Sema: ext's must add solo invertible conformances

This helps prevent confusion after not inferring requirements if the
extension adds a Copyable conformance.

Author: kavon

Diff for: include/swift/AST/DiagnosticsSema.def

@@ -7799,6 +7799,9 @@ ERROR(suppress_nonsuppressable_protocol,none,
       "conformance to %0 cannot be suppressed", (const ProtocolDecl *))
 WARNING(suppress_already_suppressed_protocol,none,
       "already suppressed conformance to %0", (const ProtocolDecl *))
+ERROR(extension_conforms_to_invertible_and_others, none,
+      "conformance to '%0' must be declared in a separate extension",
+      (StringRef))
 
 // -- older ones below --
 ERROR(noncopyable_parameter_requires_ownership, none,

Diff for: lib/AST/ASTPrinter.cpp

@@ -2922,6 +2922,7 @@ static bool isExtensionAddingInvertibleConformance(const ExtensionDecl *ext) {
   auto conformances = ext->getLocalConformances();
   for (auto *conf : conformances) {
     if (conf->getProtocol()->getInvertibleProtocolKind()) {
+      assert(conformances.size() == 1 && "expected solo conformance");
       return true;
     }
   }

Diff for: lib/Frontend/ModuleInterfaceSupport.cpp

@@ -801,7 +801,7 @@ class InheritedProtocolCollector {
   }
 
   /// If there were any conditional conformances that couldn't be printed,
-  /// make a dummy extension that conforms to all of them, constrained by a
+  /// make dummy extension(s) that conforms to all of them, constrained by a
   /// fake protocol.
   bool printInaccessibleConformanceExtensionIfNeeded(
       raw_ostream &out, const PrintOptions &printOptions,
@@ -810,20 +810,35 @@ class InheritedProtocolCollector {
       return false;
     assert(nominal->isGenericContext());
 
-    if (!printOptions.printPublicInterface())
-      out << "@_spi(" << DummyProtocolName << ")\n";
-    out << "@available(*, unavailable)\nextension ";
-    nominal->getDeclaredType().print(out, printOptions);
-    out << " : ";
-    llvm::interleave(
-        ConditionalConformanceProtocols,
-        [&out, &printOptions](const ProtocolType *protoTy) {
-          protoTy->print(out, printOptions);
-        },
-        [&out] { out << ", "; });
-    out << " where "
-        << nominal->getGenericSignature().getGenericParams().front()->getName()
-        << " : " << DummyProtocolName << " {}\n";
+    auto emitExtension =
+        [&](ArrayRef<const ProtocolType *> conformanceProtos) {
+      if (!printOptions.printPublicInterface())
+        out << "@_spi(" << DummyProtocolName << ")\n";
+      out << "@available(*, unavailable)\nextension ";
+      nominal->getDeclaredType().print(out, printOptions);
+      out << " : ";
+      llvm::interleave(
+          conformanceProtos,
+          [&out, &printOptions](const ProtocolType *protoTy) {
+            protoTy->print(out, printOptions);
+          },
+          [&out] { out << ", "; });
+      out << " where "
+          << nominal->getGenericSignature().getGenericParams()[0]->getName()
+          << " : " << DummyProtocolName << " {}\n";
+    };
+
+    // We have to print conformances for invertible protocols in separate
+    // extensions, so do those first and save the rest for one extension.
+    SmallVector<const ProtocolType *, 8> regulars;
+    for (auto *proto : ConditionalConformanceProtocols) {
+      if (proto->getDecl()->getInvertibleProtocolKind()) {
+        emitExtension(proto);
+        continue;
+      }
+      regulars.push_back(proto);
+    }
+    emitExtension(regulars);
     return true;
   }
 

Diff for: lib/Sema/TypeCheckDeclPrimary.cpp

@@ -154,6 +154,28 @@ class CheckRepressions {
   }
 };
 
+/// If the extension adds a conformance to an invertible protocol, ensure that
+/// it does not add a conformance to any other protocol. So these are illegal:
+///
+///     extension S: Copyable & P {}
+///     extension S: Q, Copyable {}
+///
+/// This policy is in place because extensions adding a conformance to an
+/// invertible protocol do _not_ add default requirements on generic parameters,
+/// so it would be confusing to mix them together in the same extension.
+static void checkExtensionAddsSoloInvertibleProtocol(const ExtensionDecl *ext) {
+  auto localConfs = ext->getLocalConformances();
+  if (localConfs.size() <= 1)
+    return;
+
+  for (auto *conf : localConfs) {
+    if (auto ip = conf->getProtocol()->getInvertibleProtocolKind()) {
+      ext->diagnose(diag::extension_conforms_to_invertible_and_others,
+                    getInvertibleProtocolKindName(*ip));
+    }
+  }
+}
+
 /// Check the inheritance clause of a type declaration or extension thereof.
 ///
 /// This routine performs detailed checking of the inheritance clause of the
@@ -3979,6 +4001,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     diagnoseExtensionOfMarkerProtocol(ED);
 
     checkTupleExtension(ED);
+
+    checkExtensionAddsSoloInvertibleProtocol(ED);
   }
 
   void visitTopLevelCodeDecl(TopLevelCodeDecl *TLCD) {

Diff for: test/Parse/inverses.swift

@@ -129,3 +129,20 @@ protocol Q: ~Copyable {}
 protocol R: ~Copyable {}
 struct Blooper<T: ~Copyable>: ~Copyable {}
 extension Blooper: (Q & (R & (~Copyable & P))) {} // expected-error {{cannot suppress 'Copyable' in extension}}
+
+protocol Edible {}
+protocol Portable {}
+typealias Alias = Portable & Copyable
+
+struct Burrito<Filling: ~Copyable>: ~Copyable {}
+extension Burrito: Alias {} // expected-error {{conformance to 'Copyable' must be declared in a separate extension}}
+// expected-note@-1 {{'Burrito<Filling>' declares conformance to protocol 'Copyable' here}}
+
+extension Burrito: Copyable & Edible & P {} // expected-error {{redundant conformance of 'Burrito<Filling>' to protocol 'Copyable'}}
+
+struct Blah<T: ~Copyable>: ~Copyable {}
+extension Blah: P, Q, Copyable, R {} // expected-error {{generic struct 'Blah' required to be 'Copyable' but is marked with '~Copyable'}}
+// expected-error@-1 {{conformance to 'Copyable' must be declared in a separate extension}}
+
+enum Hello<Gesture: ~Copyable>: ~Copyable {}
+extension Hello: Copyable & Edible & P {} // expected-error {{conformance to 'Copyable' must be declared in a separate extension}}

Diff for: validation-test/ParseableInterface/rdar128577611.swift

@@ -7,4 +7,10 @@ struct InternalStruct {}
 extension [Int: InternalStruct]: Sendable {}
 
 // CHECK: @available(*, unavailable)
-// CHECK: extension Swift.Dictionary : Swift.Copyable, Swift.Escapable, Swift.Sendable where Key : _ConstraintThatIsNotPartOfTheAPIOfThisLibrary {}
+// CHECK-NEXT: extension Swift.Dictionary : Swift.Copyable where Key : _ConstraintThatIsNotPartOfTheAPIOfThisLibrary {}
+
+// CHECK: @available(*, unavailable)
+// CHECK-NEXT: extension Swift.Dictionary : Swift.Escapable where Key : _ConstraintThatIsNotPartOfTheAPIOfThisLibrary {}
+
+// CHECK: @available(*, unavailable)
+// CHECK-NEXT: extension Swift.Dictionary : Swift.Sendable where Key : _ConstraintThatIsNotPartOfTheAPIOfThisLibrary {}