Auto merge of #31739 - steveklabnik:rollup, r=steveklabnik

- Successful merges: #31565, #31679, #31694, #31695, #31703, #31720, #31733
- Failed merges:

RELEASES.md

@@ -94,11 +94,11 @@ Misc
   the `-Z unstable-options` flag.
 * [When running tests with `--test`, rustdoc will pass `--cfg`
   arguments to the compiler][1.7dt].
-* [The compiler is built with RPATH information by default][1.7rp].
+* [The compiler is built with RPATH information by default][1.7rpa].
   This means that it will be possible to run `rustc` when installed in
   unusual configurations without configuring the dynamic linker search
   path explicitly.
-* [`rustc` passes `--enable-new-dtags` to GNU ld][1.7dt]. This makes
+* [`rustc` passes `--enable-new-dtags` to GNU ld][1.7dta]. This makes
   any RPATH entries (emitted with `-C rpath`) *not* take precedence
   over `LD_LIBRARY_PATH`.
 
@@ -132,7 +132,7 @@ Compatibility Notes
 [1.7cp]: https://github.com/rust-lang/cargo/pull/2224
 [1.7d]: https://github.com/rust-lang/rust/pull/30724
 [1.7dt]: https://github.com/rust-lang/rust/pull/30372
-[1.7dt]: https://github.com/rust-lang/rust/pull/30394
+[1.7dta]: https://github.com/rust-lang/rust/pull/30394
 [1.7f]: https://github.com/rust-lang/rust/pull/30672
 [1.7h]: https://github.com/rust-lang/rust/pull/30818
 [1.7j]: https://github.com/rust-lang/rust/pull/30711
@@ -140,7 +140,7 @@ Compatibility Notes
 [1.7m]: https://github.com/rust-lang/rust/pull/30381
 [1.7p]: https://github.com/rust-lang/rust/pull/30681
 [1.7rp]: https://github.com/rust-lang/rust/pull/29498
-[1.7rp]: https://github.com/rust-lang/rust/pull/30353
+[1.7rpa]: https://github.com/rust-lang/rust/pull/30353
 [1.7rr]: https://github.com/rust-lang/cargo/pull/2279
 [1.7sf]: https://github.com/rust-lang/rust/pull/30389
 [1.7utf8]: https://github.com/rust-lang/rust/pull/30740

src/doc/book/ownership.md

@@ -124,21 +124,65 @@ special annotation here, it’s the default thing that Rust does.
 ## The details
 
 The reason that we cannot use a binding after we’ve moved it is subtle, but
-important. When we write code like this:
+important. 
+
+When we write code like this:
+
+```rust
+let x = 10;
+```
+
+Rust allocates memory for an integer [i32] on the [stack][sh], copies the bit
+pattern representing the value of 10 to the allocated memory and binds the
+variable name x to this memory region for future reference.
+
+Now consider the following code fragment:
 
 ```rust
 let v = vec![1, 2, 3];
 
-let v2 = v;
+let mut v2 = v;
 ```
 
-The first line allocates memory for the vector object, `v`, and for the data it
+The first line allocates memory for the vector object `v` on the stack like
-contains. The vector object is stored on the [stack][sh] and contains a pointer
+it does for `x` above. But in addition to that it also allocates some memory
-to the content (`[1, 2, 3]`) stored on the [heap][sh]. When we move `v` to `v2`,
+on the [heap][sh] for the actual data (`[1, 2, 3]`). Rust copies the address
-it creates a copy of that pointer, for `v2`. Which means that there would be two
+of this heap allocation to an internal pointer, which is part of the vector
-pointers to the content of the vector on the heap. It would violate Rust’s
+object placed on the stack (let's call it the data pointer). 
-safety guarantees by introducing a data race. Therefore, Rust forbids using `v`
+
-after we’ve done the move.
+It is worth pointing out (even at the risk of stating the obvious) that the
+vector object and its data live in separate memory regions instead of being a
+single contiguous memory allocation (due to reasons we will not go into at
+this point of time). These two parts of the vector (the one on the stack and
+one on the heap) must agree with each other at all times with regards to
+things like the length, capacity etc.
+
+When we move `v` to `v2`, rust actually does a bitwise copy of the vector
+object `v` into the stack allocation represented by `v2`. This shallow copy
+does not create a copy of the heap allocation containing the actual data.
+Which means that there would be two pointers to the contents of the vector
+both pointing to the same memory allocation on the heap. It would violate
+Rust’s safety guarantees by introducing a data race if one could access both
+`v` and `v2` at the same time. 
+
+For example if we truncated the vector to just two elements through `v2`:
+
+```rust
+# let v = vec![1, 2, 3];
+# let mut v2 = v;
+v2.truncate(2);
+```
+
+and `v1` were still accessible we'd end up with an invalid vector since `v1`
+would not know that the heap data has been truncated. Now, the part of the
+vector `v1` on the stack does not agree with the corresponding part on the
+heap. `v1` still thinks there are three elements in the vector and will
+happily let us access the non existent element `v1[2]` but as you might
+already know this is a recipe for disaster. Especially because it might lead
+to a segmentation fault or worse allow an unauthorized user to read from
+memory to which they don't have access.
+
+This is why Rust forbids using `v` after we’ve done the move.
 
