lsblk: force tree on --json --tree independently on used columns

Signed-off-by: Karel Zak <kzak@redhat.com>

2 files changed, 13 insertions, 2 deletions

diff --git a/misc-utils/lsblk.8 b/misc-utils/lsblk.8
index 07cd7a16f..320158278 100644
--- a/misc-utils/lsblk.8
+++ b/misc-utils/lsblk.8
@@ -90,7 +90,8 @@ The filter is applied to the top-level devices only. This maybe be confusing for
 Use ASCII characters for tree formatting.
 .TP
 .BR \-J , " \-\-json"
-Use JSON output format.
+Use JSON output format.  It's strongly recommended to use \fB\-\-output\fR and
+also \fB\-\-tree\fR if necessary.
 .TP
 .BR \-l , " \-\-list"
 Produce output in the form of a list. The output does not provide information
@@ -111,7 +112,8 @@ Do not print a header line.
 .BR \-o , " \-\-output " \fIlist\fP
 Specify which output columns to print.  Use
 .B \-\-help
-to get a list of all supported columns.
+to get a list of all supported columns.  The columns may affect tree-like output.
+The default is to use tree for the column 'NAME' (see also \fB\-\-tree\fR).
 
 The default list of columns may be extended if \fIlist\fP is
 specified in the format \fI+list\fP (e.g. \fBlsblk -o +UUID\fP).
diff --git a/misc-utils/lsblk.c b/misc-utils/lsblk.c
index 454f067c8..3e9b96a4d 100644
--- a/misc-utils/lsblk.c
+++ b/misc-utils/lsblk.c
@@ -2054,6 +2054,15 @@ int main(int argc, char *argv[])
 		if (lsblk->dedup_hidden && lsblk->dedup_id == id)
 			fl |= SCOLS_FL_HIDDEN;
 
+		if (force_tree
+		    && lsblk->flags & LSBLK_JSON
+		    && has_tree_col == 0
+		    && i + 1 == ncolumns)
+			/* The "--tree --json" specified, but no column with
+			 * SCOLS_FL_TREE yet; force it for the last column
+			 */
+			fl |= SCOLS_FL_TREE;
+
 		cl = scols_table_new_column(lsblk->table, ci->name, ci->whint, fl);
 		if (!cl) {
 			warn(_("failed to allocate output column"));