Auto merge of #44784 - frewsxcv:rollup, r=frewsxcv

Rollup of 14 pull requests

- Successful merges: #44554, #44648, #44658, #44712, #44717, #44726, #44745, #44746, #44749, #44759, #44770, #44773, #44776, #44778
- Failed merges:

Author: bors

CONTRIBUTING.md

@@ -461,6 +461,7 @@ For people new to Rust, and just starting to contribute, or even for
 more seasoned developers, some useful places to look for information
 are:
 
+* [Rust Forge][rustforge] contains additional documentation, including write-ups of how to achieve common tasks
 * The [Rust Internals forum][rif], a place to ask questions and
   discuss Rust's internals
 * The [generated documentation for rust's compiler][gdfrustc]
@@ -476,6 +477,7 @@ are:
 [gsearchdocs]: https://www.google.com/search?q=site:doc.rust-lang.org+your+query+here
 [rif]: http://internals.rust-lang.org
 [rr]: https://doc.rust-lang.org/book/README.html
+[rustforge]: https://forge.rust-lang.org/
 [tlgba]: http://tomlee.co/2014/04/a-more-detailed-tour-of-the-rust-compiler/
 [ro]: http://www.rustaceans.org/
 [rctd]: ./src/test/COMPILER_TESTS.md

src/liballoc/arc.rs

@@ -72,13 +72,13 @@ const MAX_REFCOUNT: usize = (isize::MAX) as usize;
 /// first: after all, isn't the point of `Arc<T>` thread safety? The key is
 /// this: `Arc<T>` makes it thread safe to have multiple ownership of the same
 /// data, but it  doesn't add thread safety to its data. Consider
-/// `Arc<RefCell<T>>`. `RefCell<T>` isn't [`Sync`], and if `Arc<T>` was always
-/// [`Send`], `Arc<RefCell<T>>` would be as well. But then we'd have a problem:
-/// `RefCell<T>` is not thread safe; it keeps track of the borrowing count using
+/// `Arc<`[`RefCell<T>`]`>`. [`RefCell<T>`] isn't [`Sync`], and if `Arc<T>` was always
+/// [`Send`], `Arc<`[`RefCell<T>`]`>` would be as well. But then we'd have a problem:
+/// [`RefCell<T>`] is not thread safe; it keeps track of the borrowing count using
 /// non-atomic operations.
 ///
 /// In the end, this means that you may need to pair `Arc<T>` with some sort of
-/// `std::sync` type, usually `Mutex<T>`.
+/// [`std::sync`] type, usually [`Mutex<T>`][mutex].
 ///
 /// ## Breaking cycles with `Weak`
 ///
@@ -106,7 +106,7 @@ const MAX_REFCOUNT: usize = (isize::MAX) as usize;
 /// // a and b both point to the same memory location as foo.
 /// ```
 ///
-/// The `Arc::clone(&from)` syntax is the most idiomatic because it conveys more explicitly
+/// The [`Arc::clone(&from)`] syntax is the most idiomatic because it conveys more explicitly
 /// the meaning of the code. In the example above, this syntax makes it easier to see that
 /// this code is creating a new reference rather than copying the whole content of foo.
 ///
@@ -141,6 +141,9 @@ const MAX_REFCOUNT: usize = (isize::MAX) as usize;
 /// [upgrade]: struct.Weak.html#method.upgrade
 /// [`None`]: ../../std/option/enum.Option.html#variant.None
 /// [assoc]: ../../book/first-edition/method-syntax.html#associated-functions
+/// [`RefCell<T>`]: ../../std/cell/struct.RefCell.html
+/// [`std::sync`]: ../../std/sync/index.html
+/// [`Arc::clone(&from)`]: #method.clone
 ///
 /// # Examples
 ///

src/libcore/fmt/mod.rs

@@ -1700,8 +1700,18 @@ impl<T: ?Sized + Debug> Debug for RefCell<T> {
                     .finish()
             }
             Err(_) => {
+                // The RefCell is mutably borrowed so we can't look at its value
+                // here. Show a placeholder instead.
+                struct BorrowedPlaceholder;
+
+                impl Debug for BorrowedPlaceholder {
+                    fn fmt(&self, f: &mut Formatter) -> Result {
+                        f.write_str("<borrowed>")
+                    }
+                }
+
                 f.debug_struct("RefCell")
-                    .field("value", &"<borrowed>")
+                    .field("value", &BorrowedPlaceholder)
                     .finish()
             }
         }

