Merge pull request #4275 from milseman/3_0_noescape

[noescape-by-default] Improve diagnostics.

Author: tkremenek

lib/Sema/CSDiag.cpp

@@ -3667,10 +3667,14 @@ static bool tryDiagnoseNonEscapingParameterToEscaping(Expr *expr, Type srcType,
       !declRef->getType()->is<AnyFunctionType>())
     return false;
 
-  // Must be from non-escaping function to escaping function
+  // Must be from non-escaping function to escaping function. For the
+  // destination type, we read through optionality to give better diagnostics in
+  // the event of an implicit promotion.
   auto srcFT = srcType->getAs<AnyFunctionType>();
-  auto destFT = dstType->getAs<AnyFunctionType>();
-  if (!srcFT || !destFT || !srcFT->isNoEscape() || destFT->isNoEscape())
+  auto dstFT =
+      dstType->lookThroughAllAnyOptionalTypes()->getAs<AnyFunctionType>();
+
+  if (!srcFT || !dstFT || !srcFT->isNoEscape() || dstFT->isNoEscape())
     return false;
 
   // Pick a specific diagnostic for the specific use

test/attr/attr_escaping.swift

@@ -92,3 +92,18 @@ func callEscapingSuperGeneric(_ fn: () -> Sub) { // expected-note {{parameter 'f
 func callEscapingSuperGeneric<T: Sub>(_ fn: () -> T) { // expected-note {{parameter 'fn' is implicitly non-escaping}} {{45-45=@escaping }}
   takesEscapingSuperGeneric(fn) // expected-error {{passing non-escaping parameter 'fn' to function expecting an @escaping closure}}
 }
+
+func testModuloOptionalness() {
+  var iuoClosure: (() -> Void)! = nil
+  func setIUOClosure(_ fn: () -> Void) { // expected-note {{parameter 'fn' is implicitly non-escaping}} {{28-28=@escaping }}
+    iuoClosure = fn // expected-error{{assigning non-escaping parameter 'fn' to an @escaping closure}}
+  }
+  var iuoClosureExplicit: ImplicitlyUnwrappedOptional<() -> Void>
+  func setExplicitIUOClosure(_ fn: () -> Void) { // expected-note {{parameter 'fn' is implicitly non-escaping}} {{36-36=@escaping }}
+    iuoClosureExplicit = fn // expected-error{{assigning non-escaping parameter 'fn' to an @escaping closure}}
+  }
+  var deepOptionalClosure: (() -> Void)???
+  func setDeepOptionalClosure(_ fn: () -> Void) { // expected-note {{parameter 'fn' is implicitly non-escaping}} {{37-37=@escaping }}
+    deepOptionalClosure = fn // expected-error{{assigning non-escaping parameter 'fn' to an @escaping closure}}
+  }
+}