Module:File link/sandbox

 -- This module provides a library for formatting file wikilinks.

 localyesno=require('Module:Yesno')
 localcheckType=require('libraryUtil').checkType

 localp={}

 functionp._main(args)
 checkType('_main',1,args,'table')

 -- This is basically libraryUtil.checkTypeForNamedArg, but we are rolling our
 -- own function to get the right error level.
 localfunctioncheckArg(key,val,level)
 iftype(val)~='string'then
 error(string.format(
 "type error in '%s' parameter of '_main' (expected string, got %s)",
 key,type(val)
 ),level)
 end
 end

 localret={}

 -- Adds a positional parameter to the buffer.
 localfunctionaddPositional(key)
 localval=args[key]
 ifnotvalthen
 returnnil
 end
 checkArg(key,val,4)
 ret[#ret+1]=val
 end

 -- Adds a named parameter to the buffer. We assume that the parameter name
 -- is the same as the argument key.
 localfunctionaddNamed(key)
 localval=args[key]
 ifnotvalthen
 returnnil
 end
 checkArg(key,val,4)
 ret[#ret+1]=key..'='..val
 end

 -- Filename
 checkArg('file',args.file,3)
 ret[#ret+1]='File:'..args.file

 -- Format
 ifargs.formatthen
 checkArg('format',args.format)
 ifargs.formatfilethen
 checkArg('formatfile',args.formatfile)
 ret[#ret+1]=args.format..'='..args.formatfile
 else
 ret[#ret+1]=args.format
 end
 end

 -- Border
 ifyesno(args.border)then
 ret[#ret+1]='border'
 end

 addPositional('location')
 addPositional('alignment')
 addPositional('size')
 addNamed('upright')
 addNamed('link')
 addNamed('alt')
 addNamed('page')
 addNamed('class')
 addNamed('lang')
 addNamed('start')
 addNamed('end')
 addNamed('thumbtime')
 addPositional('caption')

 returnstring.format('[[%s]]',table.concat(ret,'|'))
 end

 functionp.main(frame)
 localorigArgs=require('Module:Arguments').getArgs(frame,{
 wrappers='Template:File link'
 })
 ifnotorigArgs.filethen
 error("'file' parameter missing from [[Template:File link]]",0)
 end

 -- Copy the arguments that were passed to a new table to avoid looking up
 -- every possible parameter in the frame object.
 localargs={}
 fork,vinpairs(origArgs)do
 -- Make _BLANK a special argument to add a blank parameter. For use in
 -- conditional templates etc. it is useful for blank arguments to be
 -- ignored, but we still need a way to specify them so that we can do
 -- things like [[File:Example.png|link=]].
 ifv=='_BLANK'then
 v=''
 end
 args[k]=v
 end
 returnp._main(args)
 end

 returnp