Rollup of 4 pull requests

src/liballoc/rc.rs

@@ -1832,8 +1832,9 @@ impl<T: ?Sized> Weak<T> {
         }
     }
 
-    /// Returns `true` if the two `Weak`s point to the same value (not just values
-    /// that compare as equal).
+    /// Returns `true` if the two `Weak`s point to the same value (not just
+    /// values that compare as equal), or if both don't point to any value
+    /// (because they were created with `Weak::new()`).
     ///
     /// # Notes
     ///
@@ -1843,7 +1844,6 @@ impl<T: ?Sized> Weak<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_ptr_eq)]
     /// use std::rc::Rc;
     ///
     /// let first_rc = Rc::new(5);
@@ -1861,7 +1861,6 @@ impl<T: ?Sized> Weak<T> {
     /// Comparing `Weak::new`.
     ///
     /// ```
-    /// #![feature(weak_ptr_eq)]
     /// use std::rc::{Rc, Weak};
     ///
     /// let first = Weak::new();
@@ -1873,7 +1872,7 @@ impl<T: ?Sized> Weak<T> {
     /// assert!(!first.ptr_eq(&third));
     /// ```
     #[inline]
-    #[unstable(feature = "weak_ptr_eq", issue = "55981")]
+    #[stable(feature = "weak_ptr_eq", since = "1.39.0")]
     pub fn ptr_eq(&self, other: &Self) -> bool {
         self.ptr.as_ptr() == other.ptr.as_ptr()
     }

src/liballoc/sync.rs

@@ -1550,19 +1550,18 @@ impl<T: ?Sized> Weak<T> {
         }
     }
 
-    /// Returns `true` if the two `Weak`s point to the same value (not just values
-    /// that compare as equal).
+    /// Returns `true` if the two `Weak`s point to the same value (not just
+    /// values that compare as equal), or if both don't point to any value
+    /// (because they were created with `Weak::new()`).
     ///
     /// # Notes
     ///
     /// Since this compares pointers it means that `Weak::new()` will equal each
     /// other, even though they don't point to any value.
     ///
-    ///
     /// # Examples
     ///
     /// ```
-    /// #![feature(weak_ptr_eq)]
     /// use std::sync::Arc;
     ///
     /// let first_rc = Arc::new(5);
@@ -1580,7 +1579,6 @@ impl<T: ?Sized> Weak<T> {
     /// Comparing `Weak::new`.
     ///
     /// ```
-    /// #![feature(weak_ptr_eq)]
     /// use std::sync::{Arc, Weak};
     ///
     /// let first = Weak::new();
@@ -1592,7 +1590,7 @@ impl<T: ?Sized> Weak<T> {
     /// assert!(!first.ptr_eq(&third));
     /// ```
     #[inline]
-    #[unstable(feature = "weak_ptr_eq", issue = "55981")]
+    #[stable(feature = "weak_ptr_eq", since = "1.39.0")]
     pub fn ptr_eq(&self, other: &Self) -> bool {
         self.ptr.as_ptr() == other.ptr.as_ptr()
     }

src/librustc/middle/entry.rs

@@ -16,16 +16,16 @@ struct EntryContext<'a, 'tcx> {
 
     map: &'a hir_map::Map<'tcx>,
 
-    /// The top-level function called 'main'.
+    /// The top-level function called `main`.
     main_fn: Option<(HirId, Span)>,
 
-    /// The function that has attribute named 'main'.
+    /// The function that has attribute named `main`.
     attr_main_fn: Option<(HirId, Span)>,
 
     /// The function that has the attribute 'start' on it.
     start_fn: Option<(HirId, Span)>,
 
