Rollup of 7 pull requests

src/doc/unstable-book/src/SUMMARY.md

@@ -154,6 +154,7 @@
     - [io](library-features/io.md)
     - [ip](library-features/ip.md)
     - [iter_rfind](library-features/iter-rfind.md)
+    - [iterator_step_by](library-features/iterator-step-by.md)
     - [libstd_io_internals](library-features/libstd-io-internals.md)
     - [libstd_sys_internals](library-features/libstd-sys-internals.md)
     - [libstd_thread_internals](library-features/libstd-thread-internals.md)

src/doc/unstable-book/src/library-features/step-trait.md

@@ -1,7 +1,7 @@
 # `step_trait`
 
-The tracking issue for this feature is: [#27741]
+The tracking issue for this feature is: [#42168]
 
-[#27741]: https://github.com/rust-lang/rust/issues/27741
+[#42168]: https://github.com/rust-lang/rust/issues/42168
 
 ------------------------

src/libcore/iter/mod.rs

@@ -309,7 +309,7 @@ pub use self::iterator::Iterator;
 
 #[unstable(feature = "step_trait",
            reason = "likely to be replaced by finer-grained traits",
-           issue = "27741")]
+           issue = "42168")]
 pub use self::range::Step;
 #[unstable(feature = "step_by", reason = "recent addition",
            issue = "27741")]
@@ -520,7 +520,7 @@ impl<I> Iterator for Cycle<I> where I: Clone + Iterator {
 #[unstable(feature = "fused", issue = "35602")]
 impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {}
 
-/// An iterator that steps by n elements every iteration.
+/// An adapter for stepping iterators by a custom amount.
 ///
 /// This `struct` is created by the [`step_by`] method on [`Iterator`]. See
 /// its documentation for more.
@@ -553,8 +553,27 @@ impl<I> Iterator for StepBy<I> where I: Iterator {
             self.iter.nth(self.step)
         }
     }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let inner_hint = self.iter.size_hint();
+
+        if self.first_take {
+            let f = |n| if n == 0 { 0 } else { 1 + (n-1)/(self.step+1) };
+            (f(inner_hint.0), inner_hint.1.map(f))
+        } else {
+            let f = |n| n / (self.step+1);
+            (f(inner_hint.0), inner_hint.1.map(f))
+        }
+    }
 }
 
+// StepBy can only make the iterator shorter, so the len will still fit.
+#[unstable(feature = "iterator_step_by",
+           reason = "unstable replacement of Range::step_by",
+           issue = "27741")]
+impl<I> ExactSizeIterator for StepBy<I> where I: ExactSizeIterator {}
+
 /// An iterator that strings two iterators together.
 ///
 /// This `struct` is created by the [`chain`] method on [`Iterator`]. See its

src/libcore/iter/range.rs

@@ -20,7 +20,7 @@ use super::{FusedIterator, TrustedLen};
 /// two `Step` objects.
 #[unstable(feature = "step_trait",
            reason = "likely to be replaced by finer-grained traits",
-           issue = "27741")]
+           issue = "42168")]
 pub trait Step: PartialOrd + Sized {
     /// Steps `self` if possible.
     fn step(&self, by: &Self) -> Option<Self>;
@@ -55,7 +55,7 @@ macro_rules! step_impl_unsigned {
     ($($t:ty)*) => ($(
         #[unstable(feature = "step_trait",
                    reason = "likely to be replaced by finer-grained traits",
-                   issue = "27741")]
+                   issue = "42168")]
         impl Step for $t {
             #[inline]
             fn step(&self, by: &$t) -> Option<$t> {
@@ -115,7 +115,7 @@ macro_rules! step_impl_signed {
     ($($t:ty)*) => ($(
         #[unstable(feature = "step_trait",
                    reason = "likely to be replaced by finer-grained traits",
-                   issue = "27741")]
+                   issue = "42168")]
         impl Step for $t {
             #[inline]
             fn step(&self, by: &$t) -> Option<$t> {
@@ -187,7 +187,7 @@ macro_rules! step_impl_no_between {
     ($($t:ty)*) => ($(
         #[unstable(feature = "step_trait",
                    reason = "likely to be replaced by finer-grained traits",
-                   issue = "27741")]
+                   issue = "42168")]
         impl Step for $t {
             #[inline]
             fn step(&self, by: &$t) -> Option<$t> {