 [sh]: the-stack-and-the-heap.html
 

src/libcollections/btree/map.rs

@@ -375,9 +375,10 @@ impl<K: Ord, V> BTreeMap<K, V> {
     ///
     /// If the map did not have this key present, `None` is returned.
     ///
-    /// If the map did have this key present, the key is not updated, the
+    /// If the map did have this key present, the value is updated, and the old
-    /// value is updated and the old value is returned.
+    /// value is returned. The key is not updated, though; this matters for
-    /// See the [module-level documentation] for more.
+    /// types that can be `==` without being identical. See the [module-level
+    /// documentation] for more.
     ///
     /// [module-level documentation]: index.html#insert-and-complex-keys
     ///

src/libcore/mem.rs

@@ -571,9 +571,25 @@ pub const POST_DROP_USIZE: usize = POST_DROP_U64 as usize;
 /// ```
 /// use std::mem;
 ///
-/// let one = unsafe { mem::transmute_copy(&1) };
+/// #[repr(packed)]
+/// struct Foo {
+///     bar: u8,
+/// }
 ///
-/// assert_eq!(1, one);
+/// let foo_slice = [10u8];
+///
+/// unsafe {
+///     // Copy the data from 'foo_slice' and treat it as a 'Foo'
+///     let mut foo_struct: Foo = mem::transmute_copy(&foo_slice);
+///     assert_eq!(foo_struct.bar, 10);
+///
+///     // Modify the copied data
+///     foo_struct.bar = 20;
+///     assert_eq!(foo_struct.bar, 20);
+/// }
+///
+/// // The contents of 'foo_slice' should not have changed
+/// assert_eq!(foo_slice, [10]);
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]

src/librustc/diagnostics.rs

@@ -20,8 +20,8 @@ This error suggests that the expression arm corresponding to the noted pattern
 will never be reached as for all possible values of the expression being
 matched, one of the preceding patterns will match.
 
-This means that perhaps some of the preceding patterns are too general, this one
+This means that perhaps some of the preceding patterns are too general, this
-is too specific or the ordering is incorrect.
+one is too specific or the ordering is incorrect.
 
 For example, the following `match` block has too many arms:
 
@@ -104,28 +104,86 @@ E0004: r##"
 This error indicates that the compiler cannot guarantee a matching pattern for
 one or more possible inputs to a match expression. Guaranteed matches are
 required in order to assign values to match expressions, or alternatively,
-determine the flow of execution.
+determine the flow of execution. Erroneous code example:
+
+```compile_fail
+enum Terminator {
+    HastaLaVistaBaby,
+    TalkToMyHand,
+}
+
+let x = Terminator::HastaLaVistaBaby;
+
+match x { // error: non-exhaustive patterns: `HastaLaVistaBaby` not covered
+    Terminator::TalkToMyHand => {}
+}
+```
 
 If you encounter this error you must alter your patterns so that every possible
 value of the input type is matched. For types with a small number of variants
 (like enums) you should probably cover all cases explicitly. Alternatively, the
 underscore `_` wildcard pattern can be added after all other patterns to match
-"anything else".
+"anything else". Example:
+
+```
+enum Terminator {
+    HastaLaVistaBaby,
+    TalkToMyHand,
+}
+
+let x = Terminator::HastaLaVistaBaby;
+
+match x {
+    Terminator::TalkToMyHand => {}
+    Terminator::HastaLaVistaBaby => {}
+}
+
+// or:
+
+match x {
+    Terminator::TalkToMyHand => {}
+    _ => {}
+}
+```
 "##,
 
 E0005: r##"
 Patterns used to bind names must be irrefutable, that is, they must guarantee
-that a name will be extracted in all cases. If you encounter this error you
+that a name will be extracted in all cases. Erroneous code example:
-probably need to use a `match` or `if let` to deal with the possibility of
+
-failure.
+```compile_fail
+let x = Some(1);
+let Some(y) = x;
+// error: refutable pattern in local binding: `None` not covered
+```
+
+If you encounter this error you probably need to use a `match` or `if let` to
+deal with the possibility of failure. Example:
+
+```compile_fail
+let x = Some(1);
+
+match x {
+    Some(y) => {
+        // do something
+    },
+    None => {}
+}
+
+// or:
+
+if let Some(y) = x {
+    // do something
+}
+```
 "##,
 
