[lldb][swift] Create thread plan for stepping through Allocating Init

These trampolines have a well defined target, which can be extracted
from the demangle tree. A similar strategy is already adopted for
stepping into conformance code. This allows LLDB to create a StepThrough
plan with a target symbol, instead of a plan that keep taking steps
until it reaches some interesting location.

We already had a test for this, but we rely on the "step avoid
libraries" setting to emulate the case of "avoid libraries without debug
info". However, they are not exactly equivalent, so the test mislead us
into believing stepping was working. A future patch should try to fold
the setting-checking code into
ThreadPlanShouldStopHere::DefaultShouldStopCallback.

With this patch, the test now works regardless of whether debug info is
present or not.

To make this work, this commit also teaches the Swift language runtime
how to recognize "type metadata accessors". These are thunks in the
sense that they jump to some other code, but not user code. Their
purposes is to eventually send the "self" message to the SwiftObject the
first time they run. As such, they should just be stepped out from,
which is accomplished by having the runtime recognize them as
trampolines but not provide any specific actions, relying on the default
behavior of ShouldStopHere.

Prior to this change, this would sometimes work accidentally because all
the functions involved had line 0 debug information, and the debugger
would keep stepping through _all_ of them. However, in debug builds of
x86, this strategy failed; sometimes the computed Symbol size is larger
than the line entry for these functions, and so the detection "all line
0" fails. Relying on this is error-prone and slow, as it causes the
debugger to stop many times.

Author: felipepiovezan

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

@@ -53,6 +53,7 @@ enum class ThunkAction {
   Unknown = 0,
   GetThunkTarget,
   StepIntoConformance,
+  StepIntoAllocatingInit,
   StepThrough,
 };
 
@@ -336,7 +337,7 @@ static const char *GetThunkKindName(ThunkKind kind) {
   case ThunkKind::Unknown:
     return "Unknown";
   case ThunkKind::AllocatingInit:
-    return "StepThrough";
+    return "StepIntoAllocatingInit";
   case ThunkKind::PartialApply:
     return "GetThunkTarget";
   case ThunkKind::ObjCAttribute:
@@ -353,7 +354,7 @@ static ThunkAction GetThunkAction(ThunkKind kind) {
   case ThunkKind::Unknown:
     return ThunkAction::Unknown;
   case ThunkKind::AllocatingInit:
-    return ThunkAction::StepThrough;
+    return ThunkAction::StepIntoAllocatingInit;
   case ThunkKind::PartialApply:
     return ThunkAction::GetThunkTarget;
   case ThunkKind::ObjCAttribute:
@@ -589,17 +590,40 @@ static lldb::ThreadPlanSP GetStepThroughTrampolinePlan(Thread &thread,
         thread, sym_addr_range, sc, function_name.c_str(), eOnlyDuringStepping,
         eLazyBoolNo, eLazyBoolNo);
   }
+  case ThunkAction::StepIntoAllocatingInit: {
+    LLDB_LOGF(log, "Stepping into allocating init: \"%s\"", symbol_name);
+    swift::Demangle::Context ctx;
+    NodePointer demangled_node =
+        SwiftLanguageRuntime::DemangleSymbolAsNode(symbol_name, ctx);
+
+    using Kind = Node::Kind;
+    NodePointer function_node = childAtPath(
+        demangled_node, {Kind::Allocator, Kind::Class, Kind::Identifier});
+    if (!function_node || !function_node->hasText()) {
+      std::string node_str = getNodeTreeAsString(demangled_node);
+      LLDB_LOGF(log,
+                "Failed to extract constructor name from demangle node: %s",
+                node_str.c_str());
+      return nullptr;
+    }
+    StringRef class_name = function_node->getText();
+    std::string ctor_name = (class_name + ".init").str();
+    AddressRange sym_addr_range(sc.symbol->GetAddress(),
+                                sc.symbol->GetByteSize());
+    ThreadPlanSP new_plan_sp = std::make_shared<ThreadPlanStepInRange>(
+        thread, sym_addr_range, sc, ctor_name.c_str(), eOnlyDuringStepping,
+        eLazyBoolNo, eLazyBoolNo);
+    return new_plan_sp;
+  }
   case ThunkAction::StepThrough: {
     if (log)
       log->Printf("Stepping through thunk: %s kind: %s", symbol_name,
                   GetThunkKindName(thunk_kind));
     AddressRange sym_addr_range(sc.symbol->GetAddress(),
                                 sc.symbol->GetByteSize());
-    ThreadPlanSP new_plan_sp = std::make_shared<ThreadPlanStepInRange>(thread, sym_addr_range, sc,
-                                                   nullptr, eOnlyDuringStepping,
-                                                   eLazyBoolNo, eLazyBoolNo);
-    static_cast<ThreadPlanStepInRange *>(new_plan_sp.get())
-        ->GetFlags().Clear(ThreadPlanShouldStopHere::eStepOutPastThunks);
+    ThreadPlanSP new_plan_sp = std::make_shared<ThreadPlanStepInRange>(
+        thread, sym_addr_range, sc, nullptr, eOnlyDuringStepping, eLazyBoolNo,
+        eLazyBoolNo);
     return new_plan_sp;     
   }
   }
@@ -613,7 +637,15 @@ bool SwiftLanguageRuntime::IsSymbolARuntimeThunk(const Symbol &symbol) {
   if (symbol_name.empty())
     return false;
   swift::Demangle::Context demangle_ctx;
-  return demangle_ctx.isThunkSymbol(symbol_name);
+  if (demangle_ctx.isThunkSymbol(symbol_name))
+    return true;
+
+  // These are not Thunks in the sense that they don't jump to *user* code.
+  // But they are language symbols that should be identified as something to act
+  // on; here, the default action of stepping out is appropriate.
+  Node *node = demangle_ctx.demangleSymbolAsNode(symbol_name);
+  return node && node->getKind() == Node::Kind::Global &&
+         hasChild(node, Node::Kind::TypeMetadataAccessFunction);
 }
 
