fix: match short flags when ShortPrefix and LongPrefix are identical (#26)

args.hxx

@@ -2744,6 +2744,22 @@ namespace args
                 // prefix instead of being swallowed as a nameless long flag.
                 if (matchesLong && matchesShort)
                 {
+                    // Identical prefixes (e.g. Windows "/") make every flag
+                    // look both short and long. Prefer short when the next
+                    // character is a registered short flag so /h and /ifile
+                    // still go through ParseShort (#26).
+                    if (longprefix == shortprefix && s.size() > shortprefix.size())
+                    {
+                        const char ch = s[shortprefix.size()];
+                        for (FlagBase *flag : GetAllFlags())
+                        {
+                            if (flag->GetMatcher().Match(ch))
+                            {
+                                return OptionType::ShortFlag;
+                            }
+                        }
+                        return OptionType::LongFlag;
+                    }
                     return longprefix.length() >= shortprefix.length() ? OptionType::LongFlag : OptionType::ShortFlag;
                 }
 

test/windows_slash_prefix.cxx

@@ -0,0 +1,55 @@
+/* Copyright (c) Taylor Richberger <taylor@axfive.net>
+ * This code is released under the license described in the LICENSE file
+ */
+
+#include "test_common.hxx"
+
+#include <args.hxx>
+
+#include "test_helpers.hxx"
+
+int main()
+{
+    // Windows-style identical "/" short and long prefixes: /h must match the
+    // short flag and /help the long one (#26).
+    {
+        args::ArgumentParser parser("This is a test program.");
+        parser.ShortPrefix("/");
+        parser.LongPrefix("/");
+        parser.LongSeparator(":");
+        args::Flag help(parser, "help", "display this help section", {'h', "help"});
+        args::Flag version(parser, "version", "show the program version", {'v', "version"});
+        args::ValueFlag<std::string> input(parser, "file", "the input file", {'i', "input"});
+        parser.ParseArgs(std::vector<std::string>{"/h", "/v", "/i", "in.txt"});
+        test::require(help);
+        test::require(version);
+        test::require(input);
+        test::require(*input == "in.txt");
+    }
+
+    {
+        args::ArgumentParser parser("This is a test program.");
+        parser.ShortPrefix("/");
+        parser.LongPrefix("/");
+        parser.LongSeparator(":");
+        args::Flag help(parser, "help", "display this help section", {'h', "help"});
+        args::ValueFlag<std::string> input(parser, "file", "the input file", {'i', "input"});
+        parser.ParseArgs(std::vector<std::string>{"/help", "/input:out.txt"});
+        test::require(help);
+        test::require(input);
+        test::require(*input == "out.txt");
+    }
+
+    // Joined short values still go through ParseShort when prefixes match.
+    {
+        args::ArgumentParser parser("This is a test program.");
+        parser.ShortPrefix("/");
+        parser.LongPrefix("/");
+        args::ValueFlag<std::string> input(parser, "file", "the input file", {'i', "input"});
+        parser.ParseArgs(std::vector<std::string>{"/ifile.txt"});
+        test::require(input);
+        test::require(*input == "file.txt");
+    }
+
+    return 0;
+}