Auto merge of #53662 - kennytm:rollup, r=kennytm

Rollup of 16 pull requests

Successful merges:

 - #53311 (Window Mutex: Document that we properly initialize the SRWLock)
 - #53503 (Discourage overuse of mem::forget)
 - #53545 (Fix #50865: ICE on impl-trait returning functions reaching private items)
 - #53559 (add macro check for lint)
 - #53562 (Lament the invincibility of the Turbofish)
 - #53563 (use String::new() instead of String::from(""), "".to_string(), "".to_owned() or "".into())
 - #53592 (docs: minor stylistic changes to str/string docs)
 - #53594 (Update RELEASES.md to include clippy-preview)
 - #53600 (Fix a grammatical mistake in "expected generic arguments" errors)
 - #53614 (update nomicon and book)
 - #53617 (tidy: Stop requiring a license header)
 - #53618 (Add missing fmt examples)
 - #53636 (Prefer `.nth(n)` over `.skip(n).next()`.)
 - #53644 (Use SmallVec for SmallCStr)
 - #53664 (Remove unnecessary closure in rustc_mir/build/mod.rs)
 - #53666 (Added rustc_codegen_llvm to compiler documentation.)

RELEASES.md

@@ -39,6 +39,8 @@ Misc
   will demote `deny` and `forbid` lints to `warn`.
 - [`rustc` and `rustdoc` will now have the exit code of `1` if compilation
   fails, and `101` if there is a panic.][52197]
+- [A preview of clippy has been made available through rustup.][51122]
+  You can install the preview with `rustup component add clippy-preview`
 
 Compatibility Notes
 -------------------
@@ -64,6 +66,7 @@ Compatibility Notes
 [51619]: https://github.com/rust-lang/rust/pull/51619/
 [51656]: https://github.com/rust-lang/rust/pull/51656/
 [51178]: https://github.com/rust-lang/rust/pull/51178/
+[51122]: https://github.com/rust-lang/rust/pull/51122
 [50494]: https://github.com/rust-lang/rust/pull/50494/
 [cargo/5614]: https://github.com/rust-lang/cargo/pull/5614/
 [cargo/5723]: https://github.com/rust-lang/cargo/pull/5723/

src/bootstrap/doc.rs

@@ -712,7 +712,7 @@ impl Step for Rustc {
 
         // Find dependencies for top level crates.
         let mut compiler_crates = HashSet::new();
-        for root_crate in &["rustc", "rustc_driver"] {
+        for root_crate in &["rustc", "rustc_driver", "rustc_codegen_llvm"] {
             let interned_root_crate = INTERNER.intern_str(root_crate);
             find_compiler_crates(builder, &interned_root_crate, &mut compiler_crates);
         }

src/liballoc/str.rs

@@ -513,7 +513,7 @@ impl str {
         unsafe { String::from_utf8_unchecked(slice.into_vec()) }
     }
 
-    /// Create a [`String`] by repeating a string `n` times.
+    /// Creates a new [`String`] by repeating a string `n` times.
     ///
     /// [`String`]: string/struct.String.html
     ///

src/liballoc/string.rs

@@ -752,7 +752,7 @@ impl String {
         self.vec
     }
 
-    /// Extracts a string slice containing the entire string.
+    /// Extracts a string slice containing the entire `String`.
     ///
     /// # Examples
     ///
@@ -1454,8 +1454,8 @@ impl String {
         self.vec.clear()
     }
 
-    /// Creates a draining iterator that removes the specified range in the string
-    /// and yields the removed chars.
+    /// Creates a draining iterator that removes the specified range in the `String`
+    /// and yields the removed `chars`.
     ///
     /// Note: The element range is removed even if the iterator is not
     /// consumed until the end.

