don't blow up if passed an unexpected value

[rubysolo]

After upgrading to Phoenix 1.5 and enabling the live dashboard, I started seeing no function clause matching errors when the StringFormatter received a tuple. This PR adds a safe fallback if the value passed in is not an expected shape.

[pmenhart]

Just my personal preference: I'd like to see "#{inspect value}" in my logs, instead of "(unprintable)".

Also note that there is yet another open gap: defp format_value(value) when is_map(value) fails if the map contains values that are not parseable by Jason.

[rubysolo]

That makes sense -- I was originally thinking that some values might not be inspectable, or some inspected values might be quite large (e.g. a Plug.Conn), but that's probably being too paranoid.

Good point about unserializable maps, but I'm not sure there's a great generic solution -- I think you would have to iterate over the map looking for key/value patterns to reject, deal with (potentially deeply) nested maps, etc.

[pmenhart]

If size of inspected values is a concern, then Inspect.Opts can help.

Each project may have different expectations. I usually end up with custom formatters. Typically I rescue errors and use inspect as a last resort - that solves issues like the unserializable map problem. (Then I check logs for such issues - a permanent remedy could be implementing Jason.Encoder for some internal structs.)