Rollup merge of rust-lang#55262 - oli-obk:dangling_alloc_id_ice, r=RalfJung

Change the ICE from rust-lang#55223 to a hard error

cc @SimonSapin

r? @RalfJung

Author: kennytm

src/librustc_mir/interpret/memory.rs

@@ -732,6 +732,11 @@ where
             if self.alloc_map.contains_key(&alloc) {
                 // Not yet interned, so proceed recursively
                 self.intern_static(alloc, mutability)?;
+            } else if self.dead_alloc_map.contains_key(&alloc) {
+                // dangling pointer
+                return err!(ValidationFailure(
+                    "encountered dangling pointer in final constant".into(),
+                ))
             }
         }
         Ok(())

src/test/ui/consts/dangling-alloc-id-ice-2.nll.stderr

@@ -0,0 +1,30 @@
+warning[E0716]: temporary value dropped while borrowed
+  --> $DIR/dangling-alloc-id-ice-2.rs:5:28
+   |
+LL |    static MAP: Slice = Slice(&[
+   |   ___________________________-^
+   |  |___________________________|
+   | ||
+LL | ||     b"CloseEvent" as &'static [u8],
+LL | || ]);
+   | || -- temporary value is freed at the end of this statement
+   | ||_|
+   | |__creates a temporary which is freed while still in use
+   |    cast requires that borrow lasts for `'static`
+   |
+   = warning: This error has been downgraded to a warning for backwards compatibility with previous releases.
+           It represents potential unsoundness in your code.
+           This warning will become a hard error in the future.
+
+error[E0080]: could not evaluate static initializer
+  --> $DIR/dangling-alloc-id-ice-2.rs:5:1
+   |
+LL | / static MAP: Slice = Slice(&[
+LL | |     b"CloseEvent" as &'static [u8],
+LL | | ]);
+   | |___^ type validation failed: encountered dangling pointer in final constant
+
+error: aborting due to previous error
+
+Some errors occurred: E0080, E0716.
+For more information about an error, try `rustc --explain E0080`.

src/test/ui/consts/dangling-alloc-id-ice-2.rs

@@ -0,0 +1,10 @@
+// FIXME(#55223) this is just a reproduction test showing the wrong behavior
+
+struct Slice(&'static [&'static [u8]]);
+
+static MAP: Slice = Slice(&[
+    b"CloseEvent" as &'static [u8],
+]);
+
+
+fn main() {}

src/test/ui/consts/dangling-alloc-id-ice-2.stderr

@@ -0,0 +1,11 @@
+error[E0080]: could not evaluate static initializer
+  --> $DIR/dangling-alloc-id-ice-2.rs:5:1
+   |
+LL | / static MAP: Slice = Slice(&[
+LL | |     b"CloseEvent" as &'static [u8],
+LL | | ]);
+   | |___^ type validation failed: encountered dangling pointer in final constant
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/dangling-alloc-id-ice.rs

@@ -0,0 +1,15 @@
+// https://github.com/rust-lang/rust/issues/55223
+
+#![feature(const_let)]
+
+union Foo<'a> {
+    y: &'a (),
+    long_live_the_unit: &'static (),
+}
+
+const FOO: &() = { //~ ERROR this constant cannot be used
+    let y = ();
+    unsafe { Foo { y: &y }.long_live_the_unit }
+};
+
+fn main() {}

src/test/ui/consts/dangling-alloc-id-ice.stderr

@@ -0,0 +1,13 @@
+error: this constant cannot be used
+  --> $DIR/dangling-alloc-id-ice.rs:10:1
+   |
+LL | / const FOO: &() = { //~ ERROR this constant cannot be used
+LL | |     let y = ();
+LL | |     unsafe { Foo { y: &y }.long_live_the_unit }
+LL | | };
+   | |__^ type validation failed: encountered dangling pointer in final constant
+   |
+   = note: #[deny(const_err)] on by default
+
+error: aborting due to previous error
+