[Sema] Enable Optional-to-Any diagnostics for IUOs

For example, the implicit coercion from `Int!` to `Any` now produces a warning. Previously a warning wasn't emitted despite the optional being implicitly erased to `Any` (but warnings were emitted in some other cases, such as `Int?!` to `Any?`; this commit fixes that inconsistency).

Author: hamishknight

lib/Sema/MiscDiagnostics.cpp

@@ -3545,12 +3545,6 @@ static void diagnoseUnintendedOptionalBehavior(TypeChecker &TC, const Expr *E,
 
       auto subExpr = E->getSubExpr();
 
-      // Currently we don't produce Optional-as-Any warnings for implicit IUO
-      // to Any coercions (this doesn't take into consideration implicit
-      // coercions such as Any?! to Any?, however; we warn on those).
-      if (subExpr->getType()->getImplicitlyUnwrappedOptionalObjectType())
-        return;
-
       // Look through any BindOptionalExprs, as the coercion may have started
       // from a higher level of optionality.
       while (auto *bindExpr = dyn_cast<BindOptionalExpr>(subExpr))

test/Sema/diag_unintended_optional_behavior.swift

@@ -82,9 +82,16 @@ func warnNestedOptionalToOptionalAnyCoercion(_ a: Int?, _ b: Any??, _ c: Int???,
   takesOptionalAny(c as Any?, d as Any?)
 }
 
-func dontWarnIUOToAnyCoercion(_ a: Int!, _ b: Any?!, _ c: Int??!, _ d: Any???!) {
-  _ = takeAny(a, b)
-  _ = takeAny(c, d)
+func warnIUOToAnyCoercion(_ a: Int!, _ b: Any?!) {
+  _ = takeAny(a, b) // expected-warning {{expression implicitly coerced from 'Int!' to 'Any'}}
+  // expected-note@-1 {{provide a default value to avoid this warning}}{{16-16= ?? <#default value#>}}
+  // expected-note@-2 {{force-unwrap the value to avoid this warning}}{{16-16=!}}
+  // expected-note@-3 {{explicitly cast to 'Any' with 'as Any' to silence this warning}}{{16-16= as Any}}
+  // expected-warning@-4 {{expression implicitly coerced from 'Any?!' to 'Any'}}
+  // expected-note@-5 {{force-unwrap the value to avoid this warning}}{{19-19=!!}}
+  // expected-note@-6 {{explicitly cast to 'Any' with 'as Any' to silence this warning}}{{19-19= as Any}}
+
+  _ = takeAny(a as Any, b as Any)
 }
 
 func warnIUOToOptionalAnyCoercion(_ a: Int!, _ b: Any?!, _ c: Int??!, _ d: Any???!) {