Be careful when comparing tuple pattern labels with tuple type labels,

in case the tuple type has fewer elements.

<rdar://problem/21081340> SourceKit crashed while rapidly undoing: Assertion failed: (Index < Length && "Invalid index!")

Swift SVN r29082

lib/Sema/TypeCheckPattern.cpp

@@ -1092,7 +1092,7 @@ bool TypeChecker::coercePatternToType(Pattern *&P, DeclContext *dc, Type type,
       // the label for the tuple type being matched.
       // TODO: detect and diagnose shuffling
       // TODO: permit shuffling
-      if (!elt.getLabel().empty() &&
+      if (!elt.getLabel().empty() && i < tupleTy->getNumElements() &&
           elt.getLabel() != tupleTy->getElement(i).getName()) {
         diagnose(elt.getLabelLoc(), diag::tuple_pattern_label_mismatch,
                  elt.getLabel(), tupleTy->getElement(i).getName());

test/decl/var/variables.swift

@@ -91,3 +91,8 @@ func test21057425() -> (Int, Int) {
   let x: Int = "not an int!", y = 0 // expected-error{{'String' is not convertible to 'Int'}}
   return (x, y)
 }
+
+// rdar://problem/21081340
+func test21081340() {
+  let (x: a, y: b): () = foo() // expected-error{{tuple pattern has the wrong length for tuple type '()'}}
+}