Optional function arguments

src/com/maddyhome/idea/vim/vimscript/model/functions/DefinedFunctionHandler.kt

@@ -30,6 +30,7 @@ import com.maddyhome.idea.vim.vimscript.model.Executable
 import com.maddyhome.idea.vim.vimscript.model.ExecutionResult
 import com.maddyhome.idea.vim.vimscript.model.datatypes.VimDataType
 import com.maddyhome.idea.vim.vimscript.model.datatypes.VimInt
+import com.maddyhome.idea.vim.vimscript.model.datatypes.VimList
 import com.maddyhome.idea.vim.vimscript.model.expressions.Expression
 import com.maddyhome.idea.vim.vimscript.model.expressions.Scope
 import com.maddyhome.idea.vim.vimscript.model.expressions.Variable
@@ -42,7 +43,7 @@ data class DefinedFunctionHandler(private val function: FunctionDeclaration) : F
   private val logger = logger<DefinedFunctionHandler>()
 
   override val minimumNumberOfArguments = function.args.size
-  override val maximumNumberOfArguments = function.args.size
+  override val maximumNumberOfArguments get() = if (function.hasOptionalArguments) null else function.args.size
 
   override fun doFunction(argumentValues: List<Expression>, editor: Editor, context: DataContext, parent: Executable): VimDataType {
     var returnValue: VimDataType? = null
@@ -135,6 +136,15 @@ data class DefinedFunctionHandler(private val function: FunctionDeclaration) : F
         function
       )
     }
+    if (function.hasOptionalArguments) {
+      VariableService.storeVariable(
+        Variable(Scope.FUNCTION_VARIABLE, "000"),
+        VimList(argumentValues.subList(function.args.size, argumentValues.size).map { it.evaluate(editor, context, function) }.toMutableList()),
+        editor,
+        context,
+        function
+      )
+    }
     VariableService.storeVariable(
       Variable(Scope.FUNCTION_VARIABLE, "firstline"),
       VimInt(ranges!!.getFirstLine(editor, editor.caretModel.currentCaret) + 1), editor, context, function

src/com/maddyhome/idea/vim/vimscript/model/statements/FunctionDeclaration.kt

@@ -16,7 +16,7 @@ data class FunctionDeclaration(
   val body: List<Executable>,
   val replaceExisting: Boolean,
   val flags: Set<FunctionFlag>,
-  val scriptName: String? = null,
+  val hasOptionalArguments: Boolean,
 ) : Executable() {
 
   /**

src/com/maddyhome/idea/vim/vimscript/parser/visitors/ExecutableVisitor.kt

@@ -71,10 +71,11 @@ object ExecutableVisitor : VimscriptBaseVisitor<Executable>() {
     val body = ctx.blockMember().mapNotNull { visitBlockMember(it) }
     val replaceExisting = ctx.replace != null
     val flags = mutableSetOf<FunctionFlag?>()
+    val hasOptionalArguments = ctx.argumentsDeclaration().ETC() != null
     for (flag in ctx.functionFlag()) {
       flags.add(FunctionFlag.getByName(flag.text))
     }
-    return FunctionDeclaration(functionScope, functionName, args, body, replaceExisting, flags.filterNotNull().toSet())
+    return FunctionDeclaration(functionScope, functionName, args, body, replaceExisting, flags.filterNotNull().toSet(), hasOptionalArguments)
   }
 
   override fun visitTryStatement(ctx: VimscriptParser.TryStatementContext): Executable {

test/org/jetbrains/plugins/ideavim/ex/implementation/statements/FunctionDeclarationTest.kt

@@ -540,4 +540,24 @@ class FunctionDeclarationTest : VimTestCase() {
 
     typeText(commandToKeys("delf! F1"))
   }
+
+  fun `test optional arguments`() {
+    configureByText("\n")
+    typeText(
+      commandToKeys(
+        "" +
+          "function GetOptionalArgs(name, ...) |" +
+          "  return a:000 | " +
+          "endfunction"
+      )
+    )
+    typeText(commandToKeys("echo GetOptionalArgs('this arg is not optional')"))
+    assertExOutput("[]\n")
+    typeText(
+      commandToKeys(
+        "echo GetOptionalArgs('this arg is not optional', 42, 'optional arg')"
+      )
+    )
+    assertExOutput("[42, 'optional arg']\n")
+  }
 }

vimscript-info/VIMSCRIPT_ROADMAP.md

@@ -22,7 +22,7 @@
 - [x] `range` function flag  
 - [x] `call` command
 - [ ] function as method
-- [ ] optional arguments `...`
+- [x] optional arguments `...`
 - [ ] funcref type
 - [ ] lambdas
 - [ ] default value in functions e.g. `function F1(a, b = 10)`