Auto merge of #68975 - Dylan-DPC:rollup-jzab8oh, r=Dylan-DPC

Rollup of 7 pull requests

Successful merges:

 - #68718 (Move `rustc_hir::def_id` to `rustc_span::def_id`)
 - #68834 (Fix and test implementation of BTreeMap's first/last_entry, pop_first/last)
 - #68857 (perf: Reduce Vec allocations in normalization by passing &mut Vec)
 - #68918 (Don't use the word "unwrap" to describe "unwrap" methods)
 - #68946 (Mark several functions and methods in core::cmp as #[must_use])
 - #68958 (Clean up E0277 and E0282 explanations)
 - #68960 (codegen: misc cleanups around debuginfo scopes and locations.)

Failed merges:

r? @ghost

3 files changed, 88 insertions, 63 deletions

diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
index e41a7afd3e2..604be7d5f68 100644
--- a/src/libcore/cmp.rs
+++ b/src/libcore/cmp.rs
@@ -361,6 +361,7 @@ impl Ordering {
     /// assert!(data == b);
     /// ```
     #[inline]
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn reverse(self) -> Ordering {
         match self {
@@ -398,6 +399,7 @@ impl Ordering {
     /// assert_eq!(result, Ordering::Less);
     /// ```
     #[inline]
+    #[must_use]
     #[stable(feature = "ordering_chaining", since = "1.17.0")]
     pub fn then(self, other: Ordering) -> Ordering {
         match self {
@@ -435,6 +437,7 @@ impl Ordering {
     /// assert_eq!(result, Ordering::Less);
     /// ```
     #[inline]
+    #[must_use]
     #[stable(feature = "ordering_chaining", since = "1.17.0")]
     pub fn then_with<F: FnOnce() -> Ordering>(self, f: F) -> Ordering {
         match self {
@@ -576,6 +579,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     /// assert_eq!(10.cmp(&5), Ordering::Greater);
     /// assert_eq!(5.cmp(&5), Ordering::Equal);
     /// ```
+    #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn cmp(&self, other: &Self) -> Ordering;
 
@@ -591,6 +595,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     /// ```
     #[stable(feature = "ord_max_min", since = "1.21.0")]
     #[inline]
+    #[must_use]
     fn max(self, other: Self) -> Self
     where
         Self: Sized,
@@ -610,6 +615,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     /// ```
     #[stable(feature = "ord_max_min", since = "1.21.0")]
     #[inline]
+    #[must_use]
     fn min(self, other: Self) -> Self
     where
         Self: Sized,
@@ -635,6 +641,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     /// assert!(0.clamp(-2, 1) == 0);
     /// assert!(2.clamp(-2, 1) == 1);
     /// ```
+    #[must_use]
     #[unstable(feature = "clamp", issue = "44095")]
     fn clamp(self, min: Self, max: Self) -> Self
     where
@@ -915,6 +922,7 @@ pub macro PartialOrd($item:item) {
 /// assert_eq!(2, cmp::min(2, 2));
 /// ```
 #[inline]
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn min<T: Ord>(v1: T, v2: T) -> T {
     v1.min(v2)
@@ -935,6 +943,7 @@ pub fn min<T: Ord>(v1: T, v2: T) -> T {
 /// assert_eq!(cmp::min_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), -2);
 /// ```
 #[inline]
+#[must_use]
 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
 pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
     match compare(&v1, &v2) {
@@ -958,6 +967,7 @@ pub fn min_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
 /// assert_eq!(cmp::min_by_key(-2, 2, |x: &i32| x.abs()), -2);
 /// ```
 #[inline]
+#[must_use]
 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
 pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
     min_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
@@ -978,6 +988,7 @@ pub fn min_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
 /// assert_eq!(2, cmp::max(2, 2));
 /// ```
 #[inline]
+#[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn max<T: Ord>(v1: T, v2: T) -> T {
     v1.max(v2)
@@ -998,6 +1009,7 @@ pub fn max<T: Ord>(v1: T, v2: T) -> T {
 /// assert_eq!(cmp::max_by(-2, 2, |x: &i32, y: &i32| x.abs().cmp(&y.abs())), 2);
 /// ```
 #[inline]
+#[must_use]
 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
 pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
     match compare(&v1, &v2) {
@@ -1021,6 +1033,7 @@ pub fn max_by<T, F: FnOnce(&T, &T) -> Ordering>(v1: T, v2: T, compare: F) -> T {
 /// assert_eq!(cmp::max_by_key(-2, 2, |x: &i32| x.abs()), 2);
 /// ```
 #[inline]
+#[must_use]
 #[unstable(feature = "cmp_min_max_by", issue = "64460")]
 pub fn max_by_key<T, F: FnMut(&T) -> K, K: Ord>(v1: T, v2: T, mut f: F) -> T {
     max_by(v1, v2, |v1, v2| f(v1).cmp(&f(v2)))
diff --git a/src/libcore/option.rs b/src/libcore/option.rs
index e35c91206b8..9b32442371c 100644
--- a/src/libcore/option.rs
+++ b/src/libcore/option.rs
@@ -317,7 +317,7 @@ impl<T> Option<T> {
     // Getting to contained values
     /////////////////////////////////////////////////////////////////////////
 
