Correct non-gui DXF C++ importer to not generate pending python exceptions (#20328)

* Add a test case for DXF import

* Test gui flag rather than look for import error to make gui decision

The new code is cleaner and faster and avoids any exception stuff

* Properly avoid trying to use Layer's View object in non-GUI

The code was trying to avoid this but had a Python None object rather than a null C++ pointer and so tried setting a property on None. This left an unhandled exception state which acted as a booby trap that caused the later failure of some unrelated code.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* De-lint, remove wong "unsupported" message
Hidden layers have been supported for a while but still generated an import note about this being unsupported.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/Mod/Test/CMakeLists.txt

@@ -25,6 +25,7 @@ SET(TestData_SRCS
     TestData/bad_xml.xml
     TestData/bad_version.xml
     TestData/content_items.xml
+    TestData/DXFSample.dxf
 )
 
 SOURCE_GROUP("" FILES ${Test_SRCS} ${TestData_SRCS})

src/Mod/Test/Document.py

@@ -21,6 +21,7 @@
 # *                                                                         *
 # ***************************************************************************/
 
+from plistlib import UID
 import FreeCAD, os, unittest, tempfile
 from FreeCAD import Base
 import math
@@ -671,6 +672,49 @@ class DocumentBasicCases(unittest.TestCase):
         FreeCAD.closeDocument("CreateTest")
 
 
+class DocumentImportCases(unittest.TestCase):
+    def testDXFImportCPPIssue20195(self):
+        import importDXF
+        from draftutils import params
+
+        # Set options, doing our best to restore them:
+        wasShowDialog = params.get_param("dxfShowDialog")
+        wasUseLayers = params.get_param("dxfUseDraftVisGroups")
+        wasUseLegacyImporter = params.get_param("dxfUseLegacyImporter")
+        wasCreatePart = params.get_param("dxfCreatePart")
+        wasCreateDraft = params.get_param("dxfCreateDraft")
+        wasCreateSketch = params.get_param("dxfCreateSketch")
+
+        try:
+            # disable Preferences dialog in gui mode (avoids popup prompt to user)
+            params.set_param("dxfShowDialog", False)
+            # Preserve the DXF layers (makes the checking of document contents easier)
+            params.set_param("dxfUseDraftVisGroups", True)
+            # Use the new C++ importer -- that's where the bug was
+            params.set_param("dxfUseLegacyImporter", False)
+            # create simple part shapes (3 params)
+            # This is required to display the bug because creation of Draft objects clears out the
+            # pending exception this test is looking for, whereas creation of the simple shape object
+            # actually throws on the pending exception so the entity is absent from the document.
+            params.set_param("dxfCreatePart", True)
+            params.set_param("dxfCreateDraft", False)
+            params.set_param("dxfCreateSketch", False)
+            importDXF.insert(
+                FreeCAD.getHomePath() + "Mod/Test/TestData/DXFSample.dxf", "ImportedDocName"
+            )
+        finally:
+            params.set_param("dxfShowDialog", wasShowDialog)
+            params.set_param("dxfUseDraftVisGroups", wasUseLayers)
+            params.set_param("dxfUseLegacyImporter", wasUseLegacyImporter)
+            params.set_param("dxfCreatePart", wasCreatePart)
+            params.set_param("dxfCreateDraft", wasCreateDraft)
+            params.set_param("dxfCreateSketch", wasCreateSketch)
+        doc = FreeCAD.getDocument("ImportedDocName")
+        # This doc should ahve 3 objects: The Layers containter, the DXF layer called 0, and one Line
+        self.assertEqual(len(doc.Objects), 3)
+        FreeCAD.closeDocument("ImportedDocName")
+
+
 # class must be defined in global scope to allow it to be reloaded on document open
 class SaveRestoreSpecialGroup:
     def __init__(self, obj):