vec/raw: Simplify `RawVec::grow` (#392)

src/vec/vec-raw.md

@@ -28,18 +28,13 @@ impl<T> RawVec<T> {
     }
 
     fn grow(&mut self) {
-        let (new_cap, new_layout) = if self.cap == 0 {
-            (1, Layout::array::<T>(1).unwrap())
-        } else {
-            // This can't overflow because we ensure self.cap <= isize::MAX.
-            let new_cap = 2 * self.cap;
-
-            // Layout::array checks that the number of bytes is <= usize::MAX,
-            // but this is redundant since old_layout.size() <= isize::MAX,
-            // so the `unwrap` should never fail.
-            let new_layout = Layout::array::<T>(new_cap).unwrap();
-            (new_cap, new_layout)
-        };
+        // This can't overflow because we ensure self.cap <= isize::MAX.
+        let new_cap = if self.cap == 0 { 1 } else { 2 * self.cap };
+
+        // Layout::array checks that the number of bytes is <= usize::MAX,
+        // but this is redundant since old_layout.size() <= isize::MAX,
+        // so the `unwrap` should never fail.
+        let new_layout = Layout::array::<T>(new_cap).unwrap();
 
         // Ensure that the new allocation doesn't exceed `isize::MAX` bytes.
         assert!(new_layout.size() <= isize::MAX as usize, "Allocation too large");