[Serialization] Opaque types: serialize conditionally available under…

include/swift/AST/Decl.h

@@ -2903,6 +2903,10 @@ class OpaqueTypeDecl final :
     UniqueUnderlyingType = subs;
   }
 
+  bool hasConditionallyAvailableSubstitutions() const {
+    return ConditionallyAvailableTypes.hasValue();
+  }
+
   ArrayRef<ConditionallyAvailableSubstitutions *>
   getConditionallyAvailableSubstitutions() const {
     assert(ConditionallyAvailableTypes);

lib/Serialization/DeclTypeRecordNodes.def

@@ -198,6 +198,8 @@ OTHER(DERIVATIVE_FUNCTION_CONFIGURATION, 154)
 
 OTHER(ERROR_FLAG, 155)
 
+TRAILING_INFO(CONDITIONAL_SUBSTITUTION)
+
 #ifndef DECL_ATTR
 #define DECL_ATTR(NAME, CLASS, OPTIONS, CODE) RECORD_VAL(CLASS##_DECL_ATTR, 180+CODE)
 #endif

lib/Serialization/Deserialization.cpp

@@ -3517,7 +3517,50 @@ class DeclDeserializer {
                                        StringRef blobData) {
     return deserializeAnyFunc(scratch, blobData, /*isAccessor*/true);
   }
-
+
+  void deserializeConditionalSubstitutions(
+      SmallVectorImpl<OpaqueTypeDecl::ConditionallyAvailableSubstitutions *>
+          &limitedAvailability) {
+    SmallVector<uint64_t, 4> scratch;
+    StringRef blobData;
+
+    while (true) {
+      llvm::BitstreamEntry entry =
+          MF.fatalIfUnexpected(MF.DeclTypeCursor.advance(AF_DontPopBlockAtEnd));
+      if (entry.Kind != llvm::BitstreamEntry::Record)
+        break;
+
+      scratch.clear();
+      unsigned recordID = MF.fatalIfUnexpected(
+          MF.DeclTypeCursor.readRecord(entry.ID, scratch, &blobData));
+      if (recordID != decls_block::CONDITIONAL_SUBSTITUTION)
+        break;
+
+      ArrayRef<uint64_t> rawConditions;
+      SubstitutionMapID substitutionMapRef;
+
+      decls_block::ConditionalSubstitutionLayout::readRecord(
+          scratch, substitutionMapRef, rawConditions);
+
+      SmallVector<VersionRange, 4> conditions;
+      llvm::transform(rawConditions, std::back_inserter(conditions),
+                      [&](uint64_t id) {
+                        llvm::VersionTuple lowerEndpoint;
+                        if (lowerEndpoint.tryParse(MF.getIdentifier(id).str()))
+                          MF.fatal();
+                        return VersionRange::allGTE(lowerEndpoint);
+                      });
+
+      auto subMapOrError = MF.getSubstitutionMapChecked(substitutionMapRef);
+      if (!subMapOrError)
+        MF.fatal();
+
+      limitedAvailability.push_back(
+          OpaqueTypeDecl::ConditionallyAvailableSubstitutions::get(
+              ctx, conditions, subMapOrError.get()));
+    }
+  }
+
   Expected<Decl *> deserializeOpaqueType(ArrayRef<uint64_t> scratch,
                                          StringRef blobData) {
     DeclID namingDeclID;
@@ -3568,7 +3611,24 @@ class DeclDeserializer {
       auto subMapOrError = MF.getSubstitutionMapChecked(underlyingTypeSubsID);
       if (!subMapOrError)
         return subMapOrError.takeError();
-      opaqueDecl->setUniqueUnderlyingTypeSubstitutions(subMapOrError.get());
+
+      // Check whether there are any conditionally available substitutions.
+      // If there are, it means that "unique" we just read is a universally
+      // available substitution.
+      SmallVector<OpaqueTypeDecl::ConditionallyAvailableSubstitutions *>
+          limitedAvailability;
+
+      deserializeConditionalSubstitutions(limitedAvailability);
+
+      if (limitedAvailability.empty()) {
+        opaqueDecl->setUniqueUnderlyingTypeSubstitutions(subMapOrError.get());
+      } else {
+        limitedAvailability.push_back(
+            OpaqueTypeDecl::ConditionallyAvailableSubstitutions::get(
+                ctx, VersionRange::empty(), subMapOrError.get()));
+
+        opaqueDecl->setConditionallyAvailableSubstitutions(limitedAvailability);
+      }
     }
     return opaqueDecl;
   }