 bool SwiftLanguageRuntime::IsSwiftMangledName(llvm::StringRef name) {

lldb/test/API/lang/swift/cxx_interop/backward/stepping/TestSwiftBackwardInteropStepping.py

@@ -53,7 +53,6 @@ def test_method_step_over_class(self):
         thread = self.setup('Break here for method - class')
         self.check_step_over(thread, 'testMethod')
 
-    @expectedFailureAll(bugnumber="rdar://106670255")
     @swiftTest
     def test_init_step_in_class(self):
         thread = self.setup('Break here for constructor - class')
@@ -115,7 +114,6 @@ def test_method_step_over_struct_class(self):
         thread = self.setup('Break here for method - struct')
         self.check_step_over(thread, 'testMethod')
 
-    @expectedFailureAll(bugnumber="rdar://106670255")
     @swiftTest
     def test_init_step_in_struct_class(self):
         thread = self.setup('Break here for constructor - struct')

lldb/test/API/lang/swift/step_through_allocating_init/TestStepThroughAllocatingInit.py

@@ -25,18 +25,6 @@ def setUp(self):
         lldbtest.TestBase.setUp(self)
         self.main_source = "main.swift"
         self.main_source_spec = lldb.SBFileSpec(self.main_source)
-        # If you are running against a debug swift you are going to
-        # end up stepping into the stdlib and that will make stepping
-        # tests impossible to write.  So avoid that.
-
-        if platform.system() == 'Darwin':
-            lib_name = "libswiftCore.dylib"
-        else:
-            lib_name = "libswiftCore.so"
-
-        self.dbg.HandleCommand(
-            "settings set "
-            "target.process.thread.step-avoid-libraries {}".format(lib_name))
 
     def do_test(self, use_api):
         """Tests that we can step reliably in swift code."""