src/libcore/ops.rs

@@ -153,6 +153,13 @@ use marker::Unsize;
 /// The `Drop` trait is used to run some code when a value goes out of scope.
 /// This is sometimes called a 'destructor'.
 ///
+/// When a value goes out of scope, if it implements this trait, it will have
+/// its `drop` method called. Then any fields the value contains will also
+/// be dropped recursively.
+///
+/// Because of the recursive dropping, you do not need to implement this trait
+/// unless your type needs its own destructor logic.
+///
 /// # Examples
 ///
 /// A trivial implementation of `Drop`. The `drop` method is called when `_x`
@@ -171,6 +178,43 @@ use marker::Unsize;
 ///     let _x = HasDrop;
 /// }
 /// ```
+///
+/// Showing the recursive nature of `Drop`. When `outer` goes out of scope, the
+/// `drop` method will be called first for `Outer`, then for `Inner`. Therefore
+/// `main` prints `Dropping Outer!` and then `Dropping Inner!`.
+///
+/// ```
+/// struct Inner;
+/// struct Outer(Inner);
+///
+/// impl Drop for Inner {
+///     fn drop(&mut self) {
+///         println!("Dropping Inner!");
+///     }
+/// }
+///
+/// impl Drop for Outer {
+///     fn drop(&mut self) {
+///         println!("Dropping Outer!");
+///     }
+/// }
+///
+/// fn main() {
+///     let _x = Outer(Inner);
+/// }
+/// ```
+///
+/// Because variables are dropped in the reverse order they are declared,
+/// `main` will print `Declared second!` and then `Declared first!`.
+///
+/// ```
+/// struct PrintOnDrop(&'static str);
+///
+/// fn main() {
+///     let _first = PrintOnDrop("Declared first!");
+///     let _second = PrintOnDrop("Declared second!");
+/// }
+/// ```
 #[lang = "drop"]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait Drop {

