Display banner from Pluto.__init__, not during precompile

Display banner only when `$JULIA_DEPOT_PATH/pluto_notebooks/` is
created, and create that folder when the module initializes.

This preserves the fact that the banner is only displayed once, while
it now no longer displays it when the package is compiled.
Compile-time display became problematic as that is counted by `Pkg` as
a warning, and users might therefore think something went wrong.

Note that this now creates `$JULIA_DEPOT_PATH/pluto_notebooks/` much
earlier, whereas previously that folder was only created when the user
saved a notebook there.

fixes fonsp#548

src/Pluto.jl

@@ -99,16 +99,26 @@ export activate_notebook_environment
 
 include("./precompile.jl")
 
-if get(ENV, "JULIA_PLUTO_SHOW_BANNER", "1") != "0" && get(ENV, "CI", "🍄") != "true"
-@info """\n
-    Welcome to Pluto $(PLUTO_VERSION_STR) 🎈
-    Start a notebook server using:
+function print_banner()
+    if (get(ENV, "JULIA_PLUTO_SHOW_BANNER", "1") != "0" &&
+        get(ENV, "CI", "🍄") != "true" && isinteractive())
+        @info """
 
-  julia> Pluto.run()
+          Welcome to Pluto $(PLUTO_VERSION_STR) 🎈
+          Start a notebook server using:
 
-    Have a look at the FAQ:
-    https://github.com/fonsp/Pluto.jl/wiki
-\n"""
+        julia> Pluto.run()
+
+          Have a look at the FAQ:
+          https://github.com/fonsp/Pluto.jl/wiki
+
+        """
+    end
+end
+
+function __init__()
+    # print banner only once, if there isn't yet a notebooks directory
+    new_notebooks_directory(mkdir_callback = print_banner)
 end
 
 end

src/notebook/path helpers.jl

@@ -90,14 +90,15 @@ function cutename()
     titlecase(rand(adjectives)) * " " * rand(nouns)
 end
 
-function new_notebooks_directory()
+function new_notebooks_directory(;mkdir_callback = nothing)
     try
         path = get(
 			ENV,
 			"JULIA_PLUTO_NEW_NOTEBOOKS_DIR",
 			joinpath(first(DEPOT_PATH), "pluto_notebooks")
 		)
         if !isdir(path)
+            mkdir_callback === nothing || mkdir_callback()
             mkdir(path)
         end
         path
@@ -206,4 +207,4 @@ function wait_until_file_unchanged(filename::String, timeout::Real, last_content
         sleep(timeout)
 		wait_until_file_unchanged(filename, timeout, new_contents)
 	end
-end
+end