forget json output: added id's in snapshots within reasons object

In order to evaluate the keep reasons for snapshots, there should be also the id's
to compare it with snapshots within the keep object. (See also Issue #3117)

In order to avoid output parameters also changed function addJSONSnapshots to asJSONSnapshots

changelog/unreleased/pull-4737

@@ -0,0 +1,5 @@
+Enhancement: include snapshot id in reason field of forget JSON output
+
+The JSON output of the `forget` command now includes the `id` and `short_id` of a snapshot in the `reason` field.
+
+https://github.com/restic/restic/pull/4737

cmd/restic/cmd_forget.go

@@ -245,16 +245,16 @@ func runForget(ctx context.Context, opts ForgetOptions, pruneOptions PruneOption
 					PrintSnapshots(globalOptions.stdout, keep, reasons, opts.Compact)
 					Printf("\n")
 				}
-				addJSONSnapshots(&fg.Keep, keep)
+				fg.Keep = asJSONSnapshots(keep)
 
 				if len(remove) != 0 && !gopts.Quiet && !gopts.JSON {
 					Printf("remove %d snapshots:\n", len(remove))
 					PrintSnapshots(globalOptions.stdout, remove, nil, opts.Compact)
 					Printf("\n")
 				}
-				addJSONSnapshots(&fg.Remove, remove)
+				fg.Remove = asJSONSnapshots(remove)
 
-				fg.Reasons = reasons
+				fg.Reasons = asJSONKeeps(reasons)
 
 				jsonGroups = append(jsonGroups, &fg)
 
@@ -302,23 +302,47 @@ func runForget(ctx context.Context, opts ForgetOptions, pruneOptions PruneOption
 
 // ForgetGroup helps to print what is forgotten in JSON.
 type ForgetGroup struct {
-	Tags    []string            `json:"tags"`
-	Host    string              `json:"host"`
-	Paths   []string            `json:"paths"`
-	Keep    []Snapshot          `json:"keep"`
-	Remove  []Snapshot          `json:"remove"`
-	Reasons []restic.KeepReason `json:"reasons"`
+	Tags    []string     `json:"tags"`
+	Host    string       `json:"host"`
+	Paths   []string     `json:"paths"`
+	Keep    []Snapshot   `json:"keep"`
+	Remove  []Snapshot   `json:"remove"`
+	Reasons []KeepReason `json:"reasons"`
 }
 
-func addJSONSnapshots(js *[]Snapshot, list restic.Snapshots) {
+func asJSONSnapshots(list restic.Snapshots) []Snapshot {
+	var resultList []Snapshot
 	for _, sn := range list {
 		k := Snapshot{
 			Snapshot: sn,
 			ID:       sn.ID(),
 			ShortID:  sn.ID().Str(),
 		}
-		*js = append(*js, k)
+		resultList = append(resultList, k)
 	}
+	return resultList
+}
+
+// KeepReason helps to print KeepReasons as JSON with Snapshots with their ID included.
+type KeepReason struct {
+	Snapshot Snapshot `json:"snapshot"`
+	Matches  []string `json:"matches"`
+}
+
+func asJSONKeeps(list []restic.KeepReason) []KeepReason {
+	var resultList []KeepReason
+	for _, keep := range list {
+		k := KeepReason{
+			Snapshot: Snapshot{
+				Snapshot: keep.Snapshot,
+				ID:       keep.Snapshot.ID(),
+				ShortID:  keep.Snapshot.ID().Str(),
+			},
+			Matches: keep.Matches,
+		}
+		resultList = append(resultList, k)
+	}
+	return resultList
 }
 
 func printJSONForget(stdout io.Writer, forgets []*ForgetGroup) error {

doc/075_scripting.rst

@@ -367,13 +367,13 @@ Snapshot object
 
 Reason object
 
-+----------------+---------------------------------------------------------+
-| ``snapshot``   | Snapshot object, without ``id`` and ``short_id`` fields |
-+----------------+---------------------------------------------------------+
-| ``matches``    | Array containing descriptions of the matching criteria  |
-+----------------+---------------------------------------------------------+
-| ``counters``   | Object containing counters used by the policies         |
-+----------------+---------------------------------------------------------+
++----------------+-----------------------------------------------------------+
+| ``snapshot``   | Snapshot object, including ``id`` and ``short_id`` fields |
++----------------+-----------------------------------------------------------+
+| ``matches``    | Array containing descriptions of the matching criteria    |
++----------------+-----------------------------------------------------------+
+| ``counters``   | Object containing counters used by the policies           |
++----------------+-----------------------------------------------------------+
 
 
 init