more extensive dead cases for more kinds of dead code

Author: RalfJung

tests/ui/consts/monomorphization/dead-code-in-dead-drop.no-opt.stderr

@@ -0,0 +1,14 @@
+error[E0080]: evaluation of `Fail::<i32>::C` failed
+  --> $DIR/dead-code-in-dead-drop.rs:9:19
+   |
+LL |     const C: () = panic!();
+   |                   ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/dead-code-in-dead-drop.rs:9:19
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: the above error was encountered while instantiating `fn <Fail<i32> as std::ops::Drop>::drop`
+  --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

tests/ui/consts/monomorphization/dead-code-in-dead-drop.opt.stderr

@@ -0,0 +1,14 @@
+error[E0080]: evaluation of `Fail::<i32>::C` failed
+  --> $DIR/dead-code-in-dead-drop.rs:9:19
+   |
+LL |     const C: () = panic!();
+   |                   ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/dead-code-in-dead-drop.rs:9:19
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: the above error was encountered while instantiating `fn <Fail<i32> as std::ops::Drop>::drop`
+  --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

tests/ui/consts/monomorphization/dead-code-in-dead-drop.rs

@@ -0,0 +1,30 @@
+//@revisions: opt no-opt
+//@ build-fail
+//@[opt] compile-flags: -O
+//! Make sure we detect erroneous constants post-monomorphization even when they are unused. This is
+//! crucial, people rely on it for soundness. (https://github.com/rust-lang/rust/issues/112090)
+
+struct Fail<T>(T);
+impl<T> Fail<T> {
+    const C: () = panic!(); //~ERROR evaluation of `Fail::<i32>::C` failed
+}
+
+// This function is not actually called, but is mentioned implicitly as destructor in dead code in a
+// function that is called. Make sure we still find this error.
+impl<T> Drop for Fail<T> {
+    fn drop(&mut self) {
+        let _ = Fail::<T>::C;
+    }
+}
+
+#[inline(never)]
+fn called<T>(x: T) {
+    if false {
+        let v = Fail(x);
+        drop(v);
+    }
+}
+
+pub fn main() {
+    called::<i32>(0);
+}

tests/ui/consts/monomorphization/dead-code-in-dead-fn.rs

@@ -9,8 +9,8 @@ impl<T> Fail<T> {
     const C: () = panic!(); //~ERROR evaluation of `Fail::<i32>::C` failed
 }
 
-// This function is not actually called, but it is mentioned in a function that is called.
-// Make sure we still find this error.
+// This function is not actually called, but it is mentioned in dead code in a function that is
+// called. Make sure we still find this error.
 #[inline(never)]
 fn not_called<T>() {
     let _ = Fail::<T>::C;

tests/ui/consts/monomorphization/dead-code-in-dead-vtable.no-opt.stderr

@@ -0,0 +1,17 @@
+error[E0080]: evaluation of `Fail::<i32>::C` failed
+  --> $DIR/dead-code-in-dead-vtable.rs:9:19
+   |
+LL |     const C: () = panic!();
+   |                   ^^^^^^^^ the evaluated program panicked at 'explicit panic', $DIR/dead-code-in-dead-vtable.rs:9:19
+   |
+   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+note: the above error was encountered while instantiating `fn <std::vec::Vec<i32> as MyTrait>::not_called`
+  --> $DIR/dead-code-in-dead-vtable.rs:28:40
+   |
+LL |         let gen_vtable: &dyn MyTrait = &v;
+   |                                        ^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

tests/ui/consts/monomorphization/dead-code-in-dead-vtable.rs

@@ -0,0 +1,34 @@
+//@revisions: opt no-opt
+//@ build-fail
+//@[opt] compile-flags: -O
+//! Make sure we detect erroneous constants post-monomorphization even when they are unused. This is
+//! crucial, people rely on it for soundness. (https://github.com/rust-lang/rust/issues/112090)
+
+struct Fail<T>(T);
+impl<T> Fail<T> {
+    const C: () = panic!(); //~ERROR evaluation of `Fail::<i32>::C` failed
+}
+
+trait MyTrait {
+    fn not_called(&self);
+}
+
+// This function is not actually called, but it is mentioned in a vtable in a function that is
+// called. Make sure we still find this error.
+impl<T> MyTrait for Vec<T> {
+    fn not_called(&self) {
+        let _ = Fail::<T>::C;
+    }
+}
+
+#[inline(never)]
+fn called<T>() {
+    if false {
+        let v: Vec<T> = Vec::new();
+        let gen_vtable: &dyn MyTrait = &v;
+    }
+}
+
+pub fn main() {
+    called::<i32>();
+}