-- If unitcode is a known combination code (and if allowed by what),
-- a table of output multiple unit tables is included in the result.
-- For compatibility with the old template, an underscore in a unitcode is
-- replaced with a space so usage like works.
-- Wikignomes may also put two spaces or "&nbsp;" in combinations, so
-- replace underscore, "&nbsp;", and multiple spaces with a single space.
utable = utable or parms.unittable or all_units
fails = fails or {}
depth = depth and depth + 1 or 1
if depth > 9 then
-- There are ways to mistakenly define units which result in infinite
-- recursion when lookup is called. That gives a long delay and very
-- confusing error messages, so the depth parameter is used as a guard.
return false, { 'cvt_lookup', unitcode }
end
if unitcode == nil or unitcode == '' then
return false, { 'cvt_no_unit' }
end
unitcode = unitcode:gsub('_', ' '):gsub('&nbsp;', ' '):gsub(' +', ' ')
local function call_make_per(t)
return make_per(unitcode, t,
function (ucode) return lookup(parms, ucode, 'no_combination', utable, fails, depth) end
end
local t = utable[unitcode]
if t then
if t.shouldbe then
return false, { 'cvt_should_be', t.shouldbe }
end
if t.sp_us then
parms.opt_sp_us = true
end
local target = t.target -- nil, or unitcode is an alias for this target
if target then
local success, result = lookup(parms, target, what, utable, fails, depth)
if not success then return false, result end
override_from(result, t, { 'customary', 'default', 'link', 'symbol', 'symlink' })
local multiplier = t.multiplier
if multiplier then
result.multiplier = tostring(multiplier)
result.scale = result.scale * multiplier
end
return true, result
end
if t.per then
return call_make_per(t)
end
local combo = t.combination -- nil or a table of unitcodes
if combo then
local multiple = t.multiple
if what == 'no_combination' or (what == 'only_multiple' and not multiple) then
return false, { 'cvt_bad_unit', unitcode }
end
-- Recursively create a combination table containing the
-- converter table of each unitcode.
local result = { utype = t.utype, multiple = multiple, combination = {} }
local cvt = result.combination
for i, v in ipairs(combo) do
local success, t = lookup(parms, v, multiple and 'no_combination' or 'only_multiple', utable, fails, depth)
if not success then return false, t end
cvt[i] = t
end
return true, result
end
local result = shallow_copy(t)
result.unitcode = unitcode
if result.prefixes then
result.si_name = ''
result.si_prefix = ''
return true, setmetatable(result, unit_prefixed_mt)
end
return true, setmetatable(result, unit_mt)
end
local SIprefixes = text_code.SIprefixes
for plen = SIprefixes[1] or 2, 1, -1 do
-- Look for an SI prefix; should never occur with an alias.
-- Check for longer prefix first ('dam' is decametre).
-- SIprefixes[1] = prefix maximum #characters (as seen by mw.ustring.sub).
local prefix = usub(unitcode, 1, plen)
local si = SIprefixes[prefix]
if si then
local t = utable[usub(unitcode, plen+1)]
if t and t.prefixes then
local result = shallow_copy(t)
result.unitcode = unitcode
result.si_name = parms.opt_sp_us and si.name_us or si.name
result.si_prefix = si.prefix or prefix
result.scale = t.scale * 10 ^ (si.exponent * t.prefixes)
return true, setmetatable(result, unit_prefixed_mt)
end
end
end
-- Accept user-defined combinations like "acre+m2+ha" or "acre m2 ha" for output.
-- If '+' is used, each unit code can include a space, and any error is fatal.
