devcontainers lack bash-completion

[thetredev]

I was messing around with devcontainers lately and I realized that there was no bash completion for the docker command inside a devcontainer with the docker-in-docker feature enabled like this:

"features": {
    "ghcr.io/devcontainers/features/docker-in-docker:2": {
      "version": "latest",
      "moby": true,
      "azureDnsAutoDetection": false,
      "defaultDockerAddressPool": "172.19.0.0/16,size=24",
      "installDockerBuildx": true
    }
  }

I boiled it down to .bashrc not being evaluated, because the shell that is launched inside the devcontainer is not a login shell (e.g., /bin/bash called without -l). This is also the case for the mcr.microsoft.com/devcontainers/base image for example, which has the following values for ENTRYPOINT and CMD:

"Cmd": [
  "bash"
],
"Entrypoint": null,

I tried pointing the devcontainer to a Dockerfile with modified ENTRYPOINT and CMD to no avail:

{
  "name": "Test container",
  "build": {
    "dockerfile": "Dockerfile"
  }
}

FROM mcr.microsoft.com/devcontainers/python:3.12-bookworm

ENTRYPOINT [ "/bin/bash", "-l" ]
CMD []

Is there anything we can do from the user side to workaround the issue? It would be best if VS Code would run a login shell inside the devcontainer but I guess that is a VS Code issue rather than a devcontainer one, so I guess a workaround would be fine, considering that you might not even want a login shell in certain scenarios.

[thetredev]

The easiest way to reproduce it is with the following Dockerfile:

FROM mcr.microsoft.com/devcontainers/base:bookworm

RUN distro=$(. /etc/os-release && echo "$ID") \
    && distro_version=$(. /etc/os-release && echo "$VERSION_CODENAME") \
    && apt-get -y update \
    && apt-get -y install \
        ca-certificates \
        curl \
        gnupg2 \
        bash-completion \
    && install -m 0755 -d /etc/apt/keyrings \
    && curl -fsSL https://download.docker.com/linux/${distro}/gpg -o /etc/apt/keyrings/docker.asc \
    && chmod a+r /etc/apt/keyrings/docker.asc \
    && mkdir -p /etc/apt/sources.list.d \
    && echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/${distro} ${distro_version} stable" > /etc/apt/sources.list.d/docker.list \
    && apt-get -y update \
    && apt-get install -y \
        docker-ce \
        docker-ce-cli \
        containerd.io \
        docker-buildx-plugin \
        docker-compose-plugin

# these are not needed, but it's better to explicitly unset them to have a defined baseline for testing
ENTRYPOINT []
CMD []

and running one of these commands after building the image:

# bash completion via TAB key for the docker command is not available:
docker run --rm -it <image previously built> bash

# bash completion via TAB key for the docker command is available:
docker run --rm -it <image previously built> bash -l