Collect nowarn symbols instead of skipping them

Allow selector aliasing

Drill thru this selections

Reduce obsolete use of NoWarnAttachment

Use the attachment to avoid warning when the user wrote underscore;
the position will be opaque, although the fresh name is longer than
the span. For good measure, also avoid warning about fresh names.

PatVarDef members warn under -Wunused:patvars

Drop local from patvar names

No warn if patvar has public accessor

Ignore annotation params

No warn unit-valued params

No warn this is trivial

util.WeakHashSet respects load factor

Author: som-snytt

library/src/scala/Array.scala

@@ -124,16 +124,16 @@ object Array {
     * @see `java.util.Arrays#copyOf`
     */
   def copyOf[A](original: Array[A], newLength: Int): Array[A] = ((original: @unchecked) match {
-    case x: Array[BoxedUnit]  => newUnitArray(newLength).asInstanceOf[Array[A]]
-    case x: Array[AnyRef]     => java.util.Arrays.copyOf(x, newLength)
-    case x: Array[Int]        => java.util.Arrays.copyOf(x, newLength)
-    case x: Array[Double]     => java.util.Arrays.copyOf(x, newLength)
-    case x: Array[Long]       => java.util.Arrays.copyOf(x, newLength)
-    case x: Array[Float]      => java.util.Arrays.copyOf(x, newLength)
-    case x: Array[Char]       => java.util.Arrays.copyOf(x, newLength)
-    case x: Array[Byte]       => java.util.Arrays.copyOf(x, newLength)
-    case x: Array[Short]      => java.util.Arrays.copyOf(x, newLength)
-    case x: Array[Boolean]    => java.util.Arrays.copyOf(x, newLength)
+    case original: Array[BoxedUnit]  => newUnitArray(newLength).asInstanceOf[Array[A]]
+    case original: Array[AnyRef]     => java.util.Arrays.copyOf(original, newLength)
+    case original: Array[Int]        => java.util.Arrays.copyOf(original, newLength)
+    case original: Array[Double]     => java.util.Arrays.copyOf(original, newLength)
+    case original: Array[Long]       => java.util.Arrays.copyOf(original, newLength)
+    case original: Array[Float]      => java.util.Arrays.copyOf(original, newLength)
+    case original: Array[Char]       => java.util.Arrays.copyOf(original, newLength)
+    case original: Array[Byte]       => java.util.Arrays.copyOf(original, newLength)
+    case original: Array[Short]      => java.util.Arrays.copyOf(original, newLength)
+    case original: Array[Boolean]    => java.util.Arrays.copyOf(original, newLength)
   }).asInstanceOf[Array[A]]
 
   /** Copy one array to another, truncating or padding with default values (if

library/src/scala/collection/Iterable.scala

@@ -725,10 +725,12 @@ trait IterableOps[+A, +CC[_], +C] extends Any with IterableOnce[A] with Iterable
    *  @return       a new $coll which contains all elements
    *                of this $coll followed by all elements of `suffix`.
    */
-  def concat[B >: A](suffix: IterableOnce[B]): CC[B] = iterableFactory.from(suffix match {
-    case xs: Iterable[B] => new View.Concat(this, xs)
-    case xs => iterator ++ suffix.iterator
-  })
+  def concat[B >: A](suffix: IterableOnce[B]): CC[B] = iterableFactory.from {
+    suffix match {
+      case suffix: Iterable[B] => new View.Concat(this, suffix)
+      case suffix => iterator ++ suffix.iterator
+    }
+  }
 
   /** Alias for `concat` */
   @inline final def ++ [B >: A](suffix: IterableOnce[B]): CC[B] = concat(suffix)