NFC: Abstract away the use of '7' to represent the next language mode

Introduce `Version::getFutureMajorLanguageVersion` to make it easier
to find clients that will need to be updated once we have a new
language mode.

Author: hamishknight

include/swift/AST/DiagnosticEngine.h

@@ -767,6 +767,17 @@ namespace swift {
       return limitBehaviorUntilSwiftVersion(limit, languageMode);
     }
 
+    /// Limit the diagnostic behavior to warning until the next future
+    /// language mode.
+    ///
+    /// This should be preferred over passing the next major version to
+    /// `warnUntilSwiftVersion` to make it easier to find and update clients
+    /// when a new language mode is introduced.
+    ///
+    /// This helps stage in fixes for stricter diagnostics as warnings
+    /// until the next major language version.
+    InFlightDiagnostic &warnUntilFutureSwiftVersion();
+
     /// Limit the diagnostic behavior to warning until the specified version.
     ///
     /// This helps stage in fixes for stricter diagnostics as warnings

include/swift/Basic/Version.h

@@ -131,6 +131,13 @@ class Version {
   /// SWIFT_VERSION_MINOR.
   static Version getCurrentLanguageVersion();
 
+  /// Returns a major version to represent the next future language mode. This
+  /// exists to make it easier to find and update clients when a new language
+  /// mode is added.
+  static constexpr unsigned getFutureMajorLanguageVersion() {
+    return 7;
+  }
+
   // List of backward-compatibility versions that we permit passing as
   // -swift-version <vers>
   static std::array<StringRef, 4> getValidEffectiveVersions() {

lib/AST/DiagnosticEngine.cpp

@@ -452,7 +452,7 @@ InFlightDiagnostic::limitBehaviorUntilSwiftVersion(
     // version. We do this before limiting the behavior, because
     // wrapIn will result in the behavior of the wrapping diagnostic.
     if (limit >= DiagnosticBehavior::Warning) {
-      if (majorVersion > 6) {
+      if (majorVersion >= version::Version::getFutureMajorLanguageVersion()) {
         wrapIn(diag::error_in_a_future_swift_lang_mode);
       } else {
         wrapIn(diag::error_in_swift_lang_mode, majorVersion);
@@ -472,6 +472,11 @@ InFlightDiagnostic::limitBehaviorUntilSwiftVersion(
   return *this;
 }
 
+InFlightDiagnostic &InFlightDiagnostic::warnUntilFutureSwiftVersion() {
+  using namespace version;
+  return warnUntilSwiftVersion(Version::getFutureMajorLanguageVersion());
+}
+
 InFlightDiagnostic &
 InFlightDiagnostic::warnUntilSwiftVersion(unsigned majorVersion) {
   return limitBehaviorUntilSwiftVersion(DiagnosticBehavior::Warning,

lib/Basic/Version.cpp

@@ -181,16 +181,19 @@ std::optional<Version> Version::getEffectiveLanguageVersion() const {
     static_assert(SWIFT_VERSION_MAJOR == 6,
                   "getCurrentLanguageVersion is no longer correct here");
     return Version::getCurrentLanguageVersion();
-  case 7:
-    // Allow version '7' in asserts compilers *only* so that we can start
-    // testing changes planned for after Swift 6. Note that it's still not
-    // listed in `Version::getValidEffectiveVersions()`.
-    // FIXME: When Swift 7 becomes real, remove 'REQUIRES: swift7' from tests
-    //        using '-swift-version 7'.
+
+  // FIXME: When Swift 7 becomes real, remove 'REQUIRES: swift7' from tests
+  //        using '-swift-version 7'.
+
+  case Version::getFutureMajorLanguageVersion():
+    // Allow the future language mode version in asserts compilers *only* so
+    // that we can start testing changes planned for after the current latest
+    // language mode. Note that it'll not be listed in
+    // `Version::getValidEffectiveVersions()`.
 #ifdef NDEBUG
     LLVM_FALLTHROUGH;
 #else
-    return Version{7};
+    return Version{Version::getFutureMajorLanguageVersion()};
 #endif
   default:
     return std::nullopt;

lib/Sema/MiscDiagnostics.cpp

@@ -2243,11 +2243,12 @@ class ImplicitSelfUsageChecker : public BaseDiagnosticWalker {
         invalidImplicitSelfShouldOnlyWarn510(base, closure)) {
       warnUntilVersion.emplace(6);
     }
-    // Prior to Swift 7, downgrade to a warning if we're in a macro to preserve
-    // compatibility with the Swift 6 diagnostic behavior where we previously
-    // skipped diagnosing.
-    if (!Ctx.isSwiftVersionAtLeast(7) && isInMacro())
-      warnUntilVersion.emplace(7);
+    // Prior to the next language mode, downgrade to a warning if we're in a
+    // macro to preserve compatibility with the Swift 6 diagnostic behavior
+    // where we previously skipped diagnosing.
+    auto futureVersion = version::Version::getFutureMajorLanguageVersion();
+    if (!Ctx.isSwiftVersionAtLeast(futureVersion) && isInMacro())
+      warnUntilVersion.emplace(futureVersion);
 
     auto diag = Ctx.Diags.diagnose(loc, ID, std::move(Args)...);
     if (warnUntilVersion)

lib/Sema/TypeCheckAttr.cpp

@@ -1249,7 +1249,7 @@ void AttributeChecker::visitAccessControlAttr(AccessControlAttr *attr) {
             diagnose(attr->getLocation(),
                      diag::access_control_non_objc_open_member, VD)
                 .fixItReplace(attr->getRange(), "public")
-                .warnUntilSwiftVersion(7);
+                .warnUntilFutureSwiftVersion();
           }
         }
       }

lib/Sema/TypeCheckConcurrency.cpp

@@ -2676,7 +2676,7 @@ namespace {
                     fromType, toType);
 
                 if (downgradeToWarning)
-                  diag.warnUntilSwiftVersion(7);
+                  diag.warnUntilFutureSwiftVersion();
               }
 
               for (auto type : nonSendableTypes) {

lib/Sema/TypeCheckProtocol.cpp

@@ -5169,7 +5169,8 @@ static bool diagnoseTypeWitnessAvailability(
     return false;
 
   // In Swift 6 and earlier type witness availability diagnostics are warnings.
-  const unsigned warnBeforeVersion = 7;
+  using namespace version;
+  const unsigned warnBeforeVersion = Version::getFutureMajorLanguageVersion();
   bool shouldError =
       ctx.LangOpts.EffectiveLanguageVersion.isVersionAtLeast(warnBeforeVersion);