-    /// Unwraps an option, yielding the content of a [`Some`].
+    /// Returns the contained [`Some`] value, consuming the `self` value.
     ///
     /// # Panics
     ///
@@ -348,17 +348,22 @@ impl<T> Option<T> {
         }
     }
 
-    /// Moves the value `v` out of the `Option<T>` if it is [`Some(v)`].
+    /// Returns the contained [`Some`] value, consuming the `self` value.
     ///
-    /// In general, because this function may panic, its use is discouraged.
+    /// Because this function may panic, its use is generally discouraged.
     /// Instead, prefer to use pattern matching and handle the [`None`]
-    /// case explicitly.
+    /// case explicitly, or call [`unwrap_or`], [`unwrap_or_else`], or
+    /// [`unwrap_or_default`].
+    ///
+    /// [`unwrap_or`]: #method.unwrap_or
+    /// [`unwrap_or_else`]: #method.unwrap_or_else
+    /// [`unwrap_or_default`]: #method.unwrap_or_default
     ///
     /// # Panics
     ///
     /// Panics if the self value equals [`None`].
     ///
-    /// [`Some(v)`]: #variant.Some
+    /// [`Some`]: #variant.Some
     /// [`None`]: #variant.None
     ///
     /// # Examples
@@ -382,12 +387,13 @@ impl<T> Option<T> {
         }
     }
 
-    /// Returns the contained value or a default.
+    /// Returns the contained [`Some`] value or a provided default.
     ///
     /// Arguments passed to `unwrap_or` are eagerly evaluated; if you are passing
     /// the result of a function call, it is recommended to use [`unwrap_or_else`],
     /// which is lazily evaluated.
     ///
+    /// [`Some`]: #variant.Some
     /// [`unwrap_or_else`]: #method.unwrap_or_else
     ///
     /// # Examples
@@ -405,7 +411,7 @@ impl<T> Option<T> {
         }
     }
 
-    /// Returns the contained value or computes it from a closure.
+    /// Returns the contained [`Some`] value or computes it from a closure.
     ///
     /// # Examples
     ///
@@ -986,7 +992,7 @@ impl<T: Clone> Option<&mut T> {
 }
 
 impl<T: fmt::Debug> Option<T> {
-    /// Unwraps an option, expecting [`None`] and returning nothing.
+    /// Consumes `self` while expecting [`None`] and returning nothing.
     ///
     /// # Panics
     ///
@@ -1029,7 +1035,7 @@ impl<T: fmt::Debug> Option<T> {
         }
     }
 
