Do proper signature equality checking for tail calls

tests/ui/explicit-tail-calls/caller-lifetime-presence.rs

@@ -12,39 +12,42 @@
 #![feature(explicit_tail_calls)]
 #![allow(incomplete_features)]
 
-fn foo<'a>(_: fn(&'a ())) {
-    become bar(dummy);
+struct A;
+struct B;
+
+fn foo<'a>(_: fn(&'a ()), _: A) {
+    become bar(dummy, B);
     //~^ ERROR mismatched signatures
     //~| NOTE `become` requires caller and callee to have matching signatures
-    //~| NOTE caller signature: `fn(fn(&'a ()))`
-    //~| NOTE callee signature: `fn(for<'a> fn(&'a ()))`
+    //~| NOTE caller signature: `fn(fn(&'a ()), A)`
+    //~| NOTE callee signature: `fn(for<'a> fn(&'a ()), B)`
 }
 
-fn bar(_: fn(&())) {}
+fn bar(_: fn(&()), _: B) {}
 
 fn dummy(_: &()) {}
 
-fn foo_(_: fn(&())) {
-    become bar1(dummy2);
+fn foo2(_: fn(&()), _: A) {
+    become bar2(dummy2, B);
     //~^ ERROR mismatched signatures
     //~| NOTE `become` requires caller and callee to have matching signatures
-    //~| NOTE caller signature: `fn(for<'a> fn(&'a ()))`
-    //~| NOTE callee signature: `fn(fn(&'a ()))`
+    //~| NOTE caller signature: `fn(for<'a> fn(&'a ()), A)`
+    //~| NOTE callee signature: `fn(fn(&'a ()), B)`
 }
 
-fn bar1<'a>(_: fn(&'a ())) {}
+fn bar2<'a>(_: fn(&'a ()), _: B) {}
 
 fn dummy2(_: &()) {}
 
-fn foo__(_: fn(&'static ())) {
-    become bar(dummy3);
+fn foo3(_: fn(&'static ()), _: A) {
+    become bar3(dummy3, B);
     //~^ ERROR mismatched signatures
     //~| NOTE `become` requires caller and callee to have matching signatures
-    //~| NOTE caller signature: `fn(fn(&'static ()))`
-    //~| NOTE callee signature: `fn(for<'a> fn(&'a ()))`
+    //~| NOTE caller signature: `fn(fn(&'static ()), A)`
+    //~| NOTE callee signature: `fn(for<'a> fn(&'a ()), B)`
 }
 
-fn bar2(_: fn(&())) {}
+fn bar3(_: fn(&()), _: B) {}
 
 fn dummy3(_: &()) {}
 

tests/ui/explicit-tail-calls/caller-lifetime-presence.stderr

@@ -1,32 +1,32 @@
 error: mismatched signatures
-  --> $DIR/caller-lifetime-presence.rs:16:5
+  --> $DIR/caller-lifetime-presence.rs:19:5
    |
-LL |     become bar(dummy);
-   |     ^^^^^^^^^^^^^^^^^
+LL |     become bar(dummy, B);
+   |     ^^^^^^^^^^^^^^^^^^^^
    |
    = note: `become` requires caller and callee to have matching signatures
-   = note: caller signature: `fn(fn(&'a ()))`
-   = note: callee signature: `fn(for<'a> fn(&'a ()))`
+   = note: caller signature: `fn(fn(&'a ()), A)`
+   = note: callee signature: `fn(for<'a> fn(&'a ()), B)`
 
 error: mismatched signatures
-  --> $DIR/caller-lifetime-presence.rs:28:5
+  --> $DIR/caller-lifetime-presence.rs:31:5
    |
-LL |     become bar1(dummy2);
-   |     ^^^^^^^^^^^^^^^^^^^
+LL |     become bar2(dummy2, B);
+   |     ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `become` requires caller and callee to have matching signatures
-   = note: caller signature: `fn(for<'a> fn(&'a ()))`
-   = note: callee signature: `fn(fn(&'a ()))`
+   = note: caller signature: `fn(for<'a> fn(&'a ()), A)`
+   = note: callee signature: `fn(fn(&'a ()), B)`
 
