Pimpl templating failure

Question

I have a straightforward and functional PIMPLed class hierarchy that I cannot succeed in templating :

template <class T>
class Constraint {
  protected:
    //! Base class for constraint implementations
    class Impl {
      public:
        virtual ~Impl() = default;
        //! Tests if params satisfy the constraint
        virtual bool test(const std::vector<double>& params) const = 0;
        //! Returns upper bound for given parameters
        virtual std::vector<double> upperBound(const std::vector<double>& params) const {
            return std::vector<double>(params.size(),
                         std::numeric_limits<std::vector<double>::value_type>::max());
        }
        //! Returns lower bound for given parameters
        virtual std::vector<double> lowerBound(const std::vector<double>& params) const {
            return std::vector<double>(params.size(),
                         -std::numeric_limits < std::vector<double>::value_type > ::max());
        }
    };
    std::shared_ptr<Impl> impl_;
  public:
    bool empty() const { return !impl_; }
    bool test(const std::vector<double>& p) const { return impl_->test(p); }
    std::vector<double> upperBound(const std::vector<double>& params) const {
        std::vector<double> result = impl_->upperBound(params);
        return result;
    }
    std::vector<double> lowerBound(const std::vector<double>& params) const {
        std::vector<double> result = impl_->lowerBound(params);
        return result;
    }
    double update(std::vector<double>& p, const std::vector<double>& direction, double beta) const;
    Constraint(std::shared_ptr<Impl> impl = std::shared_ptr<Impl>());
};

//! No constraint
template <class T>
class NoConstraint : public Constraint<T> {
  private:
    class Impl final : public Constraint<T>::Impl {
      public:
        bool test(const std::vector<double>&) const override { return true; }
    };
  public:
    NoConstraint() : Constraint<T>(std::shared_ptr<Constraint<T>::Impl>(new NoConstraint<T>::Impl)) {}
};

See

https://godbolt.org/z/G31ac4scz

for immediate use.

Namely the error is :

<source>: In constructor 'NoConstraint<T>::NoConstraint()':
<source>:55:71: error: type/value mismatch at argument 1 in template parameter list for 'template<class _Tp> class std::shared_ptr'
   55 |     NoConstraint() : Constraint<T>(std::shared_ptr<Constraint<T>::Impl>(new NoConstraint<T>::Impl)) {}
      |                                                                       ^
<source>:55:71: note:   expected a type, got 'Constraint<T>::Impl'
Compiler returned: 1

I should mention that this is with x86-64 gcc from latest trunk, while I don't have that error with latest msvc compiler. Still I don't understand this "template deduction" failure.