Module:GetShortDescription

 localfunctionisEmpty(value)returnvalue==nilorvalue==''end

 localfunctionnotEmpty(value)returnnotisEmpty(value)end

 localfunctionisNone(value)returnvalue:lower()=='none'end

 localfunctionalarmingMessage(message,preview)
 message='<span style="color:#d33">[[Module:GetShortDescription]] '..message..'.</span>'
 ifnotpreviewthen
 message=message..'[[Category:Pages displaying alarming messages about Module:GetShortDescription]]'
 end
 returnmessage
 end

 -- Grammatically reasonable concatenation of possible issues into one message per problematic link target.
 localfunctionpreviewWarning(args_name,quantity_of_things)
 localmessage=''
 ifquantity_of_things.params>3then
 message=message..' with extraneous parameters'
 end
 ifquantity_of_things.descriptions>1then
 message=message..', declaring '..quantity_of_things.descriptions..' short descriptions'
 end
 ifquantity_of_things.templates>1ornotEmpty(message)then
 message='has detected that [[:'..args_name..'|'..args_name..']] has '..
 quantity_of_things.templates..' {{tlx|short description}}'..message
 mw.addWarning(alarmingMessage(message,true))
 end
 end

 localfunctiongetWikidataDescription(title,args,fallback)
 localwikidata_id=mw.wikibase.getEntityIdForTitle(title)
 ifisEmpty(wikidata_id)then
 returnnil
 end
 localwikidata_description,wikidata_description_lang=mw.wikibase.getDescriptionWithLang(wikidata_id)
 ifisEmpty(wikidata_description)then
 returnnil
 end
 localresult={wikidata=wikidata_description}
 ifisEmpty(args.lang_no)andnotEmpty(wikidata_description_lang)andwikidata_description_lang~='en'then
 -- According to the docs this is a possibility...
 result.wikidata=require('Module:Lang')._lang{
 wikidata_description_lang,
 wikidata_description,
 italic=args.lang_italic,
 nocat=args.lang_nocat,
 size=args.lang_size,
 cat=args.lang_cat,
 rtl=args.lang_rtl
 }
 end
 result.fellback=fallback
 returnresult
 end

 localfunctiongetShortDescriptionTemplates(title_table)
 localpage_content=title_table:getContent()

 -- Assume no content means a nonexistent title because it's cheaper than testing if it exists.
 ifisEmpty(page_content)then
 return{redlink=true}
 end

 localcontents_of_all_short_description_templates={}

 -- Because there could be any number of short description templates, and not all where there should be; get all the templates.
 fortemplateinpage_content:gmatch('{%b{}}')do
 localshort_description_content=mw.ustring.match(template,'^{{%s*[Ss]hort description%s*|%s*(.-)%s*}}')
 ifnotEmpty(short_description_content)then
 -- Collect the contents of short description templates.
 contents_of_all_short_description_templates[#contents_of_all_short_description_templates+1]=short_description_content
 end
 -- An opportunity for efficiency gain exists - to break if another type of template is found e.g. citation templates,
 -- but on an appallingly formatted page, a short description template down by the categories would likely be missed.
 end
 returncontents_of_all_short_description_templates
 end

 localfunctiongetShortDescription(args_name,args_name_title_table,title,title_table,fallback)
 localcontents_of_all_short_description_templates={}
 localredirected

 -- Check for short description templates on redirect pages.
 iftitle~=args_namethen
 contents_of_all_short_description_templates=getShortDescriptionTemplates(args_name_title_table)
 ifcontents_of_all_short_description_templates.redlinkthen
 returncontents_of_all_short_description_templates
 end
 redirected=false
 end

 if#contents_of_all_short_description_templates<1then
 contents_of_all_short_description_templates=getShortDescriptionTemplates(title_table)
 ifnotEmpty(redirected)then
 redirected=true
 end
 end

 ifcontents_of_all_short_description_templates.redlinkthen
 returncontents_of_all_short_description_templates
 end

 if#contents_of_all_short_description_templates<1then
 returnnil
 end

 localquantity_of_things={
 templates=#contents_of_all_short_description_templates,
 descriptions=0,
 params=0
 }

 localpossible_short_descriptions={}

 -- Look through the short description templates:
 fortemplate_content_index,short_description_template_contentsinipairs(contents_of_all_short_description_templates)do
 -- Split the contents at pipes and trim.
 localshort_description_template_params=mw.text.split(short_description_template_contents,'%s*|%s*')
 if#short_description_template_params>quantity_of_things.paramsthen
 quantity_of_things.params=#short_description_template_params
 end
 possible_short_descriptions[template_content_index]={}
 -- Look through the params:
 fori,paraminipairs(short_description_template_params)do
 ifparam=='noreplace'ormw.ustring.match(param,'^2%s*=%s*noreplace$')then
 -- Take note of 'noreplace'-ing for establishment of hierarchy later.
 possible_short_descriptions[template_content_index].noreplace=true
 else
 localhas_equals=param:match('=')
 ifnothas_equalsorparam:match('^1')then
 -- Grab the short description.
 ifhas_equalsthen
 param=mw.ustring.gsub(param,'^1%s*=%s*','')
 end
 -- If the template has both a numbered and an unnumbered short description;
 -- whichever comes last (ltr) will be used by that template, so overwriting works out great.
 possible_short_descriptions[template_content_index].description=param
 -- And we want to know the total quantity of descriptions being declared.
 quantity_of_things.descriptions=quantity_of_things.descriptions+1
 end
 end
 end
 end

