Right now, if I try to import a calendar file (.ics) that does not follow the file format perfectly, it cannot be imported. This is a problem when other calendar programs ARE able to import them. To the end user, it looks like Thunderbird is failing at a basic task.
The bug tracker has numerous issues that stem from this like 1868843 but since the problem was caused by Microsoft, once Microsoft fixed their bug, the issue was closed.
But there's no reason why Thunderbird can't try to fix these simple formatting problems itself. Like the 7'th comment said "We should make it more accepting; if it hits EOF and our calendar structure is valid but we're missing ENDs for the still-open components, we should just assume they've ended and move on."
Other simple errors that thunderbird could handle are file lines that end with the wrong End-of-Line delimiter. (A problem that I ran into and made me look into all of this). Outlook handled this calendar file just fine.
In summary, the end user doesn't care if the file they import is valid or not, if it works with other programs, it's a bug in Thunderbird.
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