Stop promoting all the things

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -216,12 +216,6 @@ impl<'tcx> Validator<'_, 'tcx> {
                     return Err(Unpromotable);
                 }
 
-                // We cannot promote things that need dropping, since the promoted value
-                // would not get dropped.
-                if self.qualif_local::<qualifs::NeedsDrop>(place.local) {
-                    return Err(Unpromotable);
-                }
-
                 Ok(())
             }
             _ => bug!(),
@@ -262,13 +256,17 @@ impl<'tcx> Validator<'_, 'tcx> {
                 }
             }
         } else {
-            let span = self.body.local_decls[local].source_info.span;
-            span_bug!(span, "{:?} not promotable, qualif_local shouldn't have been called", local);
+            false
         }
     }
 
     fn validate_local(&mut self, local: Local) -> Result<(), Unpromotable> {
         if let TempState::Defined { location: loc, uses, valid } = self.temps[local] {
+            // We cannot promote things that need dropping, since the promoted value
+            // would not get dropped.
+            if self.qualif_local::<qualifs::NeedsDrop>(local) {
+                return Err(Unpromotable);
+            }
             valid.or_else(|_| {
                 let ok = {
                     let block = &self.body[loc.block];

src/test/ui/consts/promoted_const_call.rs

@@ -0,0 +1,19 @@
+#![feature(const_mut_refs)]
+#![feature(const_trait_impl)]
+struct Panic;
+impl const Drop for Panic { fn drop(&mut self) { panic!(); } }
+pub const fn id<T>(x: T) -> T { x }
+pub const C: () = {
+    let _: &'static _ = &id(&Panic);
+    //~^ ERROR: temporary value dropped while borrowed
+    //~| ERROR: temporary value dropped while borrowed
+};
+
+fn main() {
+    let _: &'static _ = &id(&Panic);
+    //~^ ERROR: temporary value dropped while borrowed
+    //~| ERROR: temporary value dropped while borrowed
+    let _: &'static _ = &&(Panic, 0).1;
+    //~^ ERROR: temporary value dropped while borrowed
+    //~| ERROR: temporary value dropped while borrowed
+}

src/test/ui/consts/promoted_const_call.stderr

@@ -0,0 +1,65 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call.rs:7:26
+   |
+LL |     let _: &'static _ = &id(&Panic);
+   |            ----------    ^^^^^^^^^^ creates a temporary value 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[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call.rs:7:30
+   |
+LL |     let _: &'static _ = &id(&Panic);
+   |            ----------        ^^^^^ - temporary value is freed at the end of this statement
+   |            |                 |
+   |            |                 creates a temporary value which is freed while still in use
+   |            type annotation requires that borrow lasts for `'static`
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call.rs:13:26
+   |
+LL |     let _: &'static _ = &id(&Panic);
+   |            ----------    ^^^^^^^^^^ creates a temporary value 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[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call.rs:13:30
+   |
+LL |     let _: &'static _ = &id(&Panic);
+   |            ----------        ^^^^^ - temporary value is freed at the end of this statement
+   |            |                 |
+   |            |                 creates a temporary value which is freed while still in use
+   |            type annotation requires that borrow lasts for `'static`
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call.rs:16:26
+   |
+LL |     let _: &'static _ = &&(Panic, 0).1;
+   |            ----------    ^^^^^^^^^^^^^ creates a temporary value 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[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call.rs:16:27
+   |
+LL |     let _: &'static _ = &&(Panic, 0).1;
+   |            ----------     ^^^^^^^^^^ creates a temporary value 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 6 previous errors
+
+For more information about this error, try `rustc --explain E0716`.

