fix(label): refuse duplicate label names unless --force

tea label create --name bug twice created a second "bug" label, after
which issue edit --add-labels bug failed as ambiguous and issue list
--label bug matched nothing. label create (and --file imports) now fail
with "label "bug" already exists in alice/project; pass --force to
update it", ignoring case; --force updates the existing label. The
ambiguity error for labels that already share a name lists their IDs.

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

internal/services/label_selection.go

@@ -5,11 +5,46 @@ package services
 
 import (
 	"context"
+	"errors"
 	"fmt"
+	"strconv"
 	"strings"
 )
 
-func selectLabelNames(names []string, matches map[string][]int64) ([]int64, error) {
+// Scope names the repository or organization the labels belong to.
+func (s Labels) Scope() string {
+	if s.Organization != "" {
+		return s.Organization
+	}
+	return s.Repository
+}
+
+// finder addresses the labels of the scope by ID or name (D10); byName matches numeric values as
+// names only.
+func (s Labels) finder(byName bool) NameOrID[Label] {
+	return NameOrID[Label]{Kind: "label", Scope: s.Scope(), ID: func(l Label) int64 { return l.ID }, Name: func(l Label) string { return l.Name }, ByName: byName}
+}
+
+// CreateUnique creates a label unless existing, the labels of the scope, has one with its name,
+// ignoring case. Then update edits that label with the supplied fields, keeping its name, and
+// otherwise CreateUnique fails: Gitea would create a second label that name filters cannot tell
+// apart.
+func (s Labels) CreateUnique(ctx context.Context, existing []Label, opts LabelOptions, update bool) (Label, error) {
+	current, err := s.finder(true).Find(existing, deref(opts.Name))
+	if errors.As(err, new(*NotFoundError)) {
+		return s.Create(ctx, opts)
+	}
+	if err != nil {
+		return Label{}, err
+	}
+	if !update {
+		return Label{}, &ConflictError{Reason: ReasonExists, Kind: "label", Key: strconv.Quote(current.Name), Scope: s.Scope(), Hint: "pass --force to update it"}
+	}
+	opts.Name = nil
+	return s.Edit(ctx, current.ID, opts)
+}
+
+func selectLabelNames(scope string, names []string, matches map[string][]int64) ([]int64, error) {
 	ids := make([]int64, 0, len(names))
 	seen := map[int64]bool{}
 	for _, name := range names {
@@ -18,7 +53,7 @@ func selectLabelNames(names []string, matches map[string][]int64) ([]int64, erro
 			return nil, fmt.Errorf("label %q does not exist; use tea label list", name)
 		}
 		if len(candidates) > 1 {
-			return nil, fmt.Errorf("label %q is ambiguous", name)
+			return nil, &AmbiguousError{Kind: "label", Key: strconv.Quote(name), Scope: scope, IDs: candidates}
 		}
 		if !seen[candidates[0]] {
 			ids = append(ids, candidates[0])
@@ -70,7 +105,7 @@ func (s Labels) ResolveIssueNames(ctx context.Context, names []string) ([]int64,
 		scope, name := splitLabelScope(input)
 		matches[input] = index[labelKey{scope, name}]
 	}
-	return selectLabelNames(names, matches)
+	return selectLabelNames(s.Repository, names, matches)
 }
 
 func splitLabelScope(input string) (scope, name string) {