src/libcore/tests/iter.rs

@@ -171,6 +171,79 @@ fn test_iterator_step_by_zero() {
     it.next();
 }
 
+#[test]
+fn test_iterator_step_by_size_hint() {
+    struct StubSizeHint(usize, Option<usize>);
+    impl Iterator for StubSizeHint {
+        type Item = ();
+        fn next(&mut self) -> Option<()> {
+            self.0 -= 1;
+            if let Some(ref mut upper) = self.1 {
+                *upper -= 1;
+            }
+            Some(())
+        }
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            (self.0, self.1)
+        }
+    }
+
+    // The two checks in each case are needed because the logic
+    // is different before the first call to `next()`.
+
+    let mut it = StubSizeHint(10, Some(10)).step_by(1);
+    assert_eq!(it.size_hint(), (10, Some(10)));
+    it.next();
+    assert_eq!(it.size_hint(), (9, Some(9)));
+
+    // exact multiple
+    let mut it = StubSizeHint(10, Some(10)).step_by(3);
+    assert_eq!(it.size_hint(), (4, Some(4)));
+    it.next();
+    assert_eq!(it.size_hint(), (3, Some(3)));
+
+    // larger base range, but not enough to get another element
+    let mut it = StubSizeHint(12, Some(12)).step_by(3);
+    assert_eq!(it.size_hint(), (4, Some(4)));
+    it.next();
+    assert_eq!(it.size_hint(), (3, Some(3)));
+
+    // smaller base range, so fewer resulting elements
+    let mut it = StubSizeHint(9, Some(9)).step_by(3);
+    assert_eq!(it.size_hint(), (3, Some(3)));
+    it.next();
+    assert_eq!(it.size_hint(), (2, Some(2)));
+
+    // infinite upper bound
+    let mut it = StubSizeHint(usize::MAX, None).step_by(1);
+    assert_eq!(it.size_hint(), (usize::MAX, None));
+    it.next();
+    assert_eq!(it.size_hint(), (usize::MAX-1, None));
+
+    // still infinite with larger step
+    let mut it = StubSizeHint(7, None).step_by(3);
+    assert_eq!(it.size_hint(), (3, None));
+    it.next();
+    assert_eq!(it.size_hint(), (2, None));
+
+    // propagates ExactSizeIterator
+    let a = [1,2,3,4,5];
+    let it = a.iter().step_by(2);
+    assert_eq!(it.len(), 3);
+
+    // Cannot be TrustedLen as a step greater than one makes an iterator
+    // with (usize::MAX, None) no longer meet the safety requirements
+    trait TrustedLenCheck { fn test(self) -> bool; }
+    impl<T:Iterator> TrustedLenCheck for T {
+        default fn test(self) -> bool { false }
+    }
+    impl<T:TrustedLen> TrustedLenCheck for T {
+        fn test(self) -> bool { true }
+    }
+    assert!(TrustedLenCheck::test(a.iter()));
+    assert!(!TrustedLenCheck::test(a.iter().step_by(1)));
+}
+
 #[test]
 fn test_filter_map() {
     let it = (0..).step_by(1).take(10)

src/libcore/tests/lib.rs

@@ -31,9 +31,11 @@
 #![feature(slice_patterns)]
 #![feature(sort_internals)]
 #![feature(sort_unstable)]
+#![feature(specialization)]
 #![feature(step_by)]
 #![feature(step_trait)]
 #![feature(test)]
+#![feature(trusted_len)]
 #![feature(try_from)]
 #![feature(unicode)]
 #![feature(unique)]

src/librustc_borrowck/borrowck/mod.rs

@@ -1002,7 +1002,7 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
             .span_suggestion(err.span,
                              &format!("to force the closure to take ownership of {} \
                                        (and any other referenced variables), \
-                                       use the `move` keyword, as shown:",
+                                       use the `move` keyword",
                                        cmt_path_or_string),
                              suggestion)
             .emit();

src/librustc_errors/diagnostic.rs

@@ -203,6 +203,18 @@ impl Diagnostic {
 
     /// Prints out a message with a suggested edit of the code.
     ///
+    /// In case of short messages and a simple suggestion,
+    /// rustc displays it as a label like
+    ///
+    /// "try adding parentheses: `(tup.0).1`"
+    ///
+    /// The message
+    /// * should not end in any punctuation (a `:` is added automatically)
+    /// * should not be a question
+    /// * should not contain any parts like "the following", "as shown"
+    /// * may look like "to do xyz, use" or "to do xyz, use abc"
+    /// * may contain a name of a function, variable or type, but not whole expressions
+    ///
     /// See `diagnostic::CodeSuggestion` for more information.
     pub fn span_suggestion(&mut self, sp: Span, msg: &str, suggestion: String) -> &mut Self {
         self.suggestions.push(CodeSuggestion {

src/librustc_errors/emitter.rs

@@ -46,7 +46,7 @@ impl Emitter for EmitterWriter {
                // don't display multiline suggestions as labels
                sugg.substitution_parts[0].substitutions[0].find('\n').is_none() {
                 let substitution = &sugg.substitution_parts[0].substitutions[0];
-                let msg = format!("help: {} `{}`", sugg.msg, substitution);
+                let msg = format!("help: {}: `{}`", sugg.msg, substitution);
                 primary_span.push_span_label(sugg.substitution_spans().next().unwrap(), msg);
             } else {
                 // if there are multiple suggestions, print them all in full

