Adding welcome message to the interpreter (#12511)

src/compiler/crystal/command/repl.cr

@@ -1,4 +1,5 @@
 {% skip_file if flag?(:without_interpreter) %}
+require "../config"
 
 # Implementation of the `crystal repl` command
 
@@ -34,14 +35,25 @@ class Crystal::Command
     end
 
     if options.empty?
+      show_banner
       repl.run
     else
       filename = options.shift
       unless File.file?(filename)
         error "File '#{filename}' doesn't exist"
       end
 
+      show_banner
       repl.run_file(filename, options)
     end
   end
+
+  private def show_banner
+    return unless STDERR.tty? && !ENV.has_key?("CRYSTAL_INTERPRETER_SKIP_BANNER")
+
+    formatted_sha = "[#{Config.build_commit}] " if Config.build_commit
+    STDERR.puts "Crystal interpreter #{Config.version} #{formatted_sha}(#{Config.date}).\n" \
+                "EXPERIMENTAL SOFTWARE: if you find a bug, please consider opening an issue in\n" \
+                "https://github.com/crystal-lang/crystal/issues/new/"
+  end
 end