Sample code snippet:

import sympy
from qualtran.bloqs.basic_gates import ZPowGate

t, eps = sympy.symbols(r"t \epsilon")
bloq = ZPowGate(exponent=t, eps=eps)
print(bloq.t_complexity())

Prints TComplexity(rotations=1).

One could do bloq.t_complexity().t_incl_rotations(eps), but this eps is not the same as the bloq's eps (which in general could be different for each subbloq).

Some history:

eps for rotations was introduced in the early days of Qualtran and I think is a useful parameter when constructing rotation bloqs. I agree it's probably not propagated correctly everywhere (though I remember implementing and correctly propagating eps in qvr, qft and hamming weight phasing bloq) -- we should file issues and try to get that fixed.

Originally, the rotation bloqs had a _t_complexity_ method implemented and would return the number of T gates scaling with log(1/eps); so the T-counts for call graphs with rotation bloqs would take the eps in account. (eg: #469)

As part of unifying / deprecating the T-complexity protocol; a temporary fix was to return rotations=1 for all rotation bloqs and add a method on the TComplexity class to convert rotations into T-gates. Eventually, the idea was to use the new costing framework to keep track of bloq counts and then use the eps to convert rotation bloqs to t-gates like we used to do originally. Here are some relevant discussions -
#662 (comment)
#678 (comment)

Using a single / hardcoded eps to convert all rotation bloqs to t gates was never meant to be a permanent solution. We've just not gotten around completing the migration yet I guess.

@mpharrigan As per our discussion offline, it'll be nice to have this as part of the v1.0 milestone.