Warn when using 'var' bindings in function parameters

These will no longer be allowed in a future Swift release.

rdar://problem/23172698

include/swift/AST/Decl.h

@@ -4151,6 +4151,9 @@ class VarDecl : public AbstractStorageDecl {
   /// that it can be rewritten to a 'var'.  This is used in situations where the
   /// compiler detects obvious attempts to mutate a constant.
   void emitLetToVarNoteIfSimple(DeclContext *UseDC) const;
+
+  /// Returns true if the name is the self identifier and is implicit.
+  bool isImplicitSelf() const;
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { 

include/swift/AST/DiagnosticsParse.def

@@ -642,7 +642,7 @@ ERROR(untyped_pattern_ellipsis,pattern_parsing,none,
 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 'var' binding here is deprecated and will be removed in a future version of Swift", ())
+      "Use of '%select{var|let}0' binding here is deprecated and will be removed in a future version of Swift", (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

@@ -3154,6 +3154,9 @@ Pattern *VarDecl::getParentPattern() const {
   return nullptr;
 }
 
+bool VarDecl::isImplicitSelf() const {
+  return isImplicit() && getName() == getASTContext().Id_self;
+}
 
 /// Return true if this stored property needs to be accessed with getters and
 /// setters for Objective-C.
@@ -3232,9 +3235,12 @@ void VarDecl::emitLetToVarNoteIfSimple(DeclContext *UseDC) const {
   // If it isn't a 'let', don't touch it.
   if (!isLet()) return;
 
+  // Don't suggest mutability for explicit function parameters
+  if (isa<ParamDecl>(this) && !isImplicitSelf()) return;
+
   // If this is the 'self' argument of a non-mutating method in a value type,
   // suggest adding 'mutating' to the method.
-  if (getName().str() == "self" && UseDC) {
+  if (isImplicitSelf() && UseDC) {
     // If the problematic decl is 'self', then we might be trying to mutate
     // a property in a non-mutating method.
     auto FD = dyn_cast<FuncDecl>(UseDC->getInnermostMethodContext());

lib/Parse/ParsePattern.cpp

@@ -179,9 +179,13 @@ 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,
+               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());
       param.LetVarInOutLoc = consumeToken();
       param.SpecifierKind = ParsedParameter::Var;
     }
@@ -851,7 +855,7 @@ ParserResult<Pattern> Parser::parsePattern() {
     } else {
       // In an always immutable context, `var` is not allowed.
       if (alwaysImmutable)
-        diagnose(varLoc, diag::var_not_allowed_in_pattern)
+        diagnose(varLoc, diag::var_not_allowed_in_pattern, isLetKeyword)
         .fixItRemove(varLoc);
     }
 
@@ -1063,7 +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)
+    diagnose(varLoc, diag::var_not_allowed_in_pattern, isLet)
       .fixItReplace(varLoc, "let");
 
   // In our recursive parse, remember that we're in a var/let pattern.

test/1_stdlib/CollectionDiagnostics.swift

@@ -44,10 +44,13 @@ func sortResultIgnored<
   S.Generator.Element : Comparable,
   MC.Generator.Element : Comparable
 >(
-  var sequence: S, // expected-warning {{parameter 'sequence' was never mutated; consider changing to 'let' constant}} {{3-7=}}
-  var mutableCollection: MC, // expected-warning {{parameter 'mutableCollection' was never mutated; consider changing to 'let' constant}} {{3-7=}}
-  var array: [Int] // expected-warning {{parameter 'array' was never mutated; consider changing to 'let' constant}} {{3-7=}}
+  sequence: S,
+  mutableCollection: MC,
+  array: [Int]
 ) {
+  var sequence = sequence // expected-warning {{was never mutated; consider changing to 'let' constant}}
+  var mutableCollection = mutableCollection // expected-warning {{was never mutated; consider changing to 'let' constant}}
+  var array = array // expected-warning {{was never mutated; consider changing to 'let' constant}}
 
   sequence.sort() // expected-warning {{result of call to 'sort()' is unused}}
   sequence.sort { $0 < $1 } // expected-warning {{result of call to 'sort' is unused}}
@@ -359,7 +362,8 @@ struct MyCollection : Sliceable {} // expected-error {{'Sliceable' has been rena
 protocol MyProtocol : Sliceable {} // expected-error {{'Sliceable' has been renamed to 'CollectionType'}} {{23-32=CollectionType}}
 func processCollection<E : Sliceable>(e: E) {} // expected-error {{'Sliceable' has been renamed to 'CollectionType'}} {{28-37=CollectionType}}
 
