chore(brew): Automatically install gcc if not present (#256)

modules/brew/README.md

@@ -16,6 +16,7 @@ The brew module installs [Homebrew / Linuxbrew](https://brew.sh/) on your system
 
 ### Build-time:
 
+- Necessary Brew package dependency `gcc` is installed if not present in the base image
 - Directories `/home/` & `/root/` are created
 - Empty `.dockerenv` file is created in the root of the image-builder, to convince official Brew installation script that we are **not** running as root
 - Official brew installation script is downloaded & executed

modules/brew/brew.sh

@@ -2,22 +2,24 @@
 
 set -euo pipefail
 
-# Convince the installer that we are in CI
-touch /.dockerenv
-
 # Debugging
 DEBUG="${DEBUG:-false}"
 if [[ "${DEBUG}" == true ]]; then
     set -x
 fi
 
-# Check if gcc is installed
-if ! command -v gcc &> /dev/null
-then
-    echo "ERROR: \"gcc\" package could not be found."
+# Check if gcc is installed & install it if it's not
+# (add VanillaOS package manager in the future when it gets supported)
+if ! command -v gcc &> /dev/null; then
+  if command -v rpm-ostree &> /dev/null; then
+    echo "Installing \"gcc\" package, which is necessary for Brew to function"
+    rpm-ostree install gcc
+  else
+    echo "ERROR: \"gcc\" package could not be found"
     echo "       Brew depends on \"gcc\" in order to function"
     echo "       Please include \"gcc\" in the list of packages to install with the system package manager"
     exit 1
+  fi  
 fi
 
 # Module-specific directories and paths
@@ -68,6 +70,9 @@ fi
 mkdir -p /var/home
 mkdir -p /var/roothome
 
+# Convince the installer that we are in CI
+touch /.dockerenv
+
 # Always install Brew
 echo "Downloading and installing Brew..."
 curl -Lo /tmp/brew-install https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh