Fix option matching

CHANGELOG.md

@@ -19,6 +19,7 @@ options. The project adheres to semantic versioning.
 * Fix a warning about possible loss of data.
 * Fix version numbering in CMakeLists.txt
 * Remove unused declaration of the undefined `ParseResult::get_option`.
+* Throw on invalid option syntax when beginning with a `-`.
 
 ## 2.1.1
 

include/cxxopts.hpp

@@ -368,6 +368,15 @@ namespace cxxopts
     }
   };
 
+  class option_syntax_exception : public OptionParseException {
+    public:
+    option_syntax_exception(const std::string& text)
+    : OptionParseException(u8"Argument " + LQUOTE + text + RQUOTE +
+        u8" starts with a - but has incorrect syntax")
+    {
+    }
+  };
+
   class option_not_exists_exception : public OptionParseException
   {
     public:
@@ -1701,6 +1710,11 @@ ParseResult::parse(int& argc, char**& argv)
     {
       //not a flag
 
+      // but if it starts with a `-`, then it's an error
+      if (argv[current][0] == '-') {
+        throw option_syntax_exception(argv[current]);
+      }
+
       //if true is returned here then it was consumed, otherwise it is
       //ignored
       if (consume_positional(argv[current]))

test/options.cpp

@@ -529,3 +529,19 @@ TEST_CASE("Unrecognised options", "[options]") {
     CHECK_THAT(argv[1], Catch::Equals("--unknown"));
   }
 }
+
+TEST_CASE("Invalid option syntax", "[options]") {
+  cxxopts::Options options("invalid_syntax", " - test invalid syntax");
+
+  Argv av({
+    "invalid_syntax",
+    "--a",
+  });
+
+  char** argv = av.argv();
+  auto argc = av.argc();
+
+  SECTION("Default behaviour") {
+    CHECK_THROWS_AS(options.parse(argc, argv), cxxopts::option_syntax_exception);
+  }
+}