Wrapper around swift command that makes it easier to import your own modules

swiftr

#!/usr/bin/env lua

--
-- @author Matthew M. Burke <matthew@bluedino.net>
-- @date 2017-11-17
-- @version 1.0
-- @project Wrapper for Swift command
-- @file swiftr
--
-- Want to use your own Swift modules in the Swift REPL?
--
-- To do so, there are three steps:
--       1) the module must provide a dynamic library (see below),
--       2) add the appropriate -I, -L, and -l flags when you invoke Swift
--       3) `import` the module in your Swift code.
--
-- Swiftr is a wrapper that makes this easier by automatically constructing
-- the command line flags for `swfit`. If you only want a subset of your
-- modules available, you can specify them on the `swiftr` command line. Additionally, 
-- you can use `swiftr` in "interpreter" mode by specifying a .swift file on the command line.
--
-- In order to use `swiftr` you need to first create a directory, /usr/local/share/spm,
-- and copy your modules (both the .swiftmodule and .dylib/.so) to this directory.
--
-- EXAMPLES:
--
-- Suppose you have created modules Foo, Bar, Snafu, and Possum, and you have copied
-- these four modules to /usr/local/share/spm then
--
--           > swiftr
--
--           in the REPL you can now import any or all four of these modules
--
--           > swiftr -mFoo
--
--           in the REPL you can `import Foo`. You cannot import any of the other three.
--
--           > swiftr -mSnafu -mPossum mycode.swift
--
--           "interprets" mycode.swift. In mycode.swift you can import Snafu and Possum
--           (you cannot import Foo and Bar)
--
-- BUILDING A DYNAMIC LIBRARY:
--
-- As mentioned above, in order to import a module into the REPL, you must build a dynamic library
-- when you build your module. Suppose your module is named Foo, then insert the following into
-- your manifest's lists of products:
--
--                  .product(
--                       name: "Foo",
--                       type: .dynamic,
--                       targets: ["Foo"]),
--
--
-- TODO: implement --help
-- TODO: override module directory with a command line flag
-- TODO: specify multiple module directories (1 possibility: specify a "top of tree" directory
--       and find all Swift modules in that tree)
-- TODO: pass-through args; like swift build, swift package, etc

debug = false
swiftExecutable = "/usr/bin/swift"
REPLMODS = os.getenv 'REPLMODS' or "/usr/local/share/spm"
pathFlags = string.format("-I %s -L %s", REPLMODS, REPLMODS)

function programName(fullPath)
   local f = io.popen(string.format('basename %s', fullPath))
   local result = f:read()
   f:close()
   return result
end
progname = programName(arg[0])

function errorExit(msg)
   print(string.format('%s: %s', progname, msg))
   os.exit(1)
end

function exists(arg, dir, checkDir)
   local fullPath
   if checkDir then
      fullPath = dir
   else
      local filename = string.format('lib%s.dylib', arg)
      fullPath = string.format("%s/%s", dir, filename)
   end
   local fh = io.open(fullPath)
   if fh then
      fh:close()
   end
   return fh
end

function beginsWith(option, prefix)
   local first, last = string.find(option, prefix)
   return first == 1
end

function endsWith(option, suffix)
   local first, last = string.find(option, suffix)
   return last == string.len(option)
end

function isModule(option)
   return beginsWith(option, '-m')
end

function allModules(moduleDirectory)
   local modules = {}
   local f = io.popen(string.format('ls -1 %s', moduleDirectory))
   if f then
      for file in f:lines() do
         if endsWith(file, '.swiftmodule') then
            local name = string.gsub(file, '.swiftmodule', '')
            table.insert(modules, name)
         end
      end
      f:close()
   end
   return modules
end

function process(args, moduleDirectory)
   local loadAll = true
   local modules = {}
   local script = nil
   
   for i = 1, #args do
      local option = args[i]
      if option == '--debug' then
         debug = true
      elseif isModule(option) then
         option = string.sub(option, 3)
         if exists(option, moduleDirectory) then
            table.insert(modules, option)
            loadAll = false
         else
            errorExit(string.format("Could not find module '%s'", option))
         end
      else
         if script then
            errorExit('Cannot feed more than one Swift file to the interpreter')
         else
            if not endsWith(option, '.swift')  then
               errorExit(string.format("Script argument '%s' must end in '.swift'", option))
            end
            script = option
         end
      end
   end
   
   local remainingFlags = ""

   if loadAll then
      modules = allModules(moduleDirectory)
   end

   for _, module in pairs(modules) do
      remainingFlags = remainingFlags .. string.format(" -l%s ", module)
   end
   remainingFlags = remainingFlags .. (script or '')

   return remainingFlags
end

-- -----------------------------------------------------------------------------
--
-- Now, do the work...
--
-- -----------------------------------------------------------------------------

if not exists('', REPLMODS, true) then
   errorExit(string.format("Module directory '%s' does not exist", REPLMODS))
end
command = string.format("%s %s %s", swiftExecutable, pathFlags, process(arg, REPLMODS))
if debug then
   print(command)
else
   os.execute(command)
end