-func renamedRangeReplaceableCollectionTypeMethods(var c: DefaultedForwardRangeReplaceableCollection<Int>) {
+func renamedRangeReplaceableCollectionTypeMethods(c: DefaultedForwardRangeReplaceableCollection<Int>) {
+  var c = c
   c.extend([ 10 ]) // expected-error {{'extend' has been renamed to 'appendContentsOf'}} {{5-11=appendContentsOf}}
   c.splice([ 10 ], atIndex: c.startIndex) // expected-error {{'splice(_:atIndex:)' has been renamed to 'insertContentsOf'}} {{5-11=insertContentsOf}}
 }

test/ClangModules/ctypes_parse_union.swift

@@ -2,7 +2,8 @@
 
 import ctypes
 
-func useStructWithUnion(var vec: GLKVector4) -> GLKVector4 {
+func useStructWithUnion(vec: GLKVector4) -> GLKVector4 {
+  var vec = vec
   _ = vec.v.0
   _ = vec.v.1
   _ = vec.v.2
@@ -57,7 +58,8 @@ func useStructWithAnonymousUnion(u: AnonUnion) -> AnonUnion {
   return u
 }
 
-func useStructWithUnnamedUnion(var u: UnnamedUnion) -> UnnamedUnion {
+func useStructWithUnnamedUnion(u: UnnamedUnion) -> UnnamedUnion {
+  var u = u
   u.u.i = 100
   u.u.f = 1.0
 }

test/ClangModules/objc_parse.swift

@@ -106,7 +106,7 @@ func dynamicLookupMethod(b: AnyObject) {
 }
 
 // Properties
-func properties(b: B) {  // expected-note {{mark parameter with 'var' to make it mutable}} {{17-17=var }}
+func properties(b: B) {
   var i = b.counter
   b.counter = i + 1
   i = i + b.readCounter

test/Constraints/bridging.swift

@@ -241,7 +241,8 @@ func rdar19831698() {
 }
 
 // <rdar://problem/19836341> Incorrect fixit for NSString? to String? conversions
-func rdar19836341(ns: NSString?, var vns: NSString?) {
+func rdar19836341(ns: NSString?, vns: NSString?) {
+  var vns = vns
   let _: String? = ns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}
   var _: String? = ns // expected-error{{cannot convert value of type 'NSString?' to specified type 'String?'}}
   // FIXME: there should be a fixit appending "as String?" to the line; for now

test/Constraints/closures.swift

@@ -48,8 +48,10 @@ struct X3<T> {
   init(_: (T)->()) {}
 }
 
-func testX3(var x: Int) {
+func testX3(x: Int) {
+  var x = x
   _ = X3({ x = $0 })
+  _ = x
 }
 
 // <rdar://problem/13811882>

test/Constraints/diagnostics.swift

@@ -424,7 +424,9 @@ zip(numbers, numbers).filter { $0.2 > 1 }  // expected-error {{value of tuple ty
 
 // <rdar://problem/20868864> QoI: Cannot invoke 'function' with an argument list of type 'type'
 func foo20868864(callback: ([String]) -> ()) { }
-func rdar20868864(var s: String) {
+
+func rdar20868864(s: String) {
+  var s = s
   foo20868864 { (strings: [String]) in
     s = strings   // expected-error {{cannot assign value of type '[String]' to type 'String'}}
   }

test/Constraints/keyword_arguments.swift

@@ -295,7 +295,11 @@ trailingclosure1(x: 1, { return 5 }) // expected-error{{missing argument label '
 func trailingclosure2(x x: Int, f: (() -> Int)!...) {}
 trailingclosure2(x: 5) { return 5 }
 