 E0007: r##"
 This error indicates that the bindings in a match arm would require a value to
-be moved into more than one location, thus violating unique ownership. Code like
+be moved into more than one location, thus violating unique ownership. Code
-the following is invalid as it requires the entire `Option<String>` to be moved
+like the following is invalid as it requires the entire `Option<String>` to be
-into a variable called `op_string` while simultaneously requiring the inner
+moved into a variable called `op_string` while simultaneously requiring the
-String to be moved into a variable called `s`.
+inner `String` to be moved into a variable called `s`.
 
 ```compile_fail
 let x = Some("s".to_string());
@@ -180,7 +238,7 @@ by-ref.
 
 This limitation may be removed in a future version of Rust.
 
-Wrong example:
+Erroneous code example:
 
 ```compile_fail
 struct X { x: (), }
@@ -264,7 +322,7 @@ trait Foo where Self: Sized {
 }
 ```
 
-we cannot create an object of type `Box<Foo>` or `&Foo` since in this case
+We cannot create an object of type `Box<Foo>` or `&Foo` since in this case
 `Self` would not be `Sized`.
 
 Generally, `Self : Sized` is used to indicate that the trait should not be used
@@ -294,7 +352,7 @@ impl Trait for u8 {
 ```
 
 (Note that `&self` and `&mut self` are okay, it's additional `Self` types which
-cause this problem)
+cause this problem.)
 
 In such a case, the compiler cannot predict the return type of `foo()` in a
 situation like the following:
@@ -573,15 +631,15 @@ type X = u32; // ok!
 "##,
 
 E0133: r##"
-Using unsafe functionality, is potentially dangerous and disallowed
+Using unsafe functionality is potentially dangerous and disallowed by safety
-by safety checks. Examples:
+checks. Examples:
 
-- Dereferencing raw pointers
+* Dereferencing raw pointers
-- Calling functions via FFI
+* Calling functions via FFI
-- Calling functions marked unsafe
+* Calling functions marked unsafe
 
-These safety checks can be relaxed for a section of the code
+These safety checks can be relaxed for a section of the code by wrapping the
-by wrapping the unsafe instructions with an `unsafe` block. For instance:
+unsafe instructions with an `unsafe` block. For instance:
 
 ```
 unsafe fn f() { return; }
@@ -1039,14 +1097,16 @@ let y = match x {
 println!("{}", y);
 ```
 
-In the previous example, the print statement was never reached when the wildcard
+In the previous example, the print statement was never reached when the
-match arm was hit, so we were okay with `foo()` not returning an integer that we
+wildcard match arm was hit, so we were okay with `foo()` not returning an
-could set to `y`. But in this example, `foo()` actually does return control, so
+integer that we could set to `y`. But in this example, `foo()` actually does
-the print statement will be executed with an uninitialized value.
+return control, so the print statement will be executed with an uninitialized
+value.
 
 Obviously we cannot have functions which are allowed to be used in such
 positions and yet can return control. So, if you are defining a function that
-returns `!`, make sure that there is no way for it to actually finish executing.
+returns `!`, make sure that there is no way for it to actually finish
+executing.
 "##,
 
 E0271: r##"
@@ -1206,19 +1266,19 @@ trait Index<Idx> { ... }
 foo(true); // `bool` does not implement `Index<u8>`
 ```
 
-there will be an error about `bool` not implementing `Index<u8>`, followed by a
+There will be an error about `bool` not implementing `Index<u8>`, followed by a
 note saying "the type `bool` cannot be indexed by `u8`".
 
-As you can see, you can specify type parameters in curly braces for substitution
+As you can see, you can specify type parameters in curly braces for
-with the actual types (using the regular format string syntax) in a given
+substitution with the actual types (using the regular format string syntax) in
-situation. Furthermore, `{Self}` will substitute to the type (in this case,
+a given situation. Furthermore, `{Self}` will substitute to the type (in this
-`bool`) that we tried to use.
+case, `bool`) that we tried to use.
 
 This error appears when the curly braces contain an identifier which doesn't
-match with any of the type parameters or the string `Self`. This might happen if
+match with any of the type parameters or the string `Self`. This might happen
-you misspelled a type parameter, or if you intended to use literal curly braces.
+if you misspelled a type parameter, or if you intended to use literal curly
-If it is the latter, escape the curly braces with a second curly brace of the
+braces. If it is the latter, escape the curly braces with a second curly brace
-same type; e.g. a literal `{` is `{{`
+of the same type; e.g. a literal `{` is `{{`.
 "##,
 
 E0273: r##"
@@ -1239,10 +1299,10 @@ foo(true); // `bool` does not implement `Index<u8>`
 there will be an error about `bool` not implementing `Index<u8>`, followed by a
 note saying "the type `bool` cannot be indexed by `u8`".
 
-As you can see, you can specify type parameters in curly braces for substitution
+As you can see, you can specify type parameters in curly braces for
-with the actual types (using the regular format string syntax) in a given
+substitution with the actual types (using the regular format string syntax) in
-situation. Furthermore, `{Self}` will substitute to the type (in this case,
+a given situation. Furthermore, `{Self}` will substitute to the type (in this
-`bool`) that we tried to use.
+case, `bool`) that we tried to use.
 
 This error appears when the curly braces do not contain an identifier. Please
 add one of the same name as a type parameter. If you intended to use literal
@@ -1274,8 +1334,8 @@ trait.
 
 E0275: r##"
 This error occurs when there was a recursive trait requirement that overflowed
-before it could be evaluated. Often this means that there is unbounded recursion
+before it could be evaluated. Often this means that there is unbounded
-in resolving some type bounds.
+recursion in resolving some type bounds.
 
 For example, in the following code:
 
@@ -1288,9 +1348,9 @@ impl<T> Foo for T where Bar<T>: Foo {}
 ```
 
