Auto merge of #71853 - Dylan-DPC:rollup-4qi6ry9, r=Dylan-DPC

Rollup of 4 pull requests

Successful merges:

 - #71398 (Add `RefCell::take`)
 - #71663 (Fix exceeding bitshifts not emitting for assoc. consts (properly this time, I swear!))
 - #71726 (Suggest deref when coercing `ty::Ref` to `ty::RawPtr` with arbitrary mutability)
 - #71808 (Add long error explanation for E0539)

Failed merges:

r? @ghost

src/libcore/cell.rs

@@ -1023,6 +1023,31 @@ impl<T: ?Sized> RefCell<T> {
     }
 }
 
+impl<T: Default> RefCell<T> {
+    /// Takes the wrapped value, leaving `Default::default()` in its place.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is currently borrowed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(refcell_take)]
+    /// use std::cell::RefCell;
+    ///
+    /// let c = RefCell::new(5);
+    /// let five = c.take();
+    ///
+    /// assert_eq!(five, 5);
+    /// assert_eq!(c.into_inner(), 0);
+    /// ```
+    #[unstable(feature = "refcell_take", issue = "71395")]
+    pub fn take(&self) -> T {
+        self.replace(Default::default())
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: ?Sized> Send for RefCell<T> where T: Send {}
 

src/librustc_error_codes/error_codes.rs

@@ -281,6 +281,7 @@ E0535: include_str!("./error_codes/E0535.md"),
 E0536: include_str!("./error_codes/E0536.md"),
 E0537: include_str!("./error_codes/E0537.md"),
 E0538: include_str!("./error_codes/E0538.md"),
+E0539: include_str!("./error_codes/E0539.md"),
 E0541: include_str!("./error_codes/E0541.md"),
 E0550: include_str!("./error_codes/E0550.md"),
 E0551: include_str!("./error_codes/E0551.md"),
@@ -570,7 +571,6 @@ E0753: include_str!("./error_codes/E0753.md"),
     E0521, // borrowed data escapes outside of closure
     E0523,
 //  E0526, // shuffle indices are not constant
-    E0539, // incorrect meta item
     E0540, // multiple rustc_deprecated attributes
     E0542, // missing 'since'
     E0543, // missing 'reason'

src/librustc_error_codes/error_codes/E0539.md

@@ -0,0 +1,48 @@
+An invalid meta-item was used inside an attribute.
+
+Erroneous code example:
+
+```compile_fail,E0539
+#![feature(staged_api)]
+#![stable(since = "1.0.0", feature = "test")]
+
+#[rustc_deprecated(reason)] // error!
+#[unstable(feature = "deprecated_fn", issue = "123")]
+fn deprecated() {}
+
+#[unstable(feature = "unstable_struct", issue)] // error!
+struct Unstable;
+
+#[rustc_const_unstable(feature)] // error!
+const fn unstable_fn() {}
+
+#[stable(feature = "stable_struct", since)] // error!
+struct Stable;
+
+#[rustc_const_stable(feature)] // error!
+const fn stable_fn() {}
+```
+
+Meta items are the key-value pairs inside of an attribute.
+To fix these issues you need to give required key-value pairs.
+
+```
+#![feature(staged_api)]
+#![stable(since = "1.0.0", feature = "test")]
+
+#[rustc_deprecated(since = "1.39.0", reason = "reason")] // ok!
+#[unstable(feature = "deprecated_fn", issue = "123")]
+fn deprecated() {}
+
+#[unstable(feature = "unstable_struct", issue = "123")] // ok!
+struct Unstable;
+
+#[rustc_const_unstable(feature = "unstable_fn", issue = "124")] // ok!
+const fn unstable_fn() {}
+
+#[stable(feature = "stable_struct", since = "1.39.0")] // ok!
+struct Stable;
+
+#[rustc_const_stable(feature = "stable_fn", since = "1.39.0")] // ok!
+const fn stable_fn() {}
+```

src/librustc_mir/interpret/validity.rs

@@ -11,6 +11,7 @@ use std::ops::RangeInclusive;
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
+use rustc_middle::mir::interpret::{InterpError, InterpErrorInfo};
 use rustc_middle::ty;
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_span::symbol::{sym, Symbol};
@@ -24,43 +25,71 @@ use super::{
 };
 
