were switched by accident, leading to an `unreachable` being reached in the following cases:

```zig
test {
    const eu: anyerror!u8 = 10;
    const i: comptime_int = eu;
    _ = i;
}

test {
    const op: ?u8 = 10;
    const i: comptime_int = op;
    _ = i;
}
```

Resolves: https://codeberg.org/ziglang/zig/issues/30597
Resolves: https://github.com/ziglang/zig/issues/25645
Reviewed-on: https://codeberg.org/ziglang/zig/pulls/35662
Reviewed-by: mlugg <mlugg@noreply.codeberg.org>
---
 src/Sema.zig                                  |  4 +--
 ...optional_containing_or_to_comptime_int.zig | 30 +++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 test/cases/compile_errors/coercion_from_eu_or_optional_containing_or_to_comptime_int.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index 9fe0f32b05d663463bc8abd04cf213d456f1287f..4b29027056be47f0bccaa0250f7b30a3a8980667 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -28356,7 +28356,7 @@ fn coerceExtra(
 
         // E!T to T
         if (inst_ty.zigTypeTag(zcu) == .error_union and
-            (try sema.coerceInMemoryAllowed(block, inst_ty.errorUnionPayload(zcu), dest_ty, false, target, dest_ty_src, inst_src, null)) == .ok)
+            (try sema.coerceInMemoryAllowed(block, dest_ty, inst_ty.errorUnionPayload(zcu), false, target, dest_ty_src, inst_src, null)) == .ok)
         {
             try sema.errNote(inst_src, msg, "cannot convert error union to payload type", .{});
             try sema.errNote(inst_src, msg, "consider using 'try', 'catch', or 'if'", .{});
@@ -28364,7 +28364,7 @@ fn coerceExtra(
 
         // ?T to T
         if (inst_ty.zigTypeTag(zcu) == .optional and
-            (try sema.coerceInMemoryAllowed(block, inst_ty.optionalChild(zcu), dest_ty, false, target, dest_ty_src, inst_src, null)) == .ok)
+            (try sema.coerceInMemoryAllowed(block, dest_ty, inst_ty.optionalChild(zcu), false, target, dest_ty_src, inst_src, null)) == .ok)
         {
             try sema.errNote(inst_src, msg, "cannot convert optional to payload type", .{});
             try sema.errNote(inst_src, msg, "consider using '.?', 'orelse', or 'if'", .{});
diff --git a/test/cases/compile_errors/coercion_from_eu_or_optional_containing_or_to_comptime_int.zig b/test/cases/compile_errors/coercion_from_eu_or_optional_containing_or_to_comptime_int.zig
new file mode 100644
index 0000000000000000000000000000000000000000..ecdbb5df9d7bf8a5315778895134dc022cb150d6
--- /dev/null
+++ b/test/cases/compile_errors/coercion_from_eu_or_optional_containing_or_to_comptime_int.zig
@@ -0,0 +1,30 @@
+comptime {
+    const eu: anyerror!u8 = 10;
+    const i: comptime_int = eu;
+    _ = i;
+}
+
+comptime {
+    const op: ?u8 = 10;
+    const i: comptime_int = op;
+    _ = i;
+}
+
+comptime {
+    const op: anyerror!comptime_int = 10;
+    const i: u8 = op;
+    _ = i;
+}
+
+comptime {
+    const op: ?comptime_int = 10;
+    const i: u8 = op;
+    _ = i;
+}
+
+// error
+//
+// :3:29: error: expected type 'comptime_int', found 'anyerror!u8'
+// :9:29: error: expected type 'comptime_int', found '?u8'
+// :15:19: error: expected type 'u8', found 'anyerror!comptime_int'
+// :21:19: error: expected type 'u8', found '?comptime_int'
-- 
2.54.0