src/test/ui/consts/promoted_const_call2.rs

@@ -0,0 +1,14 @@
+#![feature(const_precise_live_drops)]
+pub const fn id<T>(x: T) -> T { x }
+pub const C: () = {
+    let _: &'static _ = &id(&String::new());
+    //~^ ERROR: temporary value dropped while borrowed
+    //~| ERROR: temporary value dropped while borrowed
+    //~| ERROR: destructor of `String` cannot be evaluated at compile-time
+};
+
+fn main() {
+    let _: &'static _ = &id(&String::new());
+    //~^ ERROR: temporary value dropped while borrowed
+    //~| ERROR: temporary value dropped while borrowed
+}

src/test/ui/consts/promoted_const_call2.stderr

@@ -0,0 +1,50 @@
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call2.rs:4:26
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |            ----------    ^^^^^^^^^^^^^^^^^^ creates a temporary value 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[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call2.rs:4:30
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |            ----------        ^^^^^^^^^^^^^ - temporary value is freed at the end of this statement
+   |            |                 |
+   |            |                 creates a temporary value which is freed while still in use
+   |            type annotation requires that borrow lasts for `'static`
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call2.rs:11:26
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |            ----------    ^^^^^^^^^^^^^^^^^^ creates a temporary value 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[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call2.rs:11:30
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |            ----------        ^^^^^^^^^^^^^ - temporary value is freed at the end of this statement
+   |            |                 |
+   |            |                 creates a temporary value which is freed while still in use
+   |            type annotation requires that borrow lasts for `'static`
+
+error[E0493]: destructor of `String` cannot be evaluated at compile-time
+  --> $DIR/promoted_const_call2.rs:4:30
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |                              ^^^^^^^^^^^^^ the destructor for this type cannot be evaluated in constants
+
+error: aborting due to 5 previous errors
+
+Some errors have detailed explanations: E0493, E0716.
+For more information about an error, try `rustc --explain E0493`.

src/test/ui/consts/promoted_const_call3.rs

@@ -0,0 +1,26 @@
+pub const fn id<T>(x: T) -> T { x }
+pub const C: () = {
+    let _: &'static _ = &String::new();
+    //~^ ERROR: destructor of `String` cannot be evaluated at compile-time
+    //~| ERROR: temporary value dropped while borrowed
+
+    let _: &'static _ = &id(&String::new());
+    //~^ ERROR: destructor of `String` cannot be evaluated at compile-time
+    //~| ERROR: temporary value dropped while borrowed
+    //~| ERROR: temporary value dropped while borrowed
+
+    let _: &'static _ = &std::mem::ManuallyDrop::new(String::new());
+    //~^ ERROR: temporary value dropped while borrowed
+};
+
+fn main() {
+    let _: &'static _ = &String::new();
+    //~^ ERROR: temporary value dropped while borrowed
+
+    let _: &'static _ = &id(&String::new());
+    //~^ ERROR: temporary value dropped while borrowed
+    //~| ERROR: temporary value dropped while borrowed
+
+    let _: &'static _ = &std::mem::ManuallyDrop::new(String::new());
+    //~^ ERROR: temporary value dropped while borrowed
+}

