[IDE] Inject Sendable conformance on public types only

When getTopLevelDeclsForDisplay is called on an imported module, it may
lists non-public decls. If we they try to inject the conformance on
Sendable on internal types, the compiler may crash on failing to
deserialize internal details. As a fix, let's only inject the
conformance on public or package types.

rdar://95430471

Author: xymus

lib/IDE/IDETypeChecking.cpp

@@ -40,11 +40,20 @@ swift::getTopLevelDeclsForDisplay(ModuleDecl *M,
   auto startingSize = Results.size();
   M->getDisplayDecls(Results, Recursive);
 
-  // Force Sendable on all types, which might synthesize some extensions.
+  // Force Sendable on all public types, which might synthesize some extensions.
   // FIXME: We can remove this if @_nonSendable stops creating extensions.
   for (auto result : Results) {
-    if (auto NTD = dyn_cast<NominalTypeDecl>(result))
+    if (auto NTD = dyn_cast<NominalTypeDecl>(result)) {
+
+      // Restrict this logic to public and package types. Non-public types
+      // may refer to implementation details and fail at deserialization.
+      auto accessScope = NTD->getFormalAccessScope();
+      if (!M->isMainModule() &&
+          !accessScope.isPublic() && !accessScope.isPackage())
+        continue;
+
       (void)swift::isSendableType(M, NTD->getDeclaredInterfaceType());
+    }
   }
 
   // Remove what we fetched and fetch again, possibly now with additional

test/IDE/print_stdlib.swift

@@ -72,3 +72,8 @@
 // CHECK-GROUPS1-DAG: Collection/Type-erased
 // CHECK-GROUPS1-NOT: <NULL>
 // CHECK-GROUPS1: Module groups end.
+
+/// Check that we can still print the interface of the stdlib with
+/// deserialization safety enabled.
+// RUN: %target-swift-ide-test -print-module-groups -module-to-print=Swift -source-filename %s -print-interface -enable-deserialization-safety > %t-group.txt
+// RUN: %FileCheck -check-prefix=CHECK-GROUPS1 %s < %t-group.txt

tools/swift-ide-test/swift-ide-test.cpp

@@ -397,6 +397,11 @@ DisableAccessControl("disable-access-control",
     llvm::cl::desc("Disables access control, like a debugger"),
     llvm::cl::cat(Category));
 
+static llvm::cl::opt<bool>
+EnableDeserializationSafety("enable-deserialization-safety",
+    llvm::cl::desc("Avoid reading potentially unsafe decls from swiftmodules"),
+    llvm::cl::cat(Category));
+
 static llvm::cl::opt<bool> CodeCompleteInitsInPostfixExpr(
     "code-complete-inits-in-postfix-expr",
     llvm::cl::desc(
@@ -4447,6 +4452,8 @@ int main(int argc, char *argv[]) {
     options::ImportObjCHeader;
   InitInvok.getLangOptions().EnableAccessControl =
     !options::DisableAccessControl;
+  InitInvok.getLangOptions().EnableDeserializationSafety =
+    options::EnableDeserializationSafety;
   InitInvok.getLangOptions().EnableSwift3ObjCInference =
     options::EnableSwift3ObjCInference;
   InitInvok.getClangImporterOptions().ImportForwardDeclarations |=