src/libcore/fmt/mod.rs

@@ -1132,6 +1132,36 @@ impl<'a> Formatter<'a> {
     ///
     /// This function will correctly account for the flags provided as well as
     /// the minimum width. It will not take precision into account.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo { nb: i32 };
+    ///
+    /// impl Foo {
+    ///     fn new(nb: i32) -> Foo {
+    ///         Foo {
+    ///             nb,
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         // We need to remove "-" from the number output.
+    ///         let tmp = self.nb.abs().to_string();
+    ///
+    ///         formatter.pad_integral(self.nb > 0, "Foo ", &tmp)
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{}", Foo::new(2)), "2");
+    /// assert_eq!(&format!("{}", Foo::new(-1)), "-1");
+    /// assert_eq!(&format!("{:#}", Foo::new(-1)), "-Foo 1");
+    /// assert_eq!(&format!("{:0>#8}", Foo::new(-1)), "00-Foo 1");
+    /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn pad_integral(&mut self,
                         is_nonnegative: bool,
@@ -1232,7 +1262,7 @@ impl<'a> Formatter<'a> {
             // If our string is longer that the precision, then we must have
             // truncation. However other flags like `fill`, `width` and `align`
             // must act as always.
-            if let Some((i, _)) = s.char_indices().skip(max).next() {
+            if let Some((i, _)) = s.char_indices().nth(max) {
                 // LLVM here can't prove that `..i` won't panic `&s[..i]`, but
                 // we know that it can't panic. Use `get` + `unwrap_or` to avoid
                 // `unsafe` and otherwise don't emit any panic-related code
@@ -1381,12 +1411,48 @@ impl<'a> Formatter<'a> {
 
     /// Writes some data to the underlying buffer contained within this
     /// formatter.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo;
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         formatter.write_str("Foo")
+    ///         // This is equivalent to:
+    ///         // write!(formatter, "Foo")
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{}", Foo), "Foo");
+    /// assert_eq!(&format!("{:0>8}", Foo), "Foo");
+    /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn write_str(&mut self, data: &str) -> Result {
         self.buf.write_str(data)
     }
 
     /// Writes some formatted information into this instance.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::fmt;
+    ///
+    /// struct Foo(i32);
+    ///
+    /// impl fmt::Display for Foo {
+    ///     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+    ///         formatter.write_fmt(format_args!("Foo {}", self.0))
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(&format!("{}", Foo(-1)), "Foo -1");
+    /// assert_eq!(&format!("{:0>8}", Foo(2)), "Foo 2");
+    /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn write_fmt(&mut self, fmt: Arguments) -> Result {
         write(self.buf, fmt)

src/libcore/mem.rs

@@ -29,13 +29,15 @@ use ops::{Deref, DerefMut, CoerceUnsized};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use intrinsics::transmute;
 
-/// Leaks a value: takes ownership and "forgets" about the value **without running
-/// its destructor**.
+/// Takes ownership and "forgets" about the value **without running its destructor**.
 ///
 /// Any resources the value manages, such as heap memory or a file handle, will linger
-/// forever in an unreachable state.
+/// forever in an unreachable state. However, it does not guarantee that pointers
+/// to this memory will remain valid.
 ///
-/// If you want to dispose of a value properly, running its destructor, see
+/// * If you want to leak memory, see [`Box::leak`][leak].
+/// * If you want to obtain a raw pointer to the memory, see [`Box::into_raw`][into_raw].
+/// * If you want to dispose of a value properly, running its destructor, see
 /// [`mem::drop`][drop].
 ///
 /// # Safety
@@ -59,15 +61,6 @@ pub use intrinsics::transmute;
 ///
 /// # Examples
 ///
-/// Leak some heap memory by never deallocating it:
-///
-/// ```
-/// use std::mem;
-///
-/// let heap_memory = Box::new(3);
-/// mem::forget(heap_memory);
-/// ```
-///
 /// Leak an I/O object, never closing the file:
 ///
 /// ```no_run
@@ -137,38 +130,13 @@ pub use intrinsics::transmute;
 /// }
 /// ```
 ///
-/// ## Use case 3
-///
-/// You are transferring ownership across a [FFI] boundary to code written in
-/// another language. You need to `forget` the value on the Rust side because Rust
-/// code is no longer responsible for it.
-///
-/// ```no_run
-/// use std::mem;
-///
-/// extern "C" {
-///     fn my_c_function(x: *const u32);
-/// }
-///
-/// let x: Box<u32> = Box::new(3);
-///
-/// // Transfer ownership into C code.
-/// unsafe {
-///     my_c_function(&*x);
-/// }
-/// mem::forget(x);
-/// ```
-///
-/// In this case, C code must call back into Rust to free the object. Calling C's `free`
-/// function on a [`Box`][box] is *not* safe! Also, `Box` provides an [`into_raw`][into_raw]
-/// method which is the preferred way to do this in practice.
-///
 /// [drop]: fn.drop.html
 /// [uninit]: fn.uninitialized.html
 /// [clone]: ../clone/trait.Clone.html
 /// [swap]: fn.swap.html
 /// [FFI]: ../../book/first-edition/ffi.html
 /// [box]: ../../std/boxed/struct.Box.html
+/// [leak]: ../../std/boxed/struct.Box.html#method.leak
 /// [into_raw]: ../../std/boxed/struct.Box.html#method.into_raw
 /// [ub]: ../../reference/behavior-considered-undefined.html
 #[inline]

