fix(issue): reject unknown milestones in issue list and search filters

Gitea drops milestone filter values it cannot resolve and lists every
issue when none is left, so tea issue list --milestone nope printed all
issues and exited 0, and a pipeline closing the result would act on all
of them. issue list and search issue|pr -R now resolve each --milestone
value by ID or title and fail with "milestone "nope" not found in
alice/project". Instance-wide search cannot check the names and says so
on stderr.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/issues.go

@@ -114,6 +114,33 @@ func labelChoices(items []services.Label) []terminal.IssueLabelChoice {
 
 func issueLabel(n int64) string { return fmt.Sprintf("issue %d", n) }
 
+// nameFilter splits a comma-separated filter of kind, trimming entries and rejecting blanks.
+func nameFilter(kind, raw string) ([]string, error) {
+	if raw == "" {
+		return nil, nil
+	}
+	names := strings.Split(raw, ",")
+	return names, requireNames(kind, "", names)
+}
+
+// issueFilters checks the label and milestone filters of an issue listing in the target repository
+// and returns them as query values. Gitea ignores labels and milestones it cannot find, and lists
+// every issue when no filter value is left, so unknown names are errors.
+func issueFilters(cmd *cobra.Command, t target, labels, milestones []string) (labelQuery, milestoneQuery string, err error) {
+	if len(labels) > 0 {
+		if err := (services.Labels{Client: t.client, Repository: t.Repo}).RequireFilterNames(cmd.Context(), labels); err != nil {
+			return "", "", err
+		}
+	}
+	var ids []string
+	if len(milestones) > 0 {
+		if ids, err = (services.Milestones{Client: t.client, Repository: t.Repo}).FilterIDs(cmd.Context(), milestones); err != nil {
+			return "", "", err
+		}
+	}
+	return strings.Join(labels, ","), strings.Join(ids, ","), nil
+}
+
 // metadataFlags are the label and assignee flags shared by issue and pull request edits.
 type metadataFlags struct {
 	setLabels, addLabels, removeLabels          []string
@@ -206,6 +233,10 @@ func (a *application) issueCommand() *cobra.Command {
 		if err != nil {
 			return err
 		}
+		milestones, err := nameFilter("milestone", opts.Milestones)
+		if err != nil {
+			return err
+		}
 		target, err := a.resolve(cmd.Context(), true)
 		if err != nil {
 			if errors.Is(err, errRepositoryRequired) {
@@ -213,11 +244,8 @@ func (a *application) issueCommand() *cobra.Command {
 			}
 			return err
 		}
-		if len(labelNames) > 0 {
-			if err := (services.Labels{Client: target.client, Repository: target.Repo}).RequireFilterNames(cmd.Context(), labelNames); err != nil {
-				return err
-			}
-			opts.Labels = strings.Join(labelNames, ",")
+		if opts.Labels, opts.Milestones, err = issueFilters(cmd, target, labelNames, milestones); err != nil {
+			return err
 		}
 		items, more, err := (services.Issues{Client: target.client, Repository: target.Repo}).List(cmd.Context(), opts)
 		if err != nil {