modulecmd: use/unuse group while loading an overlay

Pmodules/libpmodules.bash.in

@@ -114,6 +114,7 @@ declare -A OverlayConfigKeys=(
 	['default_relstage']='unstable'
 	['layout']='Pmodules'
 	['has_additional_modulepaths']='false'
+	['groups']=''
 )
 
 declare -A OverlayPathConfigKeys=(
@@ -382,13 +383,13 @@ pm::read_config(){
 					esac
 					OverlayInfo[${ol_name}:${key}]="${value}"
 					;;
-				conflicts | excludes )
+				conflicts | excludes | groups)
 					yml::get_seq value yaml_input "${node}.${key}" '!!seq'
 					local -a tmp_array=()
 					readarray -t tmp_array <<<${value}
-					local excludes=''
-					printf -v excludes "%s:" "${tmp_array[@]}"
-					OverlayInfo[${ol_name}:${key}]=$(${envsubst} <<<"${excludes%:}" )
+					local -- tmp_str=''
+					printf -v tmp_str "%s:" "${tmp_array[@]}"
+					OverlayInfo[${ol_name}:${key}]=$(${envsubst} <<<"${tmp_str%:}" )
 					;;
 				path_config )
 					yml::get_value value yaml_input "${node}.${key}" '!!seq'

Pmodules/modulecmd.bash.in

@@ -1899,6 +1899,26 @@ subcommand_use() {
 					MaskedGroups[${group}]="${ol_name}:${MaskedGroups[${group}]}"
 				done
 			fi
+			if [[ -n "${OverlayInfo[${ol_name}:groups]}" ]]; then
+				local -- grp_changes=':'
+				local -a groups=()
+				IFS=':' read -r -a groups <<< "${OverlayInfo[${ol_name}:groups]}"
+				local -- group=''
+				for group in "${groups[@]}"; do
+					if [[ "${group:0:1}" == '~' ]]; then
+						if [[ ":${UsedGroups}:" == *:${group:1}:* ]]; then
+							subcommand_unuse "${group:1}"
+							grp_changes+="${group}:"
+						fi
+					else
+						if [[ ":${UsedGroups}:" != *:${group}:* ]]; then
+							use_group "${group}"
+							grp_changes+="${group}:"
+						fi
+					fi
+				done
+				OverlayInfo[${ol_name}:grp_changes]="${grp_changes:0: -1}"
+			fi
 			scan_groups "${ol_name}"
                         for group in ${UsedGroups//:/ }; do
                                 local dir="${OverlayInfo[${ol_name}:modulefiles_root]}/"
@@ -2102,6 +2122,23 @@ subcommand_unuse() {
 					std::prepend_path MODULEPATH "${dir}"
 				done
 			fi
+			if [[ -n "${OverlayInfo[${ol_name}:groups]}" ]]; then
+				local -a groups=()
+				IFS=':' read -r -a groups <<< "${OverlayInfo[${ol_name}:grp_changes]}"
+				local -- group=''
+				for group in "${groups[@]}"; do
+					if [[ "${group:0:1}" == '~' ]]; then
+						if [[ ":${UsedGroups}:" != *:${group:1}:* ]]; then
+							subcommand_use "${group:1}"
+						fi
+					else
+						if [[ ":${UsedGroups}:" == *:${group}:* ]]; then
+							unuse_group "${group}"
+						fi
+					fi
+				done
+				OverlayInfo[${ol_name}:grp_changes]=':'
+			fi
 
 			# rebuild exclude list.
 			# Note: