Rethink logging

[tlienart]

• Different levels
• warnings that should be shown in the REPL
• (errors) should ideally not happen
• things shown in the browser
• formatting of information messages should be streamlined so it's clear what caused it, what the user should do about it

[tlienart]

JuliaLogging almost certainly has stuff you can draw from but, most likely, you'll need to do things a bit differently

Some stuff to note:

• there's a level of logging in the repl which the user should be able to filter completely
• there's a level of logging in the browser which the user should not be able to disable
• the logging should not affect whatever is done within cells
• cell errors should not cause server crashes; the page should just be skipped and replaced by an error page.

[tlienart]

Can use TerminalLoggers

[tlienart]

location logging (done with FranklinParser issues) should be done with block failures as well.

Probably the right way to go here is to have dedicated logic to handle errors.

IN = (context, trigger, ...)

• context: either global (if in config / utils) or local if page
• trigger: the block / area that triggered, should have a parent_string that we can get location in file from
• ...

OUT =

• updated context to indicate either that it has (possibly how many errors it has)
• a styled warning in the REPL (potentially in stdout to avoid messing with stderr which is already severely abused, potentially use printstyled, avoid using @warn since it would indicate spurious information such as which line of code threw the warning which is not useful
• an injected banner
• ...

Should also list out every possible way that Xranklin can choke on something and what to do about it:

• start in bad directory (remove __site if xranklin is started in wrong folder #237)
• parser exception (should be handled by FranklinParser)
• problematic hfun / def
• problematic lxfun / lxcommand
• error in var cell (see below)
• error in code cell (should be already handled by IOCapture but maybe we want to adjust the msg in console)
• wrong cache loading (should not happen)
• ...