[lldb][formatter] Add children of Swift Tasks (swiftlang#10057)

When displaying a Swift `Task`, include its child tasks.

This adds a `children` child to the `Task` synthetic provider. The type of `children` is a dynamically constructed tuple of N `UnsafeCurrentTask`, where N is the number of child tasks.

This allows users to see structured concurrency child tasks, in particular `async let` child tasks, and `TaskGroup` child tasks.

Author: kastiglione

lldb/source/Plugins/Language/Swift/SwiftFormatters.cpp

@@ -15,6 +15,7 @@
 #include "Plugins/LanguageRuntime/Swift/ReflectionContextInterface.h"
 #include "Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.h"
 #include "Plugins/TypeSystem/Clang/TypeSystemClang.h"
+#include "Plugins/TypeSystem/Swift/SwiftDemangle.h"
 #include "lldb/DataFormatters/FormattersHelpers.h"
 #include "lldb/DataFormatters/StringPrinter.h"
 #include "lldb/Symbol/CompilerType.h"
@@ -28,6 +29,7 @@
 #include "lldb/ValueObject/ValueObject.h"
 #include "lldb/lldb-enumerations.h"
 #include "swift/AST/Types.h"
+#include "swift/Demangling/Demangle.h"
 #include "swift/Demangling/ManglingMacros.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -761,10 +763,10 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
     auto ts_or_err =
         target_sp->GetScratchTypeSystemForLanguage(eLanguageTypeSwift);
     if (auto err = ts_or_err.takeError()) {
-      LLDB_LOG(
-          GetLog(LLDBLog::DataFormatters | LLDBLog::Types),
-          "could not get Swift type system for Task synthetic provider: {0}",
-          fmt_consume(std::move(err)));
+      LLDB_LOG_ERROR(GetLog(LLDBLog::DataFormatters | LLDBLog::Types),
+                     std::move(err),
+                     "could not get Swift type system for Task synthetic "
+                     "provider: {0}");
       return;
     }
     m_ts = llvm::dyn_cast_or_null<TypeSystemSwiftTypeRef>(ts_or_err->get());
@@ -782,6 +784,7 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
       "isStatusRecordLocked",
       "isEscalated",
       "isEnqueued",
+      "children",
       "isRunning",
   };
 
@@ -837,7 +840,22 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
       RETURN_CHILD(m_is_escalated_sp, isEscalated, bool_type);
     case 10:
       RETURN_CHILD(m_is_enqueued_sp, isEnqueued, bool_type);
-    case 11:
+    case 11: {
+      if (!m_child_tasks_sp) {
+        const auto &tasks = m_task_info.childTasks;
+        std::string mangled_typename =
+            mangledTypenameForTasksTuple(tasks.size());
+        CompilerType tasks_tuple_type =
+            m_ts->GetTypeFromMangledTypename(ConstString(mangled_typename));
+        DataExtractor data{tasks.data(), tasks.size() * sizeof(tasks[0]),
+                           endian::InlHostByteOrder(), sizeof(void *)};
+        m_child_tasks_sp = ValueObject::CreateValueObjectFromData(
+            "children", data, m_backend.GetExecutionContextRef(),
+            tasks_tuple_type);
+      }
+      return m_child_tasks_sp;
+    }
+    case 12:
       RETURN_CHILD(m_is_running_sp, isRunning, bool_type);
     default:
       return {};
@@ -858,17 +876,17 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
         llvm::Expected<ReflectionContextInterface::AsyncTaskInfo> task_info =
             reflection_ctx->asyncTaskInfo(task_ptr);
         if (auto err = task_info.takeError()) {
-          LLDB_LOG(GetLog(LLDBLog::DataFormatters | LLDBLog::Types),
-                   "could not get info for async task {0:x}: {1}", task_ptr,
-                   fmt_consume(std::move(err)));
+          LLDB_LOG_ERROR(
+              GetLog(LLDBLog::DataFormatters | LLDBLog::Types), std::move(err),
+              "could not get info for async task {0:x}: {1}", task_ptr);
         } else {
           m_task_info = *task_info;
           for (auto child :
                {m_id_sp, m_kind_sp, m_enqueue_priority_sp, m_is_child_task_sp,
                 m_is_future_sp, m_is_group_child_task_sp,
                 m_is_async_let_task_sp, m_is_cancelled_sp,
                 m_is_status_record_locked_sp, m_is_escalated_sp,
-                m_is_enqueued_sp, m_is_running_sp})
+                m_is_enqueued_sp, m_child_tasks_sp, m_is_running_sp})
             child.reset();
         }
       }
@@ -886,6 +904,35 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
     return std::distance(children.begin(), it);
   }
 
+private:
+  std::string mangledTypenameForTasksTuple(size_t count) {
+    /*
+    Global > TypeMangling > Type > Tuple
+      TupleElement > Type > Structure
+        Module, text="Swift"
+        Identifier, text="UnsafeCurrentTask"
+    */
+    using namespace ::swift::Demangle;
+    using Kind = Node::Kind;
+    NodeFactory factory;
+    auto [root, tuple] = swift_demangle::MakeNodeChain(
+        {Kind::TypeMangling, Kind::Type, Kind::Tuple}, factory);
+
+    // Make a TupleElement subtree N times, where N is the number of subtasks.
+    for (size_t i = 0; i < count; ++i) {
+      auto *structure = swift_demangle::MakeNodeChain(
+          tuple, {Kind::TupleElement, Kind::Type, Kind::Structure}, factory);
+      if (structure) {
+        structure->addChild(
+            factory.createNode(Kind::Module, ::swift::STDLIB_NAME), factory);
+        structure->addChild(
+            factory.createNode(Kind::Identifier, "UnsafeCurrentTask"), factory);
+      }
+    }
+
+    return mangleNode(root).result();
+  }
+
 private:
   TypeSystemSwiftTypeRef *m_ts = nullptr;
   ReflectionContextInterface::AsyncTaskInfo m_task_info;
@@ -900,6 +947,7 @@ class TaskSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
   ValueObjectSP m_is_status_record_locked_sp;
   ValueObjectSP m_is_escalated_sp;
   ValueObjectSP m_is_enqueued_sp;
+  ValueObjectSP m_child_tasks_sp;
   ValueObjectSP m_is_running_sp;
 };
 }

