Auto merge of #49337 - kennytm:rollup, r=kennytm

Rollup of 21 pull requests

- Successful merges: #49046, #49076, #49089, #49120, #49121, #49122, #49162, #49193, #49194, #49203, #49229, #49235, #49254, #49268, #49273, #49274, #49290, #49312, #49314, #49318, #49299

6 files changed, 58 insertions, 14 deletions

diff --git a/src/libstd/f32.rs b/src/libstd/f32.rs
index a760922115a..ceb019bc95b 100644
--- a/src/libstd/f32.rs
+++ b/src/libstd/f32.rs
@@ -780,7 +780,7 @@ impl f32 {
         unsafe { cmath::atanf(self) }
     }
 
-    /// Computes the four quadrant arctangent of `self` (`y`) and `other` (`x`).
+    /// Computes the four quadrant arctangent of `self` (`y`) and `other` (`x`) in radians.
     ///
     /// * `x = 0`, `y = 0`: `0`
     /// * `x >= 0`: `arctan(y/x)` -> `[-pi/2, pi/2]`
@@ -791,12 +791,13 @@ impl f32 {
     /// use std::f32;
     ///
     /// let pi = f32::consts::PI;
-    /// // All angles from horizontal right (+x)
-    /// // 45 deg counter-clockwise
+    /// // Positive angles measured counter-clockwise
+    /// // from positive x axis
+    /// // -pi/4 radians (45 deg clockwise)
     /// let x1 = 3.0f32;
     /// let y1 = -3.0f32;
     ///
-    /// // 135 deg clockwise
+    /// // 3pi/4 radians (135 deg counter-clockwise)
     /// let x2 = -3.0f32;
     /// let y2 = 3.0f32;
     ///
diff --git a/src/libstd/f64.rs b/src/libstd/f64.rs
index 6f34f176a97..97adf108b73 100644
--- a/src/libstd/f64.rs
+++ b/src/libstd/f64.rs
@@ -716,7 +716,7 @@ impl f64 {
         unsafe { cmath::atan(self) }
     }
 
-    /// Computes the four quadrant arctangent of `self` (`y`) and `other` (`x`).
+    /// Computes the four quadrant arctangent of `self` (`y`) and `other` (`x`) in radians.
     ///
     /// * `x = 0`, `y = 0`: `0`
     /// * `x >= 0`: `arctan(y/x)` -> `[-pi/2, pi/2]`
@@ -727,12 +727,13 @@ impl f64 {
     /// use std::f64;
     ///
     /// let pi = f64::consts::PI;
-    /// // All angles from horizontal right (+x)
-    /// // 45 deg counter-clockwise
+    /// // Positive angles measured counter-clockwise
+    /// // from positive x axis
+    /// // -pi/4 radians (45 deg clockwise)
     /// let x1 = 3.0_f64;
     /// let y1 = -3.0_f64;
     ///
-    /// // 135 deg clockwise
+    /// // 3pi/4 radians (135 deg counter-clockwise)
     /// let x2 = -3.0_f64;
     /// let y2 = 3.0_f64;
     ///
diff --git a/src/libstd/fs.rs b/src/libstd/fs.rs
index db52ed67d3a..5caa703ee97 100644
--- a/src/libstd/fs.rs
+++ b/src/libstd/fs.rs
@@ -906,7 +906,13 @@ impl Metadata {
         FileType(self.0.file_type())
     }
 
-    /// Returns whether this metadata is for a directory.
+    /// Returns whether this metadata is for a directory. The
+    /// result is mutually exclusive to the result of
+    /// [`is_file`], and will be false for symlink metadata
+    /// obtained from [`symlink_metadata`].
+    ///
+    /// [`is_file`]: struct.Metadata.html#method.is_file
+    /// [`symlink_metadata`]: fn.symlink_metadata.html
     ///
     /// # Examples
     ///
@@ -923,7 +929,13 @@ impl Metadata {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_dir(&self) -> bool { self.file_type().is_dir() }
 
