Preserve the IRestrictedErrorInfo after reading it.

swiftwinrt/Resources/Support/Error.swift

@@ -101,13 +101,7 @@ public var E_XAMLPARSEFAILED : WinSDK.HRESULT {
   HRESULT(bitPattern: 0x802B000A)
 }
 
-private func getErrorDescription(expecting hr: HRESULT) -> String? {
-  var errorInfo: UnsafeMutablePointer<IRestrictedErrorInfo>?
-  guard GetRestrictedErrorInfo(&errorInfo) == S_OK else { return nil }
-  defer {
-    _ = errorInfo?.pointee.lpVtbl.pointee.Release(errorInfo)
-  }
-
+private func getErrorDescription(restrictedErrorInfo: UnsafeMutablePointer<IRestrictedErrorInfo>) -> String? {
   var errorDescription: BSTR?
   var restrictedDescription: BSTR?
   var capabilitySid: BSTR?
@@ -116,16 +110,14 @@ private func getErrorDescription(expecting hr: HRESULT) -> String? {
     SysFreeString(restrictedDescription)
     SysFreeString(capabilitySid)
   }
-  var resultLocal: HRESULT = S_OK
-  _ = errorInfo?.pointee.lpVtbl.pointee.GetErrorDetails(
-    errorInfo,
+  var hr: HRESULT = S_OK
+  guard restrictedErrorInfo.pointee.lpVtbl.pointee.GetErrorDetails(
+    restrictedErrorInfo,
     &errorDescription,
-    &resultLocal,
+    &hr,
     &restrictedDescription,
-    &capabilitySid)
+    &capabilitySid) == S_OK else { return nil }
 
-  guard resultLocal == hr else { return nil }
-
   // Favor restrictedDescription as this is a more user friendly message, which
   // is intended to be displayed to the caller to help them understand why the
   // api call failed. If it's not set, then fallback to the generic error message
@@ -135,7 +127,7 @@ private func getErrorDescription(expecting hr: HRESULT) -> String? {
   } else if SysStringLen(errorDescription) > 0 {
     return String(decodingCString: errorDescription!, as: UTF16.self)
   } else {
-    return nil
+    return hrToString(hr)
   }
 }
 
@@ -164,7 +156,21 @@ public struct Error : Swift.Error, CustomStringConvertible {
   public let hr: HRESULT
 
   public init(hr: HRESULT) {
-    self.description = getErrorDescription(expecting: hr) ?? hrToString(hr)
+    // RoGetMatchingRestrictedErrorInfo creates an IRestrictedErrorInfo with a generic message if it can't find one for the given HRESULT.
+    var restrictedErrorInfo: UnsafeMutablePointer<IRestrictedErrorInfo>?
+    if RoGetMatchingRestrictedErrorInfo(hr, &restrictedErrorInfo) == S_OK, let restrictedErrorInfo {
+      defer { _ = restrictedErrorInfo.pointee.lpVtbl.pointee.Release(restrictedErrorInfo) }
+
+      // From the docs: https://learn.microsoft.com/en-us/windows/win32/api/roerrorapi/nf-roerrorapi-getrestrictederrorinfo
+      // > GetRestrictedErrorInfo transfers ownership of the error object to the caller and clears the error state for the thread.
+      // Assume that RoGetMatchingRestrictedErrorInfo also clears the error state,
+      // but for crash reporting purposes, it's useful to preserve the it.
+      _ = SetRestrictedErrorInfo(restrictedErrorInfo)
+
+      self.description = getErrorDescription(restrictedErrorInfo: restrictedErrorInfo) ?? hrToString(hr)
+    } else {
+      self.description = hrToString(hr)
+    }
     self.hr = hr
   }
 }

tests/test_app/main.swift

@@ -433,6 +433,39 @@ class SwiftWinRTTests : XCTestCase {
     }
   }
 
+  public func testIRestrictedErrorInfo() {
+    let message = "You are doing a bad thing"
+    do {
+      let classy = Class()
+      try classy.fail(message)
+    } catch {
+      var restrictedErrorInfo: UnsafeMutablePointer<IRestrictedErrorInfo>?
+      guard GetRestrictedErrorInfo(&restrictedErrorInfo) == S_OK, let restrictedErrorInfo else {
+        XCTFail("Failed to get error info")
+        return
+      }
+      defer { _ = restrictedErrorInfo.pointee.lpVtbl.pointee.Release(restrictedErrorInfo) }
+
+      var errorDescription: BSTR?
+      var hr: HRESULT = S_OK
+      var restrictedDescription: BSTR?
+      var capabilitySid: BSTR?
+      defer {
+        SysFreeString(errorDescription)
+        SysFreeString(restrictedDescription)
+        SysFreeString(capabilitySid)
+      }
+      guard restrictedErrorInfo.pointee.lpVtbl.pointee.GetErrorDetails(
+          restrictedErrorInfo, &errorDescription, &hr, &restrictedDescription, &capabilitySid) == S_OK,
+          let restrictedDescription else {
+        XCTFail("Failed to get error description")
+        return
+      }
+
+      XCTAssertEqual(String(decodingCString: restrictedDescription, as: UTF16.self), message)
+    }
+  }
+
   public func testNoExcept() throws {
     let classy = Class()
     classy.noexceptVoid()
@@ -459,6 +492,7 @@ var tests: [XCTestCaseEntry] = [
     ("testStructWithIReference", SwiftWinRTTests.testStructWithIReference),
     ("testUnicode", SwiftWinRTTests.testUnicode),
     ("testErrorInfo", SwiftWinRTTests.testErrorInfo),
+    ("testIRestrictedErrorInfo", SwiftWinRTTests.testIRestrictedErrorInfo),
   ])
 ] + valueBoxingTests + eventTests + collectionTests + aggregationTests + asyncTests + memoryManagementTests + bufferTests + weakReferenceTests