src/test/ui/consts/promoted_const_call3.stderr

@@ -0,0 +1,105 @@
+error[E0493]: destructor of `String` cannot be evaluated at compile-time
+  --> $DIR/promoted_const_call3.rs:7:30
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |                              ^^^^^^^^^^^^^ - value is dropped here
+   |                              |
+   |                              the destructor for this type cannot be evaluated in constants
+
+error[E0493]: destructor of `String` cannot be evaluated at compile-time
+  --> $DIR/promoted_const_call3.rs:3:26
+   |
+LL |     let _: &'static _ = &String::new();
+   |                          ^^^^^^^^^^^^^ the destructor for this type cannot be evaluated in constants
+...
+LL | };
+   | - value is dropped here
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call3.rs:3:26
+   |
+LL |     let _: &'static _ = &String::new();
+   |            ----------    ^^^^^^^^^^^^^ creates a temporary value 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[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call3.rs:7:26
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |            ----------    ^^^^^^^^^^^^^^^^^^ creates a temporary value 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[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call3.rs:7:30
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |            ----------        ^^^^^^^^^^^^^ - temporary value is freed at the end of this statement
+   |            |                 |
+   |            |                 creates a temporary value which is freed while still in use
+   |            type annotation requires that borrow lasts for `'static`
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call3.rs:12:26
+   |
+LL |     let _: &'static _ = &std::mem::ManuallyDrop::new(String::new());
+   |            ----------    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
+   |            |
+   |            type annotation requires that borrow lasts for `'static`
+LL |
+LL | };
+   | - temporary value is freed at the end of this statement
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call3.rs:17:26
+   |
+LL |     let _: &'static _ = &String::new();
+   |            ----------    ^^^^^^^^^^^^^ creates a temporary value 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[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call3.rs:20:26
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |            ----------    ^^^^^^^^^^^^^^^^^^ creates a temporary value 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[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call3.rs:20:30
+   |
+LL |     let _: &'static _ = &id(&String::new());
+   |            ----------        ^^^^^^^^^^^^^ - temporary value is freed at the end of this statement
+   |            |                 |
+   |            |                 creates a temporary value which is freed while still in use
+   |            type annotation requires that borrow lasts for `'static`
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/promoted_const_call3.rs:24:26
+   |
+LL |     let _: &'static _ = &std::mem::ManuallyDrop::new(String::new());
+   |            ----------    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary value which is freed while still in use
+   |            |
+   |            type annotation requires that borrow lasts for `'static`
+LL |
+LL | }
+   | - temporary value is freed at the end of this statement
+
+error: aborting due to 10 previous errors
+
+Some errors have detailed explanations: E0493, E0716.
+For more information about an error, try `rustc --explain E0493`.

src/test/ui/consts/promoted_const_call4.rs

@@ -0,0 +1,18 @@
+// run-pass
+
+use std::sync::atomic::*;
+
+static FLAG: AtomicBool = AtomicBool::new(false);
+
+struct NoisyDrop(&'static str);
+impl Drop for NoisyDrop {
+    fn drop(&mut self) {
+        FLAG.store(true, Ordering::SeqCst);
+    }
+}
+fn main() {
+    {
+        let _val = &&(NoisyDrop("drop!"), 0).1;
+    }
+    assert!(FLAG.load(Ordering::SeqCst));
+}

src/test/ui/consts/promoted_const_call5.rs

@@ -0,0 +1,42 @@
+#![feature(rustc_attrs)]
+#![feature(staged_api)]
+#![stable(feature = "a", since = "1.0.0")]
+
+#[rustc_promotable]
+#[stable(feature = "a", since = "1.0.0")]
+#[rustc_const_stable(feature = "a", since = "1.0.0")]
+pub const fn id<T>(x: &'static T) -> &'static T { x }
+
+#[rustc_promotable]
+#[stable(feature = "a", since = "1.0.0")]
+#[rustc_const_stable(feature = "a", since = "1.0.0")]
+pub const fn new_string() -> String {
+    String::new()
+}
+
+#[rustc_promotable]
+#[stable(feature = "a", since = "1.0.0")]
+#[rustc_const_stable(feature = "a", since = "1.0.0")]
+pub const fn new_manually_drop<T>(t: T) -> std::mem::ManuallyDrop<T>  {
+    std::mem::ManuallyDrop::new(t)
+}
+
+
+const C: () = {
+    let _: &'static _ = &id(&new_string());
+    //~^ ERROR destructor of `String` cannot be evaluated at compile-time
+    //~| ERROR: temporary value dropped while borrowed
+    //~| ERROR: temporary value dropped while borrowed
+
+    let _: &'static _ = &new_manually_drop(new_string());
+    //~^ ERROR: temporary value dropped while borrowed
+};
+
+fn main() {
+    let _: &'static _ = &id(&new_string());
+    //~^ ERROR: temporary value dropped while borrowed
+    //~| ERROR: temporary value dropped while borrowed
+
+    let _: &'static _ = &new_manually_drop(new_string());
+    //~^ ERROR: temporary value dropped while borrowed
+}