Make function parameters and refutable patterns always immutable

All refutable patterns and function parameters marked with 'var'
is now an error.

- Using explicit 'let' keyword on function parameters causes a warning.
- Don't suggest making function parameters mutable
- Remove uses in the standard library
- Update tests

rdar://problem/23378003

include/swift/AST/DiagnosticsParse.def

@@ -641,8 +641,10 @@ ERROR(untyped_pattern_ellipsis,pattern_parsing,none,
       "'...' cannot be applied to a subpattern which is not explicitly typed", ())
 ERROR(non_func_decl_pattern_init,pattern_parsing,none,
       "default argument is only permitted for a non-curried function parameter",())
-WARNING(var_not_allowed_in_pattern,pattern_parsing, none,
-      "Use of '%select{var|let}0' binding here is deprecated and will be removed in a future version of Swift", (unsigned))
+ERROR(var_not_allowed_in_pattern,pattern_parsing, none,
+      "Use of 'var' binding here is not allowed", ())
+WARNING(let_on_param_is_redundant,pattern_parsing, none,
+      "'let' keyword is unnecessary; function parameters are immutable by default", (unsigned))
 ERROR(var_pattern_in_var,pattern_parsing,none,
       "'%select{var|let}0' cannot appear nested inside another 'var' or "
       "'let' pattern", (unsigned))

lib/AST/Decl.cpp

@@ -3268,26 +3268,6 @@ void VarDecl::emitLetToVarNoteIfSimple(DeclContext *UseDC) const {
      .fixItReplace(PBD->getLoc(), "var");
     return;
   }
-
-  // If this is an argument pattern, suggest adding 'var' to the pattern.
-  if (auto *PD = dyn_cast<ParamDecl>(this)) {
-    if (auto *P = PD->getParamParentPattern()) {
-      if (P->getStartLoc().isValid() && !PD->isImplicit()) {
-        // The pattern is: (pattern_let (pattern_typed (pattern_named)))
-        // where the outside let pattern may be missing.  If present, this is a
-        // change, otherwise this is an addition of "var"
-        auto &d = getASTContext().Diags;
-        if (auto *VP = dyn_cast<VarPattern>(P)) {
-          d.diagnose(VP->getLoc(), diag::change_let_to_var_param)
-           .fixItReplace(VP->getLoc(), "var");
-        } else {
-          d.diagnose(P->getStartLoc(), diag::mark_param_var)
-           .fixItInsert(P->getStartLoc(), "var ");
-        }
-        return;
-      }
-    }
-  }
 }
 
 

lib/Parse/ParsePattern.cpp

@@ -179,15 +179,15 @@ Parser::parseParameterClause(SourceLoc &leftParenLoc,
       param.LetVarInOutLoc = consumeToken();
       param.SpecifierKind = ParsedParameter::InOut;
     } else if (Tok.is(tok::kw_let)) {
-      diagnose(Tok.getLoc(), diag::var_not_allowed_in_pattern,
+      diagnose(Tok.getLoc(), diag::let_on_param_is_redundant,
                Tok.is(tok::kw_let)).fixItRemove(Tok.getLoc());
       param.LetVarInOutLoc = consumeToken();
       param.SpecifierKind = ParsedParameter::Let;
     } else if (Tok.is(tok::kw_var)) {
-      diagnose(Tok.getLoc(), diag::var_not_allowed_in_pattern,
-               Tok.is(tok::kw_let)).fixItRemove(Tok.getLoc());
+      diagnose(Tok.getLoc(), diag::var_not_allowed_in_pattern)
+        .fixItRemove(Tok.getLoc());
       param.LetVarInOutLoc = consumeToken();
-      param.SpecifierKind = ParsedParameter::Var;
+      param.SpecifierKind = ParsedParameter::Let;
     }
 
     // Redundant specifiers are fairly common, recognize, reject, and recover
@@ -855,8 +855,8 @@ ParserResult<Pattern> Parser::parsePattern() {
     } else {
       // In an always immutable context, `var` is not allowed.
       if (alwaysImmutable)
-        diagnose(varLoc, diag::var_not_allowed_in_pattern, isLetKeyword)
-        .fixItRemove(varLoc);
+        diagnose(varLoc, diag::var_not_allowed_in_pattern)
+          .fixItRemove(varLoc);
     }
 
     // In our recursive parse, remember that we're in a var/let pattern.
@@ -1067,7 +1067,7 @@ ParserResult<Pattern> Parser::parseMatchingPatternAsLetOrVar(bool isLet,
     diagnose(varLoc, diag::let_pattern_in_immutable_context);
 
   if (!isLet && InVarOrLetPattern == IVOLP_AlwaysImmutable)
-    diagnose(varLoc, diag::var_not_allowed_in_pattern, isLet)
+    diagnose(varLoc, diag::var_not_allowed_in_pattern)
       .fixItReplace(varLoc, "let");
 
   // In our recursive parse, remember that we're in a var/let pattern.