-    /// Unwraps an option, expecting [`None`] and returning nothing.
+    /// Consumes `self` while expecting [`None`] and returning nothing.
     ///
     /// # Panics
     ///
@@ -1074,7 +1080,7 @@ impl<T: fmt::Debug> Option<T> {
 }
 
 impl<T: Default> Option<T> {
-    /// Returns the contained value or a default
+    /// Returns the contained [`Some`] value or a default
     ///
     /// Consumes the `self` argument then, if [`Some`], returns the contained
     /// value, otherwise if [`None`], returns the [default value] for that
diff --git a/src/libcore/result.rs b/src/libcore/result.rs
index 809d4bace8e..0bc29e1bc66 100644
--- a/src/libcore/result.rs
+++ b/src/libcore/result.rs
@@ -798,8 +798,7 @@ impl<T, E> Result<T, E> {
         }
     }
 
-    /// Unwraps a result, yielding the content of an [`Ok`].
-    /// Else, it returns `optb`.
+    /// Returns the contained [`Ok`] value or a provided default.
     ///
     /// Arguments passed to `unwrap_or` are eagerly evaluated; if you are passing
     /// the result of a function call, it is recommended to use [`unwrap_or_else`],
@@ -814,27 +813,25 @@ impl<T, E> Result<T, E> {
     /// Basic usage:
     ///
     /// ```
-    /// let optb = 2;
+    /// let default = 2;
     /// let x: Result<u32, &str> = Ok(9);
-    /// assert_eq!(x.unwrap_or(optb), 9);
+    /// assert_eq!(x.unwrap_or(default), 9);
     ///
     /// let x: Result<u32, &str> = Err("error");
-    /// assert_eq!(x.unwrap_or(optb), optb);
+    /// assert_eq!(x.unwrap_or(default), default);
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn unwrap_or(self, optb: T) -> T {
+    pub fn unwrap_or(self, default: T) -> T {
         match self {
             Ok(t) => t,
-            Err(_) => optb,
+            Err(_) => default,
         }
     }
 
-    /// Unwraps a result, yielding the content of an [`Ok`].
-    /// If the value is an [`Err`] then it calls `op` with its value.
+    /// Returns the contained [`Ok`] value or computes it from a closure.
     ///
     /// [`Ok`]: enum.Result.html#variant.Ok
-    /// [`Err`]: enum.Result.html#variant.Err
     ///
     /// # Examples
     ///
@@ -937,7 +934,44 @@ impl<T: Clone, E> Result<&mut T, E> {
 }
 
 impl<T, E: fmt::Debug> Result<T, E> {
-    /// Unwraps a result, yielding the content of an [`Ok`].
+    /// Returns the contained [`Ok`] value, consuming the `self` value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the value is an [`Err`], with a panic message including the
+    /// passed message, and the content of the [`Err`].
+    ///
+    /// [`Ok`]: enum.Result.html#variant.Ok
+    /// [`Err`]: enum.Result.html#variant.Err
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```{.should_panic}
+    /// let x: Result<u32, &str> = Err("emergency failure");
+    /// x.expect("Testing expect"); // panics with `Testing expect: emergency failure`
+    /// ```
+    #[inline]
+    #[track_caller]
+    #[stable(feature = "result_expect", since = "1.4.0")]
+    pub fn expect(self, msg: &str) -> T {
+        match self {
+            Ok(t) => t,
+            Err(e) => unwrap_failed(msg, &e),
+        }
+    }
+
+    /// Returns the contained [`Ok`] value, consuming the `self` value.
+    ///
+    /// Because this function may panic, its use is generally discouraged.
+    /// Instead, prefer to use pattern matching and handle the [`Err`]
+    /// case explicitly, or call [`unwrap_or`], [`unwrap_or_else`], or
+    /// [`unwrap_or_default`].
+    ///
+    /// [`unwrap_or`]: #method.unwrap_or
+    /// [`unwrap_or_else`]: #method.unwrap_or_else
+    /// [`unwrap_or_default`]: #method.unwrap_or_default
     ///
     /// # Panics
     ///
@@ -969,13 +1003,15 @@ impl<T, E: fmt::Debug> Result<T, E> {
             Err(e) => unwrap_failed("called `Result::unwrap()` on an `Err` value", &e),
         }
     }
+}
 
