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/services/milestone_selection.go

@@ -6,6 +6,7 @@ package services
 import (
 	"context"
 	"fmt"
+	"strconv"
 	"strings"
 )
 
@@ -14,7 +15,7 @@ func (s Milestones) ResolveName(ctx context.Context, name string) (int64, error)
 	if strings.TrimSpace(name) == "" {
 		return 0, fmt.Errorf("milestone name cannot be empty")
 	}
-	items, err := listAll(func(page int) ([]Milestone, error) { return s.List(ctx, "all", 100, page) })
+	items, err := s.All(ctx)
 	if err != nil {
 		return 0, err
 	}
@@ -33,3 +34,28 @@ func (s Milestones) ResolveName(ctx context.Context, name string) (int64, error)
 	}
 	return id, nil
 }
+
+// All returns the open and closed milestones of the repository.
+func (s Milestones) All(ctx context.Context) ([]Milestone, error) {
+	return listAll(func(page int) ([]Milestone, error) { return s.List(ctx, "all", 100, page) })
+}
+
+// FilterIDs resolves the milestones that filter an issue listing, each an ID or a title, to their
+// IDs. Gitea drops filter values that name no milestone and lists every issue when none is left,
+// so an unknown milestone is an error here.
+func (s Milestones) FilterIDs(ctx context.Context, values []string) ([]string, error) {
+	items, err := s.All(ctx)
+	if err != nil {
+		return nil, err
+	}
+	finder := NameOrID[Milestone]{Kind: "milestone", Scope: s.Repository, ID: func(m Milestone) int64 { return m.ID }, Name: func(m Milestone) string { return m.Title }}
+	ids := make([]string, len(values))
+	for i, value := range values {
+		milestone, err := finder.Find(items, value)
+		if err != nil {
+			return nil, err
+		}
+		ids[i] = strconv.FormatInt(milestone.ID, 10)
+	}
+	return ids, nil
+}