Enhance array index handling and update RBS configuration

.rubocop.yml

@@ -31,4 +31,4 @@ Metrics/ClassLength:
   Max: 150
 
 Metrics/MethodLength:
-  Max: 20
+  Max: 25

.rubocop_rbs.yml

@@ -12,6 +12,7 @@ Style/RbsInline/MissingTypeAnnotation:
 Style/RbsInline/UntypedInstanceVariable:
   Exclude:
     - 'lib/structured_params/params.rb'
+    - 'lib/structured_params.rb'
 
 Style/RbsInline/RequireRbsInlineComment:
   Exclude:

Steepfile

@@ -6,4 +6,9 @@ target :lib do
   signature 'sig'
 
   check 'lib'
+
+  # Suppress errors from broken library RBS files in gem_rbs_collection
+  configure_code_diagnostics do |hash|
+    hash[Steep::Diagnostic::Ruby::LibraryRBSError] = nil
+  end
 end

docs/installation.md

@@ -6,6 +6,7 @@ Steps to add StructuredParams to a Rails application.
 
 - [Installation](#installation)
 - [Setup](#setup)
+- [Configuration](#configuration)
 - [Custom Type Registration](#custom-type-registration)
 
 ## Installation
@@ -37,6 +38,29 @@ StructuredParams.register_types
 
 This registers the `:object` and `:array` types with ActiveModel::Type.
 
+## Configuration
+
+You can configure StructuredParams in the same initializer:
+
+```ruby
+# config/initializers/structured_params.rb
+StructuredParams.register_types
+
+StructuredParams.configure do |config|
+  # Controls how array indices appear in human attribute names and full_messages.
+  #   0 (default) — 0-based: "Hobbies 0 Name can't be blank"
+  #   1           — 1-based: "Hobbies 1 Name can't be blank"
+  config.array_index_base = 1
+end
+```
+
+| Option | Default | Description |
+|--------|---------|-------------|
+| `array_index_base` | `0` | Index base for array elements in error messages (`0` or `1`) |
+
+> **Note:** `array_index_base` affects `human_attribute_name` and therefore `full_messages`.
+> For APIs returning raw error keys (the typical pattern), this setting has no visible effect.
+
 ## Custom Type Registration
 
 To avoid naming conflicts with existing code, register the types under custom names:

lib/structured_params.rb

@@ -23,17 +23,73 @@
 
 # Main module
 module StructuredParams
-  # Helper method to register types
-  #: () -> void
-  def self.register_types
-    ActiveModel::Type.register(:object, StructuredParams::Type::Object)
-    ActiveModel::Type.register(:array, StructuredParams::Type::Array)
+  # Global configuration for StructuredParams.
+  #
+  # == Options
+  #
+  # +array_index_base+ (Integer, default: +0+)::
+  #   Controls how array indices are displayed in human attribute names and
+  #   error messages.
+  #
+  #   * +0+ – 0-based (raw Ruby index): "Hobbies 0 Name"
+  #   * +1+ – 1-based (human-friendly): "Hobbies 1 Name"
+  #
+  # This setting applies to both API param error messages and Form Object
+  # +full_messages+.
+  #
+  # == Example
+  #
+  #   # config/initializers/structured_params.rb
+  #   StructuredParams.configure do |config|
+  #     config.array_index_base = 1   # show "1st" instead of "0th" to users
+  #   end
+  #
+  class Configuration
+    attr_reader :array_index_base #: Integer
+
+    #: () -> void
+    def initialize
+      @array_index_base = 0
+    end
+
+    #: (Integer) -> void
+    def array_index_base=(value)
+      raise ArgumentError, "array_index_base must be 0 or 1, got: #{value.inspect}" unless [0, 1].include?(value)
+
+      @array_index_base = value
+    end
   end
 
