makes install available for all users in docker image (psf#3202)

* makes install available for all users in docker image

moves the installation path from /root/.local to a
virtualenv. this way we still get the lightweight
multistage build without excluding non-root users.

* adds changelog entry for docker-image fix

A changelog entry has been added under the Integration
subheader

* changes dockerfile to use the venv activate script

we are now using the inbuilt venv activate script, as well
as explicitly mentioning the binary location in the entrypoint
cmd.

Co-authored-by: Nicolò <nicolo.intrieri@spinforward.it>
Co-authored-by: Cooper Lees <me@cooperlees.com>

CHANGES.md

@@ -47,6 +47,8 @@
 <!-- For example, Docker, GitHub Actions, pre-commit, editors -->
 
 - Vim plugin: prefix messages with `Black: ` so it's clear they come from Black (#3194)
+- Docker: changed to a /opt/venv installation + added to PATH to be available to
+  non-root users (#3202)
 
 ### Output
 

Dockerfile

@@ -2,16 +2,18 @@ FROM python:3-slim AS builder
 
 RUN mkdir /src
 COPY . /src/
-RUN pip install --no-cache-dir --upgrade pip setuptools wheel \
+ENV VIRTUAL_ENV=/opt/venv
+RUN python -m venv $VIRTUAL_ENV
+RUN . /opt/venv/bin/activate && pip install --no-cache-dir --upgrade pip setuptools wheel \
     # Install build tools to compile dependencies that don't have prebuilt wheels
     && apt update && apt install -y git build-essential \
     && cd /src \
-    && pip install --user --no-cache-dir .[colorama,d]
+    && pip install --no-cache-dir .[colorama,d]
 
 FROM python:3-slim
 
 # copy only Python packages to limit the image size
-COPY --from=builder /root/.local /root/.local
-ENV PATH=/root/.local/bin:$PATH
+COPY --from=builder /opt/venv /opt/venv
+ENV PATH="/opt/venv/bin:$PATH"
 
-CMD ["black"]
+CMD ["/opt/venv/bin/black"]