Unable to compute Hessian-vector product function if function calls other functions

[lericson]

Minimal test case:

import tangent
import numpy as np

def forward(theta, states):
    return states

def loss(theta, states, actions):
    err = forward(theta, actions)
    return np.mean(err, axis=(0,))

dlossdtheta   = tangent.autodiff(loss, mode='reverse')
ddlossddtheta = tangent.autodiff(dlossdtheta, mode='forward')

Fails on computation of ddlossddtheta, with

Traceback (most recent call last):
  File "scratch.py", line 12, in <module>
    ddlossddtheta = tangent.autodiff(dlossdtheta, mode='forward')
[...]
  File "/Users/lericson/devel/.../env/src/tangent/tangent/fence.py", line 256, in visit_IfExp
    self._reject(node, 'Conditional Expressions are not supported')
  File "/Users/lericson/devel/.../env/src/tangent/tangent/fence.py", line 91, in _reject
    self._raise_error(msg)
  File "/Users/lericson/devel/.../env/src/tangent/tangent/fence.py", line 74, in _raise_error
    raise TangentParseError(msg, ('<stdin>', lineno, offset + 1, line))
  File "<stdin>", line 3
    axis_shape = x.shape if axis is None else tuple(x.shape[a] for a in axis)

Replacing the function call with inlining the function solves the issue.

[lericson]

This is running 6533e83af09de7345d1b438512679992f080dcc9

[lericson]

I think the state of HVP computation is actually pretty broken in both the latest release and said commit. I can't get HVPs to work for anything that isn't basically an identity function.