-    /// The functions that one might think are 'main' but aren't, e.g.
+    /// The functions that one might think are `main` but aren't, e.g.
     /// main functions not defined at the top level. For diagnostics.
     non_main_fns: Vec<(HirId, Span)> ,
 }
@@ -88,7 +88,7 @@ fn entry_point_type(item: &Item, at_root: bool) -> EntryPointType {
                 EntryPointType::MainAttr
             } else if item.ident.name == sym::main {
                 if at_root {
-                    // This is a top-level function so can be 'main'.
+                    // This is a top-level function so can be `main`.
                     EntryPointType::MainNamed
                 } else {
                     EntryPointType::OtherMain
@@ -109,7 +109,7 @@ fn find_item(item: &Item, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
                 ctxt.main_fn = Some((item.hir_id, item.span));
             } else {
                 span_err!(ctxt.session, item.span, E0136,
-                          "multiple 'main' functions");
+                          "multiple `main` functions");
             }
         },
         EntryPointType::OtherMain => {
@@ -130,7 +130,7 @@ fn find_item(item: &Item, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
             if ctxt.start_fn.is_none() {
                 ctxt.start_fn = Some((item.hir_id, item.span));
             } else {
-                struct_span_err!(ctxt.session, item.span, E0138, "multiple 'start' functions")
+                struct_span_err!(ctxt.session, item.span, E0138, "multiple `start` functions")
                     .span_label(ctxt.start_fn.unwrap().1, "previous `start` function here")
                     .span_label(item.span, "multiple `start` functions")
                     .emit();
@@ -148,34 +148,48 @@ fn configure_main(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) -> Option<(De
     } else if let Some((hir_id, _)) = visitor.main_fn {
         Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
     } else {
-        // There is no main function.
-        let mut err = struct_err!(tcx.sess, E0601,
-            "`main` function not found in crate `{}`", tcx.crate_name(LOCAL_CRATE));
-        if !visitor.non_main_fns.is_empty() {
-            // There were some functions named 'main' though. Try to give the user a hint.
-            err.note("the main function must be defined at the crate level \
-                      but you have one or more functions named 'main' that are not \
-                      defined at the crate level. Either move the definition or \
-                      attach the `#[main]` attribute to override this behavior.");
-            for &(_, span) in &visitor.non_main_fns {
-                err.span_note(span, "here is a function named 'main'");
-            }
-            err.emit();
-        } else {
-            if let Some(ref filename) = tcx.sess.local_crate_source_file {
-                err.note(&format!("consider adding a `main` function to `{}`", filename.display()));
-            }
-            if tcx.sess.teach(&err.get_code().unwrap()) {
-                err.note("If you don't know the basics of Rust, you can go look to the Rust Book \
-                          to get started: https://doc.rust-lang.org/book/");
-            }
-            err.emit();
-        }
-
+        no_main_err(tcx, visitor);
         None
     }
 }
 
+fn no_main_err(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) {
+    // There is no main function.
+    let mut err = struct_err!(tcx.sess, E0601,
+        "`main` function not found in crate `{}`", tcx.crate_name(LOCAL_CRATE));
+    let filename = &tcx.sess.local_crate_source_file;
+    let note = if !visitor.non_main_fns.is_empty() {
+        for &(_, span) in &visitor.non_main_fns {
+            err.span_note(span, "here is a function named `main`");
+        }
+        err.note("you have one or more functions named `main` not defined at the crate level");
+        err.help("either move the `main` function definitions or attach the `#[main]` attribute \
+                  to one of them");
+        // There were some functions named `main` though. Try to give the user a hint.
+        format!("the main function must be defined at the crate level{}",
+                 filename.as_ref().map(|f| format!(" (in `{}`)", f.display())).unwrap_or_default())
+    } else if let Some(filename) = filename {
+        format!("consider adding a `main` function to `{}`", filename.display())
+    } else {
+        String::from("consider adding a `main` function at the crate level")
+    };
+    let sp = tcx.hir().krate().span;
+    // The file may be empty, which leads to the diagnostic machinery not emitting this
+    // note. This is a relatively simple way to detect that case and emit a span-less
+    // note instead.
+    if let Ok(_) = tcx.sess.source_map().lookup_line(sp.lo()) {
+        err.set_span(sp);
+        err.span_label(sp, &note);
+    } else {
+        err.note(&note);
+    }
+    if tcx.sess.teach(&err.get_code().unwrap()) {
+        err.note("If you don't know the basics of Rust, you can go look to the Rust Book \
+                  to get started: https://doc.rust-lang.org/book/");
+    }
+    err.emit();
+}
+
 pub fn find_entry_point(tcx: TyCtxt<'_>) -> Option<(DefId, EntryFnType)> {
     tcx.entry_fn(LOCAL_CRATE)
 }

