[Debug] Add pointer based stringForPrintObject (#84742)

Adds an overload of `_DebuggerSupport.stringForPrintObject` which takes a pointer and mangled typename as arguments. This will be used to improve performance and resilience of `po` in lldb.

The pointer and mangled typename are used to construct an `Any` value, which is then passed into the primary implementation of `stringForPrintObject`.

This allows calling `stringForPrintObject` without having to first construct a context that contains all necessary Swift modules. This will improve speed, and also resilience when modules cannot be loaded for whatever reason.

rdar://158968103

Author: kastiglione

stdlib/public/core/DebuggerSupport.swift

@@ -328,6 +328,38 @@ public enum _DebuggerSupport {
 
     return target
   }
+
+  // Print an object or value without the caller having a concrete type.
+  //
+  // For simplicity of data handling in LLDB avoids using an enum return type,
+  // using (Bool, String) instead of Optional<String>.
+  @available(SwiftStdlib 6.3, *)
+  public static func stringForPrintObject(_ pointer: UnsafeRawPointer?, mangledTypeName: String) -> (Bool, String) {
+    guard let pointer = unsafe pointer else {
+      return (false, "invalid pointer")
+    }
+
+    guard let type =
+      unsafe _getTypeByMangledNameInContext(
+        mangledTypeName,
+        UInt(mangledTypeName.count),
+        genericContext: nil,
+        genericArguments: nil)
+      else {
+        return (false, "type not found for mangled name: \(mangledTypeName)")
+      }
+
+    func loadPointer<T>(type: T.Type) -> Any {
+      if type is AnyObject.Type {
+        unsafe unsafeBitCast(pointer, to: T.self)
+      } else {
+        unsafe pointer.load(as: T.self)
+      }
+    }
+
+    let anyValue = _openExistential(type, do: loadPointer)
+    return (true, stringForPrintObject(anyValue))
+  }
 }
 
 public func _stringForPrintObject(_ value: Any) -> String {

test/abi/Inputs/macOS/arm64/stdlib/baseline

@@ -6815,6 +6815,7 @@ _$ss16TextOutputStreamPsE11_writeASCIIyySRys5UInt8VGF
 _$ss16TextOutputStreamPsE5_lockyyF
 _$ss16TextOutputStreamPsE7_unlockyyF
 _$ss16TextOutputStreamTL
+_$ss16_DebuggerSupportO20stringForPrintObject_15mangledTypeNameSb_SStSVSg_SStFZ
 _$ss16_DebuggerSupportO20stringForPrintObjectySSypFZ
 _$ss16_DebuggerSupportOMa
 _$ss16_DebuggerSupportOMn

test/abi/Inputs/macOS/arm64/stdlib/baseline-asserts

@@ -6815,6 +6815,7 @@ _$ss16TextOutputStreamPsE11_writeASCIIyySRys5UInt8VGF
 _$ss16TextOutputStreamPsE5_lockyyF
 _$ss16TextOutputStreamPsE7_unlockyyF
 _$ss16TextOutputStreamTL
+_$ss16_DebuggerSupportO20stringForPrintObject_15mangledTypeNameSb_SStSVSg_SStFZ
 _$ss16_DebuggerSupportO20stringForPrintObjectySSypFZ
 _$ss16_DebuggerSupportOMa
 _$ss16_DebuggerSupportOMn

test/abi/Inputs/macOS/x86_64/stdlib/baseline

@@ -6836,6 +6836,7 @@ _$ss16TextOutputStreamPsE11_writeASCIIyySRys5UInt8VGF
 _$ss16TextOutputStreamPsE5_lockyyF
 _$ss16TextOutputStreamPsE7_unlockyyF
 _$ss16TextOutputStreamTL
+_$ss16_DebuggerSupportO20stringForPrintObject_15mangledTypeNameSb_SStSVSg_SStFZ
 _$ss16_DebuggerSupportO20stringForPrintObjectySSypFZ
 _$ss16_DebuggerSupportOMa
 _$ss16_DebuggerSupportOMn

test/abi/Inputs/macOS/x86_64/stdlib/baseline-asserts

@@ -6836,6 +6836,7 @@ _$ss16TextOutputStreamPsE11_writeASCIIyySRys5UInt8VGF
 _$ss16TextOutputStreamPsE5_lockyyF
 _$ss16TextOutputStreamPsE7_unlockyyF
 _$ss16TextOutputStreamTL
+_$ss16_DebuggerSupportO20stringForPrintObject_15mangledTypeNameSb_SStSVSg_SStFZ
 _$ss16_DebuggerSupportO20stringForPrintObjectySSypFZ
 _$ss16_DebuggerSupportOMa
 _$ss16_DebuggerSupportOMn

test/stdlib/DebuggerSupport.swift

@@ -10,6 +10,11 @@ struct StructWithMembers {
   var b = "Hello World"
 }
 
+struct StructIsNonCopyable: ~Copyable {
+  var a = 1
+  var b = "Hello World"
+}
+
 class ClassWithMembers {
   var a = 1
   var b = "Hello World"
@@ -108,6 +113,64 @@ if #available(SwiftStdlib 6.1, *) {
   }
 }
 
+@available(SwiftStdlib 6.3, *)
+func _expectStringForPrintObject<T>(_ pointer: UnsafePointer<T>, output: String) {
+  guard let mangledTypeName = _mangledTypeName(T.self) else {
+    expectTrue(false)
+    return
+  }
+  let (success, printed) =
+    _DebuggerSupport.stringForPrintObject(UnsafeRawPointer(pointer), mangledTypeName: mangledTypeName)
+  expectTrue(success)
+  expectEqual(printed, output)
+}
+
+if #available(SwiftStdlib 6.3, *) {
+  StringForPrintObjectTests.test("PointerWithMangledTypeName") {
+    var num = 33
+    _expectStringForPrintObject(&num, output: "33\n")
+
+    var val1 = StructWithMembers()
+    _expectStringForPrintObject(&val1, output: "▿ StructWithMembers\n  - a : 1\n  - b : \"Hello World\"\n")
+
+    var val2: StructWithMembers? = StructWithMembers()
+    _expectStringForPrintObject(&val2,
+      output: "▿ Optional<StructWithMembers>\n  ▿ some : StructWithMembers\n    - a : 1\n    - b : \"Hello World\"\n")
+
+    do {
+      var val3 = StructIsNonCopyable()
+      if let mangledTypeName = _mangledTypeName(StructIsNonCopyable.self) {
+        withUnsafeBytes(of: &val3) { bytes in
+          guard let pointer = bytes.baseAddress else {
+            expectTrue(false)
+            return
+          }
+          let (success, printed) =
+            _DebuggerSupport.stringForPrintObject(pointer, mangledTypeName: mangledTypeName)
+          expectFalse(success)
+          expectEqual(printed, "type not found for mangled name: \(mangledTypeName)")
+        }
+      } else {
+        expectTrue(false)
+      }
+    }
+
+    do {
+      let obj = ClassWithMembers()
+      if let mangledTypeName = _mangledTypeName(ClassWithMembers.self) {
+        withExtendedLifetime(obj) { obj in
+          let pointer = unsafeBitCast(obj, to: UnsafeRawPointer.self)
+          let (success, printed) = _DebuggerSupport.stringForPrintObject(pointer, mangledTypeName: mangledTypeName)
+          expectTrue(success)
+          expectTrue(printed.hasPrefix("<ClassWithMembers: 0x"))
+        }
+      } else {
+        expectTrue(false)
+      }
+    }
+  }
+}
+
 class RefCountedObj {
   var patatino : Int
   init(_ p : Int) {