lib/Serialization/ModuleFormat.h

@@ -56,7 +56,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 683; // Remove associatedtype primary bit
+const uint16_t SWIFTMODULE_VERSION_MINOR = 684; // Cond. available underlying types for opaque
 
 /// A standard hash seed used for all string hashes in a serialized module.
 ///
@@ -1413,7 +1413,13 @@ namespace decls_block {
     // - the foreign error convention, if any
     // - inlinable body text, if any
   >;
-
+
+  using ConditionalSubstitutionLayout = BCRecordLayout<
+    CONDITIONAL_SUBSTITUTION,
+    SubstitutionMapIDField,
+    BCArray<IdentifierIDField> // N conditions where each is <major>.<minor>.<patch>
+  >;
+
   using OpaqueTypeLayout = BCRecordLayout<
     OPAQUE_TYPE_DECL,
     DeclContextIDField, // decl context
@@ -1424,6 +1430,7 @@ namespace decls_block {
     SubstitutionMapIDField, // optional substitution map for underlying type
     AccessLevelField // access level
     // trailed by generic parameters
+    // trailed by conditional substitutions
   >;
 
   // TODO: remove the unnecessary FuncDecl components here

lib/Serialization/Serialization.cpp

@@ -3897,16 +3897,44 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
     auto genericSigID = S.addGenericSignatureRef(opaqueDecl->getGenericSignature());
 
     SubstitutionMapID underlyingSubsID = 0;
-    if (auto underlying = opaqueDecl->getUniqueUnderlyingTypeSubstitutions())
+    if (auto underlying = opaqueDecl->getUniqueUnderlyingTypeSubstitutions()) {
       underlyingSubsID = S.addSubstitutionMapRef(*underlying);
+    } else if (opaqueDecl->hasConditionallyAvailableSubstitutions()) {
+      // Universally available type doesn't have any availability conditions
+      // so it could be serialized into "unique" slot to safe space.
+      auto universal =
+          opaqueDecl->getConditionallyAvailableSubstitutions().back();
+      underlyingSubsID = S.addSubstitutionMapRef(universal->getSubstitutions());
+    }
     uint8_t rawAccessLevel =
-      getRawStableAccessLevel(opaqueDecl->getFormalAccess());
+        getRawStableAccessLevel(opaqueDecl->getFormalAccess());
     unsigned abbrCode = S.DeclTypeAbbrCodes[OpaqueTypeLayout::Code];
     OpaqueTypeLayout::emitRecord(S.Out, S.ScratchRecord, abbrCode,
                                  contextID.getOpaqueValue(), namingDeclID,
                                  interfaceSigID, interfaceTypeID, genericSigID,
                                  underlyingSubsID, rawAccessLevel);
     writeGenericParams(opaqueDecl->getGenericParams());
+
+    // Serialize all of the conditionally available substitutions expect the
+    // last one - universal, it's serialized into "unique" slot.
+    if (opaqueDecl->hasConditionallyAvailableSubstitutions()) {
+      unsigned abbrCode =
+          S.DeclTypeAbbrCodes[ConditionalSubstitutionLayout::Code];
+      for (const auto *subs :
+           opaqueDecl->getConditionallyAvailableSubstitutions().drop_back()) {
+        SmallVector<IdentifierID, 4> conditions;
+
+        for (const auto &condition : subs->getAvailability()) {
+          auto lowerEndpoint = condition.getLowerEndpoint();
+          conditions.push_back(
+              S.addUniquedStringRef(lowerEndpoint.getAsString()));
+        }
+
+        ConditionalSubstitutionLayout::emitRecord(
+            S.Out, S.ScratchRecord, abbrCode,
+            S.addSubstitutionMapRef(subs->getSubstitutions()), conditions);
+      }
+    }
   }
 
   void visitAccessorDecl(const AccessorDecl *fn) {
@@ -5074,6 +5102,8 @@ void Serializer::writeAllDeclsAndTypes() {
   registerDeclTypeAbbr<MembersLayout>();
   registerDeclTypeAbbr<XRefLayout>();
 