src/librustc_resolve/lib.rs

@@ -2307,13 +2307,15 @@ impl<'a> Resolver<'a> {
                     .map(|suggestion| import_candidate_to_paths(&suggestion)).collect::<Vec<_>>();
                 enum_candidates.sort();
                 for (sp, variant_path, enum_path) in enum_candidates {
-                    let msg = format!("there is an enum variant `{}`, did you mean to use `{}`?",
-                                      variant_path,
-                                      enum_path);
                     if sp == DUMMY_SP {
+                        let msg = format!("there is an enum variant `{}`, \
+                                        try using `{}`?",
+                                        variant_path,
+                                        enum_path);
                         err.help(&msg);
                     } else {
-                        err.span_help(sp, &msg);
+                        err.span_suggestion(span, "you can try using the variant's enum",
+                                            enum_path);
                     }
                 }
             }
@@ -2322,18 +2324,20 @@ impl<'a> Resolver<'a> {
                     let self_is_available = this.self_value_is_available(path[0].ctxt, span);
                     match candidate {
                         AssocSuggestion::Field => {
-                            err.span_label(span, format!("did you mean `self.{}`?", path_str));
+                            err.span_suggestion(span, "try",
+                                                format!("self.{}", path_str));
                             if !self_is_available {
                                 err.span_label(span, format!("`self` value is only available in \
                                                                methods with `self` parameter"));
                             }
                         }
                         AssocSuggestion::MethodWithSelf if self_is_available => {
-                            err.span_label(span, format!("did you mean `self.{}(...)`?",
-                                                           path_str));
+                            err.span_suggestion(span, "try",
+                                                format!("self.{}", path_str));
                         }
                         AssocSuggestion::MethodWithSelf | AssocSuggestion::AssocItem => {
-                            err.span_label(span, format!("did you mean `Self::{}`?", path_str));
+                            err.span_suggestion(span, "try",
+                                                format!("Self::{}", path_str));
                         }
                     }
                     return err;

src/librustc_resolve/macros.rs

@@ -649,9 +649,10 @@ impl<'a> Resolver<'a> {
         if let Some(suggestion) = suggestion {
             if suggestion != name {
                 if let MacroKind::Bang = kind {
-                    err.help(&format!("did you mean `{}!`?", suggestion));
+                    err.span_suggestion(span, "you could try the macro",
+                                        format!("{}!", suggestion));
                 } else {
-                    err.help(&format!("did you mean `{}`?", suggestion));
+                    err.span_suggestion(span, "try", suggestion.to_string());
                 }
             } else {
                 err.help("have you added the `#[macro_use]` on the module/import?");

src/librustc_typeck/check/cast.rs

@@ -276,7 +276,7 @@ impl<'a, 'gcx, 'tcx> CastCheck<'tcx> {
                     match fcx.tcx.sess.codemap().span_to_snippet(self.cast_span) {
                         Ok(s) => {
                             err.span_suggestion(self.cast_span,
-                                                "try casting to a reference instead:",
+                                                "try casting to a reference instead",
                                                 format!("&{}{}", mtstr, s));
                         }
                         Err(_) => {
@@ -295,7 +295,7 @@ impl<'a, 'gcx, 'tcx> CastCheck<'tcx> {
                 match fcx.tcx.sess.codemap().span_to_snippet(self.cast_span) {
                     Ok(s) => {
                         err.span_suggestion(self.cast_span,
-                                            "try casting to a `Box` instead:",
+                                            "try casting to a `Box` instead",
                                             format!("Box<{}>", s));
                     }
                     Err(_) => span_help!(err, self.cast_span, "did you mean `Box<{}>`?", tstr),

src/librustc_typeck/check/op.rs

@@ -290,7 +290,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                                   from a string reference. String concatenation \
                                   appends the string on the right to the string \
                                   on the left and may require reallocation. This \
-                                  requires ownership of the string on the left."), suggestion);
+                                  requires ownership of the string on the left"), suggestion);
                     is_string_addition = true;
                 }