src/libcore/mem.rs

@@ -177,15 +177,59 @@ pub fn forget<T>(t: T) {
 
 /// Returns the size of a type in bytes.
 ///
-/// More specifically, this is the offset in bytes between successive
-/// items of the same type, including alignment padding.
+/// More specifically, this is the offset in bytes between successive elements
+/// in an array with that item type including alignment padding. Thus, for any
+/// type `T` and length `n`, `[T; n]` has a size of `n * size_of::<T>()`.
+///
+/// In general, the size of a type is not stable across compilations, but
+/// specific types such as primitives are.
+///
+/// The following table gives the size for primitives.
+///
+/// Type | size_of::\<Type>()
+/// ---- | ---------------
+/// () | 0
+/// u8 | 1
+/// u16 | 2
+/// u32 | 4
+/// u64 | 8
+/// i8 | 1
+/// i16 | 2
+/// i32 | 4
+/// i64 | 8
+/// f32 | 4
+/// f64 | 8
+/// char | 4
+///
+/// Furthermore, `usize` and `isize` have the same size.
+///
+/// The types `*const T`, `&T`, `Box<T>`, `Option<&T>`, and `Option<Box<T>>` all have
+/// the same size. If `T` is Sized, all of those types have the same size as `usize`.
+///
+/// The mutability of a pointer does not change its size. As such, `&T` and `&mut T`
+/// have the same size. Likewise for `*const T` and `*mut T`.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::mem;
 ///
+/// // Some primitives
 /// assert_eq!(4, mem::size_of::<i32>());
+/// assert_eq!(8, mem::size_of::<f64>());
+/// assert_eq!(0, mem::size_of::<()>());
+///
+/// // Some arrays
+/// assert_eq!(8, mem::size_of::<[i32; 2]>());
+/// assert_eq!(12, mem::size_of::<[i32; 3]>());
+/// assert_eq!(0, mem::size_of::<[i32; 0]>());
+///
+///
+/// // Pointer size equality
+/// assert_eq!(mem::size_of::<&i32>(), mem::size_of::<*const i32>());
+/// assert_eq!(mem::size_of::<&i32>(), mem::size_of::<Box<i32>>());
+/// assert_eq!(mem::size_of::<&i32>(), mem::size_of::<Option<&i32>>());
+/// assert_eq!(mem::size_of::<Box<i32>>(), mem::size_of::<Option<Box<i32>>>());
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]

src/libcore/str/mod.rs

@@ -1399,9 +1399,6 @@ Section: Comparing strings
 */
 
 /// Bytewise slice equality
-/// NOTE: This function is (ab)used in rustc::middle::trans::_match
-/// to compare &[u8] byte slices that are not necessarily valid UTF-8.
-#[lang = "str_eq"]
 #[inline]
 fn eq_slice(a: &str, b: &str) -> bool {
     a.as_bytes() == b.as_bytes()

src/librustc/README.md

@@ -37,7 +37,7 @@ incremental improves that may change.)
 
 The dependency structure of these crates is roughly a diamond:
 
-````
+```
                   rustc_driver
                 /      |       \
               /        |         \

src/librustc/hir/lowering.rs

@@ -65,7 +65,7 @@ use syntax::codemap::{self, respan, Spanned, CompilerDesugaringKind};
 use syntax::std_inject;
 use syntax::symbol::{Symbol, keywords};
 use syntax::tokenstream::{TokenStream, TokenTree, Delimited};
-use syntax::parse::token::{Token, DelimToken};
+use syntax::parse::token::Token;
 use syntax::util::small_vector::SmallVector;
 use syntax::visit::{self, Visitor};
 use syntax_pos::Span;
@@ -606,10 +606,12 @@ impl<'a> LoweringContext<'a> {
     }
 
     fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
-        tokens.into_trees().map(|tree| self.lower_token_tree(tree)).collect()
+        tokens.into_trees()
+            .flat_map(|tree| self.lower_token_tree(tree).into_trees())
+            .collect()
     }
 
-    fn lower_token_tree(&mut self, tree: TokenTree) -> TokenTree {
+    fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
         match tree {
             TokenTree::Token(span, token) => {
                 self.lower_token(token, span)
@@ -618,23 +620,19 @@ impl<'a> LoweringContext<'a> {
                 TokenTree::Delimited(span, Delimited {
                     delim: delimited.delim,
                     tts: self.lower_token_stream(delimited.tts.into()).into(),
-                })
+                }).into()
             }
         }
     }
 