 To determine if a `T` is `Foo`, we need to check if `Bar<T>` is `Foo`. However,
-to do this check, we need to determine that `Bar<Bar<T>>` is `Foo`. To determine
+to do this check, we need to determine that `Bar<Bar<T>>` is `Foo`. To
-this, we check if `Bar<Bar<Bar<T>>>` is `Foo`, and so on. This is clearly a
+determine this, we check if `Bar<Bar<Bar<T>>>` is `Foo`, and so on. This is
-recursive requirement that can't be resolved directly.
+clearly a recursive requirement that can't be resolved directly.
 
 Consider changing your trait bounds so that they're less self-referential.
 "##,
@@ -1336,7 +1396,7 @@ fn main() {
     // we now call the method with the i32 type, which doesn't implement
     // the Foo trait
     some_func(5i32); // error: the trait `Foo` is not implemented for the
-                     //     type `i32`
+                     //        type `i32`
 }
 ```
 
@@ -1564,7 +1624,9 @@ borrows were allowed:
 ```compile_fail
 match Some(()) {
     None => { },
-    option if option.take().is_none() => { /* impossible, option is `Some` */ },
+    option if option.take().is_none() => {
+        /* impossible, option is `Some` */
+    },
     Some(_) => { } // When the previous match failed, the option became `None`.
 }
 ```
@@ -1615,12 +1677,29 @@ See also https://github.com/rust-lang/rust/issues/14587
 
 E0306: r##"
 In an array literal `[x; N]`, `N` is the number of elements in the array. This
-number cannot be negative.
+must be an unsigned integer. Erroneous code example:
+
+```compile_fail
+let x = [0i32; true]; // error: expected positive integer for repeat count,
+                      //        found boolean
+```
+
+Working example:
+
+```
+let x = [0i32; 2];
+```
 "##,
 
 E0307: r##"
-The length of an array is part of its type. For this reason, this length must be
+The length of an array is part of its type. For this reason, this length must
-a compile-time constant.
+be a compile-time constant. Erroneous code example:
+
+```compile_fail
+    let len = 10;
+    let x = [0i32; len]; // error: expected constant integer for repeat count,
+                         //        found variable
+```
 "##,
 
 E0308: r##"
@@ -1713,24 +1792,22 @@ struct Foo<T: 'static> {
 "##,
 
 E0398: r##"
-In Rust 1.3, the default object lifetime bounds are expected to
+In Rust 1.3, the default object lifetime bounds are expected to change, as
-change, as described in RFC #1156 [1]. You are getting a warning
+described in RFC #1156 [1]. You are getting a warning because the compiler
-because the compiler thinks it is possible that this change will cause
+thinks it is possible that this change will cause a compilation error in your
-a compilation error in your code. It is possible, though unlikely,
+code. It is possible, though unlikely, that this is a false alarm.
-that this is a false alarm.
 
-The heart of the change is that where `&'a Box<SomeTrait>` used to
+The heart of the change is that where `&'a Box<SomeTrait>` used to default to
-default to `&'a Box<SomeTrait+'a>`, it now defaults to `&'a
+`&'a Box<SomeTrait+'a>`, it now defaults to `&'a Box<SomeTrait+'static>` (here,
-Box<SomeTrait+'static>` (here, `SomeTrait` is the name of some trait
+`SomeTrait` is the name of some trait type). Note that the only types which are
-type). Note that the only types which are affected are references to
+affected are references to boxes, like `&Box<SomeTrait>` or
-boxes, like `&Box<SomeTrait>` or `&[Box<SomeTrait>]`.  More common
+`&[Box<SomeTrait>]`. More common types like `&SomeTrait` or `Box<SomeTrait>`
-types like `&SomeTrait` or `Box<SomeTrait>` are unaffected.
+are unaffected.
 
-To silence this warning, edit your code to use an explicit bound.
+To silence this warning, edit your code to use an explicit bound. Most of the
-Most of the time, this means that you will want to change the
+time, this means that you will want to change the signature of a function that
-signature of a function that you are calling. For example, if
+you are calling. For example, if the error is reported on a call like `foo(x)`,
-the error is reported on a call like `foo(x)`, and `foo` is
+and `foo` is defined as follows:
-defined as follows:
 
