Added Scala (Community) definition.

containers/scala/.devcontainer/Dockerfile

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+# [Choice] Java version (use -bullseye variants on local arm64/Apple Silicon): 11, 17, 11-bullseye, 17-bullseye, 11-buster, 17-buster
+ARG VARIANT="17"
+FROM mcr.microsoft.com/vscode/devcontainers/java:0-${VARIANT}
+
+# [Optional] Scala version (leave blank for latest)
+ARG SCALA_VERSION=""
+
+# [Option] Install Mill
+ARG INSTALL_MILL="false"
+
+# [Option] Install SBT
+ARG INSTALL_SBT="false"
+
+# [Option] Install Clang (required for Scala Native)
+ARG INSTALL_CLANG="false"
+
+RUN curl -fLJ -o /usr/local/bin/scala-cli https://github.com/Virtuslab/scala-cli/releases/latest/download/scala-cli && \
+    chmod +x /usr/local/bin/scala-cli && \
+    su vscode -c "scala-cli compile . --scala=${SCALA_VERSION}"
+
+RUN if [ "${INSTALL_MILL}" = "true" ]; then \
+    curl -o /usr/local/bin/mill https://raw.githubusercontent.com/lefou/millw/main/millw && \
+    chmod +x /usr/local/bin/mill && \
+    (cd /tmp; su vscode -c "mill resolve _"); fi
+
+RUN if [ "${INSTALL_SBT}" = "true" ]; then \
+    echo "deb [signed-by=/usr/share/keyrings/sbt-archive-keyring.gpg] https://repo.scala-sbt.org/scalasbt/debian all main" | sudo tee /etc/apt/sources.list.d/sbt.list && \
+    echo "deb [signed-by=/usr/share/keyrings/sbt-archive-keyring.gpg] https://repo.scala-sbt.org/scalasbt/debian /" | sudo tee /etc/apt/sources.list.d/sbt_old.list && \
+    curl -sL "https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x2EE0EA64E40A89B84B2DF73499E82A75642AC823" | gpg --dearmor | sudo tee /usr/share/keyrings/sbt-archive-keyring.gpg > /dev/null && \
+    sudo apt-get update && \
+    sudo apt-get install sbt && \
+    (cd /tmp; su vscode -c "sbt --version") && \
+    rm -rf /var/lib/apt/lists/*; fi
+
+RUN if [ "${INSTALL_CLANG}" = "true" ]; then apt-get update && apt-get -y install clang && su vscode -c "scala-cli compile . --native" && rm -rf /var/lib/apt/lists/*; fi
+
+# [Choice] Node.js version: none, lts/*, 16, 14, 12, 10
+ARG NODE_VERSION="none"
+RUN if [ "${NODE_VERSION}" != "none" ]; then su vscode -c "umask 0002 && . /usr/local/share/nvm/nvm.sh && nvm install ${NODE_VERSION} 2>&1"; fi
+
+# [Optional] Uncomment this section to install additional OS packages.
+# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+#     && apt-get -y install --no-install-recommends <your-package-list-here>
+
+# [Optional] Uncomment this line to install global node packages.
+# RUN su vscode -c "source /usr/local/share/nvm/nvm.sh && npm install -g <your-package-here>" 2>&1

containers/scala/.devcontainer/devcontainer.json

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+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.205.2/containers/java
+{
+  "name": "Scala (Community)",
+  "build": {
+    "dockerfile": "Dockerfile",
+    "args": {
+      // Update the VARIANT arg to pick a Java version: 11, 17
+      // Append -bullseye or -buster to pin to an OS version.
+      // Use the -bullseye variants on local arm64/Apple Silicon.
+      "VARIANT": "17",
+      // Options
+      "INSTALL_MILL": "false",
+      "INSTALL_SBT": "false",
+      "NODE_VERSION": "lts/*"
+    }
+  },
+
+  "settings": {
+    "java.jdt.ls.java.home": "/docker-java-home"
+  },
+
+  "extensions": [
+    "vscjava.vscode-java-pack",
+    "scala-lang.scala",
+    "scalameta.metals"
+  ],
+
+  // Use 'forwardPorts' to make a list of ports inside the container available locally.
+  // "forwardPorts": [],
+
+  // Use 'postCreateCommand' to run commands after the container is created.
+  // "postCreateCommand": "scala-cli --version",
+
+  // Comment out connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+  "remoteUser": "vscode"
+}

