Memoize flag alias resolution by context

flag_aliases.go

@@ -230,14 +230,54 @@ func resolveFlagAliases(context flagAliasContext, mappings map[string]flagAliasM
 		sources = append(sources, source)
 	}
 	sort.Strings(sources)
+	type terminal struct {
+		spelling capturedFlagSpelling
+		active   bool
+	}
+	resolved := make(map[string]terminal)
+	visiting := make(map[string]int)
+	var stack []capturedFlagSpelling
+	var resolve func(capturedFlagSpelling) (terminal, error)
+	resolve = func(current capturedFlagSpelling) (terminal, error) {
+		key := flagSpellingKey(current)
+		if endpoint, exists := context.canonical[key]; exists {
+			return terminal{spelling: endpoint, active: true}, nil
+		}
+		if result, exists := resolved[key]; exists {
+			return result, nil
+		}
+		if start, exists := visiting[key]; exists {
+			cycle := append(append([]capturedFlagSpelling(nil), stack[start:]...), current)
+			spellings := make([]string, 0, len(cycle))
+			for _, spelling := range cycle {
+				spellings = append(spellings, spelling.token())
+			}
+			return terminal{}, fmt.Errorf("flag alias cycle: %s", strings.Join(spellings, " → "))
+		}
+		mapping, exists := mappings[key]
+		if !exists {
+			resolved[key] = terminal{}
+			return terminal{}, nil
+		}
+		visiting[key] = len(stack)
+		stack = append(stack, current)
+		result, err := resolve(mapping.target)
+		stack = stack[:len(stack)-1]
+		delete(visiting, key)
+		if err != nil {
+			return terminal{}, err
+		}
+		resolved[key] = result
+		return result, nil
+	}
 	for _, sourceKey := range sources {
 		mapping := mappings[sourceKey]
 		source := spellingFromKey(sourceKey)
-		target, active, err := resolveFlagTarget(source, mapping.target, mappings, context.canonical)
+		terminal, err := resolve(mapping.target)
 		if err != nil {
 			return resolvedFlagAliases{}, fmt.Errorf("%s: %w", flagContextDescription(context), err)
 		}
-		if !active {
+		if !terminal.active {
 			if mapping.scoped {
 				return resolvedFlagAliases{}, fmt.Errorf("scoped flag alias %s has no canonical destination in %s", source.token(), flagContextDescription(context))
 			}
@@ -246,38 +286,11 @@ func resolveFlagAliases(context flagAliasContext, mappings map[string]flagAliasM
 		if _, collision := context.canonical[sourceKey]; collision {
 			return resolvedFlagAliases{}, fmt.Errorf("flag alias %s conflicts with a canonical spelling in %s", source.token(), flagContextDescription(context))
 		}
-		result.bySpelling[sourceKey] = resolvedFlagAlias{source: source, target: target}
+		result.bySpelling[sourceKey] = resolvedFlagAlias{source: source, target: terminal.spelling}
 	}
 	return result, nil
 }
 
-func resolveFlagTarget(source, target capturedFlagSpelling, mappings map[string]flagAliasMapping, canonical map[string]capturedFlagSpelling) (capturedFlagSpelling, bool, error) {
-	visited := map[string]int{flagSpellingKey(source): 0}
-	chain := []capturedFlagSpelling{source}
-	current := target
-	for {
-		key := flagSpellingKey(current)
-		if endpoint, exists := canonical[key]; exists {
-			return endpoint, true, nil
-		}
-		if start, exists := visited[key]; exists {
-			cycle := append(append([]capturedFlagSpelling(nil), chain[start:]...), current)
-			spellings := make([]string, 0, len(cycle))
-			for _, spelling := range cycle {
-				spellings = append(spellings, spelling.token())
-			}
-			return capturedFlagSpelling{}, false, fmt.Errorf("flag alias cycle: %s", strings.Join(spellings, " → "))
-		}
-		visited[key] = len(chain)
-		chain = append(chain, current)
-		next, exists := mappings[key]
-		if !exists {
-			return capturedFlagSpelling{}, false, nil
-		}
-		current = next.target
-	}
-}
-
 func spellingFromKey(key string) capturedFlagSpelling {
 	if strings.HasPrefix(key, "short:") {
 		return capturedFlagSpelling{name: strings.TrimPrefix(key, "short:"), short: true}