[IDE] Fix code completion crash after already-typechecked ApplyExprs

This was due to us unconditionally setting the referenced decl to be the decl
referenced by the ApplyExpr's function, when we should only do that for
SelfApplyExprs. This caused a crash for calls returning a function type due to
a mismatch between the resulting type (the function type the applied function
returns) vs the referenced decl signature (the signature of the applied
function itself).

Resolves rdar://problem/53034130.

Author: Nathan Hawes

lib/IDE/CodeCompletion.cpp

@@ -1279,11 +1279,23 @@ class CodeCompletionCallbacksImpl : public CodeCompletionCallbacks {
     if (CheckKind == CompletionTypeCheckKind::Normal &&
         ParsedExpr->getType() && !ParsedExpr->getType()->is<ErrorType>()) {
       auto refDecl = ParsedExpr->getReferencedDecl();
+      auto exprTy = ParsedExpr->getType();
       if (!refDecl) {
-        if (auto apply = dyn_cast<ApplyExpr>(ParsedExpr))
+        // FIXME: do this in the not-already-type-checked branch too?
+        if (auto *apply = dyn_cast<SelfApplyExpr>(ParsedExpr)) {
           refDecl = apply->getFn()->getReferencedDecl();
+        } else if (auto *apply = dyn_cast<ApplyExpr>(ParsedExpr)) {
+          // If this is an IUO, use the underlying non-optional type instead
+          auto fnDecl = apply->getFn()->getReferencedDecl();
+          if (auto FD = fnDecl.getDecl()) {
+            if (FD->isImplicitlyUnwrappedOptional()) {
+              if (auto OT = exprTy->getOptionalObjectType())
+                exprTy = OT;
+            }
+          }
+        }
       }
-      return std::make_pair(ParsedExpr->getType(), refDecl);
+      return std::make_pair(exprTy, refDecl);
     }
 
     ConcreteDeclRef ReferencedDecl = nullptr;

test/IDE/complete_value_expr.swift

@@ -199,6 +199,7 @@
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=IN_ARRAY_LITERAL_2 | %FileCheck %s -check-prefix=SIMPLE_OBJECT_DOT
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=IN_DICTIONARY_LITERAL_1 | %FileCheck %s -check-prefix=SIMPLE_OBJECT_DOT
 // RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=IN_DICTIONARY_LITERAL_2 | %FileCheck %s -check-prefix=SIMPLE_OBJECT_DOT
+// RUN: %target-swift-ide-test -code-completion -source-filename %s -code-completion-token=COMPLETE_CALL_RESULT | %FileCheck %s -check-prefix=COMPLETE_CALL_RESULT
 
 // Test code completion of expressions that produce a value.
 
@@ -2173,3 +2174,17 @@ func testInCollectionLiteral(value: SimpleStruct) {
     value.#^IN_DICTIONARY_LITERAL_2^# : "test"
   ]
 }
+
+// rdar://problem/54047322
+struct Resolver<T> {
+  func fulfill(_ value: T) {}
+}
+func wrapSuccess<T>(_ onSuccess: @escaping (T) -> Void) -> (T, Bool) -> Void {
+  fatalError()
+}
+func testWrapSuccess(promise: Int, seal: Resolver<Void>) {
+  wrapSuccess(seal.fulfill)#^COMPLETE_CALL_RESULT^#
+  // COMPLETE_CALL_RESULT: Begin completions
+  // COMPLETE_CALL_RESULT: Pattern/CurrModule:                 ({#Void#}, {#Bool#})[#Void#]; name=(Void, Bool)
+  // COMPLETE_CALL_RESULT: End completions
+}