Add devcontainer-feature config

Author: gghcode

devcontainer-features.json

@@ -0,0 +1,17 @@
+{
+    "features": [
+        {
+            "id": "asdf",
+            "name": "asdf Feature",
+            "options": {
+                "version": {
+                    "type": "string",
+                    "proposals": [ "v0.10.2" ],
+                    "default": "v0.10.2",
+                    "description": "Select asdf version"
+                }
+            },
+            "include": ["ubuntu"]
+        }
+    ]
+}

install.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+set -e
+
+# The install.sh script is the installation entrypoint for any dev container 'features' in this repository. 
+#
+# The tooling will parse the devcontainer-features.json + user devcontainer, and write 
+# any build-time arguments into a feature-set scoped "devcontainer-features.env"
+# The author is free to source that file and use it however they would like.
+set -a
+. ./devcontainer-features.env
+set +a
+
+if [ ! -z ${_BUILD_ARG_ASDF} ]; then
+    echo "Activating feature 'asdf'"
+
+    # Build args are exposed to this entire feature set following the pattern:  _BUILD_ARG_<FEATURE ID>_<OPTION NAME>
+    VERSION=${_BUILD_ARG_ASDF_VERSION}
+
+    git clone https://github.com/asdf-vm/asdf.git ~/.asdf --branch $VERSION
+
+    echo ". $HOME/.asdf/asdf.sh" >> ~/.bashrc
+fi