 error: mismatched signatures
-  --> $DIR/caller-lifetime-presence.rs:40:5
+  --> $DIR/caller-lifetime-presence.rs:43:5
    |
-LL |     become bar(dummy3);
-   |     ^^^^^^^^^^^^^^^^^^
+LL |     become bar3(dummy3, B);
+   |     ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `become` requires caller and callee to have matching signatures
-   = note: caller signature: `fn(fn(&'static ()))`
-   = note: callee signature: `fn(for<'a> fn(&'a ()))`
+   = note: caller signature: `fn(fn(&'static ()), A)`
+   = note: callee signature: `fn(for<'a> fn(&'a ()), B)`
 
 error: aborting due to 3 previous errors
 

tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.rs

@@ -3,7 +3,7 @@
 
 fn foo() -> for<'a> fn(&'a i32) {
     become bar();
-    //~^ ERROR mismatched signatures
+    //~^ ERROR mismatched types
 }
 
 fn bar() -> fn(&'static i32) {

tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.stderr

@@ -1,12 +1,12 @@
-error: mismatched signatures
+error[E0308]: mismatched types
   --> $DIR/ret-ty-hr-mismatch.rs:5:5
    |
 LL |     become bar();
-   |     ^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^ one type is more general than the other
    |
-   = note: `become` requires caller and callee to have matching signatures
-   = note: caller signature: `fn() -> for<'a> fn(&'a i32)`
-   = note: callee signature: `fn() -> fn(&'static i32)`
+   = note: expected fn pointer `for<'a> fn(&'a _)`
+              found fn pointer `fn(&'static _)`
 
 error: aborting due to 1 previous error
 
+For more information about this error, try `rustc --explain E0308`.

tests/ui/explicit-tail-calls/rpit.stderr → tests/ui/explicit-tail-calls/rpit.current.stderr

@@ -1,5 +1,5 @@
 error: mismatched signatures
-  --> $DIR/rpit.rs:14:5
+  --> $DIR/rpit.rs:19:5
    |
 LL |     become foo(x, y);
    |     ^^^^^^^^^^^^^^^^

tests/ui/explicit-tail-calls/rpit.rs

@@ -1,3 +1,8 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
 #![feature(explicit_tail_calls)]
 #![expect(incomplete_features)]
 
@@ -12,7 +17,7 @@ fn foo(x: u32, y: u32) -> u32 {
 
 fn bar(x: u32, y: u32) -> impl ToString {
     become foo(x, y);
-    //~^ ERROR mismatched signatures
+    //[current]~^ ERROR mismatched signatures
 }
 
 fn main() {

tests/ui/explicit-tail-calls/safety.rs

@@ -0,0 +1,19 @@
+// Checks that you can tail call functions with different unsafety
+//
+//@ check-pass
+#![feature(explicit_tail_calls)]
+#![expect(incomplete_features)]
+
+fn a() {
+    unsafe {
+        become b();
+    }
+}
+
+unsafe fn b() {
+    become c();
+}
+
+fn c() {}
+
+fn main() {}

tests/ui/explicit-tail-calls/subtyping.rs

@@ -0,0 +1,28 @@
+// Check that signature comparison for tail calls allows subtyping.
+//
+//@ check-pass
+#![expect(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+fn f<'short>(
+    a: &'static (),
+    b: &'short (),
+    c: fn(&'static ()),
+    d: for<'a> fn(&'a ()),
+) -> (&'short (), fn(&'static ()), for<'a> fn(&'a ())) {
+    become g(b, a, d, c);
+}
+
+fn g<'short>(
+    // swapped short/static
+    a: &'short (),
+    b: &'static (),
+    // swapped binder/non binder
+    c: for<'a> fn(&'a ()),
+    d: fn(&'static ()),
+    // 'short=>'static; non binder=>binder
+) -> (&'static (), for<'a> fn(&'a ()), for<'a> fn(&'a ())) {
+    (b, c, c)
+}
+
+fn main() {}

tests/ui/explicit-tail-calls/tail-call-with-projection-arg.rs

@@ -0,0 +1,21 @@
+// Check that tail call checks correctly handle projections in signatures.
+// (this was briefly broken while working on #156007)
+//
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@ check-pass
+#![expect(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+trait Trait {
+    type Assoc;
+}
+
+fn a<T: Trait>(_: T::Assoc) {}
+
+fn b<T: Trait>(x: T::Assoc) {
+    become a::<T>(x)
+}
+
+fn main() {}