Don't consume the terminator during parsing.

Sources/ArgumentParser/Parsing/ArgumentSet.swift

@@ -348,8 +348,8 @@ extension ArgumentSet {
           try parseValue(argument, parsed, origin, update, &result, &usedOrigins)
         }
       case .terminator:
-        // Mark the terminator as used:
-        result.set(ParsedValues.Element(key: .terminator, value: 0, inputOrigin: [origin]))
+        // Ignore the terminator, it might get picked up as a positional value later.
+        break
       }
     }
 

Sources/ArgumentParser/Parsing/CommandParser.swift

@@ -85,7 +85,7 @@ extension CommandParser {
     try checkForBuiltInFlags(split)
 
     // We should have used up all arguments at this point:
-    guard split.isEmpty else {
+    guard !split.containsNonTerminatorArguments else {
       // Check if one of the arguments is an unknown option
       for (index, element) in split.elements {
         if case .option(let argument) = element {

Sources/ArgumentParser/Parsing/SplitArguments.swift

@@ -196,10 +196,20 @@ extension SplitArguments.Element {
 }
 
 extension SplitArguments {
+  /// `true` if the arguments are empty.
   var isEmpty: Bool {
     elements.isEmpty
   }
-
+
+  /// `true` if the arguments are empty, or if the only remaining argument is the `--` terminator.
+  var containsNonTerminatorArguments: Bool {
+    if elements.isEmpty { return false }
+    if elements.count > 1 { return true }
+
+    if case .terminator = elements[0].element { return false }
+    else { return true }
+  }
+
   subscript(position: Index) -> Element? {
     return elements.first {
       $0.0 == position

Tests/ArgumentParserEndToEndTests/OptionGroupEndToEndTests.swift

@@ -16,7 +16,7 @@ import ArgumentParser
 final class OptionGroupEndToEndTests: XCTestCase {
 }
 
-struct Inner: TestableParsableArguments {
+fileprivate struct Inner: TestableParsableArguments {
   @Flag(name: [.short, .long])
   var extraVerbiage: Bool
   @Option(default: 0)
@@ -33,7 +33,7 @@ struct Inner: TestableParsableArguments {
   }
 }
 
-struct Outer: TestableParsableArguments {
+fileprivate struct Outer: TestableParsableArguments {
   @Flag()
   var verbose: Bool
   @Argument()
@@ -53,7 +53,7 @@ struct Outer: TestableParsableArguments {
   }
 }
 
-struct Command: TestableParsableCommand {
+fileprivate struct Command: TestableParsableCommand {
   static let configuration = CommandConfiguration(commandName: "testCommand")
 
   @OptionGroup()

Tests/ArgumentParserEndToEndTests/RepeatingEndToEndTests.swift

@@ -129,6 +129,32 @@ extension RepeatingEndToEndTests {
 
 // MARK: -
 
+fileprivate struct Outer: ParsableCommand {
+  static let configuration = CommandConfiguration(subcommands: [Inner.self])
+}
+
+fileprivate struct Inner: ParsableCommand {
+  @Flag() 
+  var verbose: Bool
+
+  @Argument(parsing: .unconditionalRemaining) 
+  var files: [String]
+}
+
+extension RepeatingEndToEndTests {
+  func testParsing_subcommandRemaining() {
+    AssertParseCommand(
+      Outer.self, Inner.self,
+      ["inner", "--verbose", "one", "two", "--", "three", "--other"]) 
+    { inner in
+      XCTAssertTrue(inner.verbose)
+      XCTAssertEqual(inner.files, ["one", "two", "--", "three", "--other"])
+    }
+  }
+}
+
+// MARK: -
+
 fileprivate struct Qux: ParsableArguments {
   @Option(parsing: .upToNextOption) var names: [String]
   @Flag() var verbose: Bool