Add default devcontainer using conda

.devcontainer/devcontainer.json

@@ -0,0 +1,35 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.245.2/containers/debian
+{
+	"name": "Conda",
+	"image": "mcr.microsoft.com/vscode/devcontainers/base:0-bullseye",
+
+	// Comment out to connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+	"remoteUser": "vscode",
+
+	// Setup conda environment
+	"onCreateCommand": ".devcontainer/onCreate-conda.sh",
+
+	// Install additional features.
+	"features": {
+		// For config options, see https://github.com/devcontainers/features/tree/main/src/conda
+		"ghcr.io/devcontainers/features/conda": {
+            "version": "latest",
+			"addCondaForge": "true"
+        }
+	},
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"guyskk.language-cython",
+				"ms-python.isort",
+				"ms-toolsai.jupyter",
+				"ms-python.vscode-pylance",
+				"ms-python.pylint",
+				"ms-python.python",
+				"lextudio.restructuredtext",
+				"trond-snekvik.simple-rst"
+			]
+		}
+	}
+}

.devcontainer/onCreate-conda.sh

@@ -0,0 +1,14 @@
+# Do not keep running on errors
+set -e
+
+# Create conda environment
+./bootstrap-conda
+conda install mamba -n base -c conda-forge -y
+mamba env create --file src/environment-dev.yml || mamba env update --file src/environment-dev.yml
+conda init bash
+
+# Build sage
+conda run -n sage-dev ./bootstrap
+conda run -n sage-dev ./configure --with-python=/opt/conda/envs/sage-dev/bin/python --prefix=/opt/conda/envs/sage-dev
+conda run -n sage-dev pip install --no-build-isolation -v -v -e ./pkgs/sage-conf ./pkgs/sage-setup 
+conda run -n sage-dev pip install --no-build-isolation -v -v -e ./src

.gitignore

@@ -221,9 +221,6 @@ src/ENV/
 src/env.bak/
 src/venv.bak/
 
-# devcontainer
-/.devcontainer/devcontainer.json
-
 # mypy
 **/.mypy_cache/
 

src/doc/en/developer/portability_testing.rst

@@ -1164,23 +1164,7 @@ provides sample ``devcontainer.json`` configuration files
 <https://github.com/sagemath/sage/tree/develop/.devcontainer/>`_ for this
 purpose.
 
-To get started, symlink (or copy) one of the sample files to
-``$SAGE_ROOT/.devcontainer/devcontainer.json``. For example, choose
-`$SAGE_ROOT/.devcontainer/portability-ubuntu-jammy-standard/devcontainer.json
-<https://github.com/sagemath/sage/tree/develop/.devcontainer/portability-ubuntu-jammy-standard/devcontainer.json>`_, which uses the Docker image based on ``ubuntu-jammy-standard``,
-the most recent
-development version of Sage (``dev`` tag), and a full installation of
-the Sage distribution (``with-targets``).
-
-In macOS for example, you can do this using the shell as follows::
-
-  [mkoeppe@sage sage] $ (cd .devcontainer && ln -s portability-ubuntu-jammy-standard/devcontainer.json .)
-
-Now start VS Code::
-
-  [mkoeppe@sage sage] $ code .
-
-Then VS Code may prompt you whether you would like to open the current
+If you open the sage folder in VS Code, it may prompt you whether you would like to open the current
 directory in the dev container (yes).  If it does not, use the command palette
 (:kbd:`Ctrl` + :kbd:`Shift` + :kbd:`P`), enter the command "Remote-Containers:
 Reopen Folder in Container" , and hit :kbd:`Enter`.
@@ -1225,8 +1209,7 @@ in a terminal, `open a new terminal in VS Code
    ``configure`` script.
 
 You can edit a copy of the configuration file to change to a different platform, another
-version, or build stage.  After editing the configuration file (or changing the
-symlink), run "Remote-Containers: Rebuild Container" from the command
+version, or build stage.  After editing the configuration file, run "Remote-Containers: Rebuild Container" from the command
 palette. See the `VS Code devcontainer.json reference
 <https://code.visualstudio.com/docs/remote/devcontainerjson-reference>`_
 and the `GitHub introduction to dev containers
@@ -1248,8 +1231,7 @@ installation of SageMath in this container by building from the current source t
   project <https://hub.docker.com/r/computop/sage/>`_, providing
   SnapPy, Regina, PHCPack, etc.
 
-If you want to use one of these ``devcontainer.json`` files, symlink (or copy)
-it and start VS Code as explained above. After VS Code finished configuring the
+After VS Code finished configuring the
 dev container, to use Sage in a terminal, `open a new terminal in VS Code
 <https://code.visualstudio.com/docs/terminal/basics>`_, type ``./sage`` and hit
 :kbd:`Enter`.
@@ -1284,8 +1266,7 @@ work without change) or to adapt them to your needs.
   project <https://hub.docker.com/r/computop/sage/>`_, providing
   SnapPy, Regina, PHCPack, etc.
 
-If you want to use one of these ``devcontainer.json`` files, symlink (or copy)
-it and start VS Code as explained above. After VS Code finished configuring the
+After VS Code finished configuring the
 dev container, to use Sage in a terminal, `open a new terminal in VS Code
 <https://code.visualstudio.com/docs/terminal/basics>`_, type ``sage`` and hit
 :kbd:`Enter`. (Do not use ``./sage``; this will not work because the source