Support capturing remaining() arguments

This kind of argument works as if having the "remaining" nargs,
inspired by Python's `argparse.REMAINDER`.

This change also reduces the size of `Argument` by 8 bytes.

See also: https://docs.python.org/2/library/argparse.html#nargs

fixes: p-ranav/argparse#17

include/argparse.hpp

@@ -36,6 +36,7 @@ SOFTWARE.
 #include <list>
 #include <map>
 #include <numeric>
+#include <optional>
 #include <sstream>
 #include <stdexcept>
 #include <string>
@@ -159,11 +160,18 @@ public:
     return *this;
   }
 
-  Argument &nargs(size_t aNumArgs) {
+  Argument &nargs(int aNumArgs) {
+    if (aNumArgs < 0)
+      throw std::logic_error("Number of arguments must be non-negative");
     mNumArgs = aNumArgs;
     return *this;
   }
 
+  Argument &remaining() {
+    mNumArgs = -1;
+    return *this;
+  }
+
   template <typename Iterator>
   Iterator consume(Iterator start, Iterator end, std::string usedName = {}) {
     if (mIsUsed) {
@@ -174,11 +182,14 @@ public:
     if (mNumArgs == 0) {
       mValues.emplace_back(mImplicitValue);
       return start;
-    } else if (mNumArgs <= static_cast<size_t>(std::distance(start, end))) {
-      end = std::next(start, mNumArgs);
-      if (std::any_of(start, end, Argument::is_optional)) {
-        throw std::runtime_error("optional argument in parameter sequence");
+    } else if (mNumArgs <= std::distance(start, end)) {
+      if (auto expected = maybe_nargs()) {
+        end = std::next(start, *expected);
+        if (std::any_of(start, end, Argument::is_optional)) {
+          throw std::runtime_error("optional argument in parameter sequence");
+        }
       }
+
       struct action_apply {
         void operator()(valued_action &f) {
           std::transform(start, end, std::back_inserter(self.mValues), f);
@@ -186,8 +197,10 @@ public:
 
         void operator()(void_action &f) {
           std::for_each(start, end, f);
-          if (!self.mDefaultValue.has_value())
-            self.mValues.resize(self.mNumArgs);
+          if (!self.mDefaultValue.has_value()) {
+            if (auto expected = self.maybe_nargs())
+              self.mValues.resize(*expected);
+          }
         }
 
         Iterator start, end;
@@ -206,35 +219,45 @@ public:
    * @throws std::runtime_error if argument values are not valid
    */
   void validate() const {
-    if (mIsOptional) {
-      if (mIsUsed && mValues.size() != mNumArgs && !mDefaultValue.has_value()) {
-        std::stringstream stream;
-        stream << mUsedName << ": expected " << mNumArgs << " argument(s). "
-               << mValues.size() << " provided.";
-        throw std::runtime_error(stream.str());
+    if (auto expected = maybe_nargs()) {
+      if (mIsOptional) {
+        if (mIsUsed && mValues.size() != *expected &&
+            !mDefaultValue.has_value()) {
+          std::stringstream stream;
+          stream << mUsedName << ": expected " << *expected << " argument(s). "
+                 << mValues.size() << " provided.";
+          throw std::runtime_error(stream.str());
+        } else {
+          // TODO: check if an implicit value was programmed for this argument
+          if (!mIsUsed && !mDefaultValue.has_value() && mIsRequired) {
+            std::stringstream stream;
+            stream << mNames[0] << ": required.";
+            throw std::runtime_error(stream.str());
+          }
+          if (mIsUsed && mIsRequired && mValues.size() == 0) {
+            std::stringstream stream;
+            stream << mUsedName << ": no value provided.";
+            throw std::runtime_error(stream.str());
+          }
+        }
       } else {
-        // TODO: check if an implicit value was programmed for this argument
-        if (!mIsUsed && !mDefaultValue.has_value() && mIsRequired) {
+        if (mValues.size() != expected && !mDefaultValue.has_value()) {
           std::stringstream stream;
-          stream << mNames[0] << ": required.";
+          stream << mUsedName << ": expected " << *expected << " argument(s). "
+                 << mValues.size() << " provided.";
           throw std::runtime_error(stream.str());
         }
-        if (mIsUsed && mIsRequired && mValues.size() == 0) {
-          std::stringstream stream;
-          stream << mUsedName << ": no value provided.";
-          throw std::runtime_error(stream.str());
-        }
-      }
-    } else {
-      if (mValues.size() != mNumArgs && !mDefaultValue.has_value()) {
-        std::stringstream stream;
-        stream << mUsedName << ": expected " << mNumArgs << " argument(s). "
-               << mValues.size() << " provided.";
-        throw std::runtime_error(stream.str());
       }
     }
   }
 