+  registerDeclTypeAbbr<ConditionalSubstitutionLayout>();
+
 #define DECL_ATTR(X, NAME, ...) \
   registerDeclTypeAbbr<NAME##DeclAttrLayout>();
 #include "swift/AST/Attr.def"

test/Serialization/Inputs/opaque_with_limited_availability.swift

@@ -0,0 +1,61 @@
+public protocol P {
+  func hello()
+}
+
+public struct Empty : P {
+  public func hello() { print("Hello from Empty") }
+}
+
+public struct Tuple<T>: P {
+  public init(_ tuple: T) {}
+
+  public func hello() { print("Hello from Tuple") }
+}
+
+@available(macOS 10.15, *)
+struct Named : P {
+  public func hello() { print("Hello from Named") }
+}
+
+@resultBuilder
+public struct Example {
+  public static func buildOptional<T: P>(_ v: T?) -> some P {
+    if #available(macOS 100.0.1, *) {
+      let result = v!
+      result.hello()
+      return result
+    } else {
+      let result = Empty()
+      result.hello()
+      return result
+    }
+  }
+
+  public static func buildLimitedAvailability<T: P>(_ component: T) -> some P {
+    component
+  }
+
+  public static func buildBlock<T: P>(_ components: T) -> T {
+    return components
+  }
+
+  public static func buildBlock<T1: P, T2: P>(_ v1: T1, _ v2: T2) -> Tuple<(T1, T2)> {
+    return Tuple((v1, v2))
+  }
+}
+
+public func test() -> some P {
+  if #available(macOS 100.0.1, *) {
+    return Tuple<(Int, Int)>((0, 0))
+  }
+
+  return Empty()
+}
+
+public func test_return_from_conditional() -> some P {
+  if #available(macOS 10.15, *) {
+    return Named()
+  }
+
+  return Tuple<(String, Int)>(("", 0))
+}

test/Serialization/opaque_with_availability_cross_module.swift

@@ -0,0 +1,47 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -target %target-cpu-apple-macosx10.15 -parse-as-library -emit-library -emit-module-path %t/LimitedAvailOpaque.swiftmodule -module-name LimitedAvailOpaque %S/Inputs/opaque_with_limited_availability.swift -o %t/%target-library-name(LimitedAvailOpaque)
+// RUN: %target-build-swift -target %target-cpu-apple-macosx10.15 -lLimitedAvailOpaque -module-name main -I %t -L %t %s -o %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s --color
+
+// REQUIRES: OS=macosx && (CPU=x86_64 || CPU=arm64)
+// REQUIRES: executable_test
+
+import LimitedAvailOpaque
+
+struct S: P {
+  func hello() { print("Hello from S") }
+}
+
+@available(macOS 100.0.1, *)
+struct NewS: P {
+  func hello() { print("Hello from NewS") }
+}
+
+public struct Test {
+  @Example
+  var body: some P {
+    // TODO(diagnostics): This is incorrect warning due to `some P` return of `buildWithLimitedAvailability`
+    // expected-warning@+1 {{result builder 'Example' does not implement 'buildLimitedAvailability'; this code may crash on earlier versions of the OS}}
+    if #available(macOS 100.0.1, *) {
+      NewS()
+    }
+
+    S()
+  }
+
+  func sayHello() {
+    body.hello()
+  }
+}
+
+let result = LimitedAvailOpaque.test()
+result.hello()
+// CHECK: Hello from Empty
+
+Test().sayHello()
+// CHECK: Hello from Empty
+// CHECK: Hello from Tuple
+
+let conditionalR = LimitedAvailOpaque.test_return_from_conditional()
+conditionalR.hello()
+// CHECK: Hello from Named