Switch to builtin venv instead of virtualenv

For our purposes, venv should be a drop-in replacement for
virtualenv, with the advantage that it's maintained in the
standard library and is a bit slimmer. Diffoscoping shows
internal changes to the activation scripts and entry points
but nothing that should functionally affect us.

SecureDrop server is already using venv for its packages, so this
brings us into alignment.

Also do a little cleanup on the dependencies because lintian started
complaining a bit more; ensure that both securedrop-client and
securedrop-export have explicit `python3` dependencies, and remove
the now obsolete `${python3:Depends}` magic dependencies.

debian/control

@@ -2,19 +2,19 @@ Source: securedrop-client
 Section: unknown
 Priority: optional
 Maintainer: SecureDrop Team <[email protected]>
-Build-Depends: debhelper-compat (= 11), dh-apparmor, dh-exec, python3-virtualenv, libssl-dev, pkg-config, libclang-dev, qubesdb-dev
+Build-Depends: debhelper-compat (= 11), dh-apparmor, dh-exec, python3-venv, libssl-dev, pkg-config, libclang-dev, qubesdb-dev
 Standards-Version: 3.9.8
 Homepage: https://github.com/freedomofpress/securedrop-client
 X-Python3-Version: >= 3.5
 
 Package: securedrop-client
 Architecture: any
-Depends: ${python3:Depends}, ${shlibs:Depends}, ${misc:Depends}, python3-pyqt5, python3-pyqt5.qtsvg, python3-qubesdb, desktop-file-utils
+Depends: ${shlibs:Depends}, ${misc:Depends}, python3, python3-pyqt5, python3-pyqt5.qtsvg, python3-qubesdb, desktop-file-utils
 Description: securedrop client for qubes workstation
 
 Package: securedrop-export
 Architecture: all
-Depends: ${python3:Depends}, ${misc:Depends}, udisks2, cups, printer-driver-brlaser, printer-driver-hpcups, system-config-printer, xpp, libcups2, gnome-disk-utility, libreoffice,
+Depends: ${misc:Depends}, python3, udisks2, cups, printer-driver-brlaser, printer-driver-hpcups, system-config-printer, xpp, libcups2, gnome-disk-utility, libreoffice,
  desktop-file-utils, shared-mime-info, libfile-mimeinfo-perl
 Description: Submission export scripts for SecureDrop Workstation
  This package provides scripts used by the SecureDrop Qubes Workstation to
@@ -27,7 +27,7 @@ Description: Provides an apt keyring for SecureDrop-related packages, so the mas
 
 Package: securedrop-log
 Architecture: all
-Depends: python3-distutils, ${misc:Depends}, ${python3:Depends}
+Depends: python3-distutils, ${misc:Depends}
 Description: Python module and qrexec service to store logs for SecureDrop Workstation
  This package provides Python module and qrexec service files to create a logging VM in
  SecureDrop Workstation project in Qubes.
@@ -56,7 +56,7 @@ Description: Whonix configuration for SecureDrop.
 
 Package: securedrop-workstation-config
 Architecture: all
-Depends: ${python3:Depends}, python3-qubesdb, rsyslog, mailcap, apparmor, nautilus, securedrop-keyring, xfce4-terminal
+Depends: python3-qubesdb, rsyslog, mailcap, apparmor, nautilus, securedrop-keyring, xfce4-terminal
 Description: This is the SecureDrop workstation template configuration package.
  This package provides dependencies and configuration for the Qubes SecureDrop workstation VM Templates.
 

debian/securedrop-client.lintian-overrides

@@ -21,3 +21,4 @@ securedrop-client: script-not-executable
 
 # This is our virtualenv's interpreter
 securedrop-client: unusual-interpreter
+securedrop-client: wrong-path-for-interpreter

debian/securedrop-export.lintian-overrides

@@ -21,6 +21,7 @@ securedrop-export: script-not-executable
 
 # This is our virtualenv's interpreter
 securedrop-export: unusual-interpreter
+securedrop-export: wrong-path-for-interpreter
 
 # This is intentional
 securedrop-export: file-in-etc-not-marked-as-conffile [etc/udisks2/tcrypt.conf]

debian/setup-venv.sh

@@ -11,7 +11,7 @@ fi
 WHEELS_DIR="/builder/securedrop-${NAME}/wheels"
 PIP_ARGS="--ignore-installed --no-index --find-links ${WHEELS_DIR} --no-deps --no-cache-dir --no-use-pep517"
 
-/usr/bin/python3 -m virtualenv $VENV_ARGS ./debian/securedrop-${NAME}/opt/venvs/securedrop-${NAME}
+/usr/bin/python3 -m venv $VENV_ARGS ./debian/securedrop-${NAME}/opt/venvs/securedrop-${NAME}
 ./debian/securedrop-${NAME}/opt/venvs/securedrop-${NAME}/bin/pip install $PIP_ARGS --require-hashes \
     -r ${NAME}/build-requirements.txt
 ./debian/securedrop-${NAME}/opt/venvs/securedrop-${NAME}/bin/pip install $PIP_ARGS ./${NAME}