cmArgumentParser: Model maybe-empty and non-empty lists with wrapper types

Previously bindings to `std::vector<std::string>` required at least one
value.  Some clients have been filtering `keywordsMissingValue` to
support keywords followed by empty lists.  Instead, require clients to
specify whether a keyword's list can be empty as part of the binding
type.

1 files changed, 10 insertions, 1 deletions

diff --git a/Source/cmArgumentParser.cxx b/Source/cmArgumentParser.cxx
index 1a05dbc..1bb9051 100644
--- a/Source/cmArgumentParser.cxx
+++ b/Source/cmArgumentParser.cxx
@@ -4,6 +4,8 @@
 
 #include <algorithm>
 
+#include "cmArgumentParserTypes.h"
+
 namespace ArgumentParser {
 
 auto ActionMap::Emplace(cm::string_view name, Action action)
@@ -44,7 +46,14 @@ void Instance::Bind(std::string& val)
   this->ExpectValue = true;
 }
 
-void Instance::Bind(std::vector<std::string>& val)
+void Instance::Bind(MaybeEmpty<std::vector<std::string>>& val)
+{
+  this->CurrentString = nullptr;
+  this->CurrentList = &val;
+  this->ExpectValue = false;
+}
+
+void Instance::Bind(NonEmpty<std::vector<std::string>>& val)
 {
   this->CurrentString = nullptr;
   this->CurrentList = &val;