Tuple restrictions (#486)

* implement tuple restrictions: (1) named fields after positional, (2) order matters

* after_named_member => seen_named_member

executable_semantics/testdata/fun6_fail_type.golden

@@ -1,4 +1,2 @@
-10: type error in call
-expected: (0 = Int@0, 1 = Int@1)
-actual: (0 = (0 = Int@6, 1 = Int@7)@8)
+10: compilation error, tuples of different length
 EXIT CODE: 255

executable_semantics/testdata/fun_named_params2.6c

@@ -5,5 +5,5 @@
 fn f(Int: x, .d = Int: y, Int: z, .e = Int: a) => (x + y) - (z + a);
 
 fn main() -> Int {
-  return f(.e = 2, 1, 3, .d = 4);
+  return 0;
 }

executable_semantics/testdata/fun_named_params2.golden

@@ -1 +1,2 @@
-result: 0
+5: positional members must come before named members
+EXIT CODE: 255

executable_semantics/testdata/match_type.6c

@@ -5,12 +5,8 @@
 fn main() -> Int {
   var auto: t = fnty (Int,Int);
   var Int: x = 0;
-//  match (t) {
-//    case fnty(Int: x, Int: y): z =>
-//      x = x - 1;
-//  }
   match (t) {
-    case fnty(Int,Int): z =>
+    case Type: z =>
       x = x + 1;
   }
   match (t) {

executable_semantics/testdata/record1.6c

@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 fn main() -> Int {
-  var (.x = Int, .y = Int): t2 = (.y = 5, .x = 2);
+  var (.x = Int, .y = Int): t2 = (.x = 2, .y = 5);
   t2.y = 3;
   return t2.y - t2.x - 1; // 3 - 2 - 1
 }

executable_semantics/testdata/tuple3.6c

@@ -3,6 +3,6 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 fn main() -> Int {
-  var (.x = Int, Int): t = (3, .x = 2);
+  var (Int, .x = Int): t = (3, .x = 2);
   return t.x + 1 - t[0];
 }

executable_semantics/testdata/tuple4.6c

@@ -0,0 +1,8 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+fn main() -> Int {
+  var auto: t = (.x = 2, 3);
+  return 0;
+}

executable_semantics/testdata/tuple4.golden

@@ -0,0 +1,2 @@
+6: positional members must come before named members
+EXIT CODE: 255

executable_semantics/testdata/tuple5.6c

@@ -0,0 +1,10 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// Test the that field order matters for tuples.
+
+fn main() -> Int {
+  var (.x = Int, .y = Int): t = (.y = 2, .x = 3);
+  return 0;
+}

executable_semantics/testdata/tuple5.golden

@@ -0,0 +1,4 @@
+8: type error in pattern variable
+expected: (x = Int@2, y = Int@3)
+actual: (y = Int@0, x = Int@1)
+EXIT CODE: 255

executable_semantics/testdata/tuple_equality3.6c

@@ -4,7 +4,7 @@
 
 fn main() -> Int {
   var (Int,Int): t1 = (5, 2);
-  var (Int,Int): t2 = (5,);
+  var (Int,): t2 = (5,);
   if (t1 == t2) {
     return 1;
   } else {

executable_semantics/testdata/tuple_equality3.golden

@@ -1 +1,4 @@
-result: 0
+8: type error in ==
+expected: (0 = Int@2, 1 = Int@3)
+actual: (0 = Int@5)
+EXIT CODE: 255

executable_semantics/testdata/tuple_match2.6c

@@ -5,7 +5,7 @@
 // Test matching with a mixture of positional and named fields.
 
 fn main() -> Int {
-  var auto: t = (.x = 5, 2);
+  var auto: t = (2, .x = 5);
   match (t) {
     case (auto: a, .x = auto: b) =>
       return a - b + 3;