fix(lapp) add file name to arg table when using the default value

CHANGELOG.md

@@ -13,7 +13,8 @@ see [CONTRIBUTING.md](CONTRIBUTING.md#release-instructions-for-a-new-version) fo
    [#413](https://github.com/lunarmodules/Penlight/pull/413)
  - feat: `utils.kpairs` new iterator over all non-integer keys
    [#413](https://github.com/lunarmodules/Penlight/pull/413)
-
+ - fix: `lapp` provides the file name when using the default argument
+   [#427](https://github.com/lunarmodules/Penlight/pull/427)
 
 ## 1.12.0 (2022-Jan-10)
  - deprecate: module `pl.text` the contents have moved to `pl.stringx` (removal later)

lua/pl/lapp.lua

@@ -246,6 +246,7 @@ function lapp.process_options_string(str,args)
             line = res.rest
             res = {}
             local optional
+            local defval_str
             -- do we have ([optional] [<type>] [default <val>])?
             if match('$({def} $',line,res) or match('$({def}',line,res) then
                 local typespec = strip(res.def)
@@ -288,6 +289,7 @@ function lapp.process_options_string(str,args)
                 -- optional 'default value' clause. Type is inferred as
                 -- 'string' or 'number' if there's no explicit type
                 if default or match('default $r{rest}',typespec,res) then
+                    defval_str = res.rest
                     defval,vtype = process_default(res.rest,vtype)
                 end
             else -- must be a plain flag, no extra parameter required
@@ -297,6 +299,7 @@ function lapp.process_options_string(str,args)
             local ps = {
                 type = vtype,
                 defval = defval,
+                defval_str = defval_str,
                 required = defval == nil and not optional,
                 comment = res.rest or optparm,
                 constraint = constraint,
@@ -426,6 +429,9 @@ function lapp.process_options_string(str,args)
         if not ps.used then
             if ps.required then lapp.error("missing required parameter: "..parm) end
             set_result(ps,parm,ps.defval)
+            if builtin_types[ps.type] == "file" then
+                set_result(ps, parm .. "_name", ps.defval_str)
+            end
         end
     end
     return results

tests/test-lapp.lua

@@ -47,16 +47,16 @@ Various flags and option types
 
 check(simple,
     {'-o','in'},
-    {quiet=false,p=false,o='in',input='<file>'})
+    {quiet=false,p=false,o='in',input='<file>', input_name="stdin"})
 
 ---- value of flag may be separated by '=' or ':'
 check(simple,
     {'-o=in'},
-    {quiet=false,p=false,o='in',input='<file>'})
+    {quiet=false,p=false,o='in',input='<file>', input_name="stdin"})
 
 check(simple,
     {'-o:in'},
-    {quiet=false,p=false,o='in',input='<file>'})
+    {quiet=false,p=false,o='in',input='<file>', input_name="stdin"})
 
 -- Check lapp.callback.
 local calls = {}
@@ -156,6 +156,13 @@ check (false_flag,{'-g','-f'},{f=false,g=true})
 check (false_flag,{'-g','--'},{f=true,g=true})
 check (false_flag,{'-g','--','-a','frodo'},{f=true,g=true; '-a','frodo'})
 
+
+local default_file_flag = [[
+    -f (file-out default stdout)
+]]
+
+check (default_file_flag,{},{f="<file>", f_name = "stdout"})
+
 local addtype = [[
   -l (intlist) List of items
 ]]