 ```ignore
 fn foo(arg: &Box<SomeTrait>) { ... }
@@ -1742,8 +1819,8 @@ You might change it to:
 fn foo<'a>(arg: &Box<SomeTrait+'a>) { ... }
 ```
 
-This explicitly states that you expect the trait object `SomeTrait` to
+This explicitly states that you expect the trait object `SomeTrait` to contain
-contain references (with a maximum lifetime of `'a`).
+references (with a maximum lifetime of `'a`).
 
 [1]: https://github.com/rust-lang/rfcs/pull/1156
 "##,
@@ -1812,8 +1889,8 @@ Also, for now, it is not possible to write deprecation messages either.
 "##,
 
 E0517: r##"
-This error indicates that a `#[repr(..)]` attribute was placed on an unsupported
+This error indicates that a `#[repr(..)]` attribute was placed on an
-item.
+unsupported item.
 
 Examples of erroneous code:
 
@@ -1829,29 +1906,29 @@ struct Foo {bar: bool, baz: bool}
 
 #[repr(C)]
 impl Foo {
-    ...
+    // ...
 }
 ```
 
- - The `#[repr(C)]` attribute can only be placed on structs and enums
+* The `#[repr(C)]` attribute can only be placed on structs and enums.
- - The `#[repr(packed)]` and `#[repr(simd)]` attributes only work on structs
+* The `#[repr(packed)]` and `#[repr(simd)]` attributes only work on structs.
- - The `#[repr(u8)]`, `#[repr(i16)]`, etc attributes only work on enums
+* The `#[repr(u8)]`, `#[repr(i16)]`, etc attributes only work on enums.
 
 These attributes do not work on typedefs, since typedefs are just aliases.
 
 Representations like `#[repr(u8)]`, `#[repr(i64)]` are for selecting the
-discriminant size for C-like enums (when there is no associated data, e.g. `enum
+discriminant size for C-like enums (when there is no associated data, e.g.
-Color {Red, Blue, Green}`), effectively setting the size of the enum to the size
+`enum Color {Red, Blue, Green}`), effectively setting the size of the enum to
-of the provided type. Such an enum can be cast to a value of the same type as
+the size of the provided type. Such an enum can be cast to a value of the same
-well. In short, `#[repr(u8)]` makes the enum behave like an integer with a
+type as well. In short, `#[repr(u8)]` makes the enum behave like an integer
-constrained set of allowed values.
+with a constrained set of allowed values.
 
 Only C-like enums can be cast to numerical primitives, so this attribute will
 not apply to structs.
 
 `#[repr(packed)]` reduces padding to make the struct size smaller. The
-representation of enums isn't strictly defined in Rust, and this attribute won't
+representation of enums isn't strictly defined in Rust, and this attribute
-work on enums.
+won't work on enums.
 
 `#[repr(simd)]` will give a struct consisting of a homogenous series of machine
 types (i.e. `u8`, `i32`, etc) a representation that permits vectorization via
@@ -1860,8 +1937,8 @@ single list of data.
 "##,
 
 E0518: r##"
-This error indicates that an `#[inline(..)]` attribute was incorrectly placed on
+This error indicates that an `#[inline(..)]` attribute was incorrectly placed
-something other than a function or method.
+on something other than a function or method.
 