-func trailingclosure3(x x: Int, var f: (() -> Int)!) { f = nil}
+func trailingclosure3(x x: Int, f: (() -> Int)!) {
+  var f = f
+  _ = f
+  f = nil
+}
 trailingclosure3(x: 5) { return 5 }
 
 func trailingclosure4(f f: () -> Int) {}

test/Constraints/lvalues.swift

@@ -174,7 +174,8 @@ takeArrayRef(["asdf", "1234"]) // expected-error{{contextual type 'inout Array<S
 // <rdar://problem/19835413> Reference to value from array changed
 func rdar19835413() {
   func f1(p: UnsafeMutablePointer<Void>) {}
-  func f2(var a: [Int], i: Int, pi: UnsafeMutablePointer<Int>) {
+  func f2(a: [Int], i: Int, pi: UnsafeMutablePointer<Int>) {
+    var a = a
     f1(&a)
     f1(&a[i])
     f1(&a[0])

test/Constraints/members.swift

@@ -187,7 +187,8 @@ protocol ClassP : class {
   func bas(x: Int)
 }
 
-func generic<T: P>(var t: T) {
+func generic<T: P>(t: T) {
+  var t = t
   // Instance member of archetype
   let _: Int -> () = id(t.bar)
   let _: () = id(t.bar(0))
@@ -250,7 +251,8 @@ func genericClassP<T: ClassP>(t: T) {
 // Members of existentials
 ////
 
-func existential(var p: P) {
+func existential(p: P) {
+  var p = p
   // Fully applied mutating method
   p.mut(1)
   _ = p.mut // expected-error{{partial application of 'mutating' method is not allowed}}

test/Constraints/subscript.swift

@@ -72,11 +72,12 @@ let _ = 1["1"]  // expected-error {{ambiguous use of 'subscript'}}
 
 
 // rdar://17687826 - QoI: error message when reducing to an untyped dictionary isn't helpful
-let squares = [ 1, 2, 3 ].reduce([:]) { (var dict, n) in // expected-error {{cannot invoke 'reduce' with an argument list of type '([_ : _], @noescape (_, Int) throws -> _)'}}
+let squares = [ 1, 2, 3 ].reduce([:]) { (dict, n) in // expected-error {{cannot invoke 'reduce' with an argument list of type '([_ : _], @noescape (_, Int) throws -> _)'}}
   // expected-note @-1 {{expected an argument list of type '(T, combine: @noescape (T, Self.Generator.Element) throws -> T)'}}
+  var dict = dict // expected-error {{type of expression is ambiguous without more context}}
 
-  dict[n] = n * n // expected-error {{type of expression is ambiguous without more context}}
-  return dict // expected-error {{type of expression is ambiguous without more context}}
+  dict[n] = n * n
+  return dict
 }
 
 

test/Constraints/tuple.swift

@@ -91,7 +91,8 @@ class C {
   func f(_: C) {}
 }
 
-func testLValue(var c: C) {
+func testLValue(c: C) {
+  var c = c
   c.f(c)
 
   let x = c
@@ -100,7 +101,7 @@ func testLValue(var c: C) {
 
 
 // <rdar://problem/21444509> Crash in TypeChecker::coercePatternToType
-func invalidPatternCrash(let k : Int) {
+func invalidPatternCrash(k : Int) {
   switch k {
   case (k, cph_: k) as UInt8:  // expected-error {{tuple pattern cannot match values of the non-tuple type 'UInt8'}} expected-warning {{cast from 'Int' to unrelated type 'UInt8' always fails}}
     break

test/Constraints/unchecked_optional.swift

@@ -36,7 +36,8 @@ struct B {
   var x : Int
 }
 
-func test2(var b : B!) {
+func test2(b : B!) {
+  var b = b
   let x = b.x
   b.x = x
   b = nil
@@ -85,7 +86,8 @@ func test10(x : Int?) -> Int! { return test10_helper(x) }
 protocol P11 { }
 extension Int : P11 { }
 func test11_helper<T : P11>(t: T) { }
-func test11(i: Int!, var j: Int!) {
+func test11(i: Int!, j: Int!) {
+  var j = j
   test11_helper(i)
   test11_helper(j)
   j = nil

test/DebugInfo/autoclosure.swift

@@ -18,7 +18,8 @@ func &&&&&(lhs: BooleanType, @autoclosure rhs: ()->BooleanType) -> Bool {
   return lhs.boolValue ? rhs().boolValue : false
 }
 
