[lldb] Adopt new pointer and mangled typename based stringForPrintObject #11916

kastiglione · 2025-12-03T00:00:43Z

Adopt stringForPrintObject(_:mangledTypeName:), an overload added in swiftlang/swift#84742.

This new overload allows lldb to call stringForPrintObject using only a pointer referencing the value, and the mangled typename corresponding to the value. The resulting expression does not reference the concrete type.

By not referencing a value's type, po can be performed on variables (and their nested stored properties) without loading the modules corresponding to the value's type. This will improve performance and reliability of po.

rdar://158968103

Adopt `stringForPrintObject(_:mangledTypeName:)`, an overload added in swiftlang/swift#84742. This new overload allows lldb to call `stringForPrintObject` using only a pointer referencing the value, and the mangled typename corresponding to the value. The resulting expression does not reference the concrete type. By not referencing a value's type, `po` can be performed on variables (and their nested stored properties) without loading the modules corresponding to the value's type. This will improve performance and reliability of `po`.

kastiglione · 2025-12-03T00:00:45Z

@swift-ci test

kastiglione · 2025-12-03T00:02:23Z

Draft mode: follow up will include experimental setting, and tests.

kastiglione · 2025-12-03T00:06:05Z

@swift-ci test

kastiglione · 2025-12-03T06:38:12Z

@swift-ci test macOS

kastiglione · 2025-12-03T16:42:17Z

Existing tests all pass with new po.

kastiglione · 2025-12-03T23:38:58Z

@swift-ci test

adrian-prantl · 2025-12-03T23:46:26Z

lldb/source/Target/TargetProperties.td

  def SwiftCacheTaskPointerLocation: Property<"swift-cache-task-pointer-location", "Boolean">,
    DefaultTrue,
    Desc<"Enables caching of task pointers inside the swift tasks plugin">;
+  def SwiftUseNewPrintObject: Property<"swift-use-new-po", "Boolean">,


How about calling this swift-use-context-free-po or something else more specific than "new"?

I can, though I intentionally didn't fret on the naming because the plan is to delete it, hopefully in weeks. I also don't expect to broadcast its existence.

adrian-prantl · 2025-12-03T23:49:01Z

lldb/source/Plugins/ExpressionParser/Swift/SwiftExpressionSourceCode.cpp

-          os_vers << platform->GetOSVersion(process_sp.get()).getAsString();
+        if (options.GetDisableAvailability()) {
+          // Disable availability by setting the OS version to 9999, the
+          // placeholder number used for future OS versions.


... when building the Swift standard library locally. ?

adrian-prantl · 2025-12-03T23:51:13Z

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

  return false;
 }

+static bool printObjectViaPointer(Stream &strm, ValueObject &object,


Should this function return llvm::Error and return createStringError for the various failure modes for easier debugging?

adrian-prantl · 2025-12-03T23:51:41Z

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

+  auto result_or_err = runObjectDescription(object, expr_string, process, true);
+  if (!result_or_err) {
+    LLDB_LOG_ERROR(log, result_or_err.takeError(),
+                   "stringForPrintObject(_:mangledTypeName:) failed: {0}");


then this could just be return result_or_err.takeError()

adrian-prantl · 2025-12-03T23:54:36Z

...est/API/lang/swift/po/pointer_and_mangled_typename/TestSwiftPrintObjectPointerAndTypeName.py

+        )
+        self.expect("po value", substrs=["2025"])
+        self._filecheck("INT")
+        # CHECK-INT: stringForPrintObject(UnsafeRawPointer(bitPattern: {{[0-9]+}}), mangledTypeName: "SiD")


Neat test, reusing filecheck this way!

augusto2112 · 2025-12-04T13:59:44Z

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

-llvm::Error SwiftLanguageRuntime::RunObjectDescriptionExpr(
-    ValueObject &object, std::string &expr_string, Stream &result) {
+static llvm::Expected<ValueObjectSP>
+runObjectDescription(ValueObject &object, std::string &expr_string,


