Support rest/spread placeholder args

src/index.lsc

@@ -45,9 +45,12 @@ Lightscript(babel) ->
     //// AST transforms
     // Perform basic ast fixups (block bodies, etc)
     fixAst(path)
+
     // Transform placeholder expressions first.
-    transformPlaceholders(path)
+    if compilerState.opts.placeholderArgs:
+      transformPlaceholders(path)
 
+    // Main LSC transforms
     path.traverse({
       ForInArrayStatement(path): void ->
         // TODO: push the linter conditional down into the transform

src/placeholders.lsc

@@ -1,3 +1,5 @@
+import t from './types'
+
 registerPlaceholder(functions, path, programPath) ->
   fnPath = path.getFunctionParent()
   if fnPath == programPath || !fnPath.node || !fnPath.node.params:
@@ -6,6 +8,10 @@ registerPlaceholder(functions, path, programPath) ->
   if fnPath.node.params.length:
     throw path.buildCodeFrameError("Placeholders cannot be used in functions with arguments.")
 
+  if path.parentPath?.node?.type == "SpreadElement":
+    if path.node?.index?:
+      throw path.buildCodeFrameError("Cannot use indices with spread placeholders.")
+
   let fnInfo = functions.get(fnPath)
   if fnInfo:
     fnInfo.placeholders.push(path)
@@ -17,14 +23,29 @@ liftPlaceholders(fnPath, phPaths) ->
   ixPhPaths = phPaths.filter(x -> x.node.index?)
   nixPhPaths = phPaths.filter(x-> not x.node.index?)
   ixPhPaths.sort((a, b) -> a.node.index - b.node.index)
+  nixPhPaths.sort((a, b) ->
+    // SpreadElements are last
+    if a.parentPath?.node.type == "SpreadElement":
+      1
+    elif b.parentPath?.node.type == "SpreadElement":
+      -1
+    else:
+      0
+  )
   sortedPhPaths = ixPhPaths.concat(nixPhPaths)
 
   // Formulate args
   args = []
-  let prevIndex = undefined
+  let prevIndex = undefined, restArg = undefined
   for elem phPath in sortedPhPaths:
     { node } = phPath
-    if node.index? and node.index == prevIndex:
+    if phPath.parentPath?.node.type == "SpreadElement":
+      if not restArg:
+        now restArg = fnPath.scope.generateUidIdentifier("arg")
+        args.push(t.restElement(restArg))
+      phPath.replaceWith(restArg)
+    elif node.index? and node.index == prevIndex:
+      // Repeated use of an index = same arg.
       phPath.replaceWith(args[args.length - 1])
     else:
       args.push(fnPath.scope.generateUidIdentifier("arg"))

test/fixtures/placeholder-args/spread-index-illegal/actual.js

@@ -0,0 +1,2 @@
+->
+  a = [..._1]

test/fixtures/placeholder-args/spread-index-illegal/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Cannot use indices with spread placeholders."
+}

test/fixtures/placeholder-args/spread/actual.js

@@ -0,0 +1,9 @@
+-> f(_2, _1, _, ..._)
+
+->
+  a = [..._]
+  f(_2, _1, _, a)
+
+->
+  a = [..._]
+  b = [..._]

test/fixtures/placeholder-args/spread/expected.js

@@ -0,0 +1,10 @@
+(function (_arg, _arg2, _arg3, ..._arg4) {
+  return f(_arg2, _arg, _arg3, ..._arg4);
+});(function (_arg5, _arg6, _arg7, ..._arg8) {
+  const a = [..._arg8];
+  return f(_arg6, _arg5, _arg7, a);
+});(function (..._arg9) {
+  const a = [..._arg9];
+  const b = [..._arg9];
+  return b;
+});