Fix default list processing

The previous release had set up default arguments to add to the existing
default list.  Now making a match will clear the list and replace it.

Author: Taylor C. Richberger

args.hxx

@@ -3506,6 +3506,17 @@ namespace args
                 FlagBase::Reset();
                 values = defaultValues;
             }
+
+            virtual FlagBase *Match(const EitherFlag &arg) override
+            {
+                const bool wasMatched = Matched();
+                auto me = FlagBase::Match(arg);
+                if (me && !wasMatched)
+                {
+                    values.clear();
+                }
+                return me;
+            }
     };
 
     /** An argument-accepting flag class that pushes the found values into a list
@@ -3583,6 +3594,17 @@ namespace args
                 values = defaultValues;
             }
 
+            virtual FlagBase *Match(const EitherFlag &arg) override
+            {
+                const bool wasMatched = Matched();
+                auto me = FlagBase::Match(arg);
+                if (me && !wasMatched)
+                {
+                    values.clear();
+                }
+                return me;
+            }
+
             iterator begin() noexcept
             {
                 return values.begin();
@@ -3799,6 +3821,17 @@ namespace args
                 values = defaultValues;
             }
 
+            virtual FlagBase *Match(const EitherFlag &arg) override
+            {
+                const bool wasMatched = Matched();
+                auto me = FlagBase::Match(arg);
+                if (me && !wasMatched)
+                {
+                    values.clear();
+                }
+                return me;
+            }
+
             iterator begin() noexcept
             {
                 return values.begin();
@@ -3960,6 +3993,17 @@ namespace args
                 values = defaultValues;
             }
 
+            virtual PositionalBase *GetNextPositional() override
+            {
+                const bool wasMatched = Matched();
+                auto me = PositionalBase::GetNextPositional();
+                if (me && !wasMatched)
+                {
+                    values.clear();
+                }
+                return me;
+            }
+
             iterator begin() noexcept
             {
                 return values.begin();
@@ -4170,6 +4214,17 @@ namespace args
                 values = defaultValues;
             }
 
+            virtual PositionalBase *GetNextPositional() override
+            {
+                const bool wasMatched = Matched();
+                auto me = PositionalBase::GetNextPositional();
+                if (me && !wasMatched)
+                {
+                    values.clear();
+                }
+                return me;
+            }
+
             iterator begin() noexcept
             {
                 return values.begin();

test.cxx

@@ -137,6 +137,46 @@ TEST_CASE("Argument flag lists work as expected", "[args]")
     REQUIRE((args::get(foo) == std::vector<int>{7, 2, 9, 42}));
 }
 
+TEST_CASE("Argument flag lists use default values", "[args]")
+{
+    args::ArgumentParser parser("This is a test program.", "This goes after the options.");
+    args::ValueFlagList<int> foo(parser, "FOO", "test flag", {'f', "foo"}, {9, 7, 5});
+    parser.ParseArgs(std::vector<std::string>());
+    REQUIRE((args::get(foo) == std::vector<int>{9, 7, 5}));
+}
+
+TEST_CASE("Argument flag lists replace default values", "[args]")
+{
+    args::ArgumentParser parser("This is a test program.", "This goes after the options.");
+    args::ValueFlagList<int> foo(parser, "FOO", "test flag", {'f', "foo"}, {9, 7, 5});
+    parser.ParseArgs(std::vector<std::string>{"--foo=7", "-f2", "-f", "9", "--foo", "42"});
+    REQUIRE((args::get(foo) == std::vector<int>{7, 2, 9, 42}));
+}
+
+TEST_CASE("Positional lists work as expected", "[args]")
+{
+    args::ArgumentParser parser("This is a test program.", "This goes after the options.");
+    args::PositionalList<int> foo(parser, "FOO", "test flag");
+    parser.ParseArgs(std::vector<std::string>{"7", "2", "9", "42"});
+    REQUIRE((args::get(foo) == std::vector<int>{7, 2, 9, 42}));
+}
+
+TEST_CASE("Positional lists use default values", "[args]")
+{
+    args::ArgumentParser parser("This is a test program.", "This goes after the options.");
+    args::PositionalList<int> foo(parser, "FOO", "test flag", {9, 7, 5});
+    parser.ParseArgs(std::vector<std::string>());
+    REQUIRE((args::get(foo) == std::vector<int>{9, 7, 5}));
+}
+
+TEST_CASE("Positional lists replace default values", "[args]")
+{
+    args::ArgumentParser parser("This is a test program.", "This goes after the options.");
+    args::PositionalList<int> foo(parser, "FOO", "test flag", {9, 7, 5});
+    parser.ParseArgs(std::vector<std::string>{"7", "2", "9", "42"});
+    REQUIRE((args::get(foo) == std::vector<int>{7, 2, 9, 42}));
+}
+
 #include <unordered_set>
 
 TEST_CASE("Argument flag lists work with sets", "[args]")