 Examples of erroneous code:
 
@@ -1871,7 +1948,7 @@ struct Foo;
 
 #[inline(never)]
 impl Foo {
-    ...
+    // ...
 }
 ```
 

src/librustc_borrowck/diagnostics.rs

@@ -26,7 +26,8 @@ fn foo() -> Box<Fn(u32) -> u32> {
 
 Notice that `x` is stack-allocated by `foo()`. By default, Rust captures
 closed-over data by reference. This means that once `foo()` returns, `x` no
-longer exists. An attempt to access `x` within the closure would thus be unsafe.
+longer exists. An attempt to access `x` within the closure would thus be
+unsafe.
 
 Another situation where this might be encountered is when spawning threads:
 
@@ -73,7 +74,14 @@ fn main() {
 ```
 
 To fix this, ensure that any declared variables are initialized before being
-used.
+used. Example:
+
+```
+fn main() {
+    let x: i32 = 0;
+    let y = x; // ok!
+}
+```
 "##,
 
 E0382: r##"
@@ -210,8 +218,8 @@ let mut y: Box<_> = Box::new(&mut x);
 **y = 2;
 ```
 
-It can also be fixed by using a type with interior mutability, such as `Cell` or
+It can also be fixed by using a type with interior mutability, such as `Cell`
-`RefCell`:
+or `RefCell`:
 
 ```
 use std::cell::Cell;
@@ -259,8 +267,8 @@ fn foo<F: FnMut()>(f: F) { }
 ```
 
 Alternatively, we can consider using the `Cell` and `RefCell` types to achieve
-interior mutability through a shared reference. Our example's `mutable` function
+interior mutability through a shared reference. Our example's `mutable`
-could be redefined as below:
+function could be redefined as below:
 
 ```
 use std::cell::Cell;

src/librustc_privacy/diagnostics.rs

@@ -27,8 +27,8 @@ pub fn foo<T: Foo> (t: T) {} // same error
 ```
 
 To solve this error, please ensure that the trait is also public. The trait
-can be made inaccessible if necessary by placing it into a private inner module,
+can be made inaccessible if necessary by placing it into a private inner
-but it still has to be marked with `pub`. Example:
+module, but it still has to be marked with `pub`. Example:
 
 ```ignore
 pub trait Foo { // we set the Foo trait public
@@ -55,8 +55,8 @@ mod Foo {
 ```
 
 To solve this error, please ensure that the type is also public. The type
-can be made inaccessible if necessary by placing it into a private inner module,
+can be made inaccessible if necessary by placing it into a private inner
-but it still has to be marked with `pub`.
+module, but it still has to be marked with `pub`.
 Example:
 
 ```
@@ -165,7 +165,7 @@ let f = Bar::Foo(0); // error: cannot invoke tuple struct constructor with
 ```
 
 To solve this issue, please ensure that all of the fields of the tuple struct
-are public. Alternatively, provide a new() method to the tuple struct to
+are public. Alternatively, provide a `new()` method to the tuple struct to
 construct it from a given inner value. Example:
 
 ```

src/librustc_resolve/diagnostics.rs

@@ -94,8 +94,8 @@ mod bar {
 "##,
 
 E0253: r##"
-Attempt was made to import an unimportable value. This can happen when
+Attempt was made to import an unimportable value. This can happen when trying
-trying to import a method from a trait. An example of this error:
+to import a method from a trait. An example of this error:
 
 ```compile_fail
 mod foo {
@@ -149,10 +149,10 @@ fn main() {}
 "##,
 
 E0259: r##"
-The name chosen for an external crate conflicts with another external crate that
+The name chosen for an external crate conflicts with another external crate
-has been imported into the current module.
+that has been imported into the current module.
 
-Wrong example:
+Erroneous code example:
 
 ```compile_fail
 extern crate a;
@@ -251,8 +251,8 @@ https://doc.rust-lang.org/reference.html#types
 "##,
 
 E0364: r##"
-Private items cannot be publicly re-exported.  This error indicates that
+Private items cannot be publicly re-exported.  This error indicates that you
-you attempted to `pub use` a type or value that was not itself public.
+attempted to `pub use` a type or value that was not itself public.
 
 Here is an example that demonstrates the error:
 
@@ -275,15 +275,15 @@ mod foo {
 pub use foo::X;
 ```
 
-See the 'Use Declarations' section of the reference for more information
+See the 'Use Declarations' section of the reference for more information on
-on this topic:
+this topic:
 
 https://doc.rust-lang.org/reference.html#use-declarations
 "##,
 
 E0365: r##"
-Private modules cannot be publicly re-exported.  This error indicates
+Private modules cannot be publicly re-exported. This error indicates that you
-that you attempted to `pub use` a module that was not itself public.
+attempted to `pub use` a module that was not itself public.
 
 Here is an example that demonstrates the error:
 
@@ -313,8 +313,8 @@ https://doc.rust-lang.org/reference.html#use-declarations
 "##,
 
 E0401: r##"
-Inner items do not inherit type parameters from the functions they are
+Inner items do not inherit type parameters from the functions they are embedded
-embedded in. For example, this will not compile:
+in. For example, this will not compile:
 