src/librustc/ich/impls_ty.rs

@@ -1091,6 +1091,7 @@ impl_stable_hash_for!(enum traits::Reveal {
 });
 
 impl_stable_hash_for!(enum ::middle::privacy::AccessLevel {
+    ReachableFromImplTrait,
     Reachable,
     Exported,
     Public

src/librustc/infer/error_reporting/mod.rs

@@ -1330,7 +1330,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             s
         };
         let var_description = match var_origin {
-            infer::MiscVariable(_) => "".to_string(),
+            infer::MiscVariable(_) => String::new(),
             infer::PatternRegion(_) => " for pattern".to_string(),
             infer::AddrOfRegion(_) => " for borrow expression".to_string(),
             infer::Autoref(_) => " for autoref".to_string(),

src/librustc/middle/privacy.rs

@@ -21,6 +21,8 @@ use syntax::ast::NodeId;
 // Accessibility levels, sorted in ascending order
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub enum AccessLevel {
+    // Superset of Reachable used to mark impl Trait items.
+    ReachableFromImplTrait,
     // Exported items + items participating in various kinds of public interfaces,
     // but not directly nameable. For example, if function `fn f() -> T {...}` is
     // public, then type `T` is reachable. Its values can be obtained by other crates
@@ -40,7 +42,7 @@ pub struct AccessLevels<Id = NodeId> {
 
 impl<Id: Hash + Eq> AccessLevels<Id> {
     pub fn is_reachable(&self, id: Id) -> bool {
-        self.map.contains_key(&id)
+        self.map.get(&id) >= Some(&AccessLevel::Reachable)
     }
     pub fn is_exported(&self, id: Id) -> bool {
         self.map.get(&id) >= Some(&AccessLevel::Exported)

src/librustc/middle/reachable.rs

@@ -434,6 +434,8 @@ fn reachable_set<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum) ->
     // Step 2: Mark all symbols that the symbols on the worklist touch.
     reachable_context.propagate();
 
+    debug!("Inline reachability shows: {:?}", reachable_context.reachable_symbols);
+
     // Return the set of reachable symbols.
     ReachableSet(Lrc::new(reachable_context.reachable_symbols))
 }

src/librustc/mir/mod.rs

@@ -2105,7 +2105,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                     region
                 } else {
                     // Do not even print 'static
-                    "".to_owned()
+                    String::new()
                 };
                 write!(fmt, "&{}{}{:?}", region, kind_str, place)
             }

