Rename some identifiers in `RawVec` and `libarena`.

- Use `len` more consistently for the number of elements in a vector,
  because that's the usual name.
- Use `additional` more consistently for the number of elements we want
  to add, because that's what `Vec::reserve()` uses.
- Use `cap` consistently rather than `capacity`.
- Plus a few other tweaks.

This increases consistency and conciseness.

2 files changed, 36 insertions, 53 deletions

diff --git a/src/liballoc/raw_vec.rs b/src/liballoc/raw_vec.rs
index 8a22f267bf2..805dbfe2775 100644
--- a/src/liballoc/raw_vec.rs
+++ b/src/liballoc/raw_vec.rs
@@ -235,13 +235,13 @@ impl<T, A: AllocRef> RawVec<T, A> {
         }
     }
 
-    /// Ensures that the buffer contains at least enough space to hold
-    /// `used_capacity + needed_extra_capacity` elements. If it doesn't already have
-    /// enough capacity, will reallocate enough space plus comfortable slack
-    /// space to get amortized `O(1)` behavior. Will limit this behavior
-    /// if it would needlessly cause itself to panic.
+    /// Ensures that the buffer contains at least enough space to hold `len +
+    /// additional` elements. If it doesn't already have enough capacity, will
+    /// reallocate enough space plus comfortable slack space to get amortized
+    /// `O(1)` behavior. Will limit this behavior if it would needlessly cause
+    /// itself to panic.
     ///
-    /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
+    /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
     /// the requested space. This is not really unsafe, but the unsafe
     /// code *you* write that relies on the behavior of this function may break.
     ///
@@ -287,8 +287,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// #   vector.push_all(&[1, 3, 5, 7, 9]);
     /// # }
     /// ```
-    pub fn reserve(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
-        match self.try_reserve(used_capacity, needed_extra_capacity) {
+    pub fn reserve(&mut self, len: usize, additional: usize) {
+        match self.try_reserve(len, additional) {
             Err(CapacityOverflow) => capacity_overflow(),
             Err(AllocError { layout, .. }) => handle_alloc_error(layout),
             Ok(()) => { /* yay */ }
@@ -296,28 +296,23 @@ impl<T, A: AllocRef> RawVec<T, A> {
     }
 
     /// The same as `reserve`, but returns on errors instead of panicking or aborting.
-    pub fn try_reserve(
-        &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
-    ) -> Result<(), TryReserveError> {
-        if self.needs_to_grow(used_capacity, needed_extra_capacity) {
-            self.grow_amortized(used_capacity, needed_extra_capacity)
+    pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
+        if self.needs_to_grow(len, additional) {
+            self.grow_amortized(len, additional)
         } else {
             Ok(())
         }
     }
 
-    /// Ensures that the buffer contains at least enough space to hold
-    /// `used_capacity + needed_extra_capacity` elements. If it doesn't already,
-    /// will reallocate the minimum possible amount of memory necessary.
-    /// Generally this will be exactly the amount of memory necessary,
-    /// but in principle the allocator is free to give back more than what
-    /// we asked for.
+    /// Ensures that the buffer contains at least enough space to hold `len +
+    /// additional` elements. If it doesn't already, will reallocate the
+    /// minimum possible amount of memory necessary. Generally this will be
+    /// exactly the amount of memory necessary, but in principle the allocator
+    /// is free to give back more than we asked for.
     ///
-    /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
-    /// the requested space. This is not really unsafe, but the unsafe
-    /// code *you* write that relies on the behavior of this function may break.
+    /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
+    /// the requested space. This is not really unsafe, but the unsafe code
+    /// *you* write that relies on the behavior of this function may break.
     ///
     /// # Panics
     ///
@@ -328,8 +323,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// # Aborts
     ///
     /// Aborts on OOM.
-    pub fn reserve_exact(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
-        match self.try_reserve_exact(used_capacity, needed_extra_capacity) {
+    pub fn reserve_exact(&mut self, len: usize, additional: usize) {
+        match self.try_reserve_exact(len, additional) {
             Err(CapacityOverflow) => capacity_overflow(),
             Err(AllocError { layout, .. }) => handle_alloc_error(layout),
             Ok(()) => { /* yay */ }
@@ -339,14 +334,10 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
     pub fn try_reserve_exact(
         &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
+        len: usize,
+        additional: usize,
     ) -> Result<(), TryReserveError> {
-        if self.needs_to_grow(used_capacity, needed_extra_capacity) {
-            self.grow_exact(used_capacity, needed_extra_capacity)
-        } else {
-            Ok(())
-        }
+        if self.needs_to_grow(len, additional) { self.grow_exact(len, additional) } else { Ok(()) }
     }
 
