[AST] Implement printing suppression for ~Sendable

include/swift/AST/Decl.h

@@ -85,6 +85,7 @@ namespace swift {
   struct ExternalSourceLocs;
   class CaptureListExpr;
   class DeclRefExpr;
+  class InverseTypeRepr;
   class LiteralExpr;
   class BraceStmt;
   class DeclAttributes;
@@ -1970,6 +1971,12 @@ public:
   Type getResolvedType(unsigned i, TypeResolutionStage stage =
                                        TypeResolutionStage::Interface) const;
 
+  /// If the given index corresponds to a "suppressed" entry, returns the
+  /// information associated with it, and `std::nullopt` otherwise.
+  std::optional<std::pair<Type, InverseTypeRepr *>> getAsSuppressed(
+      unsigned i,
+      TypeResolutionStage stage = TypeResolutionStage::Interface) const;
+
   /// Returns the underlying array of inherited type entries.
   ///
   /// NOTE: The `Type` associated with an entry may not be resolved yet.

lib/AST/ASTPrinter.cpp

@@ -8223,9 +8223,19 @@ swift::getInheritedForPrinting(
       }
     }
 
-    if (options.SuppressConformanceSuppression &&
-        inherited.getEntry(i).isSuppressed()) {
-      continue;
+    if (inherited.getEntry(i).isSuppressed()) {
+      // All `~<<Protocol>>` inheritances are suppressed.
+      if (options.SuppressConformanceSuppression)
+        continue;
+
+      if (options.SuppressTildeSendable) {
+        if (auto type = inherited.getAsSuppressed(i)->first) {
+          auto *sendable =
+              decl->getASTContext().getProtocol(KnownProtocolKind::Sendable);
+          if (sendable && sendable == type->getAnyNominal())
+            continue;
+        }
+      }
     }
 
     Results.push_back(inherited.getEntry(i));

lib/AST/Decl.cpp

@@ -2034,6 +2034,20 @@ Type InheritedTypes::getResolvedType(unsigned i,
       .getInheritedTypeOrNull(getASTContext());
 }
 
+std::optional<std::pair<Type, InverseTypeRepr *>>
+InheritedTypes::getAsSuppressed(unsigned i, TypeResolutionStage stage) const {
+  ASTContext &ctx = isa<const ExtensionDecl *>(Decl)
+                        ? cast<const ExtensionDecl *>(Decl)->getASTContext()
+                        : cast<const TypeDecl *>(Decl)->getASTContext();
+  auto result =
+      evaluateOrDefault(ctx.evaluator, InheritedTypeRequest{Decl, i, stage},
+                        InheritedTypeResult::forDefault());
+  if (result != InheritedTypeResult::Kind::Suppressed)
+    return std::nullopt;
+
+  return result.getSuppressed();
+}
+
 ExtensionDecl::ExtensionDecl(SourceLoc extensionLoc,
                              TypeRepr *extendedType,
                              ArrayRef<InheritedEntry> inherited,

test/ModuleInterface/tilde_sendable.swift

@@ -0,0 +1,35 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-emit-module-interface(%t/Library.swiftinterface) %s -module-name Library -enable-experimental-feature TildeSendable
+// RUN: %target-swift-typecheck-module-from-interface(%t/Library.swiftinterface) -module-name Library
+// RUN: %FileCheck %s < %t/Library.swiftinterface
+
+// REQUIRES: swift_feature_TildeSendable
+
+// CHECK: #if compiler(>=5.3) && $TildeSendable
+// CHECK: public class A : ~Swift.Sendable {
+// CHECK: }
+// CHECK: #else
+// CHECK: public class A {
+// CHECK: }
+// CHECK: #endif
+public class A: ~Sendable {
+  public init() {}
+}
+
+protocol P {
+}
+
+// CHECK: #if compiler(>=5.3) && $TildeSendable
+// CHECK: public struct S : ~Swift.Sendable {
+// CHECK:   public let x: Swift.Int
+// CHECK: }
+// CHECK: #else
+// CHECK: public struct S {
+// CHECK:   public let x: Swift.Int
+// CHECK: }
+// CHECK: #endif
+
+// CHECK-NOT: extension Library.S : Swift.Sendable {}
+public struct S: P, ~Sendable {
+  public let x: Int
+}