Add Java Development Environment 21 (#58)

Some tools (specifically PlantUML in this case) require a JDK, hence we install it. Bazel's rules_java requires that JAVA_HOME is set appropriately, so we do that as well.

Author: opajonk

src/s-core-devcontainer/.devcontainer/s-core-local/install.sh

@@ -41,6 +41,12 @@ apt-get install -y python${python_version} python3-pip python3-venv
 # devcontainer feature "python" (cf. https://github.com/devcontainers/features/tree/main/src/python )
 apt-get install -y flake8 python3-autopep8 black python3-yapf mypy pydocstyle pycodestyle bandit pipenv virtualenv python3-pytest pylint
 
+# OpenJDK 21, via APT
+# Set JAVA_HOME environment variable system-wide, since some tools rely on it (e.g., Bazel's rules_java)
+apt-get install -y openjdk-21-jdk-headless="${openjdk_21_version}*"
+export JAVA_HOME="$(dirname $(dirname $(realpath $(which javac))))"
+echo "export JAVA_HOME=\"$(dirname $(dirname $(realpath $(which javac))))\"" > /etc/profile.d/java_home.sh
+
 # Bazelisk, directly from GitHub
 # Using the existing devcontainer feature is not optimal:
 # - it does not check the SHA256 checksum of the downloaded file

src/s-core-devcontainer/.devcontainer/s-core-local/tests/test_default.sh

@@ -41,6 +41,10 @@ check "validate buildifier is working and has the correct version" bash -c "buil
 check "validate starpls is working and has the correct version" bash -c "starpls version | grep '${starpls_version}'"
 check "validate bazel-compile-commands is working and has the correct version" bash -c "bazel-compile-commands --version 2>&1 | grep '${bazel_compile_commands_version}'"
 
+# OpenJDK
+check "validate java is working and has the correct version" bash -c "java -version 2>&1 | grep '${openjdk_21_version}'"
+check "validate JAVA_HOME is set correctly" bash -c 'echo $JAVA_HOME | xargs readlink -f | grep "java-21-openjdk"'
+
 # additional developer tools
 check "validate gdb is working and has the correct version" bash -c "gdb --version | grep '${gdb_version}'"
 check "validate gh is working and has the correct version" bash -c "gh --version | grep '${gh_version}'"

src/s-core-devcontainer/.devcontainer/s-core-local/versions.yaml

@@ -25,6 +25,9 @@ gdb:
 gh:
   version: "2.45.0"
 
+openjdk_21:
+  version: "21.0.9"
+
 bazel:
   # https://github.com/bazelbuild/bazel/releases -- latest version as of 2025-09-24
   version: 8.4.1

scripts/test-utils.sh …-devcontainer/test-project/test-utils.shscripts/test-utils.sh renamed to src/s-core-devcontainer/test-project/test-utils.sh scripts/test-utils.sh renamed to src/s-core-devcontainer/test-project/test-utils.sh

@@ -3,7 +3,8 @@ set -euo pipefail
 
 SCRIPT_PATH=$(readlink -f "$0")
 SCRIPT_DIR=$(dirname -- "${SCRIPT_PATH}")
-source "${SCRIPT_DIR}/../../../scripts/test-utils.sh" vscode
+
+source "test-utils.sh" vscode
 
 # C++ tooling
 check "validate clangd is working and has the correct version" bash -c "clangd --version | grep '20.1.8'"