src/librustc/session/config.rs

@@ -1051,7 +1051,7 @@ options! {CodegenOptions, CodegenSetter, basic_codegen_options,
         "perform LLVM link-time optimizations"),
     target_cpu: Option<String> = (None, parse_opt_string, [TRACKED],
         "select target processor (rustc --print target-cpus for details)"),
-    target_feature: String = ("".to_string(), parse_string, [TRACKED],
+    target_feature: String = (String::new(), parse_string, [TRACKED],
         "target specific attributes (rustc --print target-features for details)"),
     passes: Vec<String> = (Vec::new(), parse_list, [TRACKED],
         "a list of extra LLVM passes to run (space separated)"),
@@ -1085,7 +1085,7 @@ options! {CodegenOptions, CodegenSetter, basic_codegen_options,
          "choose the code model to use (rustc --print code-models for details)"),
     metadata: Vec<String> = (Vec::new(), parse_list, [TRACKED],
          "metadata to mangle symbol names with"),
-    extra_filename: String = ("".to_string(), parse_string, [UNTRACKED],
+    extra_filename: String = (String::new(), parse_string, [UNTRACKED],
          "extra data to put in each output filename"),
     codegen_units: Option<usize> = (None, parse_opt_uint, [UNTRACKED],
         "divide crate into N units to optimize in parallel"),
@@ -1992,7 +1992,7 @@ pub fn build_session_options_and_crate_config(
     };
     if cg.target_feature == "help" {
         prints.push(PrintRequest::TargetFeatures);
-        cg.target_feature = "".to_string();
+        cg.target_feature = String::new();
     }
     if cg.relocation_model.as_ref().map_or(false, |s| s == "help") {
         prints.push(PrintRequest::RelocationModels);

src/librustc/traits/error_reporting.rs

@@ -472,7 +472,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                           if len > 5 {
                               format!("\nand {} others", len - 4)
                           } else {
-                              "".to_owned()
+                              String::new()
                           }
                           ));
     }
@@ -917,7 +917,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                                  remove_refs);
 
                         err.span_suggestion_short_with_applicability(
-                            sp, &format_str, String::from(""), Applicability::MachineApplicable
+                            sp, &format_str, String::new(), Applicability::MachineApplicable
                         );
                         break;
                     }
@@ -1116,7 +1116,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                         .collect::<Vec<String>>()
                                         .join(", "))
                         } else {
-                            "".to_owned()
+                            String::new()
                         },
                     );
                     err.span_suggestion_with_applicability(

src/librustc/traits/select.rs

@@ -120,13 +120,13 @@ impl IntercrateAmbiguityCause {
             &IntercrateAmbiguityCause::DownstreamCrate { ref trait_desc, ref self_desc } => {
                 let self_desc = if let &Some(ref ty) = self_desc {
                     format!(" for type `{}`", ty)
-                } else { "".to_string() };
+                } else { String::new() };
                 format!("downstream crates may implement trait `{}`{}", trait_desc, self_desc)
             }
             &IntercrateAmbiguityCause::UpstreamCrateUpdate { ref trait_desc, ref self_desc } => {
                 let self_desc = if let &Some(ref ty) = self_desc {
                     format!(" for type `{}`", ty)
-                } else { "".to_string() };
+                } else { String::new() };
                 format!("upstream crates may add new impl of trait `{}`{} \
                          in future versions",
                         trait_desc, self_desc)

src/librustc/util/common.rs

@@ -213,7 +213,7 @@ fn print_time_passes_entry_internal(what: &str, dur: Duration) {
             let mb = n as f64 / 1_000_000.0;
             format!("; rss: {}MB", mb.round() as usize)
         }
-        None => "".to_owned(),
+        None => String::new(),
     };
     println!("{}time: {}{}\t{}",
              "  ".repeat(indentation),

src/librustc/util/profiling.rs

@@ -73,7 +73,7 @@ macro_rules! define_categories {
                         (format!("{:.2}",
                         (((hits as f32) / (total as f32)) * 100.0)), total.to_string())
                     } else {
-                        ("".into(), "".into())
+                        (String::new(), String::new())
                     };
 
                     writeln!(

src/librustc_borrowck/borrowck/unused.rs

@@ -87,7 +87,7 @@ impl<'a, 'tcx> UnusedMutCx<'a, 'tcx> {
                 .span_suggestion_short_with_applicability(
                     mut_span,
                     "remove this `mut`",
-                    "".to_owned(),
+                    String::new(),
                     Applicability::MachineApplicable)
                 .emit();
         }