 macro_rules! throw_validation_failure {
-    ($what:expr, $where:expr, $details:expr) => {{
-        let mut msg = format!("encountered {}", $what);
-        let where_ = &$where;
-        if !where_.is_empty() {
-            msg.push_str(" at ");
-            write_path(&mut msg, where_);
-        }
-        write!(&mut msg, ", but expected {}", $details).unwrap();
-        throw_ub!(ValidationFailure(msg))
-    }};
-    ($what:expr, $where:expr) => {{
+    ($what:expr, $where:expr $(, $expected:expr )?) => {{
         let mut msg = format!("encountered {}", $what);
         let where_ = &$where;
         if !where_.is_empty() {
             msg.push_str(" at ");
             write_path(&mut msg, where_);
         }
+        $( write!(&mut msg, ", but expected {}", $expected).unwrap(); )?
         throw_ub!(ValidationFailure(msg))
     }};
 }
 
+/// Returns a validation failure for any Err value of $e.
+// FIXME: Replace all usages of try_validation! with try_validation_pat!.
 macro_rules! try_validation {
-    ($e:expr, $what:expr, $where:expr, $details:expr) => {{
-        match $e {
-            Ok(x) => x,
-            // We re-throw the error, so we are okay with allocation:
-            // this can only slow down builds that fail anyway.
-            Err(_) => throw_validation_failure!($what, $where, $details),
-        }
+    ($e:expr, $what:expr, $where:expr $(, $expected:expr )?) => {{
+        try_validation_pat!($e, $where, {
+            _ => { "{}", $what } $( expected { "{}", $expected } )?,
+        })
     }};
-
-    ($e:expr, $what:expr, $where:expr) => {{
+}
+/// Like try_validation, but will throw a validation error if any of the patterns in $p are
+/// matched. Other errors are passed back to the caller, unchanged. This lets you use the patterns
+/// as a kind of validation blacklist:
+///
+/// ```
+/// let v = try_validation_pat!(some_fn(), some_path, {
+///     Foo | Bar | Baz => { "some failure" },
+/// });
+/// // Failures that match $p are thrown up as validation errors, but other errors are passed back
+/// // unchanged.
+/// ```
+///
+/// An additional expected parameter can also be added to the failure message:
+///
+/// ```
+/// let v = try_validation_pat!(some_fn(), some_path, {
+///     Foo | Bar | Baz => { "some failure" } expected { "something that wasn't a failure" },
+/// });
+/// ```
+///
+/// An additional nicety is that both parameters actually take format args, so you can just write
+/// the format string in directly:
+///
+/// ```
+/// let v = try_validation_pat!(some_fn(), some_path, {
+///     Foo | Bar | Baz => { "{:?}", some_failure } expected { "{}", expected_value },
+/// });
+/// ```
+///
+macro_rules! try_validation_pat {
+    ($e:expr, $where:expr, { $( $p:pat )|+ =>
+        { $( $what_fmt:expr ),+ } $( expected { $( $expected_fmt:expr ),+ } )? $( , )?}) => {{
         match $e {
             Ok(x) => x,
-            // We re-throw the error, so we are okay with allocation:
-            // this can only slow down builds that fail anyway.
-            Err(_) => throw_validation_failure!($what, $where),
+            // We catch the error and turn it into a validation failure. We are okay with
+            // allocation here as this can only slow down builds that fail anyway.
+            $( Err(InterpErrorInfo { kind: $p, .. }) )|+ =>
+                throw_validation_failure!(
+                    format_args!($( $what_fmt ),+),
+                    $where
+                    $(, format_args!($( $expected_fmt ),+))?
+                ),
+            #[allow(unreachable_patterns)]
+            Err(e) => Err::<!, _>(e)?,
         }
     }};
 }
@@ -492,11 +521,9 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 // We are conservative with undef for integers, but try to
                 // actually enforce the strict rules for raw pointers (mostly because
                 // that lets us re-use `ref_to_mplace`).
-                let place = try_validation!(
-                    self.ecx.ref_to_mplace(self.ecx.read_immediate(value)?),
-                    "uninitialized raw pointer",
-                    self.path
-                );
+                let place = try_validation_pat!(self.ecx.ref_to_mplace(self.ecx.read_immediate(value)?), self.path, {
+                    err_ub!(InvalidUndefBytes(..)) => { "uninitialized raw pointer" },
+                });
                 if place.layout.is_unsized() {
                     self.check_wide_ptr_meta(place.meta, place.layout)?;
                 }
@@ -800,7 +827,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
 