     /// Shrinks the allocation down to the specified amount. If the given amount
@@ -371,8 +362,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
 impl<T, A: AllocRef> RawVec<T, A> {
     /// Returns if the buffer needs to grow to fulfill the needed extra capacity.
     /// Mainly used to make inlining reserve-calls possible without inlining `grow`.
-    fn needs_to_grow(&self, used_capacity: usize, needed_extra_capacity: usize) -> bool {
-        needed_extra_capacity > self.capacity().wrapping_sub(used_capacity)
+    fn needs_to_grow(&self, len: usize, additional: usize) -> bool {
+        additional > self.capacity().wrapping_sub(len)
     }
 
     fn capacity_from_bytes(excess: usize) -> usize {
@@ -392,13 +383,10 @@ impl<T, A: AllocRef> RawVec<T, A> {
     // so that all of the code that depends on `T` is within it, while as much
     // of the code that doesn't depend on `T` as possible is in functions that
     // are non-generic over `T`.
-    fn grow_amortized(
-        &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
-    ) -> Result<(), TryReserveError> {
+    fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
         // This is ensured by the calling contexts.
-        debug_assert!(needed_extra_capacity > 0);
+        debug_assert!(additional > 0);
+
         if mem::size_of::<T>() == 0 {
             // Since we return a capacity of `usize::MAX` when `elem_size` is
             // 0, getting to here necessarily means the `RawVec` is overfull.
@@ -406,8 +394,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
         }
 
         // Nothing we can really do about these checks, sadly.
-        let required_cap =
-            used_capacity.checked_add(needed_extra_capacity).ok_or(CapacityOverflow)?;
+        let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
 
         // This guarantees exponential growth. The doubling cannot overflow
         // because `cap <= isize::MAX` and the type of `cap` is `usize`.
@@ -440,18 +427,14 @@ impl<T, A: AllocRef> RawVec<T, A> {
     // The constraints on this method are much the same as those on
     // `grow_amortized`, but this method is usually instantiated less often so
     // it's less critical.
-    fn grow_exact(
-        &mut self,
-        used_capacity: usize,
-        needed_extra_capacity: usize,
-    ) -> Result<(), TryReserveError> {
+    fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
         if mem::size_of::<T>() == 0 {
             // Since we return a capacity of `usize::MAX` when the type size is
             // 0, getting to here necessarily means the `RawVec` is overfull.
             return Err(CapacityOverflow);
         }
 
-        let cap = used_capacity.checked_add(needed_extra_capacity).ok_or(CapacityOverflow)?;
+        let cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
         let new_layout = Layout::array::<T>(cap);
 
         // `finish_grow` is non-generic over `T`.
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index af943ecfd48..2226737757b 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -2977,12 +2977,12 @@ impl<T> Drain<'_, T> {
     }
 
     /// Makes room for inserting more elements before the tail.
-    unsafe fn move_tail(&mut self, extra_capacity: usize) {
+    unsafe fn move_tail(&mut self, additional: usize) {
         let vec = self.vec.as_mut();
-        let used_capacity = self.tail_start + self.tail_len;
-        vec.buf.reserve(used_capacity, extra_capacity);
+        let len = self.tail_start + self.tail_len;
+        vec.buf.reserve(len, additional);
 
-        let new_tail_start = self.tail_start + extra_capacity;
+        let new_tail_start = self.tail_start + additional;
         let src = vec.as_ptr().add(self.tail_start);
         let dst = vec.as_mut_ptr().add(new_tail_start);
         ptr::copy(src, dst, self.tail_len);