Remove quotes from safe characters

src/icalendar/parser.py

@@ -129,7 +129,7 @@ def validate_param_value(value, quoted=True):
 
 # chars presence of which in parameter value will be cause the value
 # to be enclosed in double-quotes
-QUOTABLE = re.compile("[,;: ’']")
+QUOTABLE = re.compile("[,;:’]")
 
 
 def dquote(val, always_quote=False):

src/icalendar/tests/calendars/issue_836_do_not_quote_tzid.ics

@@ -0,0 +1,27 @@
+BEGIN:VCALENDAR
+METHOD:PUBLISH
+PRODID:Microsoft Exchange Server 2010
+VERSION:2.0
+BEGIN:VTIMEZONE
+TZID:Eastern Standard Time
+BEGIN:STANDARD
+DTSTART:16010101T020000
+TZOFFSETFROM:-0400
+TZOFFSETTO:-0500
+RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=1SU;BYMONTH=11
+END:STANDARD
+BEGIN:DAYLIGHT
+DTSTART:16010101T020000
+TZOFFSETFROM:-0500
+TZOFFSETTO:-0400
+RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=2SU;BYMONTH=3
+END:DAYLIGHT
+END:VTIMEZONE
+BEGIN:VEVENT
+UID:minimal-demo-event-est-20241028@example.com
+SUMMARY:Anonymous Test Event for TZID
+DTSTART;TZID=Eastern Standard Time:20241028T170000
+DTEND;TZID=Eastern Standard Time:20241028T180000
+DTSTAMP:20250514T023916Z
+END:VEVENT
+END:VCALENDAR

src/icalendar/tests/test_issue_836_do_not_quote_tzid.py

@@ -0,0 +1,80 @@
+"""Quoting the TZID parameter creates compatibility problems.
+
+See https://github.com/collective/icalendar/issues/836
+
+:rfc:`5545`:
+
+.. code-block:: text
+
+    param-value   = paramtext / quoted-string
+    paramtext     = *SAFE-CHAR
+    quoted-string = DQUOTE *QSAFE-CHAR DQUOTE
+    SAFE-CHAR     = WSP / %x21 / %x23-2B / %x2D-39 / %x3C-7E
+                   / NON-US-ASCII
+     ; Any character except CONTROL, DQUOTE, ";", ":", ","
+     NON-US-ASCII  = UTF8-2 / UTF8-3 / UTF8-4
+     ; UTF8-2, UTF8-3, and UTF8-4 are defined in [RFC3629]
+
+"""
+from datetime import datetime, time
+from icalendar import Event, Parameters, vDDDTypes, vDatetime, vPeriod, vTime
+import pytest
+
+from icalendar.prop import vDDDLists
+
+# All the controls except HTAB
+CONTROL = {
+    i for i in range(256) if 0x00 <= i <= 0x08 or 0x0A <= i <= 0x1F or i == 0x7F
+}
+
+# Any character except CONTROL, DQUOTE, ";", ":", ","
+SAFE_CHAR = set(range(256)) - CONTROL - set(b'";:,')
+
+param_tzid = pytest.mark.parametrize(
+    "tzid",
+    [
+        "Europe/London",
+        "Eastern Standard Time",
+    ]
+)
+
+@param_tzid
+@pytest.mark.parametrize(
+    "vdt",
+    [
+        vDatetime(datetime(2024, 10, 11, 12, 0)),
+        vTime(time(23, 59, 59)),
+        vDDDTypes(datetime(2024, 10, 11, 12, 0)),
+        vPeriod((datetime(2024, 10, 11, 12, 0), datetime(2024, 10, 11, 13, 0))),
+        vDDDLists([datetime(2024, 10, 11, 12, 0)]),
+    ]
+)
+def test_parameter_is_not_quoted_when_not_needed(tzid, vdt):
+    """Check that serializing the value works without quoting."""
+    e = Event()
+    vdt.params["TZID"] = tzid
+    e["DTSTART"] = vdt
+    ics = e.to_ical().decode()
+    print(ics)
+    assert tzid in ics
+    assert f'"{tzid}' not in ics
+    assert f'{tzid}"' not in ics
+
+
+@pytest.mark.parametrize(
+    "safe_char",
+    list(map(chr, sorted(SAFE_CHAR)))
+)
+def test_safe_char_is_not_escaped(safe_char):
+    """Check that paramerter serialization is without quotes for safe chars."""
+    params = Parameters(tzid=safe_char)
+    result = params.to_ical().decode()
+    assert '"'  not in result
+
+
+def test_get_calendar_and_serialize_it_wihtout_quotes(calendars):
+    """The example calendar should not contain the timezone with quotes."""
+    ics = calendars.issue_836_do_not_quote_tzid.to_ical().decode()
+    assert '"Eastern Standard' not in ics
+    assert 'Standard Time"' not in ics
+    assert "Eastern Standard Time" in ics