The non-intrusive bits of my hopefully pending ...

The non-intrusive bits of my hopefully pending "use the static type of
the scrutinee to rule out some type/extractor patterns" patch. Includes
a cleanup of the (still inadequate) type-parameter-ignoring match test
which had been interfering with martin's digestion.

Also: implicit search is disabled when typing a pattern, because the
matcher never invokes implicits to satisfy a pattern. At worst maybe
we'll get a performance bump. No review.

1 files changed, 7 insertions, 14 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 879dadcbed..aeb3762afc 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -4206,20 +4206,13 @@ trait Typers { self: Analyzer =>
 
     /** Types a pattern with prototype <code>pt</code> */
     def typedPattern(tree: Tree, pt: Type): Tree = {
-      // The commented out code stems from investigation into whether
-      //   "abc" match { case Seq('a', 'b', 'c') => true }
-      // can be ruled out statically.  At present this is a runtime
-      // error both because there is an implicit from String to Seq
-      // (even though such implicits are not used by the matcher) and
-      // because the typer is fine with concluding that "abc" might
-      // be of type "String with Seq[T]" and thus eligible for a call
-      // to unapplySeq.
-      //
-      // val savedImplicitsEnabled = context.implicitsEnabled
-      // context.implicitsEnabled = false
-      // try
-      typed(tree, PATTERNmode, pt)
-      // finally context.implicitsEnabled = savedImplicitsEnabled
+      // We disable implicits because otherwise some constructs will
+      // type check which should not.  The pattern matcher does not
+      // perform implicit conversions in an attempt to consummate a match.
+      val savedImplicitsEnabled = context.implicitsEnabled
+      context.implicitsEnabled = false
+      try typed(tree, PATTERNmode, pt)
+      finally context.implicitsEnabled = savedImplicitsEnabled
     }
 
     /** Types a (fully parameterized) type tree */