-func call_me(var input: Int64) -> Void {
+func call_me(input: Int64) -> Void {
+  var input = input
 // rdar://problem/14627460
 // An autoclosure should have a line number in the debug info and a scope line of 0.
 // CHECK-DAG: !DISubprogram({{.*}}linkageName: "_TFF11autoclosure7call_meFVs5Int64T_u_KT_Ps11BooleanType_",{{.*}} line: [[@LINE+3]],{{.*}} isLocal: false, isDefinition: true

test/Generics/algorithms.swift

@@ -61,8 +61,10 @@ func countIf<
 
 func equal<R1 : GeneratorType, R2 : GeneratorType where R1.Element : Eq,
                                            R1.Element == R2.Element>
-       (var range1 : R1, var range2 : R2) -> Bool {
+       (range1 : R1, range2 : R2) -> Bool {
 
+  var range1 = range1
+  var range2 = range2
   var e1 = range1.next()
   var e2 = range2.next()
 
@@ -77,8 +79,10 @@ func equal<R1 : GeneratorType, R2 : GeneratorType where R1.Element : Eq,
 }
 
 func equalIf<R1 : GeneratorType, R2 : GeneratorType>
-       (var range1 : R1, var range2 : R2,
+       (range1 : R1, range2 : R2,
         predicate : (R1.Element, R2.Element)-> Bool) -> Bool {
+  var range1 = range1
+  var range2 = range2
   var e1 = range1.next()
   var e2 = range2.next()
 
@@ -94,7 +98,9 @@ func equalIf<R1 : GeneratorType, R2 : GeneratorType>
 
 func mismatch<R1 : GeneratorType, R2 : GeneratorType where R1.Element : Eq,
                                               R1.Element == R2.Element>
-       (var range1 : R1, var range2 : R2) -> (R1, R2) {
+       (range1 : R1, range2 : R2) -> (R1, R2) {
+  var range1 = range1
+  var range2 = range2
   var prev1 = range1, prev2 = range2
 
   while true {
@@ -109,8 +115,10 @@ func mismatch<R1 : GeneratorType, R2 : GeneratorType where R1.Element : Eq,
 }
 
 func mismatchIf<R1 : GeneratorType, R2 : GeneratorType>
-       (var range1 : R1, var range2 : R2,
+       (range1 : R1, range2 : R2,
         predicate : (R1.Element, R2.Element) -> Bool) -> (R1, R2) {
+  var range1 = range1
+  var range2 = range2
   var prev1 = range1, prev2 = range2
 
   while true {
@@ -124,8 +132,9 @@ func mismatchIf<R1 : GeneratorType, R2 : GeneratorType>
   return (prev1, prev2)
 }
 
-func minElement<R : GeneratorType where R.Element : Comparable>(var range: R)
+func minElement<R : GeneratorType where R.Element : Comparable>(range: R)
        -> R.Element {
+  var range = range
   var result = range.next()!
   for next in GeneratorSequence(range) {
     if next < result {
@@ -135,8 +144,9 @@ func minElement<R : GeneratorType where R.Element : Comparable>(var range: R)
   return result
 }
 
-func maxElement<R : GeneratorType where R.Element : Comparable>(var range: R)
+func maxElement<R : GeneratorType where R.Element : Comparable>(range: R)
        -> R.Element {
+  var range = range
   var result = range.next()!
   for next in GeneratorSequence(range) {
     if next > result {
@@ -146,8 +156,9 @@ func maxElement<R : GeneratorType where R.Element : Comparable>(var range: R)
   return result
 }
 
-func minMaxElement<R : GeneratorType where R.Element : Comparable>(var range: R)
+func minMaxElement<R : GeneratorType where R.Element : Comparable>(range: R)
        -> (R.Element, R.Element) {
+  var range = range
   var min = range.next()!, max = min
   for next in GeneratorSequence(range) {
     if next < min { min = next }

test/Generics/function_defs.swift

@@ -145,7 +145,6 @@ protocol IntSubscriptable {
   subscript (index : Int) -> ElementType { get  }
 }
 
-// expected-note @+1 {{mark parameter with 'var' to make it mutable}} {{66-66=var }}
 func subscripting<T : protocol<Subscriptable, IntSubscriptable>>(t: T) {
   var index = t.getIndex()
   var value = t.getValue()

test/Generics/generic_types.swift

@@ -66,7 +66,8 @@ struct GenericReq<
   T : GeneratorType, U : GeneratorType where T.Element == U.Element
 > {}
 
-func getFirst<R : GeneratorType>(var r: R) -> R.Element {
+func getFirst<R : GeneratorType>(r: R) -> R.Element {
+  var r = r
   return r.next()!
 }