[Sema] Don’t allow unresolved type variables if LeaveBraceStmtBodyUnchecked is true

According to Pavel, we want to eliminate allowing unresolved variables as much as possible. Removing this flag doesn’t break any test cases (at least not in a meaningful way) and fixes a crasher, so it seems reasonable to remove it.

Fixes rdar://76686564

Author: ahoppen

lib/Sema/TypeCheckStmt.cpp

@@ -1506,7 +1506,6 @@ void StmtChecker::typeCheckASTNode(ASTNode &node) {
       options |= TypeCheckExprFlags::IsDiscarded;
     if (LeaveBraceStmtBodyUnchecked) {
       options |= TypeCheckExprFlags::LeaveClosureBodyUnchecked;
-      options |= TypeCheckExprFlags::AllowUnresolvedTypeVariables;
     }
 
     auto resultTy =

test/IDE/complete_call_arg.swift

@@ -439,7 +439,7 @@ func curry<T1, T2, R>(_ f: @escaping (T1, T2) -> R) -> (T1) -> (T2) -> R {
   return { t1 in { t2 in f(#^NESTED_CLOSURE^#, t2) } }
   // NESTED_CLOSURE: Begin completions
   // FIXME: Should be '/TypeRelation[Invalid]: t2[#T2#]'
-  // NESTED_CLOSURE: Decl[LocalVar]/Local:               t2[#_#]; name=t2
+  // NESTED_CLOSURE: Decl[LocalVar]/Local:               t2; name=t2
   // NESTED_CLOSURE: Decl[LocalVar]/Local:               t1[#T1#]; name=t1
 }
 

validation-test/IDE/crashers_2_fixed/rdar76686564.swift

@@ -0,0 +1,21 @@
+// RUN: %target-swift-ide-test --conforming-methods -code-completion-token=COMPLETE --conforming-methods-expected-types=s:14swift_ide_test10MySequenceP -source-filename %s
+
+protocol MySequence {
+  associatedtype Element
+}
+
+struct Foo<X>: MySequence {
+	typealias Element = X
+}
+
+struct ArgumentDefinition {
+  fileprivate func bashCompletionWords() -> Foo<String> { fatalError() }
+}
+
+func myFlatMap<SegmentOfResult: MySequence>(_ transform: (ArgumentDefinition) -> SegmentOfResult) -> Foo<SegmentOfResult.Element> {
+  fatalError()
+}
+
+func generateArgumentWords() {
+  _ = myFlatMap { $0.#^COMPLETE^# } as Foo<String>
+}