-    fn lower_token(&mut self, token: Token, span: Span) -> TokenTree {
+    fn lower_token(&mut self, token: Token, span: Span) -> TokenStream {
         match token {
             Token::Interpolated(_) => {}
-            other => return TokenTree::Token(span, other),
+            other => return TokenTree::Token(span, other).into(),
         }
 
         let tts = token.interpolated_to_tokenstream(&self.sess.parse_sess, span);
-        let tts = self.lower_token_stream(tts);
-        TokenTree::Delimited(span, Delimited {
-            delim: DelimToken::NoDelim,
-            tts: tts.into(),
-        })
+        self.lower_token_stream(tts)
     }
 
     fn lower_arm(&mut self, arm: &Arm) -> hir::Arm {

src/librustc/middle/lang_items.rs

@@ -280,8 +280,6 @@ language_item_table! {
     EqTraitLangItem,                 "eq",                      eq_trait;
     OrdTraitLangItem,                "ord",                     ord_trait;
 
-    StrEqFnLangItem,                 "str_eq",                  str_eq_fn;
-
     // A number of panic-related lang items. The `panic` item corresponds to
     // divide-by-zero and various panic cases with `match`. The
     // `panic_bounds_check` item is for indexing arrays.

src/librustc/session/mod.rs

@@ -411,7 +411,8 @@ impl Session {
     }
     pub fn emit_end_regions(&self) -> bool {
         self.opts.debugging_opts.emit_end_regions ||
-            (self.opts.debugging_opts.mir_emit_validate > 0)
+            (self.opts.debugging_opts.mir_emit_validate > 0) ||
+            self.opts.debugging_opts.borrowck_mir
     }
     pub fn lto(&self) -> bool {
         self.opts.cg.lto

src/librustc_mir/borrow_check.rs

@@ -419,7 +419,7 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
             self.each_borrow_involving_path(
                 context, lvalue_span.0, flow_state, |this, _idx, borrow| {
                     if !borrow.compatible_with(BorrowKind::Shared) {
-                        this.report_use_while_mutably_borrowed(context, lvalue_span);
+                        this.report_use_while_mutably_borrowed(context, lvalue_span, borrow);
                         Control::Break
                     } else {
                         Control::Continue
@@ -914,11 +914,17 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
 
     fn report_use_while_mutably_borrowed(&mut self,
                                          _context: Context,
-                                         (lvalue, span): (&Lvalue, Span)) {
+                                         (lvalue, span): (&Lvalue, Span),
+                                         borrow : &BorrowData) {
+        let described_lvalue = self.describe_lvalue(lvalue);
+        let borrow_span = self.retrieve_borrow_span(borrow);
+
         let mut err = self.tcx.cannot_use_when_mutably_borrowed(
-            span, &self.describe_lvalue(lvalue), Origin::Mir);
-        // FIXME 1: add span_label for "borrow of `()` occurs here"
-        // FIXME 2: add span_label for "use of `{}` occurs here"
+            span, &described_lvalue, Origin::Mir);
+
+        err.span_label(borrow_span, format!("borrow of `{}` occurs here", described_lvalue));
+        err.span_label(span, format!("use of borrowed `{}`", described_lvalue));
+
         err.emit();
     }
 
@@ -998,7 +1004,7 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
                     ProjectionElem::Downcast(..) =>
                         ("",   format!(""), None), // (dont emit downcast info)
                     ProjectionElem::Field(field, _ty) =>
-                        ("",   format!(".{}", field.index()), None),
+                        ("",   format!(".{}", field.index()), None), // FIXME: report name of field
                     ProjectionElem::Index(index) =>
                         ("",   format!(""), Some(index)),
                     ProjectionElem::ConstantIndex { offset, min_length, from_end: true } =>
@@ -1024,6 +1030,13 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
             }
         }
     }
+
+    // Retrieve span of given borrow from the current MIR representation
+    fn retrieve_borrow_span(&self, borrow: &BorrowData) -> Span {
+        self.mir.basic_blocks()[borrow.location.block]
+            .statements[borrow.location.statement_index]
+            .source_info.span
+    }
 }
 
 impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx> {