stdlib/private/StdlibUnittest/CheckCollectionType.swift

@@ -287,7 +287,7 @@ extension TestSuite {
     Collection.SubSequence.SubSequence == Collection.SubSequence,
     CollectionWithEquatableElement.Generator.Element : Equatable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -302,6 +302,8 @@ extension TestSuite {
     outOfBoundsSubscriptOffset: Int = 1
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }
@@ -786,7 +788,7 @@ self.test("\(testNamePrefix).removeFirst(n: Int)/slice/removeTooMany/semantics")
     CollectionWithEquatableElement.Index : BidirectionalIndexType,
     CollectionWithEquatableElement.Generator.Element : Equatable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -800,6 +802,9 @@ self.test("\(testNamePrefix).removeFirst(n: Int)/slice/removeTooMany/semantics")
     outOfBoundsIndexOffset: Int = 1,
     outOfBoundsSubscriptOffset: Int = 1
   ) {
+
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }
@@ -1088,7 +1093,7 @@ self.test("\(testNamePrefix).suffix/semantics") {
     CollectionWithEquatableElement.Index : RandomAccessIndexType,
     CollectionWithEquatableElement.Generator.Element : Equatable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -1103,6 +1108,8 @@ self.test("\(testNamePrefix).suffix/semantics") {
     outOfBoundsSubscriptOffset: Int = 1
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }

stdlib/private/StdlibUnittest/CheckMutableCollectionType.swift.gyb

@@ -79,7 +79,7 @@ extension TestSuite {
     CollectionWithEquatableElement.Generator.Element : Equatable,
     CollectionWithComparableElement.Generator.Element : Comparable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -99,6 +99,8 @@ extension TestSuite {
     withUnsafeMutableBufferPointerIsSupported: Bool
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }
@@ -383,7 +385,7 @@ self.test("\(testNamePrefix).sort/${'Predicate' if predicate else 'WhereElementI
     CollectionWithComparableElement.Index : BidirectionalIndexType,
     CollectionWithComparableElement.Generator.Element : Comparable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -403,6 +405,8 @@ self.test("\(testNamePrefix).sort/${'Predicate' if predicate else 'WhereElementI
     withUnsafeMutableBufferPointerIsSupported: Bool
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }
@@ -500,7 +504,7 @@ if resiliencyChecks.subscriptOnOutOfBoundsIndicesBehavior != .None {
     CollectionWithComparableElement.Index : RandomAccessIndexType,
     CollectionWithComparableElement.Generator.Element : Comparable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -520,6 +524,8 @@ if resiliencyChecks.subscriptOnOutOfBoundsIndicesBehavior != .None {
     withUnsafeMutableBufferPointerIsSupported: Bool
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }

stdlib/private/StdlibUnittest/CheckRangeReplaceableCollectionType.swift

@@ -348,7 +348,7 @@ extension TestSuite {
     Collection.SubSequence.SubSequence == Collection.SubSequence,
     CollectionWithEquatableElement.Generator.Element : Equatable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -362,6 +362,8 @@ extension TestSuite {
     outOfBoundsIndexOffset: Int = 1
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }
@@ -1108,7 +1110,7 @@ self.test("\(testNamePrefix).OperatorPlus") {
     CollectionWithEquatableElement.Index : BidirectionalIndexType,
     CollectionWithEquatableElement.Generator.Element : Equatable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -1122,6 +1124,8 @@ self.test("\(testNamePrefix).OperatorPlus") {
     outOfBoundsIndexOffset: Int = 1
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }
@@ -1233,7 +1237,7 @@ self.test("\(testNamePrefix).removeLast(n: Int)/whereIndexIsBidirectional/remove
     CollectionWithEquatableElement.Index : RandomAccessIndexType,
     CollectionWithEquatableElement.Generator.Element : Equatable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -1247,6 +1251,8 @@ self.test("\(testNamePrefix).removeLast(n: Int)/whereIndexIsBidirectional/remove
     outOfBoundsIndexOffset: Int = 1
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }

stdlib/private/StdlibUnittest/CheckRangeReplaceableSliceType.swift

@@ -20,7 +20,7 @@ extension TestSuite {
     Collection.SubSequence == Collection,
     CollectionWithEquatableElement.Generator.Element : Equatable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -34,6 +34,8 @@ extension TestSuite {
     outOfBoundsIndexOffset: Int = 1
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     // Don't run the same tests twice.
     if checksAdded.value.contains(__FUNCTION__) {
       return
@@ -150,7 +152,7 @@ extension TestSuite {
     CollectionWithEquatableElement.SubSequence == CollectionWithEquatableElement,
     CollectionWithEquatableElement.Generator.Element : Equatable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -164,6 +166,8 @@ extension TestSuite {
     outOfBoundsIndexOffset: Int = 1
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     // Don't run the same tests twice.
     if checksAdded.value.contains(__FUNCTION__) {
       return
@@ -294,7 +298,7 @@ extension TestSuite {
     CollectionWithEquatableElement.SubSequence == CollectionWithEquatableElement,
     CollectionWithEquatableElement.Generator.Element : Equatable
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeCollection: ([Collection.Generator.Element]) -> Collection,
     wrapValue: (OpaqueValue<Int>) -> Collection.Generator.Element,
     extractValue: (Collection.Generator.Element) -> OpaqueValue<Int>,
@@ -308,6 +312,8 @@ extension TestSuite {
     outOfBoundsIndexOffset: Int = 1
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     // Don't run the same tests twice.
     if checksAdded.value.contains(__FUNCTION__) {
       return

