Fix the -Wunused-parameter build-time warning.

[ikmsk10]

The methods of the AstVisitor base class defines interface only and
have no implementation. These should be marked as [[maybe_unused]] to
prevent propagate the build warnings.

Signed-off-by: Igor Kononenko singleton.dev.ik@gmail.com

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Igor Kononenko (c39e449)

[mmatsa]

[[maybe_unused]] was "only" added in C++17.
https://en.cppreference.com/w/cpp/language/attributes/maybe_unused

While many of us are past that at this point, not all users are.
Many of us don't see the warnings, possibly because of this line of code:
https://github.com/graphql/libgraphqlparser/blob/master/CMakeLists.txt#L8

Is it possible that the warning only comes when not compiling with the repo's cmake files?

[vvd170501]

C++11 allows unnamed function parameters, which also prevent -Wunused-parameter warnings when the source file is compiled with a newer standard.

--- a/ast/cxx_visitor.py
+++ b/ast/cxx_visitor.py
@@ -38,11 +38,11 @@ public:
   def start_type(self, name):
     titleName = title(name)
     camelName = camel(titleName)
-    print '  virtual bool visit%s(const %s &%s) { return true; }' % (
+    print '  virtual bool visit%s(const %s &/* %s */) { return true; }' % (
       titleName,
       titleName,
       camelName)
-    print '  virtual void endVisit%s(const %s &%s) { }' % (
+    print '  virtual void endVisit%s(const %s &/* %s */) { }' % (
       titleName,
       titleName,
       camelName)