(core) Handle importing xls files with invalid dimensions

Summary:
This addresses a rare bug where xls files with invalid dimensions
could not be imported into Grist due to how openpyxl handles
parsing them.

Test Plan: Server test.

Reviewers: alexmojaki

Reviewed By: alexmojaki

Differential Revision: https://phab.getgrist.com/D3485

sandbox/grist/imports/import_xls.py

@@ -39,6 +39,10 @@ def parse_open_file(file_obj):
   export_list = []
   # A table set is a collection of tables:
   for sheet in workbook:
+    # openpyxl fails to read xlsx files with incorrect dimensions; we reset here as a precaution.
+    # See https://openpyxl.readthedocs.io/en/stable/optimized.html#worksheet-dimensions.
+    sheet.reset_dimensions()
+
     table_name = sheet.title
     rows = [
       list(row)
@@ -50,7 +54,9 @@ def parse_open_file(file_obj):
     sample = [
       # Create messytables.Cells for the sake of messytables.headers_guess
       [messytables.Cell(cell) for cell in row]
-      for row in rows[:1000]
+      # Resetting dimensions via openpyxl causes rows to not be padded. Make sure
+      # sample rows are padded; get_table_data will handle padding the rest.
+      for row in _with_padding(rows[:1000])
     ]
     offset, headers = messytables.headers_guess(sample)
     data_offset = offset + 1  # Add the header line
@@ -100,3 +106,14 @@ def parse_open_file(file_obj):
 
   parse_options = {}
   return parse_options, export_list
+
+def _with_padding(rows):
+  if not rows:
+    return []
+  max_width = max(len(row) for row in rows)
+  min_width = min(len(row) for row in rows)
+  if min_width == max_width:
+    return rows
+  for row in rows:
+    row.extend([""] * (max_width - len(row)))
+  return rows

sandbox/grist/imports/test_import_xls.py

@@ -163,7 +163,27 @@ class TestImportXLS(unittest.TestCase):
       ],
       'table_data': [
         [0, None, 1],
-        [None, 0, 2],
+        [u'', 0, 2],
+      ],
+    }])
+
+  def test_invalid_dimensions(self):
+    # Check that files with invalid dimensions (typically a result of software
+    # incorrectly writing the xlsx file) are imported correctly. Previously, Grist
+    # would fail to import any rows from such files due to how openpyxl parses them.
+    parsed_file = import_xls.parse_file(*_get_fixture('test_invalid_dimensions.xlsx'))
+    tables = parsed_file[1]
+    self.assertEqual(tables, [{
+      'table_name': 'Sheet1',
+      'column_metadata': [
+        {'id': u'A', 'type': 'Numeric'},
+        {'id': u'B', 'type': 'Numeric'},
+        {'id': u'C', 'type': 'Numeric'},
+      ],
+      'table_data': [
+        [1, 2, 3],
+        [4, 5, 6],
+        [7, 8, 9],
       ],
     }])