fix: prefix_command should not stop parsing at unrecognized options (#1374)

include/CLI/App.hpp

@@ -500,8 +500,9 @@ class App {
     }
 
     /// Enable or disable prefix command mode. If enabled, parsing stops at the
-    /// first unrecognized option and all remaining arguments are stored in
-    /// remaining args.
+    /// first positional argument (or the `--` separator) and all remaining
+    /// arguments are stored in remaining args. Unrecognized options do not stop
+    /// parsing; they are collected as extras.
     App *prefix_command(bool is_prefix = true) {
         prefix_command_ = is_prefix ? PrefixCommandMode::On : PrefixCommandMode::Off;
         return this;

include/CLI/impl/App_inl.hpp

@@ -2187,15 +2187,12 @@ App::_parse_arg(std::vector<std::string> &args, detail::Classifier current_type,
         if(parent_ != nullptr && fallthrough_)
             return _get_fallthrough_parent()->_parse_arg(args, current_type, false);
 
-        // Otherwise, add to missing
+        // Otherwise, add to missing. Note prefix_command only stops parsing at a positional or "--"
+        // (handled in _parse_positional/_parse_single); an unrecognized option is left as an extra
+        // and parsing continues so later registered options are still matched (#1374).
         args.pop_back();
         _move_to_missing(current_type, current);
-        if(get_prefix_command_mode() == PrefixCommandMode::On) {
-            while(!args.empty()) {
-                missing_.emplace_back(detail::Classifier::NONE, args.back());
-                args.pop_back();
-            }
-        } else if(allow_extras_ == ExtrasMode::AssumeSingleArgument) {
+        if(allow_extras_ == ExtrasMode::AssumeSingleArgument) {
             if(!args.empty() && _recognize(args.back(), false) == detail::Classifier::NONE) {
                 _move_to_missing(detail::Classifier::NONE, args.back());
                 args.pop_back();

tests/AppTest.cpp

@@ -2590,7 +2590,9 @@ TEST_CASE_METHOD(TApp, "PrefixCommand", "[app]") {
 
     run();
     rem = app.remaining();
-    CHECK(rem.size() == 5U);
+    // "--test4" is unrecognized but parsing continues, so "-f 27" is still recognized
+    CHECK(rem.size() == 3U);
+    CHECK(v1 == 27);
 
     app.prefix_command(CLI::PrefixCommandMode::SeparatorOnly);
     CHECK_THROWS_AS(run(), CLI::ExtrasError);
@@ -2613,6 +2615,25 @@ TEST_CASE_METHOD(TApp, "PrefixCommand", "[app]") {
     CHECK(rem.size() == 4U);
 }
 
+// prefix_command(On) must not stop parsing at an unrecognized *option*; a
+// registered option after one still gets recognized regardless of order (#1374)
+TEST_CASE_METHOD(TApp, "PrefixCommandUnknownOptionKeepsParsing", "[app]") {
+    bool known{false};
+    app.add_flag("--known", known);
+    app.prefix_command(true);
+    app.allow_extras(true);
+
+    args = {"--known", "--unknown"};  // App::parse consumes from the back
+    run();
+    CHECK(known);
+
+    known = false;
+    args = {"--unknown", "--known"};
+    run();
+    CHECK(known);
+    CHECK(app.remaining().size() == 1U);  // only "--unknown" left over
+}
+
 // makes sure the error throws on the rValue version of the parse
 TEST_CASE_METHOD(TApp, "ExtrasErrorRvalueParse", "[app]") {