[CS] Upgrade tuple label mismatch warning to error for future lang mode

I missed upgrading this to an error for Swift 6 mode, let's upgrade it
to an error for a future language mode. It's important we reject these
cases since we're otherwise allowing subtyping to be a weaker constraint
than conversion.

include/swift/AST/DiagnosticsSema.def

@@ -1586,9 +1586,9 @@ WARNING(coercion_may_fail_warning,none,
         "coercion from %0 to %1 may fail; use 'as?' or 'as!' instead",
         (Type, Type))
 
-WARNING(tuple_label_mismatch_warning,none,
-        "tuple conversion from %0 to %1 mismatches labels",
-        (Type, Type))
+ERROR(tuple_label_mismatch,none,
+      "tuple conversion from %0 to %1 mismatches labels",
+      (Type, Type))
 
 ERROR(missing_explicit_conversion,none,
       "%0 is not implicitly convertible to %1; "

include/swift/Sema/CSFix.h

@@ -3458,7 +3458,8 @@ public:
   }
 };
 
-/// Emit a warning for mismatched tuple labels.
+/// Emit a warning for mismatched tuple labels, which is upgraded to an error
+/// for a future language mode.
 class AllowTupleLabelMismatch final : public ContextualMismatch {
   AllowTupleLabelMismatch(ConstraintSystem &cs, Type fromType, Type toType,
                           ConstraintLocator *locator)

lib/Sema/CSDiagnostics.cpp

@@ -9419,8 +9419,9 @@ bool InvalidWeakAttributeUse::diagnoseAsError() {
 }
 
 bool TupleLabelMismatchWarning::diagnoseAsError() {
-  emitDiagnostic(diag::tuple_label_mismatch_warning, getFromType(), getToType())
-      .highlight(getSourceRange());
+  emitDiagnostic(diag::tuple_label_mismatch, getFromType(), getToType())
+      .highlight(getSourceRange())
+      .warnUntilFutureSwiftVersion();
   return true;
 }
 

lib/Sema/CSDiagnostics.h

@@ -3009,7 +3009,8 @@ public:
   bool diagnoseAsError() override;
 };
 
-/// Emit a warning for mismatched tuple labels.
+/// Emit a warning for mismatched tuple labels, which is upgraded to an error
+/// for a future language mode.
 class TupleLabelMismatchWarning final : public ContextualFailure {
 public:
   TupleLabelMismatchWarning(const Solution &solution, Type fromType,

test/Constraints/tuple.swift

@@ -342,27 +342,6 @@ optionalTuple = (bignum, 1) // expected-error {{cannot assign value of type '(In
 optionalTuple = optionalTuple2 // expected-error {{cannot assign value of type '(Int64, Int)?' to type '(Int, Int)?'}}
 // expected-note@-1 {{arguments to generic parameter 'Wrapped' ('(Int64, Int)' and '(Int, Int)') are expected to be equal}}
 
-func testTupleLabelMismatchFuncConversion(fn1: @escaping ((x: Int, y: Int)) -> Void,
-                                          fn2: @escaping () -> (x: Int, Int)) {
-  // Warn on mismatches
-  let _: ((a: Int, b: Int)) -> Void = fn1 // expected-warning {{tuple conversion from '(a: Int, b: Int)' to '(x: Int, y: Int)' mismatches labels}}
-  let _: ((x: Int, b: Int)) -> Void = fn1 // expected-warning {{tuple conversion from '(x: Int, b: Int)' to '(x: Int, y: Int)' mismatches labels}}
-
-  let _: () -> (y: Int, Int) = fn2 // expected-warning {{tuple conversion from '(x: Int, Int)' to '(y: Int, Int)' mismatches labels}}
-  let _: () -> (y: Int, k: Int) = fn2 // expected-warning {{tuple conversion from '(x: Int, Int)' to '(y: Int, k: Int)' mismatches labels}}
-
-  // Attempting to shuffle has always been illegal here
-  let _: () -> (y: Int, x: Int) = fn2 // expected-error {{cannot convert value of type '() -> (x: Int, Int)' to specified type '() -> (y: Int, x: Int)'}}
-
-  // Losing labels is okay though.
-  let _: () -> (Int, Int) = fn2
-
-  // Gaining labels also okay.
-  let _: ((x: Int, Int)) -> Void = fn1
-  let _: () -> (x: Int, y: Int) = fn2
-  let _: () -> (Int, y: Int) = fn2
-}
-
 func testTupleLabelMismatchKeyPath() {
   // FIXME: The warning should be upgraded to an error for key paths.
   let _: KeyPath<(x: Int, y: Int), Int> = \(a: Int, b: Int).x

test/Constraints/tuple_subtype_label_mismatch.swift

@@ -0,0 +1,33 @@
+// RUN: %target-typecheck-verify-swift -language-mode 6 -verify-additional-prefix swift6-
+// RUN: %target-typecheck-verify-swift -language-mode 7 -verify-additional-prefix swift7-
+// REQUIRES: swift7
+
+func testTupleLabelMismatchFuncConversion(fn1: @escaping ((x: Int, y: Int)) -> Void,
+                                          fn2: @escaping () -> (x: Int, Int)) {
+  // Warn on mismatches in Swift 6, upgrading to an error for Swift 7
+  let _: ((a: Int, b: Int)) -> Void = fn1
+  // expected-swift6-warning@-1 {{tuple conversion from '(a: Int, b: Int)' to '(x: Int, y: Int)' mismatches labels}}
+  // expected-swift7-error@-2 {{tuple conversion from '(a: Int, b: Int)' to '(x: Int, y: Int)' mismatches labels}}
+  let _: ((x: Int, b: Int)) -> Void = fn1
+  // expected-swift6-warning@-1 {{tuple conversion from '(x: Int, b: Int)' to '(x: Int, y: Int)' mismatches labels}}
+  // expected-swift7-error@-2 {{tuple conversion from '(x: Int, b: Int)' to '(x: Int, y: Int)' mismatches labels}}
+
+  let _: () -> (y: Int, Int) = fn2
+  // expected-swift6-warning@-1 {{tuple conversion from '(x: Int, Int)' to '(y: Int, Int)' mismatches labels}}
+  // expected-swift7-error@-2 {{tuple conversion from '(x: Int, Int)' to '(y: Int, Int)' mismatches labels}}
+  let _: () -> (y: Int, k: Int) = fn2
+  // expected-swift6-warning@-1 {{tuple conversion from '(x: Int, Int)' to '(y: Int, k: Int)' mismatches labels}}
+  // expected-swift7-error@-2 {{tuple conversion from '(x: Int, Int)' to '(y: Int, k: Int)' mismatches labels}}
+
+  // Attempting to shuffle has always been illegal here
+  let _: () -> (y: Int, x: Int) = fn2
+  // expected-error@-1 {{cannot convert value of type '() -> (x: Int, Int)' to specified type '() -> (y: Int, x: Int)'}}
+
+  // Losing labels is okay though.
+  let _: () -> (Int, Int) = fn2
+
+  // Gaining labels also okay.
+  let _: ((x: Int, Int)) -> Void = fn1
+  let _: () -> (x: Int, y: Int) = fn2
+  let _: () -> (Int, y: Int) = fn2
+}