[Constraint system] Handle implicit tupling during pattern matching.

SE-0110 strikes again!

Author: DougGregor

lib/Sema/CSSimplify.cpp

@@ -1658,6 +1658,12 @@ ConstraintSystem::matchFunctionTypes(FunctionType *func1, FunctionType *func2,
             implodeParams(func2Params);
           }
         }
+      } else if (last->getKind() == ConstraintLocator::PatternMatch &&
+          isa<EnumElementPattern>(
+            last->castTo<LocatorPathElt::PatternMatch>().getPattern()) &&
+          isSingleTupleParam(ctx, func1Params) &&
+          canImplodeParams(func2Params)) {
+        implodeParams(func2Params);
       }
     }
 

test/stmt/if_while_var.swift

@@ -148,6 +148,7 @@ func testWhileScoping(_ a: Int?) {// expected-note {{did you mean 'a'?}}
 public enum SomeParseResult<T> {
   case error(length: Int)
   case repeated(value: String, repetitions: Int)
+  // expected-note@-1{{'repeated(value:repetitions:)' declared here}}
 
   var _error: Int? {
     if case .error(let result) = self { return result }
@@ -199,3 +200,9 @@ public enum SomeParseResult<T> {
     return nil
   }
 }
+
+func matchImplicitTupling(pr: SomeParseResult<Int>) {
+  if case .repeated(let x) = pr { // expected-warning{{enum case 'repeated' has 2 associated values; matching them as a tuple is deprecated}}
+    let y: Int = x // expected-error{{cannot convert value of type '(value: String, repetitions: Int)' to specified type 'Int'}}
+  }
+}