I'm getting this exact issue on Python 3.5 (xenial system installation).

All my existing venvs (from before my upgrade to xenial) work. Here's the diff:


> diff .venv/bin/activate.fish ../wrapt/.venv/bin/activate.fish 
35c35
< set -gx VIRTUAL_ENV "/home/tin/pg/hypothesis/.venv"
---
> set -gx VIRTUAL_ENV "/home/tin/pg/wrapt/.venv"
58,59c58,59
<         if test -n "$(.venv) "
<             printf "%s%s%s" "$(.venv) " (set_color normal) (_old_fish_prompt)
---
>         if test -n "(.venv) "
>             printf "%s%s%s" "(.venv) " (set_color normal) (_old_fish_prompt)

The added dollar signs are the issue. Removing them fixes the problem.

For the record:

> fish --version
fish, version 2.2.0

And here's the actual error message, the same as in the png:

> . .venv/bin/activate.fish 
$(...) is not supported. In fish, please use '(.venv)'.
.venv/bin/activate.fish (line 58):         if test -n "$(.venv) "
                                                       ^
from sourcing file .venv/bin/activate.fish
	called on line 151 of file /usr/share/fish/config.fish

in function “.”
	called on standard input

source: Error while reading file “.venv/bin/activate.fish”