[Parse] Mark closure parameters as definitively not destructured in

parseClosureSignatureIfPresent.

Otherwise, closure parameters that were parsed as "potentially destructured"
will fail constraint generation, even after the parser has decided
they are not destructured.

Author: hborla

lib/Parse/ParseExpr.cpp

@@ -2738,8 +2738,10 @@ parseClosureSignatureIfPresent(SourceRange &bracketRange,
 
   for (unsigned i = 0, e = params->size(); i != e; ++i) {
     auto *param = params->get(i);
-    if (!isTupleDestructuring(param))
+    if (!isTupleDestructuring(param)) {
+      param->setDestructured(false);
       continue;
+    }
 
     auto argName = "arg" + std::to_string(i);
 

test/Constraints/closures.swift

@@ -992,3 +992,10 @@ func rdar_59741308() {
     }
   }
 }
+
+func r60074136() {
+  func takesClosure(_ closure: ((Int) -> Void) -> Void) {}
+
+  takesClosure { ((Int) -> Void) -> Void in // expected-warning {{unnamed parameters must be written with the empty name '_'}}
+  }
+}