Adjust for 5.3 branch

Author: DougGregor

lib/Sema/CSApply.cpp

@@ -5703,7 +5703,7 @@ Expr *ExprRewriter::coerceCallArguments(
     SmallVector<LocatorPathElt, 4> path;
     auto anchor = locator.getLocatorParts(path);
     if (!path.empty() && path.back().is<LocatorPathElt::ApplyArgument>() &&
-        (anchor.isExpr(ExprKind::Call) || anchor.isExpr(ExprKind::Subscript))) {
+        (isa<CallExpr>(anchor) || isa<SubscriptExpr>(anchor))) {
       auto locatorPtr = cs.getConstraintLocator(locator);
       assert(solution.trailingClosureMatchingChoices.count(locatorPtr) == 1);
       trailingClosureMatching = solution.trailingClosureMatchingChoices.find(

lib/Sema/CSGen.cpp

@@ -1409,7 +1409,8 @@ namespace {
       auto funcType = constr->getMethodInterfaceType()->castTo<FunctionType>();
       ::matchCallArguments(
           CS, funcType, args, params, ConstraintKind::ArgumentConversion,
-          CS.getConstraintLocator(expr, ConstraintLocator::ApplyArgument));
+          CS.getConstraintLocator(expr, ConstraintLocator::ApplyArgument),
+          TrailingClosureMatching::Forward);
 
       Type result = tv;
       if (constr->isFailable())

test/Constraints/diagnostics.swift

@@ -1259,8 +1259,11 @@ func rdar17170728() {
   }
 
   let _ = [i, j, k].reduce(0 as Int?) {
+    // expected-error@-1 {{missing argument label 'into:' in call}}
+    // expected-error@-2 {{cannot convert value of type 'Int?' to expected argument type '(inout @escaping (Bool, Bool) -> Bool, Int?) throws -> ()'}}
     $0 && $1 ? $0 + $1 : ($0 ? $0 : ($1 ? $1 : nil))
     // expected-error@-1 {{binary operator '+' cannot be applied to two 'Bool' operands}}
+    // expected-error@-2 {{'nil' cannot be used in context expecting type 'Bool'}}
   }
 }