src/librustc/mir/interpret/error.rs

@@ -393,6 +393,7 @@ pub enum UnsupportedOpInfo<'tcx> {
     InvalidPointerMath,
     ReadUndefBytes(Size),
     DeadLocal,
+    UninitializedLocal,
     InvalidBoolOp(mir::BinOp),
     UnimplementedTraitSelection,
     CalledClosureAsFunction,
@@ -420,6 +421,7 @@ pub enum UnsupportedOpInfo<'tcx> {
     HeapAllocNonPowerOfTwoAlignment(u64),
     ReadFromReturnPointer,
     PathNotFound(Vec<String>),
+    ReadOfStaticInConst,
 }
 
 impl fmt::Debug for UnsupportedOpInfo<'tcx> {
@@ -491,6 +493,8 @@ impl fmt::Debug for UnsupportedOpInfo<'tcx> {
                     addresses, e.g., comparing pointers into different allocations"),
             DeadLocal =>
                 write!(f, "tried to access a dead local variable"),
+            UninitializedLocal =>
+                write!(f, "tried to access an uninitialized local variable"),
             DerefFunctionPointer =>
                 write!(f, "tried to dereference a function pointer"),
             ExecuteMemory =>
@@ -532,6 +536,8 @@ impl fmt::Debug for UnsupportedOpInfo<'tcx> {
                     not a power of two"),
             Unsupported(ref msg) =>
                 write!(f, "{}", msg),
+            ReadOfStaticInConst =>
+                write!(f, "tried to read from a static during const evaluation"),
         }
     }
 }

src/librustc_mir/interpret/eval_context.rs

@@ -136,7 +136,8 @@ impl<'tcx, Tag: Copy + 'static> LocalState<'tcx, Tag> {
         match self.value {
             LocalValue::Dead => throw_unsup!(DeadLocal),
             LocalValue::Uninitialized =>
-                bug!("The type checker should prevent reading from a never-written local"),
+                // this is reachable from ConstProp
+                throw_unsup!(UninitializedLocal),
             LocalValue::Live(val) => Ok(val),
         }
     }

src/librustc_mir/interpret/operand.rs

@@ -470,7 +470,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
     // Evaluate a place with the goal of reading from it.  This lets us sometimes
     // avoid allocations.
-    pub(super) fn eval_place_to_op(
+    pub fn eval_place_to_op(
         &self,
         place: &mir::Place<'tcx>,
         layout: Option<TyLayout<'tcx>>,

src/librustc_mir/interpret/place.rs

@@ -595,6 +595,14 @@ where
             }
 
             StaticKind::Static => {
+                //if the first frame on the stack isn't a static item, then we shouldn't
+                //eval any static places
+                if let ty::InstanceDef::Item(item_def_id) = self.stack[0].instance.def {
+                    if !self.tcx.is_static(item_def_id) {
+                        trace!("eval_static_to_mplace: can't eval static in constant");
+                        throw_unsup!(ReadOfStaticInConst);
+                    }
+                }
                 let ty = place_static.ty;
                 assert!(!ty.needs_subst());
                 let layout = self.layout_of(ty)?;

src/librustc_mir/interpret/step.rs

@@ -132,7 +132,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     ///
     /// There is no separate `eval_rvalue` function. Instead, the code for handling each rvalue
     /// type writes its results directly into the memory specified by the place.
-    fn eval_rvalue_into_place(
+    pub fn eval_rvalue_into_place(
         &mut self,
         rvalue: &mir::Rvalue<'tcx>,
         place: &mir::Place<'tcx>,