(core) Adding traceback to trigger formulas

Summary:
Traceback is available on the Creator Panel in the formula editor. It is evaluated the same way as for normal formulas.
In case when the traceback is not available, only the error name is displayed with information that traceback is not available.
Cell with an error, when edited, shows the previous valid value that was used before the error happened (or None for new rows).
Value is stored inside the RaisedException object that is stored in a cell.

Test Plan: Created tests

Reviewers: alexmojaki

Reviewed By: alexmojaki

Subscribers: alexmojaki, dsagal

Differential Revision: https://phab.getgrist.com/D3033

sandbox/grist/engine.py

@@ -642,7 +642,16 @@ class Engine(object):
     col = table.get_column(col_id)
     checkpoint = self._get_undo_checkpoint()
     try:
-      return self._recompute_one_cell(None, table, col, row_id)
+      result = self._recompute_one_cell(None, table, col, row_id)
+      # If the error is gone for a trigger formula
+      if col.has_formula() and not col.is_formula():
+        if not isinstance(result, objtypes.RaisedException):
+          # Get the error stored in the cell
+          # and change it to show to the user that no traceback is available
+          error_in_cell = objtypes.decode_object(col.raw_get(row_id))
+          assert isinstance(error_in_cell, objtypes.RaisedException)
+          return error_in_cell.no_traceback()
+      return result
     finally:
       # It is possible for formula evaluation to have side-effects that produce DocActions (e.g.
       # lookupOrAddDerived() creates those). In case of get_formula_error(), these aren't fully
@@ -775,7 +784,8 @@ class Engine(object):
             if is_first:
               self._is_node_exception_reported.add(node)
               log.info(value.details)
-              value = objtypes.RaisedException(value.error)  # strip out details after logging
+              # strip out details after logging
+              value = objtypes.RaisedException(value.error, user_input=value.user_input)
 
           # TODO: validation columns should be wrapped to always return True/False (catching
           # exceptions), so that we don't need special handling here.
@@ -831,11 +841,13 @@ class Engine(object):
 
     checkpoint = self._get_undo_checkpoint()
     record = table.Record(row_id, table._identity_relation)
+    value = None
     try:
       if cycle:
         raise depend.CircularRefError("Circular Reference")
       if not col.is_formula():
-        result = col.method(record, table.user_table, col.get_cell_value(int(record)), self._user)
+        value = col.get_cell_value(int(record), restore=True)
+        result = col.method(record, table.user_table, value, self._user)
       else:
         result = col.method(record, table.user_table)
       if self._cell_required_error:
@@ -866,7 +878,10 @@ class Engine(object):
       self.formula_tracer(col, record)
 
       include_details = (node not in self._is_node_exception_reported) if node else True
-      return objtypes.RaisedException(regular_error, include_details)
+      if not col.is_formula():
+        return objtypes.RaisedException(regular_error, include_details, user_input=value)
+      else:
+        return objtypes.RaisedException(regular_error, include_details)
 
   def convert_action_values(self, action):
     """