-    /// Returns whether this metadata is for a regular file.
+    /// Returns whether this metadata is for a regular file. The
+    /// result is mutually exclusive to the result of
+    /// [`is_dir`], and will be false for symlink metadata
+    /// obtained from [`symlink_metadata`].
+    ///
+    /// [`is_dir`]: struct.Metadata.html#method.is_dir
+    /// [`symlink_metadata`]: fn.symlink_metadata.html
     ///
     /// # Examples
     ///
@@ -1148,7 +1160,13 @@ impl Permissions {
 }
 
 impl FileType {
-    /// Test whether this file type represents a directory.
+    /// Test whether this file type represents a directory. The
+    /// result is mutually exclusive to the results of
+    /// [`is_file`] and [`is_symlink`]; only zero or one of these
+    /// tests may pass.
+    ///
+    /// [`is_file`]: struct.FileType.html#method.is_file
+    /// [`is_symlink`]: struct.FileType.html#method.is_symlink
     ///
     /// # Examples
     ///
@@ -1167,6 +1185,12 @@ impl FileType {
     pub fn is_dir(&self) -> bool { self.0.is_dir() }
 
     /// Test whether this file type represents a regular file.
+    /// The result is  mutually exclusive to the results of
+    /// [`is_dir`] and [`is_symlink`]; only zero or one of these
+    /// tests may pass.
+    ///
+    /// [`is_dir`]: struct.FileType.html#method.is_dir
+    /// [`is_symlink`]: struct.FileType.html#method.is_symlink
     ///
     /// # Examples
     ///
@@ -1185,6 +1209,9 @@ impl FileType {
     pub fn is_file(&self) -> bool { self.0.is_file() }
 
     /// Test whether this file type represents a symbolic link.
+    /// The result is mutually exclusive to the results of
+    /// [`is_dir`] and [`is_file`]; only zero or one of these
+    /// tests may pass.
     ///
     /// The underlying [`Metadata`] struct needs to be retrieved
     /// with the [`fs::symlink_metadata`] function and not the
@@ -1195,6 +1222,8 @@ impl FileType {
     /// [`Metadata`]: struct.Metadata.html
     /// [`fs::metadata`]: fn.metadata.html
     /// [`fs::symlink_metadata`]: fn.symlink_metadata.html
+    /// [`is_dir`]: struct.FileType.html#method.is_dir
+    /// [`is_file`]: struct.FileType.html#method.is_file
     /// [`is_symlink`]: struct.FileType.html#method.is_symlink
     ///
     /// # Examples
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 36eb7291822..0b06c5d4d65 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -308,7 +308,6 @@
 #![feature(str_char)]
 #![feature(str_internals)]
 #![feature(str_utf16)]
-#![feature(termination_trait)]
 #![feature(test, rustc_private)]
 #![feature(thread_local)]
 #![feature(toowned_clone_into)]
@@ -325,6 +324,7 @@
 #![cfg_attr(test, feature(update_panic_count))]
 #![cfg_attr(windows, feature(used))]
 #![cfg_attr(stage0, feature(never_type))]
+#![cfg_attr(stage0, feature(termination_trait))]
 
 #![default_lib_allocator]
 
diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index 000f9713615..47609f17221 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -335,6 +335,18 @@ pub mod builtin {
     /// proxied through this one.  `format_args!`, unlike its derived macros, avoids
     /// heap allocations.
     ///
+    /// You can use the [`fmt::Arguments`] value that `format_args!` returns
+    /// in `Debug` and `Display` contexts as seen below. The example also shows
+    /// that `Debug` and `Display` format to the same thing: the interpolated
+    /// format string in `format_args!`.
+    ///
+    /// ```rust
+    /// let display = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
+    /// let debug = format!("{}", format_args!("{} foo {:?}", 1, 2));
+    /// assert_eq!("1 foo 2", display);
+    /// assert_eq!(display, debug);
+    /// ```
+    ///
     /// For more information, see the documentation in [`std::fmt`].
     ///
     /// [`Display`]: ../std/fmt/trait.Display.html
diff --git a/src/libstd/process.rs b/src/libstd/process.rs
index d5ac2d19e83..c877bf6aa35 100644
--- a/src/libstd/process.rs
+++ b/src/libstd/process.rs
@@ -1442,8 +1442,9 @@ pub fn id() -> u32 {
 /// a successful execution. In case of a failure, `libc::EXIT_FAILURE` is returned.
 #[cfg_attr(not(test), lang = "termination")]
 #[unstable(feature = "termination_trait_lib", issue = "43301")]
-#[rustc_on_unimplemented =
-  "`main` can only return types that implement {Termination}, not `{Self}`"]
+#[rustc_on_unimplemented(
+  message="`main` has invalid return type `{Self}`",
+  label="`main` can only return types that implement {Termination}")]
 pub trait Termination {
     /// Is called to get the representation of the value as status code.
     /// This status code is returned to the operating system.