Capitalize the function?

augusto2112 · 2025-12-04T14:03:11Z

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

+  return result_sp;
+}
+
+static llvm::Error dumpString(ValueObjectSP result_sp, Stream &strm);


Can you move the function up here instead of forward declaring it?

augusto2112 · 2025-12-04T14:11:51Z

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

+
+  StringRef mangled_type_name = object.GetMangledTypeName();
+  // Swift's APIs that accept mangled names require the "$s" prefix removed.
+  mangled_type_name.consume_front("$s");


"$e" is also valid mangling for embedded Swift.

Also, when I see mangled names without the front "$s" omitted, I also see it with the last "D" omitted too (I think that's a "TypeMangling" node). I guess this isn't necessary here?

jimingham · 2025-12-04T22:41:44Z

lldb/source/Plugins/ExpressionParser/Swift/SwiftExpressionSourceCode.cpp

+          bool is_simulator = platform->GetPluginName().ends_with("-simulator");
+          if (is_simulator) {
+            // The simulators look like the host OS to Process, but Platform
+            // can the version out of an environment variable.


"can the" -> "can get the"

jimingham · 2025-12-04T22:42:37Z

lldb/source/Plugins/ExpressionParser/Swift/SwiftExpressionSourceCode.cpp

-          llvm::VersionTuple version = process_sp->GetHostOSVersion();
-          os_vers << version.getAsString();
+          auto platform = target->GetPlatform();
+          bool is_simulator = platform->GetPluginName().ends_with("-simulator");


Do we really not have a nicer way to tell if a Platform is a simulator?

jimingham · 2025-12-04T22:45:11Z

lldb/include/lldb/Target/Target.h


  bool GetPreparePlaygroundStubFunctions() const { return m_prepare_playground_stub_functions; }

+  void SetDisableAvailability() { m_disable_availability = true; }


This is an odd set API. It only allows you to set it to true, which the name doesn't really imply?

We usually do:

SetWhatever(bool new_value)

jimingham · 2025-12-04T22:47:00Z

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

+  return dumpString(*result_or_err, strm);
+}
+
+static llvm::Error dumpString(ValueObjectSP result_sp, Stream &strm) {


lldb doesn't do lower-case first letter functions for the most part. This should be DumpString.

jimingham · 2025-12-04T22:50:01Z

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

+  addr_t addr = LLDB_INVALID_ADDRESS;
+  if (flags.Test(eTypeInstanceIsPointer)) {
+    // Objects are pointers.
+    addr = object.GetValueAsUnsigned(LLDB_INVALID_ADDRESS);


This should use GetValueAsAddress.

kastiglione requested a review from a team as a code owner December 3, 2025 00:00

kastiglione marked this pull request as draft December 3, 2025 00:00

Fix missing rename

9cd7c44

kastiglione requested a review from adrian-prantl December 3, 2025 00:21

kastiglione added 2 commits December 3, 2025 10:50

Add setting gating the new po, initially disabled by default

3c969d6

Add tests for new po

caade22

kastiglione marked this pull request as ready for review December 3, 2025 23:38

kastiglione requested review from augusto2112, felipepiovezan and jimingham December 3, 2025 23:45

adrian-prantl reviewed Dec 3, 2025

View reviewed changes

augusto2112 approved these changes Dec 4, 2025

View reviewed changes

jimingham reviewed Dec 4, 2025

View reviewed changes


		bool GetPreparePlaygroundStubFunctions() const { return m_prepare_playground_stub_functions; }

		void SetDisableAvailability() { m_disable_availability = true; }

[lldb] Adopt new pointer and mangled typename based stringForPrintObject #11916

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[lldb] Adopt new pointer and mangled typename based stringForPrintObject #11916

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kastiglione commented Dec 3, 2025 •

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