stdlib/private/StdlibUnittest/CheckSequenceType.swift

@@ -1439,7 +1439,7 @@ extension TestSuite {
     Sequence.SubSequence.Generator.Element == Sequence.Generator.Element,
     Sequence.SubSequence.SubSequence == Sequence.SubSequence
   >(
-    var testNamePrefix: String = "",
+    testNamePrefix: String = "",
     makeSequence: ([Sequence.Generator.Element]) -> Sequence,
     wrapValue: (OpaqueValue<Int>) -> Sequence.Generator.Element,
     extractValue: (Sequence.Generator.Element) -> OpaqueValue<Int>,
@@ -1452,6 +1452,8 @@ extension TestSuite {
     resiliencyChecks: CollectionMisuseResiliencyChecks = .all
   ) {
 
+    var testNamePrefix = testNamePrefix
+
     if checksAdded.value.contains(__FUNCTION__) {
       return
     }

stdlib/private/StdlibUnittest/OpaqueIdentityFunctions.swift

@@ -27,7 +27,8 @@ func _blackHolePtr<T>(x: UnsafePointer<T>) {
   _stdlib_getPointer(COpaquePointer(x))
 }
 
-public func _blackHole<T>(var x: T) {
+public func _blackHole<T>(x: T) {
+  var x = x
   _blackHolePtr(&x)
 }
 

stdlib/private/StdlibUnittest/StdlibUnittest.swift.gyb

@@ -2008,7 +2008,8 @@ public func check${traversal}Collection<
     x + offset0 >= 0 && x + offset1 <= count
   }
 
-  func nextN(n: C.Index.Distance, var _ i: C.Index) -> C.Index {
+  func nextN(n: C.Index.Distance, _ i: C.Index) -> C.Index {
+    var i = i
     if n < 0 {
       for _ in 0 ..< -(n.toIntMax()) {
         --i

stdlib/private/SwiftPrivateSerialization/MsgPackSerialization.swift.gyb

@@ -17,7 +17,8 @@
 public struct MsgPackSerializer {
   public static func serialize<
     T : SerializableFixedDictionaryType
-  >(var value: T) -> [UInt8] {
+  >(value: T) -> [UInt8] {
+    var value = value
     // FIXME(performance): we could serialize directly into a byte stream
     // without creating an intermediate data structure if our MsgPack
     // serializer could accept arrays and dictionaries of unknown length and
@@ -76,7 +77,8 @@ internal func _toMsgPackVariant<
   }
 %   end
   return .Array(MsgPackVariantArray(value.map {
-    (var element) -> MsgPackVariant in
+    element -> MsgPackVariant in
+    var element = element
     var serializerImpl = _MsgPackSerializerImpl()
     element.serializeDeserialize(&serializerImpl)
     return serializerImpl._value!

stdlib/public/SDK/AssetsLibrary/AssetsLibrary.swift

@@ -17,9 +17,10 @@
 //===----------------------------------------------------------------------===//
 extension ALAssetsLibrary { 
   @nonobjc
-  public func enumerateGroupsWithTypes(var types: UInt32, 
+  public func enumerateGroupsWithTypes(types: UInt32, 
       usingBlock enumerationBlock: ALAssetsLibraryGroupsEnumerationResultsBlock!,
       failureBlock: ALAssetsLibraryAccessFailureBlock!) {
+    var types = types
     if (types == ALAssetsGroupAll) {
       types = ALAssetsGroupLibrary | ALAssetsGroupAlbum | ALAssetsGroupEvent | 
               ALAssetsGroupFaces | ALAssetsGroupSavedPhotos | 

stdlib/public/core/Arrays.swift.gyb

@@ -484,8 +484,9 @@ public func _allocateUninitializedArray<Element>(_count: Builtin.Word)
 @warn_unused_result
 @_semantics("array.dealloc_uninitialized")
 public func _deallocateUninitialized${Self}<Element>(
-  var array: ${Self}<Element>
+  array: ${Self}<Element>
 ) {
+  var array = array
   array._deallocateUninitialized()
 }
 %end

stdlib/public/core/CollectionAlgorithms.swift.gyb

@@ -129,8 +129,9 @@ ${partitionDocComment}
 ${orderingRequirementForPredicate}
   public mutating func partition(
     range: Range<Index>,
-    var isOrderedBefore: (${GElement}, ${GElement}) -> Bool
+    isOrderedBefore: (${GElement}, ${GElement}) -> Bool
   ) -> Index {
+    var isOrderedBefore = isOrderedBefore
 
 %   else: