move never type tests to subdirectories and add some comments

tests/ui/never_type/diverging-tuple-parts-39485.rs

@@ -1,16 +0,0 @@
-//@ edition:2015..2021
-// After #39485, this test used to pass, but that change was reverted
-// due to numerous inference failures like #39808, so it now fails
-// again. #39485 made it so that diverging types never propagate
-// upward; but we now do propagate such types upward in many more
-// cases.
-
-fn g() {
-    &panic!() //~ ERROR mismatched types
-}
-
-fn f() -> isize {
-    (return 1, return 2) //~ ERROR mismatched types
-}
-
-fn main() {}

tests/ui/never_type/expr-empty-ret.rs

@@ -1,14 +0,0 @@
-//@ run-pass
-
-#![allow(dead_code)]
-// Issue #521
-
-
-fn f() {
-    let _x = match true {
-        true => { 10 }
-        false => { return }
-    };
-}
-
-pub fn main() { }

tests/ui/never_type/fallback_change/from_infer_breaking_with_unit_fallback.rs

@@ -2,7 +2,7 @@
 //
 // This is a *minimization* of the issue.
 // Note that the original version with the `?` does not fail anymore even with fallback to unit,
-// see `tests/ui/never_type/question_mark_from_never.rs`.
+// see `tests/ui/never_type/fallback_change/question_mark_from_never.rs`.
 //
 //@ revisions: unit never
 //@[never] check-pass

tests/ui/never_type/fallback_change/question_mark_from_never.rs

@@ -1,6 +1,6 @@
 // Regression test for <https://github.com/rust-lang/rust/issues/66757>.
 //
-// See also: `tests/ui/never_type/from_infer_breaking_with_unit_fallback.rs`.
+// See also: `tests/ui/never_type/fallback_change/from_infer_breaking_with_unit_fallback.rs`.
 //
 //@ revisions: unit never
 //@ check-pass

tests/ui/never_type/issue-10176.rs

@@ -1,9 +0,0 @@
-fn f() -> isize { //~ NOTE expected `isize` because of return type
-    (return 1, return 2)
-//~^ ERROR mismatched types
-//~| NOTE expected type `isize`
-//~| NOTE found tuple `(!, !)`
-//~| NOTE expected `isize`, found `(!, !)`
-}
-
-fn main() {}

tests/ui/never_type/issue-10176.stderr

@@ -1,14 +0,0 @@
-error[E0308]: mismatched types
-  --> $DIR/issue-10176.rs:2:5
-   |
-LL | fn f() -> isize {
-   |           ----- expected `isize` because of return type
-LL |     (return 1, return 2)
-   |     ^^^^^^^^^^^^^^^^^^^^ expected `isize`, found `(!, !)`
-   |
-   = note: expected type `isize`
-             found tuple `(!, !)`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0308`.

tests/ui/never_type/issue-2149.rs

@@ -1,15 +0,0 @@
-trait VecMonad<A> {
-    fn bind<B, F>(&self, f: F) where F: FnMut(A) -> Vec<B>;
-}
-
-impl<A> VecMonad<A> for Vec<A> {
-    fn bind<B, F>(&self, mut f: F) where F: FnMut(A) -> Vec<B> {
-        let mut r = panic!();
-        for elt in self { r = r + f(*elt); }
-        //~^ ERROR E0277
-   }
-}
-fn main() {
-    ["hi"].bind(|x| [x] );
-    //~^ ERROR no method named `bind` found
-}

tests/ui/never_type/issue-2149.stderr

@@ -1,25 +0,0 @@
-error[E0277]: cannot add `Vec<B>` to `()`
-  --> $DIR/issue-2149.rs:8:33
-   |
-LL |         for elt in self { r = r + f(*elt); }
-   |                                 ^ no implementation for `() + Vec<B>`
-   |
-   = help: the trait `Add<Vec<B>>` is not implemented for `()`
-
-error[E0599]: no method named `bind` found for array `[&str; 1]` in the current scope
-  --> $DIR/issue-2149.rs:13:12
-   |
-LL |     ["hi"].bind(|x| [x] );
-   |            ^^^^ method not found in `[&str; 1]`
-   |
-   = help: items from traits can only be used if the trait is implemented and in scope
-note: `VecMonad` defines an item `bind`, perhaps you need to implement it
-  --> $DIR/issue-2149.rs:1:1
-   |
-LL | trait VecMonad<A> {
-   | ^^^^^^^^^^^^^^^^^
-
-error: aborting due to 2 previous errors
-
-Some errors have detailed explanations: E0277, E0599.
-For more information about an error, try `rustc --explain E0277`.

tests/ui/never_type/regress/divergent-block-with-tail.rs

@@ -0,0 +1,20 @@
+// Rust briefly used to allow blocks with divergent statements to type check as `!`, even if they
+// had a tail expression. This led to a number of regressions (because type information no longer
+// flowed from the tail expression) and was quickly reverted.i
+//
+// See <https://github.com/rust-lang/rust/pull/39485>,
+// <https://github.com/rust-lang/rust/pull/40636>,
+// <https://github.com/rust-lang/rust/pull/39808>.
+//
+//@ edition:2015..2021
+
+fn g() {
+    &panic!() //~ ERROR mismatched types
+}
+
+// This used to ICE, see <https://github.com/rust-lang/rust/issues/10176>
+fn f() -> isize {
+    (return 1, return 2) //~ ERROR mismatched types
+}
+
+fn main() {}

tests/ui/parser/return-without-semicolon-in-match.rs

@@ -0,0 +1,13 @@
+// Tests that `return` without a semicolon parses correctly in a match arm.
+// See <https://github.com/rust-lang/rust/issues/521>
+//
+//@ run-pass
+
+fn f() {
+    let _x = match true {
+        true => { 10 }
+        false => { return }
+    };
+}
+
+fn main() {}