Only chain on 404 errors, log and return others as 500

[Nemo157]

Results in logs like

web_1  | 2020/06/02 08:13:07 [ERROR] cratesfyi::web: internal server error: Error rendering "releases_feed" line 10, col 10: Helper not defined: "content"

and a page like

when I reapply the bug in #728

Fixes #801

[Nemo157]

Suggestions on ways to rewrite this would be appreciated, seems like it needs some sort of conditional or_else_if(|e| e.response.status == Some(status::NotFound), |e| self.router_handler.handle(req)).

[jyn514]

I think a helper handle_if_404 closure would be nice.

[jyn514]

Something like

let handle_if_404 = |e, handler| if e.response.status == Some(status::NotFound) {
    handler(req)
} else {
    Err(e)
};

[jyn514]

Do we want to link to the GitHub page so people can make an issue?

[Nemo157]

Might be a good followup issue to do once the template changes are in, all the error pages could do with a bit of a sprucing up.

[pietroalbini]

I don't think asking to open an issue on GitHub this way is much beneficial for us: without a backtrace it's hard to then debug those issues.

A thing we could do is generate a random UUID, print it in the same line as the error and show it in the error page, so when people open the issue we can simply do a journalctl -u docs.rs | grep UUID to get the exact error the user encountered.

[jyn514]

The UUID sounds useful but it can go in a follow-up, for now I want to get the bug fix in.

[jyn514]

I think a helper handle_if_404 closure would be nice.

[jyn514]

The UUID sounds useful but it can go in a follow-up, for now I want to get the bug fix in.