tdf#136143 - reset SbxFlagBits::Fixed SbiRuntime::StepPARAM

In order to prevent type conversion errors, reset a variable of type
SbxERROR to not fixed. Variable will be of type SbxERROR, but can be
converted to any requested type.

Change-Id: Ic856376e3f8232577a5e894a2adb2545c8723033
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/101419
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

basic/qa/basic_coverage/test_ismissing_cascade.vb

@@ -0,0 +1,51 @@
+Dim passCount As Integer
+Dim failCount As Integer
+Dim result As String
+
+Function doUnitTest() As String
+    result = verify_testIsMissingCascade()
+    If failCount <> 0 Or passCount = 0 Then
+        doUnitTest = 0
+    Else
+        doUnitTest = 1
+    End If
+End Function
+
+Function verify_testIsMissingCascade() As String
+
+    passCount = 0
+    failCount = 0
+
+    result = "Test Results" & Chr$(10) & "============" & Chr$(10)
+    testName = "Test missing (IsMissing with cascading optionals)"
+    On Error GoTo errorHandler
+
+    ' tdf#136143 - test cascading optionals in order to prevent type conversion errors, because
+    ' optional arguments are of type SbxERROR and set to not fixed.
+    TestLog_ASSERT TestOpt(), 2, "Cascading optionals"
+
+    result = result & Chr$(10) & "Tests passed: " & passCount & Chr$(10) & "Tests failed: " & failCount & Chr$(10)
+    verify_testIsMissingCascade = result
+
+    Exit Function
+errorHandler:
+    TestLog_ASSERT False, True, Err.Description
+End Function
+
+Function TestOpt(Optional A)
+    TestOpt = TestOptCascade(A)
+End Function
+
+Function TestOptCascade(Optional A)
+    If IsMissing(A) Then A = 2
+    TestOptCascade = A
+End Function
+
+Sub TestLog_ASSERT(actual As Variant, expected As Integer, testName As String)
+    If expected = actual Then
+        passCount = passCount + 1
+    Else
+        result = result & Chr$(10) & " Failed: " & testName & " returned " & actual & ", expected " & expected
+        failCount = failCount + 1
+    End If
+End Sub

basic/source/runtime/runtime.cxx

@@ -4110,6 +4110,8 @@ void SbiRuntime::StepPARAM( sal_uInt32 nOp1, sal_uInt32 nOp2 )
                 const SbxParamInfo* pParam = pInfo->GetParam( nIdx );
                 if( pParam && ( pParam->nFlags & SbxFlagBits::Optional ) )
                 {
+                    // tdf#136143 - reset SbxFlagBits::Fixed in order to prevent type conversion errors
+                    pVar->ResetFlag( SbxFlagBits::Fixed );
                     // Default value?
                     sal_uInt16 nDefaultId = static_cast<sal_uInt16>(pParam->nUserData & 0x0ffff);
                     if( nDefaultId > 0 )