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authorTomasz Miąsko <tomasz.miasko@gmail.com>2021-10-17 00:00:00 +0000
committerTomasz Miąsko <tomasz.miasko@gmail.com>2021-10-18 21:56:57 +0200
commit915a581bcb3d9b7e1e2ef0da4fbfbae6b1a7fa7f (patch)
tree68eada5eecef18c90f66a77762037c80958d178e /src
parent171cbc01efe103f255f83afa2a70768e1d373edb (diff)
downloadrust-915a581bcb3d9b7e1e2ef0da4fbfbae6b1a7fa7f.tar.gz
rust-915a581bcb3d9b7e1e2ef0da4fbfbae6b1a7fa7f.zip
Do not promote values with const drop that need to be dropped
Changes from #88558 allowed using `~const Drop` in constants by
introducing a new `NeedsNonConstDrop` qualif.

The new qualif was also used for promotion purposes, and allowed
promotion to happen for values that needs to be dropped but which
do have a const drop impl.

Since for promoted the drop implementation is never executed,
this lead to observable change in behaviour. For example:

```rust

struct Panic();

impl const Drop for Panic {
    fn drop(&mut self) {
        panic!();
    }
}

fn main() {
    let _ = &Panic();
}
```

Restore the use of `NeedsDrop` qualif during promotion to avoid the issue.
Diffstat (limited to 'src')
-rw-r--r--src/test/ui/consts/promoted-const-drop.rs15
-rw-r--r--src/test/ui/consts/promoted-const-drop.stderr24
2 files changed, 39 insertions, 0 deletions
diff --git a/src/test/ui/consts/promoted-const-drop.rs b/src/test/ui/consts/promoted-const-drop.rs
new file mode 100644
index 00000000000..c896c011ab6
--- /dev/null
+++ b/src/test/ui/consts/promoted-const-drop.rs
@@ -0,0 +1,15 @@
+#![feature(const_trait_impl)]
+#![feature(const_mut_refs)]
+
+struct A();
+
+impl const Drop for A {
+    fn drop(&mut self) {}
+}
+
+const C: A = A();
+
+fn main() {
+    let _: &'static A = &A(); //~ ERROR temporary value dropped while borrowed
+    let _: &'static [A] = &[C]; //~ ERROR temporary value dropped while borrowed
+}
diff --git a/src/test/ui/consts/promoted-const-drop.stderr b/src/test/ui/consts/promoted-const-drop.stderr
new file mode 100644
index 00000000000..184ba0ea3b3
--- /dev/null
+++ b/src/test/ui/consts/promoted-const-drop.stderr
@@ -0,0 +1,24 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted-const-drop.rs:13:26
+   |
+LL |     let _: &'static A = &A();
+   |            ----------    ^^^ creates a temporary which is freed while still in use
+   |            |
+   |            type annotation requires that borrow lasts for `'static`
+LL |     let _: &'static [A] = &[C];
+LL | }
+   | - temporary value is freed at the end of this statement
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted-const-drop.rs:14:28
+   |
+LL |     let _: &'static [A] = &[C];
+   |            ------------    ^^^ creates a temporary which is freed while still in use
+   |            |
+   |            type annotation requires that borrow lasts for `'static`
+LL | }
+   | - temporary value is freed at the end of this statement
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0716`.