                                 throw_validation_failure!("uninitialized bytes", self.path)
                             }
-                            // Other errors shouldn't be possible
+                            // Propagate upwards (that will also check for unexpected errors).
                             _ => return Err(err),
                         }
                     }
@@ -843,9 +870,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         // Run it.
         match visitor.visit_value(op) {
             Ok(()) => Ok(()),
-            // We should only get validation errors here. Avoid other errors as
-            // those do not show *where* in the value the issue lies.
+            // Pass through validation failures.
             Err(err) if matches!(err.kind, err_ub!(ValidationFailure { .. })) => Err(err),
+            // Also pass through InvalidProgram, those just indicate that we could not
+            // validate and each caller will know best what to do with them.
+            Err(err) if matches!(err.kind, InterpError::InvalidProgram(_)) => Err(err),
+            // Avoid other errors as those do not show *where* in the value the issue lies.
             Err(err) => bug!("Unexpected error during validation: {}", err),
         }
     }

src/librustc_mir/transform/const_prop.rs

@@ -549,11 +549,6 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             return None;
         }
 
-        // FIXME we need to revisit this for #67176
-        if rvalue.needs_subst() {
-            return None;
-        }
-
         // Perform any special handling for specific Rvalue types.
         // Generally, checks here fall into one of two categories:
         //   1. Additional checking to provide useful lints to the user
@@ -594,6 +589,11 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             _ => {}
         }
 
+        // FIXME we need to revisit this for #67176
+        if rvalue.needs_subst() {
+            return None;
+        }
+
         self.use_ecx(|this| {
             trace!("calling eval_rvalue_into_place(rvalue = {:?}, place = {:?})", rvalue, place);
             this.ecx.eval_rvalue_into_place(rvalue, place)?;

src/librustc_typeck/check/coercion.rs

@@ -74,7 +74,7 @@ use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
 use smallvec::{smallvec, SmallVec};
 use std::ops::Deref;
 
-pub struct Coerce<'a, 'tcx> {
+struct Coerce<'a, 'tcx> {
     fcx: &'a FnCtxt<'a, 'tcx>,
     cause: ObligationCause<'tcx>,
     use_lub: bool,
@@ -126,15 +126,15 @@ fn success<'tcx>(
 }
 
 impl<'f, 'tcx> Coerce<'f, 'tcx> {
-    pub fn new(
+    fn new(
         fcx: &'f FnCtxt<'f, 'tcx>,
         cause: ObligationCause<'tcx>,
         allow_two_phase: AllowTwoPhase,
     ) -> Self {
         Coerce { fcx, cause, allow_two_phase, use_lub: false }
     }
 
-    pub fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> {
+    fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> {
         debug!("unify(a: {:?}, b: {:?}, use_lub: {})", a, b, self.use_lub);
         self.commit_if_ok(|_| {
             if self.use_lub {
@@ -841,6 +841,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.probe(|_| coerce.coerce(source, target)).is_ok()
     }
 
+    /// Given a type and a target type, this function will calculate and return
+    /// how many dereference steps needed to achieve `expr_ty <: target`. If
+    /// it's not possible, return `None`.
+    pub fn deref_steps(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> Option<usize> {
+        let cause = self.cause(rustc_span::DUMMY_SP, ObligationCauseCode::ExprAssignable);
+        // We don't ever need two-phase here since we throw out the result of the coercion
+        let coerce = Coerce::new(self, cause, AllowTwoPhase::No);
+        coerce
+            .autoderef(rustc_span::DUMMY_SP, expr_ty)
+            .find_map(|(ty, steps)| coerce.unify(ty, target).ok().map(|_| steps))
+    }
+
     /// Given some expressions, their known unified type and another expression,
     /// tries to unify the types, potentially inserting coercions on any of the
     /// provided expressions and returns their LUB (aka "common supertype").