scripts: merge_config: add strict mode to fail upon any redefinition

When merging configuration fragments, it might be of interest to
identify mismatches (redefinitions) programmatically. Hence add the
option -s (strict mode) to instruct merge_config.sh to bail out in
case any redefinition has been detected.

With strict mode, warnings are emitted as before, but the script
terminates with rc=1. If -y is set to define "builtin having
precedence over modules", fragments are still allowed to set =m (while
the base config has =y). Strict mode will tolerate that as demotions
from =y to =m are ignored when setting -y.

Signed-off-by: Matthias Maennich <maennich@google.com>
Reviewed-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/kconfig/merge_config.sh

@@ -28,6 +28,7 @@ usage() {
 	echo "  -r    list redundant entries when merging fragments"
 	echo "  -y    make builtin have precedence over modules"
 	echo "  -O    dir to put generated output files.  Consider setting \$KCONFIG_CONFIG instead."
+	echo "  -s    strict mode. Fail if the fragment redefines any value."
 	echo
 	echo "Used prefix: '$CONFIG_PREFIX'. You can redefine it with \$CONFIG_ environment variable."
 }
@@ -37,6 +38,7 @@ ALLTARGET=alldefconfig
 WARNREDUN=false
 BUILTIN=false
 OUTPUT=.
+STRICT=false
 CONFIG_PREFIX=${CONFIG_-CONFIG_}
 
 while true; do
@@ -75,6 +77,11 @@ while true; do
 		shift 2
 		continue
 		;;
+	"-s")
+		STRICT=true
+		shift
+		continue
+		;;
 	*)
 		break
 		;;
@@ -141,6 +148,9 @@ for ORIG_MERGE_FILE in $MERGE_LIST ; do
 			echo Previous  value: $PREV_VAL
 			echo New value:       $NEW_VAL
 			echo
+			if [ "$STRICT" = "true" ]; then
+				STRICT_MODE_VIOLATED=true
+			fi
 		elif [ "$WARNREDUN" = "true" ]; then
 			echo Value of $CFG is redundant by fragment $ORIG_MERGE_FILE:
 		fi
@@ -153,6 +163,11 @@ for ORIG_MERGE_FILE in $MERGE_LIST ; do
 	cat $MERGE_FILE >> $TMP_FILE
 done
 
+if [ "$STRICT_MODE_VIOLATED" = "true" ]; then
+	echo "The fragment redefined a value and strict mode had been passed."
+	exit 1
+fi
+
 if [ "$RUNMAKE" = "false" ]; then
 	cp -T -- "$TMP_FILE" "$KCONFIG_CONFIG"
 	echo "#"