For Swift 3/4 mode, do not treat IUOs in illegal positions as Optionals.

Instead, just emit a deprecation warning and suggest switching to Optionals.

The old behavior caused several projects to break, so before we change
the behavior here we need to investigate whether we can mitigate most
of those breaks.

Author: rudkx

include/swift/AST/DiagnosticsSema.def

@@ -3117,11 +3117,11 @@ WARNING(implicitly_unwrapped_optional_spelling_deprecated,none,
 WARNING(implicitly_unwrapped_optional_spelling_deprecated_with_fixit,none,
         "the spelling 'ImplicitlyUnwrappedOptional' is deprecated; use '!' after the type name", ())
 
-WARNING(implicitly_unwrapped_optional_spelling_decay_to_optional,none,
-        "'ImplicitlyUnwrappedOptional' is not allowed here; interpreting this as 'Optional' instead", ())
+WARNING(implicitly_unwrapped_optional_spelling_suggest_optional,none,
+        "using 'ImplicitlyUnwrappedOptional' in this location is deprecated and will be removed in a future release; consider changing this to 'Optional' instead", ())
 
-WARNING(implicitly_unwrapped_optional_in_illegal_position_decay_to_optional,none,
-        "'!' is not allowed here; interpreting this as '?' instead", ())
+WARNING(implicitly_unwrapped_optional_in_illegal_position_suggest_optional,none,
+        "using '!' in this location is deprecated and will be removed in a future release; consider changing this to '?' instead", ())
 
 ERROR(implicitly_unwrapped_optional_spelling_error,none,
         "the spelling 'ImplicitlyUnwrappedOptional' is unsupported; use an explicit type followed by '!'", ())

lib/Sema/TypeCheckType.cpp

@@ -1130,14 +1130,6 @@ resolveTopLevelIdentTypeComponent(TypeChecker &TC, DeclContext *DC,
 
   auto id = comp->getIdentifier();
 
-  // If we're compiling for Swift version < 5 and we have a mention of
-  // ImplicitlyUnwrappedOptional where it is not allowed, treat it as
-  // if it was spelled Optional.
-  if (id == TC.Context.Id_ImplicitlyUnwrappedOptional
-      && !options.contains(TypeResolutionFlags::AllowIUO)
-      && !TC.Context.isSwiftVersionAtLeast(5))
-    id = TC.Context.Id_Optional;
-
   NameLookupOptions lookupOptions = defaultUnqualifiedLookupOptions;
   if (options.contains(TypeResolutionFlags::KnownNonCascadingDependency))
     lookupOptions |= NameLookupFlags::KnownPrivate;
@@ -1239,7 +1231,7 @@ resolveTopLevelIdentTypeComponent(TypeChecker &TC, DeclContext *DC,
       }
     } else if (isa<GenericIdentTypeRepr>(comp)) {
       Diagnostic diag =
-          diag::implicitly_unwrapped_optional_spelling_decay_to_optional;
+          diag::implicitly_unwrapped_optional_spelling_suggest_optional;
 
       if (TC.Context.isSwiftVersionAtLeast(5))
         diag = diag::implicitly_unwrapped_optional_spelling_in_illegal_position;
@@ -1258,7 +1250,7 @@ resolveTopLevelIdentTypeComponent(TypeChecker &TC, DeclContext *DC,
               genericTyR->getAngleBrackets().End.getAdvancedLoc(1));
     } else {
       Diagnostic diag =
-          diag::implicitly_unwrapped_optional_spelling_decay_to_optional;
+          diag::implicitly_unwrapped_optional_spelling_suggest_optional;
 
       if (TC.Context.isSwiftVersionAtLeast(5))
         diag = diag::
@@ -2847,7 +2839,7 @@ Type TypeResolver::resolveImplicitlyUnwrappedOptionalType(
        TypeResolutionOptions options) {
   if (!options.contains(TypeResolutionFlags::AllowIUO)) {
     Diagnostic diag = diag::
-        implicitly_unwrapped_optional_in_illegal_position_decay_to_optional;
+        implicitly_unwrapped_optional_in_illegal_position_suggest_optional;
 
     if (TC.Context.isSwiftVersionAtLeast(5))
       diag = diag::implicitly_unwrapped_optional_in_illegal_position;
@@ -2865,12 +2857,8 @@ Type TypeResolver::resolveImplicitlyUnwrappedOptionalType(
   if (!baseTy || baseTy->hasError()) return baseTy;
 
   Type uncheckedOptionalTy;
-  if (!options.contains(TypeResolutionFlags::AllowIUO))
-    // Treat IUOs in illegal positions as optionals.
-    uncheckedOptionalTy = TC.getOptionalType(repr->getExclamationLoc(), baseTy);
-  else
-    uncheckedOptionalTy = TC.getImplicitlyUnwrappedOptionalType(
-        repr->getExclamationLoc(), baseTy);
+  uncheckedOptionalTy =
+      TC.getImplicitlyUnwrappedOptionalType(repr->getExclamationLoc(), baseTy);
 
   if (!uncheckedOptionalTy)
     return ErrorType::get(Context);

test/Migrator/Inputs/API.json

@@ -319,7 +319,7 @@
     "NodeKind": "Function",
     "NodeAnnotation": "WrapOptional",
     "ChildIndex": "1",
-    "LeftUsr": "s:6Cities05ExtraA0P6blibliySSSgAE_SStc1x_tF",
+    "LeftUsr": "s:6Cities05ExtraA0P6blibliySQySSGSSSg_SStc1x_tF",
     "LeftComment": "",
     "RightUsr": "",
     "RightComment": "",
@@ -330,7 +330,7 @@
     "NodeKind": "Function",
     "NodeAnnotation": "WrapOptional",
     "ChildIndex": "1",
-    "LeftUsr": "s:6Cities05ExtraA0P6blibliySSSgAE_SStc1x_tF",
+    "LeftUsr": "s:6Cities05ExtraA0P6blibliySQySSGSSSg_SStc1x_tF",
     "LeftComment": "",
     "RightUsr": "",
     "RightComment": "",
@@ -341,7 +341,7 @@
     "NodeKind": "Function",
     "NodeAnnotation": "WrapOptional",
     "ChildIndex": "1",
-    "LeftUsr": "s:6Cities05ExtraA0P6blibliySSSgAE_SStc1x_tF",
+    "LeftUsr": "s:6Cities05ExtraA0P6blibliySQySSGSSSg_SStc1x_tF",
     "LeftComment": "",
     "RightUsr": "",
     "RightComment": "",
@@ -352,7 +352,7 @@
     "NodeKind": "Function",
     "NodeAnnotation": "ImplicitOptionalToOptional",
     "ChildIndex": "1:0",
-    "LeftUsr": "s:6Cities05ExtraA0P6blibliySSSgAE_SStc1x_tF",
+    "LeftUsr": "s:6Cities05ExtraA0P6blibliySQySSGSSSg_SStc1x_tF",
     "LeftComment": "",
     "RightUsr": "",
     "RightComment": "",
@@ -363,7 +363,7 @@
     "NodeKind": "Function",
     "NodeAnnotation": "UnwrapOptional",
     "ChildIndex": "1:1:0",
-    "LeftUsr": "s:6Cities05ExtraA0P6blibliySSSgAE_SStc1x_tF",
+    "LeftUsr": "s:6Cities05ExtraA0P6blibliySQySSGSSSg_SStc1x_tF",
     "LeftComment": "",
     "RightUsr": "",
     "RightComment": "",