containers/scala/.npmignore

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+test-project
+README.md
+.npmignore

containers/scala/README.md

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+# Scala (Community)
+
+## Summary
+
+*Develop Scala applications. Includes the Metals and Scala Syntax extensions.*
+
+| Metadata                    | Value                 |
+|-----------------------------|-----------------------|
+| *Contributors*              | @heksesang            |
+| *Categories*                | Community, Languages  |
+| *Definition Type*           | Dockerfile            |
+| *Works in Codespaces*       | Yes                   |
+| *Container host OS support* | Linux, MacOS, Windows |
+| *Container OS*              | Debian                |
+| *Languages, platforms*      | Scala                 |
+
+## Using this definition
+
+While this definition should work unmodified, you can select the version of Java the container uses by updating the `VARIANT` arg in the included `devcontainer.json` (and rebuilding if you've already created the container).
+
+```json
+// Or you can use 17-bullseye or 17-buster if you want to pin to an OS version
+"args": { "VARIANT": "17" }
+```
+
+### Installing a specific Scala Version
+
+You can set the default Scala version that is pre-loaded with Scala CLI by adding the `"SCALA_VERSION"` to the build arguments in `.devcontainer/devcontainer.json`.
+
+```json
+"args": {
+   "SCALA_VERSION": "2.13.5"
+}
+```
+
+### Installing Mill
+
+Mill can be installed by setting the `"INSTALL_MILL"` build argument to true in `.devcontainer/devcontainer.json`.
+
+```json
+"args": {
+   "INSTALL_MILL": "true"
+}
+```
+
+### Installing SBT
+
+SBT can be installed by setting the `"INSTALL_SBT"` build argument to true in `.devcontainer/devcontainer.json`.
+
+```json
+"args": {
+   "INSTALL_SBT": "true"
+}
+```
+
+### Installing Clang
+
+Scala Native is a compiler for Scala that targets native code, and depends on the Clang compiler frontend. You can enable support for this by setting the `"INSTALL_CLANG"` build argument to true in `.devcontainer/devcontainer.json`.
+
+```json
+"args": {
+   "INSTALL_CLANG": "true"
+}
+```
+
+### Adding the definition to your folder
+
+1. If this is your first time using a development container, please see getting started information on [setting up](https://aka.ms/vscode-remote/containers/getting-started) Remote-Containers or [creating a codespace](https://aka.ms/ghcs-open-codespace) using GitHub Codespaces.
+
+2. Start VS Code and open your project folder or connect to a codespace.
+
+3. Press <kbd>F1</kbd> select and **Add Development Container Configuration Files...** command for **Remote-Containers** or **Codespaces**.
+
+4. Select this definition. You may also need to select **Show All Definitions...** for it to appear.
+
+5. Finally, press <kbd>F1</kbd> and run **Remote-Containers: Reopen Folder in Container** or **Codespaces: Rebuild Container** to start using the definition.
+
+## Testing the definition
+
+This definition includes some test code that will help you verify it is working as expected on your system. Follow these steps:
+
+1. If this is your first time using a development container, please follow the [getting started steps](https://aka.ms/vscode-remote/containers/getting-started) to set up your machine.
+
+2. Clone this repository.
+
+3. Start VS Code, press <kbd>F1</kbd>, and select **Remote-Containers: Open Folder in Container...**
+
+4. Select the `containers/scala` folder.
+
+5. After the folder has opened in the container, press <kbd>Ctrl-Shift-`</kbd>
+   to open a new terminal.
+
+6. Run the following command to execute a simple application.
+   ```bash
+   scala-cli run test-project
+   ```
+
+7. You should see "Hello world!" in the terminal after the program executes.
+
+8. From here, you can add breakpoints or edit the contents of the `test-project` folder to do further testing.
+
+## License
+
+Licensed under the MIT License. See [LICENSE](https://github.com/microsoft/vscode-dev-containers/blob/main/LICENSE).

containers/scala/test-project/Hello.scala

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+//> using scala "3"
+
+@main def run =
+  println("Hello world!")