mix help app:APP: Compile current Mix project (if any)

[wojtekmach]

Prior to this patch, it was impossible to get help for the current app:

nimble_csv$ mix help app:nimble_csv
Application nimble_csv does not exist or is not loaded

It also helps with projects with depenendencies when they haven't been
compiled yet:

req$ mix deps.get && mix help app:finch # mix deps.compile haven't been run yet
Application finch does not exist or is not loaded

Now it works:

nimble_csv$ mix help app:nimble_csv
Compiling 1 file (.ex)
Generated nimble_csv app
# NimbleCSV

NimbleCSV is a small and fast parsing and dumping library.

# NimbleCSV.RFC4180

A CSV parser that uses comma as separator and double-quotes as escape according
to RFC4180.

# NimbleCSV.Spreadsheet

A parser with spreadsheet friendly settings.

The task continues to work as expected outside of a Mix project:

/tmp$ mix help app:nimble_csv
Application nimble_csv does not exist or is not loaded

/tmp$ mix help app:public_key
# :public_key

API module for public-key infrastructure.

[josevalim]

But then if the project doesn't compile, we can't get help. I would do this:

if app != "" and Atom.to_string(Mix.Project.config[:app]) == app do
  Mix.Task.run("compile")
end

Also, we can probably add a test for this feature.

[wojtekmach]

this would not solve:

It also helps with projects with depenendencies when they haven't been
compiled yet:

req$ mix deps.get && mix help app:finch # mix deps.compile haven't been run yet
Application finch does not exist or is not loaded

but dunno how big of a deal it is in practice, I suppose we can always guide users towards that with error messages or something. So yeah, I will move forward with this, thank you!

[josevalim]

@wojtekmach what if we change the rescue branch of Mix.ensure_application! to call Mix.Task.run("compile")? So we compile only when we cannot find the app?

[josevalim]

Suggested change

	Mix.ensure_application!(app)

[josevalim]

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