Ways to edit attachments

[romanofski]

We need a way to view/edit attachments.

My initial thoughts were to add a parser for a mailcap file, but in 2018 perhaps there are better ways.

[romanofski]

After implementing #10, I think what would be useful to add in the configuration is a:

Map ContentType (ProcessConfig ()()())

Meaning, if we can lookup the ProcessConfig type (which supports IsString) by the given ContentType use it as a command, otherwise prompt the user.

Perhaps a Plugin could be later utilized which could for example parse an existing mailcap file and provide the Map ...

[romanofski]

I looked into this. The tricky bit could be ProcessConfig and using the above type, because we're getting into trouble with NFData:

src/Types.hs:348:24-29: error:
    • No instance for (NFData (ProcessConfig () () ()))
        arising from the 'deriving' clause of a data type declaration
      Possible fix:
        use a standalone 'deriving instance' declaration,
          so you can specify the instance context yourself
    • When deriving the instance for (NFData MailViewSettings)
    |
348 |     deriving (Generic, NFData)
    |                        ^^^^^^

It seems ProcessConfig is only exported as a type from the API which will make it harder for us to declare the NFData instance.

[frasertweedale]

@romanofski I think we want a richer type anyway - one that we can easily convert into a ProcessConfig - that allows more fine-grained control over where the filename appears, and supports pipes (perhaps). For now I would say make the simplest data type that expresses what we currently support, create an NFData instance for it, and put that in the config. Then we convert that to a ProcessConfig just in time to actually use it.

Alternatively, just make the NFData instance of the config record type that immediately includes the ProcessConfig values skip the ProcessConfig values. It's not lawful, and not ideal, but there is precedent: see instance NFData (Keybinding v ctx) in Types.hs (there is no NFData instance for Vty.Event so I skip it.)

[romanofski]

I tried the latter, but that means I can pattern match on the ProcessConfig constructor, yes? Since the constructor is not exported I think I need to pick the first idea.

[frasertweedale]

@romanofski write the NFData instance for the thing that contains the ProcessConfig, and just don't force the ProcessConfig value. There's no need to pattern match.

Push your WIP and let me help if you are unsure how to continue.

[romanofski]

Cheers! I'll try it out. I'll finish #263 off first since it's mostly mechanical work ...

[romanofski]

Will have to open this, since I filed this when I was hacking on listing attachments. I stumbled over a comment:

-- in src/UI/Actions.hs
        Nothing -> pure $ setError (GenericError "No file selected to edit") s
        Just (_, m) -> case preview (headers . contentDisposition . dispositionType) m of
          (Just Inline) -> invokeEditor' s
          _ -> pure $ setError (GenericError "Not implemented. See #182") s

Stumbling over this FIXME string actually reminded me of what #182 originally was intended when I filed it: The ability that the author of an e-mail can edit attachments on a newly composed email. We currently support only text/plain editing of the inline body, but this issue was intended that any attachment can be edited, saved and updated on composed mail.

[romanofski]

I'm thinking of adding an additional mailcap setting for editing attachments, e.g.

data MailViewSettings = MailViewSettings
    {  -- [...]
    , _mvMailcap :: [(ContentType -> Bool, MailcapHandler)]
    }

to

data MailViewSettings = MailViewSettings
    {  -- [...]
    , _mvOpenMailcap :: [(ContentType -> Bool, MailcapHandler)]
    , _mvEditMailcap :: [(ContentType -> Bool, MailcapHandler)]
    }

and use mvEditMailcap for editing attachments when composing mails, while mvOpenMailcap is used to open attachments from received mails. Both can default to use xdg-open ...

[romanofski]

In the discussion for #318 we concluded to postpone this until we have a tree widget. The card to close this off is #322