lldb/source/Plugins/LanguageRuntime/Swift/ReflectionContext.cpp

@@ -407,6 +407,8 @@ class TargetReflectionContext : public ReflectionContextInterface {
     result.kind = task_info.Kind;
     result.enqueuePriority = task_info.EnqueuePriority;
     result.resumeAsyncContext = task_info.ResumeAsyncContext;
+    for (auto child : task_info.ChildTasks)
+      result.childTasks.push_back(child);
     return result;
   }
 

lldb/source/Plugins/LanguageRuntime/Swift/ReflectionContextInterface.h

@@ -170,6 +170,7 @@ class ReflectionContextInterface {
     uint32_t kind = 0;
     uint32_t enqueuePriority = 0;
     lldb::addr_t resumeAsyncContext = LLDB_INVALID_ADDRESS;
+    std::vector<lldb::addr_t> childTasks;
   };
   // The default limits are copied from swift-inspect.
   virtual llvm::Expected<AsyncTaskInfo>

lldb/source/Plugins/TypeSystem/Swift/SwiftDemangle.h

@@ -17,6 +17,7 @@
 #include "swift/Demangling/Demangler.h"
 #include "swift/Demangling/ManglingFlavor.h"
 #include "llvm/ADT/ArrayRef.h"
+#include <initializer_list>
 
 namespace lldb_private {
 namespace swift_demangle {
@@ -116,6 +117,41 @@ GetDemangledTypeMangling(swift::Demangle::Demangler &dem,
   return GetTypeMangling(dem.demangleSymbol(name));
 }
 
+/// Create a parent-child chain of demangle nodes for the specified node kinds.
+///
+/// \param initial[in] The starting node to construct the chain from.
+/// \param kinds[in] The node kind for each created node.
+/// \param factory[in] The factory to create nodes.
+/// \return The tail leaf node created, whose kind is the last kind in \c kinds.
+inline NodePointer
+MakeNodeChain(NodePointer initial,
+              std::initializer_list<swift::Demangle::Node::Kind> kinds,
+              NodeFactory &factory) {
+  auto *current = initial;
+  for (auto kind : kinds) {
+    if (!current)
+      return nullptr;
+    auto *child = factory.createNode(kind);
+    current->addChild(child, factory);
+    current = child;
+  }
+  return current;
+}
+
+/// Create a parent-child chain of demangle nodes for the specified node kinds.
+///
+/// \param initial[in] The starting node to construct the chain from.
+/// \param kinds[in] The node kind for each created node.
+/// \param factory[in] The factory to create nodes.
+/// \return A pair of nodes: the head and tail of the constructed nodes.
+inline std::pair<NodePointer, NodePointer>
+MakeNodeChain(std::initializer_list<swift::Demangle::Node::Kind> kinds,
+              NodeFactory &factory) {
+  auto *root = factory.createNode(Node::Kind::Global);
+  auto *leaf = MakeNodeChain(root, kinds, factory);
+  return {root, leaf};
+}
+
 /// Wrap node in Global/TypeMangling/Type.
 inline swift::Demangle::NodePointer
 MangleType(swift::Demangle::Demangler &dem,

lldb/test/API/lang/swift/async/formatters/task/TestSwiftTaskSyntheticProvider.py

@@ -28,6 +28,7 @@ def test_top_level_task(self):
                 "isAsyncLetTask = false",
                 "isCancelled = false",
                 "isEnqueued = ",
+                "children = {}",
             ],
         )
 
@@ -49,5 +50,6 @@ def test_current_task(self):
                 "isAsyncLetTask = true",
                 "isCancelled = false",
                 "isEnqueued = false",
+                "children = {}",
             ],
         )

lldb/test/API/lang/swift/async/formatters/task/children/Makefile

@@ -0,0 +1,3 @@
+SWIFT_SOURCES := main.swift
+SWIFTFLAGS_EXTRAS := -parse-as-library
+include Makefile.rules

lldb/test/API/lang/swift/async/formatters/task/children/TestSwiftSyntheticTaskChildren.py

@@ -0,0 +1,31 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestCase(TestBase):
+
+    @skipUnlessDarwin
+    @swiftTest
+    def test(self):
+        """"""
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.swift")
+        )
+        self.expect(
+            "language swift task info",
+            substrs=[
+                "(UnsafeCurrentTask) current_task = {",
+                "id = 1",
+                "isChildTask = false",
+                "isAsyncLetTask = false",
+                "children = {",
+                "0 = {",
+                "id = 2",
+                "isChildTask = true",
+                "isAsyncLetTask = true",
+                "children = {}",
+            ],
+        )

lldb/test/API/lang/swift/async/formatters/task/children/main.swift

@@ -0,0 +1,11 @@
+func f() async -> Int {
+    try? await Task.sleep(for: .seconds(300))
+    return 30
+}
+
+@main struct Main {
+    static func main() async {
+        async let number = f()
+        await print("break here \(number)")
+    }
+}