add a 'ta delete' subcommand

cli/src/argparse/subcommand.rs

@@ -218,6 +218,7 @@ impl Modify {
                 "start" => modification.active = Some(true),
                 "stop" => modification.active = Some(false),
                 "done" => modification.status = Some(Status::Completed),
+                "delete" => modification.status = Some(Status::Deleted),
                 "annotate" => {
                     // what would be parsed as a description is, here, used as the annotation
                     if let DescriptionMod::Set(s) = modification.description {
@@ -243,6 +244,7 @@ impl Modify {
                     arg_matching(literal("start")),
                     arg_matching(literal("stop")),
                     arg_matching(literal("done")),
+                    arg_matching(literal("delete")),
                     arg_matching(literal("annotate")),
                 )),
                 Modification::parse,
@@ -297,10 +299,19 @@ impl Modify {
                 Mark all tasks matching the required filter as completed, additionally applying any given
                 modifications.",
         });
+        u.subcommands.push(usage::Subcommand {
+            name: "delete",
+            syntax: "<filter> delete [modification]",
+            summary: "Mark tasks as deleted",
+            description: "
+                Mark all tasks matching the required filter as deleted, additionally applying any given
+                modifications.  Deleted tasks remain until they are expired in a 'ta gc' operation at
+                least six months after their last modification.",
+        });
         u.subcommands.push(usage::Subcommand {
             name: "annotate",
             syntax: "<filter> annotate [modification]",
-            summary: "Mark tasks as completed",
+            summary: "Annotate a task",
             description: "
                 Add an annotation to all tasks matching the required filter.",
         });
@@ -761,6 +772,23 @@ mod test {
         );
     }
 
+    #[test]
+    fn test_delete() {
+        let subcommand = Subcommand::Modify {
+            filter: Filter {
+                conditions: vec![Condition::IdList(vec![TaskId::WorkingSetId(123)])],
+            },
+            modification: Modification {
+                status: Some(Status::Deleted),
+                ..Default::default()
+            },
+        };
+        assert_eq!(
+            Subcommand::parse(argv!["123", "delete"]).unwrap(),
+            (&EMPTY[..], subcommand)
+        );
+    }
+
     #[test]
     fn test_annotate() {
         let subcommand = Subcommand::Modify {