Print statements inside a model are buffered into a stringstream and only printed when log_prob returns

[WardBrian]

Summary:

In situations like stan-dev/cmdstan#1207, where there is an infinite loop which never exits, a user may try to debug-by-print the loop condition. This will never be useful, as the infinite loop prevents the code from exiting and actually logging to the user.

Relevant code:

stan/src/stan/model/gradient.hpp

Lines 25 to 35 in b22074b

	std::stringstream ss;
	try {
	stan::math::gradient(model_functional<M>(model, &ss), x, f, grad_f);
	} catch (std::exception& e) {
	if (ss.str().length() > 0)
	logger.info(ss);
	throw;
	}
	if (ss.str().length() > 0)
	logger.info(ss);
	}

Current Version:

v2.33.0