-- If ' ' is used and if each space-separated word is a unit code, it is a combo,
-- but errors are not fatal so the unit code can be looked up as an extra unit.
local err_is_fatal
local combo = collection
if unitcode:find('+', 1, true) then
err_is_fatal = true
for item in (unitcode .. '+'):gmatch('%s*(.-)%s*%+') do
if item ~= '' then
combo:add(item)
end
end
elseif unitcode:find('%s') then
for item in unitcode:gmatch('%S+') do
combo:add(item)
end
end
if combo.n > 1 then
local function lookup_combo
if what == 'no_combination' or what == 'only_multiple' then
return false, { 'cvt_bad_unit', unitcode }
end
local result = { combination = {} }
local cvt = result.combination
for i, v in ipairs(combo) do
local success, t = lookup(parms, v, 'only_multiple', utable, fails, depth)
if not success then return false, t end
if i == 1 then
result.utype = t.utype
else
local mismatch = check_mismatch(result, t)
if mismatch then
return false, mismatch
end
end
cvt[i] = t
end
return true, result
end
local success, result = lookup_combo
if success or err_is_fatal then
return success, result
end
end
-- Accept any unit with an engineering notation prefix like "e6cuft"
-- (million cubic feet), but not chained prefixes like "e3e6cuft",
-- and not if the unit is a combination or multiple,
-- and not if the unit has an offset or is a built-in.
-- Only en digits are accepted.
local exponent, baseunit = unitcode:match('^e(%d+)(.*)')
if exponent then
local engscale = text_code.eng_scales[exponent]
if engscale then
local success, result = lookup(parms, baseunit, 'no_combination', utable, fails, depth)
if success and not (result.offset or result.builtin or result.engscale) then
result.unitcode = unitcode -- 'e6cuft' not 'cuft'
result.defkey = unitcode -- key to lookup default exception
result.engscale = engscale
result.scale = result.scale * 10 ^ tonumber(exponent)
return true, result
end
end
end
-- Look for x/y; split on -most slash to get scale correct (x/y/z is x/y per z).
local top, bottom = unitcode:match('^(.-)/([^/]+)$')
if top and not unitcode:find('e%d') then
-- If valid, create an automatic per unit for an "x/y" unit code.
-- The unitcode must not include extraneous spaces.
-- Engineering notation (apart from at start and which has been stripped before here),
-- is not supported so do not make a per unit if find text like 'e3' in unitcode.
local success, result = call_make_per({ per = {top, bottom} })
if success then
return true, result
end
end
if not parms.opt_ignore_error and not get_range(unitcode) then
-- Want the "what links here" list for the extra_module to show only cases
-- where an extra unit is used, so do not require it if invoked from
-- or if looking up a range word which cannot be a unit.
if not extra_units then
local success, extra = pcall(function return require(extra_module).extra_units end)
if success and type(extra) == 'table' then
extra_units = extra
end
end
if extra_units then
-- A unit in one data table might refer to a unit in the other table, so
-- switch between them, relying on fails or depth to terminate loops.
if not fails[unitcode] then
fails[unitcode] = true
local other = (utable == all_units) and extra_units or all_units
local success, result = lookup(parms, unitcode, what, other, fails, depth)
if success then
return true, result
end
end
end
end
if to_en_table then
-- At fawiki it is common to translate all digits so a unit like "km2" becomes "km۲".
local en_code = ustring.gsub(unitcode, '%d', to_en_table)
if en_code ~= unitcode then
return lookup(parms, en_code, what, utable, fails, depth)
end
end
return false, { 'cvt_unknown', unitcode }
end  
local function valid_number(num)
-- Return true if num is a valid number.
-- In Scribunto (different from some standard Lua), when expressed as a string,
-- overflow or other problems are indicated with text like "inf" or "nan"
-- which are regarded as invalid here (each contains "n").
if type(num) == 'number' and tostring(num):find('n', 1, true) == nil then
return true
end
end  
local function hyphenated(name, parts)
-- Return a hyphenated form of given name (for adjectival usage).
-- The name may be linked and the target of the link must not be changed.
-- Hypothetical examples:
-- ton → ton (no change)
-- long ton → long-ton
-- long ton → long-ton
-- long ton → long-ton
-- Input can also have multiple links in a single name like:
-- U.S. gallon
-- miles per U.S. quart
-- long tons per short ton
-- Assume that links cannot be nested (never like "abc[[defghi]]").