armbian-next: officially support WSL2; pester user for UTF-8 terminal

- new `wsl2.sh` file with WSL2-related functions; checking/validating/pestering user; allow WSL2 (not WSL1)

Co-authored-by: Ricardo Pardini <ricardo@pardini.net>

lib/functions/host/prepare-host.sh

@@ -9,6 +9,7 @@ function prepare_host() {
 	# Those are not logged, and might be interactive.
 	display_alert "Checking" "host" "info"
 	obtain_and_check_host_release_and_arch # sets HOSTRELEASE and validates it for sanity; also HOSTARCH
+	check_windows_wsl2                     # checks if on Windows, on WSL2, (not 1) and exits if not supported
 	check_host_has_enough_disk_space       # Checks disk space and exits if not enough
 	wait_for_package_manager               # wait until dpkg is not locked...
 

lib/functions/host/wsl2.sh

@@ -0,0 +1,45 @@
+function check_windows_wsl2() {
+	declare wsl2_type
+	wsl2_detect_type
+	case "${wsl2_type}" in
+		"none")
+			return 0 # not on any type of WSDL1/2/Windows, move along
+			;;
+		"WSL2")
+			display_alert "Detected WSL2 - experimental support" "Windows Subsystem for Linux 2" "info"
+			wsl2_pester_user_for_terminal # Pester user for a correct terminal
+			return 0
+			;;
+		*)
+			exit_with_error "Unsupported Windows scenario: ${wsl2_type}"
+			;;
+	esac
+}
+
+function wsl2_pester_user_for_terminal() {
+	[[ "x${SSH_CLIENT}x" != "xx" ]] && return 0 # not if being accessed over SSH
+	[[ "x${WT_SESSION}x" != "xx" ]] && return 0 # WT_SESSION from Windows Terminal # From info in https://stackoverflow.com/questions/59733731/how-to-detect-if-running-in-the-new-windows-terminal
+
+	if [[ "${PESTER_TERMINAL}" != "no" ]]; then # Or, send a PR with detection code for your favorite Windows UTF-8 capable terminal.
+		display_alert "Please use a terminal that supports UTF-8. For example:" "Windows Terminal" "warn"
+		display_alert "Get it at the Microsoft Store" "https://apps.microsoft.com/store/detail/windows-terminal/9N0DX20HK701" "warn"
+		exit_if_countdown_not_aborted 10 "WSL2 Terminal does not support UTF-8" # This pauses & exits if error if ENTER is not pressed in 10 seconds
+	fi
+
+	return 0
+}
+
+# From info in https://github.com/microsoft/WSL/issues/4071
+function wsl2_detect_type() {
+	wsl2_type="none" # outer scope var
+	declare unameOut
+	unameOut="$(uname -a)"
+	case "${unameOut}" in
+		*"microsoft-standard-WSL2"*) wsl2_type="WSL2" ;;
+		*"Microsoft"*) wsl2_type="WSL1" ;; # @TODO: do these catch Azure? send a PR!
+		*"microsoft"*) wsl2_type="WSL2" ;;
+		"CYGWIN"*) wsl2_type="cygwin" ;;
+		"MINGW"*) wsl2_type="windows" ;;
+		*"Msys") wsl2_type="windows" ;;
+	esac
+}

lib/library-functions.sh

@@ -568,6 +568,15 @@ set -o errexit  ## set -e : exit the script if any statement returns a non-true
 # shellcheck source=lib/functions/host/vagrant.sh
 source "${SRC}"/lib/functions/host/vagrant.sh
 
+# no errors tolerated. invoked before each sourced file to make sure.
+#set -o pipefail  # trace ERR through pipes - will be enabled "soon"
+#set -o nounset   ## set -u : exit the script if you try to use an uninitialised variable - one day will be enabled
+set -o errtrace # trace ERR through - enabled
+set -o errexit  ## set -e : exit the script if any statement returns a non-true return value - enabled
+### lib/functions/host/wsl2.sh
+# shellcheck source=lib/functions/host/wsl2.sh
+source "${SRC}"/lib/functions/host/wsl2.sh
+
 # no errors tolerated. invoked before each sourced file to make sure.
 #set -o pipefail  # trace ERR through pipes - will be enabled "soon"
 #set -o nounset   ## set -u : exit the script if you try to use an uninitialised variable - one day will be enabled