 ```compile_fail
 fn foo<T>(x: T) {
@@ -543,16 +543,15 @@ impl Bar {
 "##,
 
 E0411: r##"
-The `Self` keyword was used outside an impl or a trait. Erroneous
+The `Self` keyword was used outside an impl or a trait. Erroneous code example:
-code example:
 
 ```compile_fail
 <Self>::foo; // error: use of `Self` outside of an impl or trait
 ```
 
-The `Self` keyword represents the current type, which explains why it
+The `Self` keyword represents the current type, which explains why it can only
-can only be used inside an impl or a trait. It gives access to the
+be used inside an impl or a trait. It gives access to the associated items of a
-associated items of a type:
+type:
 
 ```
 trait Foo {
@@ -564,7 +563,7 @@ trait Baz : Foo {
 }
 ```
 
-However, be careful when two types has a common associated type:
+However, be careful when two types have a common associated type:
 
 ```compile_fail
 trait Foo {
@@ -581,8 +580,8 @@ trait Baz : Foo + Foo2 {
 }
 ```
 
-This problem can be solved by specifying from which trait we want
+This problem can be solved by specifying from which trait we want to use the
-to use the `Bar` type:
+`Bar` type:
 
 ```
 trait Foo {
@@ -604,16 +603,20 @@ An undeclared type name was used. Example of erroneous codes:
 
 ```compile_fail
 impl Something {} // error: use of undeclared type name `Something`
+
 // or:
+
 trait Foo {
     fn bar(N); // error: use of undeclared type name `N`
 }
+
 // or:
+
 fn foo(x: T) {} // error: use of undeclared type name `T`
 ```
 
-To fix this error, please verify you didn't misspell the type name,
+To fix this error, please verify you didn't misspell the type name, you did
-you did declare it or imported it into the scope. Examples:
+declare it or imported it into the scope. Examples:
 
 ```
 struct Something;
@@ -635,8 +638,8 @@ fn foo<T>(x: T) {} // ok!
 "##,
 
 E0413: r##"
-A declaration shadows an enum variant or unit-like struct in scope.
+A declaration shadows an enum variant or unit-like struct in scope. Example of
-Example of erroneous code:
+erroneous code:
 
 ```compile_fail
 struct Foo;
@@ -666,8 +669,7 @@ The goal here is to avoid a conflict of names.
 "##,
 
 E0415: r##"
-More than one function parameter have the same name. Example of erroneous
+More than one function parameter have the same name. Example of erroneous code:
-code:
 
 ```compile_fail
 fn foo(f: i32, f: i32) {} // error: identifier `f` is bound more than
@@ -682,8 +684,7 @@ fn foo(f: i32, g: i32) {} // ok!
 "##,
 
 E0416: r##"
-An identifier is bound more than once in a pattern. Example of erroneous
+An identifier is bound more than once in a pattern. Example of erroneous code:
-code:
 
 ```compile_fail
 match (1, 2) {
@@ -739,8 +740,7 @@ match 0 {
 "##,
 
 E0419: r##"
-An unknown enum variant, struct or const was used. Example of
+An unknown enum variant, struct or const was used. Example of erroneous code:
-erroneous code:
 
 ```compile_fail
 match 0 {
@@ -766,8 +766,8 @@ match Something::NotFoo {
 "##,
 
 E0422: r##"
-You are trying to use an identifier that is either undefined or not a
+You are trying to use an identifier that is either undefined or not a struct.
-struct. For instance:
+For instance:
 
 ``` compile_fail
 fn main () {
@@ -785,13 +785,13 @@ fn main () {
 }
 ```
 
-In this case, `foo` is defined, but is not a struct, so Rust can't use
+In this case, `foo` is defined, but is not a struct, so Rust can't use it as
-it as one.
+one.
 "##,
 
 E0423: r##"
-A `struct` variant name was used like a function name. Example of
+A `struct` variant name was used like a function name. Example of erroneous
-erroneous code:
+code:
 
 ```compile_fail
 struct Foo { a: bool};
@@ -801,8 +801,8 @@ let f = Foo();
 //        it like a function name
 ```
 
-Please verify you didn't misspell the name of what you actually wanted
+Please verify you didn't misspell the name of what you actually wanted to use
-to use here. Example:
+here. Example:
 
 ```
 fn Foo() -> u32 { 0 }
@@ -851,6 +851,7 @@ something_that_doesnt_exist::foo;
 // error: unresolved name `something_that_doesnt_exist::foo`
 
 // or:
+
 trait Foo {
     fn bar() {
         Self; // error: unresolved name `Self`
@@ -858,6 +859,7 @@ trait Foo {
 }
 
 // or:
+
 let x = unknown_variable;  // error: unresolved name `unknown_variable`
 ```
 
@@ -941,7 +943,7 @@ use something::self; // ok!
 "##,
 
 E0431: r##"
-`self` import was made. Erroneous code example:
+An invalid `self` import was made. Erroneous code example:
 
 ```compile_fail
 use {self}; // error: `self` import can only appear in an import list with a

src/libstd/collections/hash/map.rs

@@ -1157,9 +1157,10 @@ impl<K, V, S> HashMap<K, V, S>
     ///
     /// If the map did not have this key present, `None` is returned.
     ///
-    /// If the map did have this key present, the key is not updated, the
+    /// If the map did have this key present, the value is updated, and the old
-    /// value is updated and the old value is returned.
+    /// value is returned. The key is not updated, though; this matters for
-    /// See the [module-level documentation] for more.
+    /// types that can be `==` without being identical. See the [module-level
+    /// documentation] for more.
     ///
     /// [module-level documentation]: index.html#insert-and-complex-keys
     ///

src/libstd/collections/mod.rs

@@ -397,12 +397,15 @@
 //! }
 //!
 //! let mut map = BTreeMap::new();
-//! map.insert(Foo { a: 1, b: "baz" }, ());
+//! map.insert(Foo { a: 1, b: "baz" }, 99);
 //!
 //! // We already have a Foo with an a of 1, so this will be updating the value.
-//! map.insert(Foo { a: 1, b: "xyz" }, ());
+//! map.insert(Foo { a: 1, b: "xyz" }, 100);
 //!
-//! // ... but the key hasn't changed. b is still "baz", not "xyz"
+//! // The value has been updated...
+//! assert_eq!(map.values().next().unwrap(), &100);
+//!
+//! // ...but the key hasn't changed. b is still "baz", not "xyz".
 //! assert_eq!(map.keys().next().unwrap().b, "baz");
 //! ```
 

src/libstd/path.rs

@@ -1582,8 +1582,10 @@ impl Path {
 
     /// Returns a path that, when joined onto `base`, yields `self`.
     ///
+    /// # Errors
+    ///
     /// If `base` is not a prefix of `self` (i.e. `starts_with`
-    /// returns false), then `relative_from` returns `None`.
+    /// returns `false`), returns `Err`.
     #[stable(since = "1.7.0", feature = "path_strip_prefix")]
     pub fn strip_prefix<'a, P: ?Sized>(&'a self, base: &'a P)
                                        -> Result<&'a Path, StripPrefixError>

src/libstd/primitive_docs.rs

@@ -50,18 +50,21 @@ mod prim_bool { }
 /// [`String`]: string/struct.String.html
 ///
 /// As always, remember that a human intuition for 'character' may not map to
-/// Unicode's definitions. For example, emoji symbols such as '❤️' are more than
+/// Unicode's definitions. For example, emoji symbols such as '❤️' can be more
-/// one byte; ❤️ in particular is six:
+/// than one Unicode code point; this ❤️ in particular is two:
 ///
 /// ```
 /// let s = String::from("❤️");
 ///
-/// // six bytes times one byte for each element
+/// // we get two chars out of a single ❤️
-/// assert_eq!(6, s.len() * std::mem::size_of::<u8>());
+/// let mut iter = s.chars();
+/// assert_eq!(Some('\u{2764}'), iter.next());
+/// assert_eq!(Some('\u{fe0f}'), iter.next());
+/// assert_eq!(None, iter.next());
 /// ```
 ///
-/// This also means it won't fit into a `char`, and so trying to create a
+/// This means it won't fit into a `char`. Trying to create a literal with
-/// literal with `let heart = '❤️';` gives an error:
+/// `let heart = '❤️';` gives an error:
 ///
 /// ```text
 /// error: character literal may only contain one codepoint: '❤
@@ -69,8 +72,8 @@ mod prim_bool { }
 ///             ^~
 /// ```
 ///
-/// Another implication of this is that if you want to do per-`char`acter
+/// Another implication of the 4-byte fixed size of a `char`, is that
-/// processing, it can end up using a lot more memory:
+/// per-`char`acter processing can end up using a lot more memory:
 ///
 /// ```
 /// let s = String::from("love: ❤️");
@@ -79,19 +82,6 @@ mod prim_bool { }
 /// assert_eq!(12, s.len() * std::mem::size_of::<u8>());
 /// assert_eq!(32, v.len() * std::mem::size_of::<char>());
 /// ```
-///
-/// Or may give you results you may not expect:
-///
-/// ```
-/// let s = String::from("❤️");
-///
-/// let mut iter = s.chars();
-///
-/// // we get two chars out of a single ❤️
-/// assert_eq!(Some('\u{2764}'), iter.next());
-/// assert_eq!(Some('\u{fe0f}'), iter.next());
-/// assert_eq!(None, iter.next());
-/// ```
 mod prim_char { }
 
 #[doc(primitive = "unit")]