Issue 'due date' format checking / 500 ISE

[bugreport0]

• Gitea version (or commit ref): 1.1.0+1205-gbb801488
• Git version:
• Operating system:
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant
• Log gist:

Description

The issue due date entry box is finicky:

• entering '1234' gives a HTTP 500 error page instead of an 'invalid format' warning
• entering '1234-01-01' makes parts of Gitea think a due date was entered, but others ignore it

Screenshots

[daviian]

@bugreport0 It ought to be a date input field. ;-) But you're right, the input format should be checked.
It's also possible to input a date before 1970, despite an "modified date" - action is generated the due date don't get set.

[kolaente]

The error 500 is because the validation happens server side, therefore the functions returns an err which leads to having 500 returned.
Validation is currently done directly by Macaron,so I don't know if we could return a message telling the user what went wrong instead 🤔

[daviian]

@kolaente But a 500 suggest an internal server error and not a validation error (4xx status code)

[kolaente]

I've submitted a pr for issue due dates prior to 1970 not being displayed on the issue page: #3930
The validation error will be resolved with #3890. The api returns proper errorcodes, after that it's just a small thing to display a message to the user.