Usage warning (#66)

src/icr/cli.cr

@@ -1,14 +1,36 @@
 require "option_parser"
 require "../icr"
 
+XDG_CONFIG_HOME        = ENV.fetch("XDG_CONFIG_HOME", "~/.config")
+CONFIG_HOME            = File.expand_path "#{XDG_CONFIG_HOME}/icr"
+USAGE_WARNING_ACCEPTED = "#{CONFIG_HOME}/usage_warning_accepted"
+
 is_debug = false
 libs = [] of String
+usage_warning_accepted = File.exists? USAGE_WARNING_ACCEPTED
 
 def print_stamp
   puts "Author: #{Icr::AUTHOR}"
   puts "Homepage: #{Icr::HOMEPAGE}"
 end
 
+def print_usage_warning
+  puts <<-WARN
+  WARNING: ICR is not a full featured REPL.
+  It works by building up a source file, compiling and re-running all of it on each input.
+  That has side effects:
+
+    * Current time and random numbers change retroactively
+    * Files and network/database connections are reopened on every run
+    * Running a sleep or benchmark will delay execution of next inputs
+    * Unexpected behavior of fibers, channels, shell commands and maybe others
+
+  Be careful while running your commands.
+
+  You can disable this warning with --disable-usage-warning flag.
+  WARN
+end
+
 OptionParser.parse! do |parser|
   parser.banner = "Usage: icr [options]"
 
@@ -32,7 +54,18 @@ OptionParser.parse! do |parser|
   parser.on("-r FILE", "--require=FILE", "auto require FILE") do |filename|
     libs.push(%{require "#{filename}"})
   end
+
+  parser.on("--disable-usage-warning", "Disable usage warning") do
+    Dir.mkdir_p CONFIG_HOME
+    File.touch USAGE_WARNING_ACCEPTED
+    usage_warning_accepted = true
+
+    puts "Usage warning disabled. Run ICR again to continue."
+    exit 0
+  end
 end
 
+print_usage_warning unless usage_warning_accepted
+
 code = libs.join(";")
 Icr::Console.new(is_debug).start(code)