 localshort_descriptions={}

 -- Look through the possible short descriptions for definite short descriptions,
 -- and prepare for working out which of possibly multiple short descriptions is actually being applied for the page:
 fori,possible_short_descriptioninipairs(possible_short_descriptions)do
 ifpossible_short_description.descriptionthen
 -- If a description is 'noreplace'-ing or 'none'; demote it.
 if(possible_short_description.noreplaceorisNone(possible_short_description.description))and
 #possible_short_descriptions>1then
 -- But don't demote it if it's already at the bottom.
 ifi>1then
 table.insert(short_descriptions,#short_descriptions,possible_short_description)
 else
 short_descriptions[#short_descriptions+1]=possible_short_description
 end
 else
 short_descriptions[#short_descriptions+1]=possible_short_description
 end
 end
 end

 -- Let previewWarning() work out if these numbers are bad.
 previewWarning(args_name,quantity_of_things)

 if#short_descriptions>=1then
 -- Pop!
 localshort_description=short_descriptions[#short_descriptions].description
 ifnotEmpty(short_description)then
 return{explicit=short_description,fellback=fallback,redirected=redirected}
 end
 end
 returnnil
 end

 localfunctionisSisterProjectLink(title)
 localsister_project_prefixes={
 'wiktionary','wikt',
 'wikinews','n',
 'wikibooks','b',
 'wikiquote','q',
 'wikisource','s',
 'wikispecies','species',
 'wikiversity','v',
 'wikivoyage','voy',
 'commons','c',
 'wikidata','d',
 'mediawikiwiki','mw',
 'wikimedia','foundation','wmf',
 'meta','m',
 'incubator',
 'phabricator','phab'
 }
 localpre_colon=title:match('^(%a+):')
 ifpre_colonthen
 fori,sisterinipairs(sister_project_prefixes)do
 ifpre_colon==sisterthen
 returntrue
 end
 end
 end
 returnfalse
 end

 -- Literally testing if title_table.isRedirect can be expensive;
 -- processing this way resolves (multiple) redirects without the possibly expensive check.
 localfunctiongetTitleAndTable(orig_name)
 localtitle_table=mw.title.new(orig_name)
 title_table=title_table.redirectTargetortitle_table
 localtitle=title_table.prefixedText
 iftitle==orig_namethen
 returntitle,title_table
 end
 returngetTitleAndTable(title)
 end

 localfunctiongetDescription(args)
 localargs_name=args.name
 ifisEmpty(args_name)then
 return{alarm='requires a page name (including namespace)'}
 end

 -- Keep the orginal name, cleaned up, and its title_table for later.
 localargs_name_title_table=mw.title.new(args_name)
 args_name=args_name_title_table.prefixedText

 ifisSisterProjectLink(args_name)then
 returnnil
 end

 localtitle,title_table=getTitleAndTable(args_name)

 iftitle~=args_namethen
 ifisSisterProjectLink(title)then
 returnnil
 end
 end

 localonly=args.only
 localprefer=args.preferor'explicit'

 -- Pass args_name to getShortDescription() so previewWarning()s won't be confusing for redirects.

 ifnotEmpty(only)then
 ifonly=='explicit'then
 returngetShortDescription(args_name,args_name_title_table,title,title_table)
 end
 ifonly=='wikidata'then
 returngetWikidataDescription(title,args)
 end
 return{alarm='accepts either "explicit" or "wikidata" as the value of |only='}
 end

 ifnotEmpty(prefer)then
 ifprefer=='explicit'then
 localshort_description=getShortDescription(args_name,args_name_title_table,title,title_table)
 ifnotEmpty(short_description)then
 -- Assume a Wikidata search would be a bad idea for an assumed nonexistent title.
 ifshort_description.redlinkor(notisNone(short_description.explicit)orargs.none_is_valid)then
 returnshort_description
 end
 end
 returngetWikidataDescription(title,args,true)
 end
 ifprefer=='wikidata'then
 returngetWikidataDescription(title,args)orgetShortDescription(args_name,args_name_title_table,title,title_table,true)
 end
 return{alarm='accepts either "explicit" or "wikidata" as the value of |prefer='}
 end
 end

 localfunctionmain(args)
 localresult=getDescription(args)
 ifnotEmpty(result)then
 ifresult.alarmthen
 result.alarm=alarmingMessage(result.alarm)
 end
 ifargs.stringifythen
 ifresult.alarmthen
 result=result.alarm
 else
 result=result.explicitorresult.wikidata
 ifargs.none_is_nilandisNone(result)then
 result=nil
 end
 end
 elseifnotresult.alarmandargs.none_is_nilthen
 localdescription=result.explicitorresult.wikidata
 ifdescriptionandargs.none_is_nilandisNone(description)then
 result=nil
 end
 end
 end
 returnresult
 end

 localp={}

 functionp.main(frame)
 localargs=require('Module:Arguments').getArgs(frame)
 ifisEmpty(args)then
 returnalarmingMessage('could not getArgs')-- This really would be alarming.
 end
 returnmain(args)
 end

 returnp