Enable Binder environment for PRs

.github/workflows/binder-dockerfile

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+# Dockerfile for Binder
+# Reference: https://mybinder.readthedocs.io/en/latest/tutorials/dockerfile.html
+
+# Pull the Sage docker image
+FROM ghcr.io/sagemath/sage/sage-ubuntu-focal-standard-with-targets:dev
+
+USER root
+
+# Remove warnings
+ENV DEBIAN_FRONTEND noninteractive
+ENV DEBCONF_NOWARNINGS="yes"
+
+# Install system packages
+RUN apt-get update
+RUN apt-get install -y apt-utils
+RUN apt-get install -y git
+RUN apt-get install -y sudo
+RUN apt-get install -y python3-pip
+
+# Recommended system packages for latex
+# RUN apt-get install -y texlive
+# RUN apt-get install -y texlive-luatex
+# RUN apt-get install -y preview-latex-style
+# RUN apt-get install -y fonts-freefont-otf
+# RUN apt-get install -y xindy
+# RUN apt-get install -y imagemagick
+
+# Install jupyterlab
+RUN python3 -m pip install --no-warn-script-location jupyterlab
+
+# Disable the pupup of Jupyter news
+RUN jupyter labextension disable "@jupyterlab/apputils-extension:announcements"
+
+# Create the user alice with uid 1000 and password alice
+ARG NB_USER=alice
+ARG NB_UID=1000
+ENV NB_USER alice
+ENV NB_UID 1000
+ENV HOME /home/${NB_USER}
+RUN adduser --disabled-password --gecos "Default user" --uid ${NB_UID} ${NB_USER}
+RUN echo 'alice:alice' | chpasswd
+
+# Allow the user to sudo (presently not working in Binder)
+RUN echo "${NB_USER} ALL=(ALL) NOPASSWD: ALL" > /etc/sudoers
+
+# Prepare for building Sage
+ENV PR_REPO https://github.com/REPO_NAME
+ENV PR_BRANCH BRANCH_NAME
+ENV BINDER_BRANCH sagemath-environment
+
+# Build Sage incrementally
+WORKDIR /sage
+RUN export PATH="/sage/build/bin:$PATH"
+RUN git config --global user.email ${NB_USER}@wonderland
+RUN git config --global user.name ${NB_USER}
+RUN git config --global --add safe.directory $(pwd)
+COPY .gitignore /sage/.gitignore
+RUN if [ ! -d .git ]; then git init && git add -A; fi
+RUN git fetch ${PR_REPO} ${PR_BRANCH}
+RUN git checkout -f -b ${BINDER_BRANCH} FETCH_HEAD
+RUN ./bootstrap && ./configure --enable-build-as-root && make -j4 build
+
+# Make sure the contents of the notebooks directory are in ${HOME}
+COPY notebooks/* ${HOME}/
+RUN chown -R ${NB_UID} ${HOME}
+
+# Install jupyterlab to Sage
+RUN /sage/sage -pip install --no-warn-script-location jupyterlab
+
+# Install Sage packages
+# RUN /sage/sage -i <spkg-name>
+
+# Switch to the user
+USER ${NB_USER}
+
+# This is where kernels are installed
+RUN mkdir -p $(jupyter --data-dir)/kernels
+
+# Install sagemath kernel
+RUN ln -s /sage/venv/share/jupyter/kernels/sagemath $(jupyter --data-dir)/kernels
+
+# Start in the home directory of the user
+WORKDIR /home/${NB_USER}

.github/workflows/binder.yml

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+name: Create Binder branch
+
+# How to use this workflow
+#
+# (1) Go to your forked Sage repo
+# (2) In the Actions tab, find "Create Binder branch" workflow
+# (3) Run the workflow with your PR branch named say "contribution"
+# (4) Wait for the workflow run to finish
+# (5) In the Code tab, select the new "contribution-binder" branch
+# (6) Find the Binder badge in README.md
+# (7) Copy the Binder badge from README.md (in edit mode)
+# (8) Paste the Binder badge into the description of your PR in the sagemath/sage repo
+# (9) Click the Binder badge to start creating the Binder environment
+# (10) Leave it open and come back after an hour.
+# (11) The Binder badge is now ready for reviewers of your PR
+
+on: workflow_dispatch
+
+jobs:
+  create-branch:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Create binder branch
+        run: |
+          set -ex
+          REPO_NAME=${{ github.repository }}
+          BRANCH_NAME=${GITHUB_REF#refs/heads/}
+          BINDER_REPO_NAME=${REPO_NAME}
+          BINDER_BRANCH_NAME=${BRANCH_NAME}-binder
+          cp .github/workflows/binder-dockerfile Dockerfile
+          sed -i 's/REPO_NAME/'$(echo "${REPO_NAME}" | sed 's/\//\\\//g')'/' Dockerfile
+          sed -i 's/BRANCH_NAME/'$(echo "${BRANCH_NAME}" | sed 's/\//\\\//g')'/' Dockerfile
+          sed -i 's/sagemath\/sage-binder-env\/master/'$(echo "${BINDER_REPO_NAME}/${BINDER_BRANCH_NAME}" | sed 's/\//\\\//g')'/' README.md
+          if [ ! -d .git ]; then git init; fi
+          if [ ! -d notebooks ]; then mkdir notebooks && touch notebooks/my_favorite_notebooks.md; fi
+          git config --global user.email alice@wonderland
+          git config --global user.name Alice
+          git config --global --add safe.directory $(pwd)
+          git checkout -b $BINDER_BRANCH_NAME
+          git add -A
+          git commit -a -m "Binder environment for '${BRANCH_NAME}' branch"
+          git push -f origin $BINDER_BRANCH_NAME