+  auto maybe_nargs() const -> std::optional<size_t> {
+    if (mNumArgs < 0)
+      return std::nullopt;
+    else
+      return static_cast<size_t>(mNumArgs);
+  }
+
   size_t get_arguments_length() const {
     return std::accumulate(std::begin(mNames), std::end(mNames), size_t(0),
                            [](const auto &sum, const auto &s) {
@@ -345,7 +368,7 @@ private:
       std::in_place_type<valued_action>,
       [](const std::string &aValue) { return aValue; }};
   std::vector<std::any> mValues;
-  size_t mNumArgs = 1;
+  int mNumArgs = 1;
   bool mIsOptional : 1;
   bool mIsRequired : 1;
   bool mIsUsed : 1; // True if the optional argument is used by user

test/test_actions.hpp

@@ -119,3 +119,15 @@ TEST_CASE("Users can bind arguments to actions", "[actions]") {
     }
   }
 }
+
+TEST_CASE("Users can use actions on remaining arguments", "[actions]") {
+  argparse::ArgumentParser program("sum");
+
+  int result = 0;
+  program.add_argument("all").remaining().action(
+      [](int &sum, std::string const &value) { sum += std::stoi(value); },
+      std::ref(result));
+
+  program.parse_args({"sum", "42", "100", "-3", "-20"});
+  REQUIRE(result == 119);
+}

test/test_optional_arguments.hpp

@@ -45,6 +45,35 @@ TEST_CASE("Parse multiple toggle arguments with implicit values", "[optional_arg
   REQUIRE(program.get<bool>("-x") == true);
 }
 
+TEST_CASE("Parse optional arguments of many values", "[optional_arguments]") {
+  GIVEN("a program that accepts an optional argument of many values") {
+    argparse::ArgumentParser program("test");
+    program.add_argument("-i").remaining().action(
+        [](const std::string &value) { return std::stoi(value); });
+
+    WHEN("provided no argument") {
+      THEN("the program accepts it but gets nothing") {
+        REQUIRE_NOTHROW(program.parse_args({"test"}));
+        REQUIRE_THROWS_AS(program.get<std::vector<int>>("-i"),
+                          std::logic_error);
+      }
+    }
+
+    WHEN("provided remaining arguments follow the option") {
+      program.parse_args({"test", "-i", "-42", "8", "100", "300"});
+
+      THEN("the optional parameter consumes all of them") {
+        auto inputs = program.get<std::vector<int>>("-i");
+        REQUIRE(inputs.size() == 4);
+        REQUIRE(inputs[0] == -42);
+        REQUIRE(inputs[1] == 8);
+        REQUIRE(inputs[2] == 100);
+        REQUIRE(inputs[3] == 300);
+      }
+    }
+  }
+}
+
 TEST_CASE("Parse arguments of different types", "[optional_arguments]") {
   using namespace std::literals;
 

test/test_positional_arguments.hpp

@@ -47,6 +47,59 @@ TEST_CASE("Parse positional arguments with optional arguments in the middle", "[
   REQUIRE_THROWS(program.parse_args({ "test", "rocket.mesh", "thrust_profile.csv", "--num_iterations", "15", "output.mesh" }));
 }
 
+TEST_CASE("Parse remaining arguments deemed positional",
+          "[positional_arguments]") {
+  GIVEN("a program that accepts an optional argument and remaining arguments") {
+    argparse::ArgumentParser program("test");
+    program.add_argument("-o");
+    program.add_argument("input").remaining();
+
+    WHEN("provided no argument") {
+      THEN("the program accepts it but gets nothing") {
+        REQUIRE_NOTHROW(program.parse_args({"test"}));
+        REQUIRE_THROWS_AS(program.get<std::vector<std::string>>("input"),
+                          std::logic_error);
+      }
+    }
+
+    WHEN("provided an optional followed by remaining arguments") {
+      program.parse_args({"test", "-o", "a.out", "a.c", "b.c", "main.c"});
+
+      THEN("the optional parameter consumes an argument") {
+        using namespace std::literals;
+        REQUIRE(program["-o"] == "a.out"s);
+
+        auto inputs = program.get<std::vector<std::string>>("input");
+        REQUIRE(inputs.size() == 3);
+        REQUIRE(inputs[0] == "a.c");
+        REQUIRE(inputs[1] == "b.c");
+        REQUIRE(inputs[2] == "main.c");
+      }
+    }
+
+    WHEN("provided remaining arguments including optional arguments") {
+      program.parse_args({"test", "a.c", "b.c", "main.c", "-o", "a.out"});
+
+      THEN("the optional argument is deemed remaining") {
+        REQUIRE_THROWS_AS(program.get("-o"), std::logic_error);
+
+        auto inputs = program.get<std::vector<std::string>>("input");
+        REQUIRE(inputs.size() == 5);
+        REQUIRE(inputs[0] == "a.c");
+        REQUIRE(inputs[1] == "b.c");
+        REQUIRE(inputs[2] == "main.c");
+        REQUIRE(inputs[3] == "-o");
+        REQUIRE(inputs[4] == "a.out");
+      }
+    }
+  }
+}
+
+TEST_CASE("Negative nargs is not allowed", "[positional_arguments]") {
+  argparse::ArgumentParser program("test");
+  REQUIRE_THROWS_AS(program.add_argument("output").nargs(-1), std::logic_error);
+}
+
 TEST_CASE("Square a number", "[positional_arguments]") {
   argparse::ArgumentParser program;
   program.add_argument("--verbose", "-v")
@@ -60,4 +113,4 @@ TEST_CASE("Square a number", "[positional_arguments]") {
 
   program.parse_args({"./main", "15"});
   REQUIRE(program.get<double>("square") == 225);
-}
+}