Improvement to error handling

Previously, if error occured during the creation of inner
type instance from iCalendar string, the error with the
name of the bogus property would be stored in the
appropriate component's errors attribute along with the error
string  but the property's value would be removed from the
parsed representation. This patch keeps the value even with its
parameters at that certain property, the value's type is changed
to vText.

Should allow implementation of
#158

Improves
#174

CHANGES.rst

@@ -11,6 +11,11 @@ Breaking changes:
   Refs #187
   [stlaz]
 
+- Improved error handling. The value and parameters of a property should no longer
+  be lost upon error.
+  Refs #158 #174
+  [stlaz]
+
 New features:
 
 - *add item here*

src/icalendar/cal.py

@@ -385,7 +385,17 @@ def from_ical(cls, st, multiple=False):
                 try:
                     factory = types_factory.for_property(name,
                                                          params.get('VALUE'))
-                    if types_factory.is_list_property(name):
+                except ValueError as e:
+                    if not component.ignore_exceptions:
+                        raise
+                    else:
+                        # add error message and fall back to vText value type
+                        component.errors.append((uname, str(e)))
+                        factory = types_factory['text']
+                try:
+                    if (types_factory.is_list_property(name) and
+                            factory != vText):
+                        # TODO: list type currenty supports only datetime types
                         vals = vDDDLists(
                             vDDDLists.from_ical(vals, params.get('TZID'),
                                                 factory))
@@ -399,10 +409,11 @@ def from_ical(cls, st, multiple=False):
                     if not component.ignore_exceptions:
                         raise
                     component.errors.append((uname, unicode_type(e)))
-                    component.add(name, None, encode=0)
-                else:
-                    vals.params = params
-                    component.add(name, vals, encode=0)
+                    # fallback to vText and store the original value
+                    vals = types_factory['text'](vals)
+
+                vals.params = params
+                component.add(name, vals, encode=0)
 
         if multiple:
             return comps

src/icalendar/tests/test_fixed_issues.py

@@ -512,13 +512,17 @@ def test_issue_187(self):
         event = icalendar.Event.from_ical('\r\n'.join(ical_str))
         self.assertEqual(event.errors,
                          [('MYPROP', "Expected time, got: '20050520T200505'")])
+        self.assertEqual(event['MYPROP'],
+                         icalendar.prop.vText('20050520T200505'))
 
         # Wrong default property value (DATE instead of DATE-TIME)
         ical_str = orig_str[:]
         ical_str[2] = 'DTSTART:20150408'
         event = icalendar.Event.from_ical('\r\n'.join(ical_str))
         self.assertEqual(event.errors,
                          [('DTSTART', "Wrong datetime format '20150408'")])
+        self.assertEqual(event['DTSTART'],
+                         icalendar.prop.vText('20150408'))
 
         # -------- Wrong vDDDLists setups follow --------
         ical_str = orig_str[:]
@@ -527,10 +531,17 @@ def test_issue_187(self):
         event = icalendar.Event.from_ical('\r\n'.join(ical_str))
         self.assertEqual(event.errors,
                          [('RDATE', "Wrong date format '20150217T095800'")])
+        self.assertEqual(event['RDATE'],
+                         icalendar.prop.vText('20150217T095800'))
 
         ical_str[3] = ('RDATE;FMTTYPE=text/plain;ENCODING=BASE64;VALUE=BINARY:'
                        'c3RsYXo=')
         event = icalendar.Event.from_ical('\r\n'.join(ical_str))
         self.assertEqual(event.errors,
                          [('RDATE', "The VALUE parameter of RDATE property "
                                     "is not supported: 'BINARY'")])
+        self.assertEqual(event['RDATE'],
+                         icalendar.prop.vText('c3RsYXo='))
+        self.assertEqual(event['RDATE'].params,
+                         {'VALUE': 'BINARY', 'ENCODING': 'BASE64',
+                          'FMTTYPE': 'text/plain'})