Make always-immutable pattern bindings a warning for now

These will become errors after the next release branch.

rdar://problem/23172698

include/swift/AST/DiagnosticsParse.def

@@ -641,8 +641,8 @@ 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",())
-ERROR(var_not_allowed_in_pattern,pattern_parsing, none,
-      "'var' is not allowed in this pattern binding", ())
+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", ())
 ERROR(var_pattern_in_var,pattern_parsing,none,
       "'%select{var|let}0' cannot appear nested inside another 'var' or "
       "'let' pattern", (unsigned))

lib/Parse/ParseStmt.cpp

@@ -1234,7 +1234,8 @@ ParserStatus Parser::parseStmtCondition(StmtCondition &Condition,
       if (BindingKind == BK_Case) {
         // In our recursive parse, remember that we're in a matching pattern.
         llvm::SaveAndRestore<decltype(InVarOrLetPattern)>
-          T(InVarOrLetPattern, IVOLP_InMatchingPattern);
+          T(InVarOrLetPattern, IVOLP_AlwaysImmutable);
+
         ThePattern = parseMatchingPattern(/*isExprBasic*/ true);
       } else if (BindingKind == BK_LetCase || BindingKind == BK_VarCase) {
         // Recover from the 'if let case' typo gracefully.
@@ -2268,6 +2269,7 @@ ParserResult<Stmt> Parser::parseStmtForEach(SourceLoc ForLoc,
     // if desired by using a 'var' pattern.
     assert(InVarOrLetPattern == IVOLP_NotInVarOrLet &&
            "for-each loops cannot exist inside other patterns");
+
     InVarOrLetPattern = IVOLP_AlwaysImmutable;
     pattern = parseTypedPattern();
     assert(InVarOrLetPattern == IVOLP_AlwaysImmutable);

test/Constraints/patterns.swift

@@ -165,8 +165,11 @@ case x ?? 42: break // match value
 default: break
 }
 
-for (var x) in 0...100 {} // expected-error {{'var' is not allowed in this pattern binding}}
-for var x in 0...100 {}  // expected-error {{'var' is not allowed in this pattern binding}}
+// FIXME: rdar://problem/23378003
+// These will eventually become errors.
+for (var x) in 0...100 {} // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{6-9=}}
+for var x in 0...100 {}  // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{5-9=}}
+
 for (let x) in 0...100 {} // expected-error {{'let' pattern is already in an immutable context}}
 
 var (let y) = 42  // expected-error {{'let' cannot appear nested inside another 'var' or 'let' pattern}}

test/Parse/foreach.swift

@@ -33,6 +33,9 @@ func for_each(r: Range<Int>, iir: IntRange<Int>) {
   for i r { // expected-error 2{{expected ';' in 'for' statement}} expected-error {{use of unresolved identifier 'i'}}
   }
   for i in r sum = sum + i; // expected-error{{expected '{' to start the body of for-each loop}}
-  for var x in 0..<10 {} // expected-error {{'var' is not allowed in this pattern binding}} {{7-11=}}
   for let x in 0..<10 {} // expected-error {{'let' pattern is already in an immutable context}} {{7-11=}}
+
+  // FIXME: rdar://problem/23378003
+  // This will eventually become an error.
+  for var x in 0..<10 {} // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{7-11=}}
 }

test/Parse/matching_patterns.swift

@@ -32,9 +32,11 @@ case let (let b): // expected-error {{'let' cannot appear nested inside another
   print(b)
 
 // 'var' patterns (not allowed)
-case var a: // expected-error {{'var' is not allowed in this pattern binding}}
+// FIXME: rdar://problem/23378003
+// This will eventually be an error.
+case var a: // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{6-9=let}}
   a += 1
-case var let a: // expected-error {{'var' is not allowed in this pattern binding}}
+case var let a: // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{6-9=let}}
   // expected-error@-1 {{'let' cannot appear nested inside another 'var' or 'let' pattern}}
   print(a, terminator: "")
 

test/Parse/switch.swift

@@ -214,9 +214,11 @@ case (1, let b): // let bindings
   ()
 
 // var bindings are not allowed in cases.
-case (1, var b): // expected-error {{'var' is not allowed in this pattern binding}}
+// FIXME: rdar://problem/23378003
+// This will eventually be an error.
+case (1, var b): // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{10-13=let}}
   ()
-case (var a, 2): // expected-error {{'var' is not allowed in this pattern binding}}
+case (var a, 2): // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{7-10=let}}
   ()
 
 case (let a, 2), (1, let b): // expected-error {{'case' labels with multiple patterns cannot declare variables}}

test/decl/var/usage.swift

@@ -170,27 +170,35 @@ func testOpenExistential(var x: Fooable,
 func couldThrow() throws {}
 
 func testFixitsInStatementsWithPatterns(a : Int?) {
-  if var b = a,    // expected-error {{'var' is not allowed in this pattern binding}} {{6-9=let}}
-      var b2 = a {  // expected-error {{'var' is not allowed in this pattern binding}} {{7-10=let}}
+  // FIXME: rdar://problem/23378003
+  // This will eventually be an error.
+  if var b = a,    // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{6-9=let}}
+      var b2 = a {  // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{7-10=let}}
     b = 1
     b2 = 1
     _ = b
     _ = b2
   }
 
   var g = [1,2,3].generate()
-  while var x = g.next() { // expected-error {{'var' is not allowed in this pattern binding}} {{9-12=let}}
+  // FIXME: rdar://problem/23378003
+  // This will eventually be an error.
+  while var x = g.next() { // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{9-12=let}}
     x = 0
     _ = x
   }
 
-  guard var y = Optional.Some(1) else { // expected-error {{'var' is not allowed in this pattern binding}} {{9-12=let}}
+  // FIXME: rdar://problem/23378003
+  // This will eventually be an error.
+  guard var y = Optional.Some(1) else { // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{9-12=let}}
     return
   }
   y = 0
   _ = y
 
-  for var b in [42] {   // expected-error {{'var' is not allowed in this pattern binding}} {{7-11=}}
+  // FIXME: rdar://problem/23378003
+  // This will eventually be an error.
+  for var b in [42] {   // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{7-11=}}
     b = 42
     _ = b
   }
@@ -201,13 +209,17 @@ func testFixitsInStatementsWithPatterns(a : Int?) {
 
   do {
     try couldThrow()
-  } catch var err {  // expected-error {{'var' is not allowed in this pattern binding}} {{11-14=let}}
+  // FIXME: rdar://problem/23378003
+  // This will eventually be an error.
+  } catch var err {  // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{11-14=let}}
     // expected-warning@-1 {{variable 'err' was never mutated; consider changing to 'let' constant}}
     _ = err
   }
 
   switch a {
-    case var b: // expected-error {{'var' is not allowed in this pattern binding}} {{10-13=let}}
+    // FIXME: rdar://problem/23378003
+    // This will eventually be an error.
+    case var b: // expected-warning {{Use of 'var' binding here is deprecated and will be removed in a future version of Swift}} {{10-13=let}}
       // expected-warning@-1 {{variable 'b' was never mutated; consider changing to 'let' constant}}
       _ = b
   }