debconf prompts not supressed for build-packages

[Evan]

$ snapcraft --version
snapcraft, version 3.0.1

```
build-packages:
      - wireshark
```

$ SNAPCRAFT_BUILD_ENVIRONMENT_CHANNEL_SNAPCRAFT=latest/edge snapcraft --shell-after
Launching a VM.
Launched: snapcraft-wireshark
2019-03-22T10:27:56Z INFO Waiting for restart...
core 16-2.37.4 from Canonical✓ installed
Channel latest/stable for core is closed; temporarily forwarding to stable.
SNAPCRAFT_BUILD_ENVIRONMENT_CHANNEL_SNAPCRAFT is set: installing snapcraft from latest/edge
snapcraft (edge) 3.2+git16.g841b41f from Canonical✓ installed
Channel latest/edge for snapcraft is closed; temporarily forwarding to edge.
core18 18 from Canonical✓ installed
Channel latest/stable for core18 is closed; temporarily forwarding to stable.
Hit:1 http://archive.ubuntu.com/ubuntu bionic InRelease
Get:2 http://archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
…
Setting up wireshark-common (2.6.6-1~ubuntu18.04.0) ...
debconf: unable to initialize frontend: Dialog
debconf: (No usable dialog-like program is installed, so the dialog based frontend cannot be used. at /usr/share/perl5/Debconf/FrontEnd/Dialog.pm line 76.)
debconf: falling back to frontend: Readline
Configuring wireshark-common
----------------------------

Dumpcap can be installed in a way that allows members of
the "wireshark" system group to capture packets. This is
recommended over the alternative of running
Wireshark/Tshark directly as root, because less of the
code will run with elevated privileges.

For more detailed information please see
/usr/share/doc/wireshark-common/README.Debian.

Enabling this feature may be a security risk, so it is
disabled by default. If in doubt, it is suggested to leave
it disabled.

Should non-superusers be able to capture packets? [yes/no]
Progress: [ 94%] [##################################...]

[Evan (ev)]

Wireshark's use of debconf is standard:

$ cat wireshark-common.config
#! /bin/sh

set -e

. /usr/share/debconf/confmodule

db_input high wireshark-common/install-setuid || true
db_go

exit 0

$ grep wireshark-common/install-setuid templates -A7
Template: wireshark-common/install-setuid
Type: boolean
Default: false
_Description: Should non-superusers be able to capture packets?
 Dumpcap can be installed in a way that allows members of the "wireshark"
 system group to capture packets. This is recommended over the
 alternative of running Wireshark/Tshark directly as root, because
 less of the code will run with elevated privileges.

[Evan (ev)]

As just discussed on "Unbreakable Snapcraft", we should neuter debconf so we never get prompts, regardless of whether the scripts respect DEBIAN_FRONTEND=noninteractive. One approach would be to replace /usr/share/debconf/confmodule with shell code that for any called function returns 0.

[Adam Conrad (adconrad)]

Neutering Debconf is a bit heavy-handed, and has literally never been necessary on Debian or Ubuntu buildds, so I'm not sure why Snapcraft would be special here. On buildd chroots, we set debconf to priority=critical and frontend=noninteractive, and I don't recall ever having an issue with that in the last decade or two.

(The obvious downside of neutering is if debconf is used to configure one of your build-dependencies and shorting out that configure step means that your build-dep isn't actually installed correctly)

[Sergio Schvezov (sergiusens)]

https://github.com/snapcore/snapcraft/pull/2600