From f29c5168b205bfa51316ab79d04c143f1937edef Mon Sep 17 00:00:00 2001
From: AprilNEA <github@sku.moe>
Date: Sat, 27 Dec 2025 22:35:40 +0800
Subject: [PATCH] Add test for never type fallback in try blocks with Into<!>

Closes #125364

This test verifies that the never type fallback behavior
in try blocks with `Into<!>` bounds works correctly across
different editions:

- Edition 2021: Fallback to `()` causes type error
- Edition 2024: Fallback to `!` compiles successfully
---
 ...try-block-never-type-fallback.e2021.stderr | 20 +++++++++++++++
 .../try-block-never-type-fallback.rs          | 25 +++++++++++++++++++
 2 files changed, 45 insertions(+)
 create mode 100644 tests/ui/never_type/try-block-never-type-fallback.e2021.stderr
 create mode 100644 tests/ui/never_type/try-block-never-type-fallback.rs

diff --git a/tests/ui/never_type/try-block-never-type-fallback.e2021.stderr b/tests/ui/never_type/try-block-never-type-fallback.e2021.stderr
new file mode 100644
index 000000000000..7e23c86bcbcc
--- /dev/null
+++ b/tests/ui/never_type/try-block-never-type-fallback.e2021.stderr
@@ -0,0 +1,20 @@
+error[E0277]: the trait bound `!: From<()>` is not satisfied
+  --> $DIR/try-block-never-type-fallback.rs:20:9
+   |
+LL |     bar(try { x? });
+   |     --- ^^^^^^^^^^ the trait `From<()>` is not implemented for `!`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = note: this error might have been caused by changes to Rust's type-inference algorithm (see issue #148922 <https://github.com/rust-lang/rust/issues/148922> for more information)
+   = help: you might have intended to use the type `()` here instead
+   = note: required for `()` to implement `Into<!>`
+note: required by a bound in `bar`
+  --> $DIR/try-block-never-type-fallback.rs:15:23
+   |
+LL | fn bar(_: Result<impl Into<!>, u32>) {
+   |                       ^^^^^^^ required by this bound in `bar`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/never_type/try-block-never-type-fallback.rs b/tests/ui/never_type/try-block-never-type-fallback.rs
new file mode 100644
index 000000000000..94107a0ff103
--- /dev/null
+++ b/tests/ui/never_type/try-block-never-type-fallback.rs
@@ -0,0 +1,25 @@
+//@ revisions: e2021 e2024
+//@[e2021] edition: 2021
+//@[e2024] edition: 2024
+//@[e2024] check-pass
+
+// Issue #125364: Bad interaction between never_type, try_blocks, and From/Into
+//
+// In edition 2021, the never type in try blocks falls back to (),
+// causing a type error (since (): Into<!> does not hold).
+// In edition 2024, it falls back to !, allowing the code to compile correctly.
+
+#![feature(never_type)]
+#![feature(try_blocks)]
+
+fn bar(_: Result<impl Into<!>, u32>) {
+    unimplemented!()
+}
+
+fn foo(x: Result<!, u32>) {
+    bar(try { x? });
+    //[e2021]~^ ERROR the trait bound `!: From<()>` is not satisfied
+}
+
+fn main() {
+}