-    /// Unwraps a result, yielding the content of an [`Ok`].
+impl<T: fmt::Debug, E> Result<T, E> {
+    /// Returns the contained [`Err`] value, consuming the `self` value.
     ///
     /// # Panics
     ///
-    /// Panics if the value is an [`Err`], with a panic message including the
-    /// passed message, and the content of the [`Err`].
+    /// Panics if the value is an [`Ok`], with a panic message including the
+    /// passed message, and the content of the [`Ok`].
     ///
     /// [`Ok`]: enum.Result.html#variant.Ok
     /// [`Err`]: enum.Result.html#variant.Err
@@ -985,22 +1021,20 @@ impl<T, E: fmt::Debug> Result<T, E> {
     /// Basic usage:
     ///
     /// ```{.should_panic}
-    /// let x: Result<u32, &str> = Err("emergency failure");
-    /// x.expect("Testing expect"); // panics with `Testing expect: emergency failure`
+    /// let x: Result<u32, &str> = Ok(10);
+    /// x.expect_err("Testing expect_err"); // panics with `Testing expect_err: 10`
     /// ```
     #[inline]
     #[track_caller]
-    #[stable(feature = "result_expect", since = "1.4.0")]
-    pub fn expect(self, msg: &str) -> T {
+    #[stable(feature = "result_expect_err", since = "1.17.0")]
+    pub fn expect_err(self, msg: &str) -> E {
         match self {
-            Ok(t) => t,
-            Err(e) => unwrap_failed(msg, &e),
+            Ok(t) => unwrap_failed(msg, &t),
+            Err(e) => e,
         }
     }
-}
 
-impl<T: fmt::Debug, E> Result<T, E> {
-    /// Unwraps a result, yielding the content of an [`Err`].
+    /// Returns the contained [`Err`] value, consuming the `self` value.
     ///
     /// # Panics
     ///
@@ -1031,38 +1065,10 @@ impl<T: fmt::Debug, E> Result<T, E> {
             Err(e) => e,
         }
     }
-
-    /// Unwraps a result, yielding the content of an [`Err`].
-    ///
-    /// # Panics
-    ///
-    /// Panics if the value is an [`Ok`], with a panic message including the
-    /// passed message, and the content of the [`Ok`].
-    ///
-    /// [`Ok`]: enum.Result.html#variant.Ok
-    /// [`Err`]: enum.Result.html#variant.Err
-    ///
-    /// # Examples
-    ///
-    /// Basic usage:
-    ///
-    /// ```{.should_panic}
-    /// let x: Result<u32, &str> = Ok(10);
-    /// x.expect_err("Testing expect_err"); // panics with `Testing expect_err: 10`
-    /// ```
-    #[inline]
-    #[track_caller]
-    #[stable(feature = "result_expect_err", since = "1.17.0")]
-    pub fn expect_err(self, msg: &str) -> E {
-        match self {
-            Ok(t) => unwrap_failed(msg, &t),
-            Err(e) => e,
-        }
-    }
 }
 
 impl<T: Default, E> Result<T, E> {
-    /// Returns the contained value or a default
+    /// Returns the contained [`Ok`] value or a default
     ///
     /// Consumes the `self` argument then, if [`Ok`], returns the contained
     /// value, otherwise if [`Err`], returns the default value for that
@@ -1101,7 +1107,7 @@ impl<T: Default, E> Result<T, E> {
 
 #[unstable(feature = "unwrap_infallible", reason = "newly added", issue = "61695")]
 impl<T, E: Into<!>> Result<T, E> {
-    /// Unwraps a result that can never be an [`Err`], yielding the content of the [`Ok`].
+    /// Returns the contained [`Ok`] value, but never panics.
     ///
     /// Unlike [`unwrap`], this method is known to never panic on the
     /// result types it is implemented for. Therefore, it can be used