-  # Helper method to register types with custom names
-  #: (object_name: Symbol, array_name: Symbol) -> void
-  def self.register_types_as(object_name:, array_name:)
-    ActiveModel::Type.register(object_name, StructuredParams::Type::Object)
-    ActiveModel::Type.register(array_name, StructuredParams::Type::Array)
+  class << self
+    # @rbs self.@configuration: Configuration?
+
+    #: () -> Configuration
+    def configuration
+      @configuration ||= Configuration.new
+    end
+
+    #: () { (Configuration) -> void } -> void
+    def configure
+      yield configuration
+    end
+
+    #: () -> void
+    def reset_configuration!
+      @configuration = Configuration.new
+    end
+
+    # Helper method to register types
+    #: () -> void
+    def register_types
+      ActiveModel::Type.register(:object, StructuredParams::Type::Object)
+      ActiveModel::Type.register(:array, StructuredParams::Type::Array)
+    end
+
+    # Helper method to register types with custom names
+    #: (object_name: Symbol, array_name: Symbol) -> void
+    def register_types_as(object_name:, array_name:)
+      ActiveModel::Type.register(object_name, StructuredParams::Type::Object)
+      ActiveModel::Type.register(array_name, StructuredParams::Type::Array)
+    end
   end
 end

lib/structured_params/i18n.rb

@@ -22,9 +22,12 @@ module StructuredParams
   #           array:  "%{parent} %{index} 番目の%{child}"
   #           object: "%{parent}の%{child}"
   #
-  # Without these keys the defaults are:
+  # Without these keys the defaults are (with array_index_base: 0):
   #   array  → "<parent> <index> <child>"   (e.g. "Hobbies 0 Name")
   #   object → "<parent> <child>"           (e.g. "Address Postal code")
+  #
+  # With array_index_base: 1 (human-friendly):
+  #   array  → "Hobbies 1 Name"
   module I18n
     extend ActiveSupport::Concern
 
@@ -34,11 +37,11 @@ module I18n
       # Flat attributes (no dot) are delegated to the default ActiveModel
       # behaviour unchanged.
       #
-      # Example (en default):
+      # Example (en default, array_index_base: 0):
       #   human_attribute_name(:'hobbies.0.name') # => "Hobbies 0 Name"
       #
-      # Example with i18n (ja):
-      #   human_attribute_name(:'hobbies.0.name') # => "趣味 0 番目の名前"
+      # Example with i18n (ja) and array_index_base: 1:
+      #   human_attribute_name(:'hobbies.0.name') # => "趣味 1 番目の名前"
       #
       #: (Symbol | String, ?Hash[untyped, untyped]) -> String
       def human_attribute_name(attribute, options = {})
@@ -99,6 +102,11 @@ def attr_segments(parts)
       #   activemodel.errors.nested_attribute.array  (parent, index, child)
       #   activemodel.errors.nested_attribute.object (parent, child)
       #
+      # The index value passed to the i18n template is adjusted by
+      # +StructuredParams.configuration.array_index_base+:
+      #   * +0+ (default) – raw 0-based Ruby index (e.g. 0, 1, 2, …)
+      #   * +1+           – human-friendly 1-based index (e.g. 1, 2, 3, …)
+      #
       # The +locale:+ key from +options+ is forwarded to ::I18n.t so that an
       # explicit locale passed to human_attribute_name is honoured.
       #
@@ -109,12 +117,13 @@ def build_nested_label(result, index, attr_human, options)
         i18n_opts = options.slice(:locale)
 
         if index
+          display_index = index.to_i + StructuredParams.configuration.array_index_base
           ::I18n.t(
             'activemodel.errors.nested_attribute.array',
             parent: result,
-            index: index,
+            index: display_index,
             child: attr_human,
-            default: "#{result} #{index} #{attr_human}",
+            default: "#{result} #{display_index} #{attr_human}",
             **i18n_opts
           )
         else

rbs_collection.lock.yaml

@@ -6,39 +6,39 @@ gems:
   source:
     type: git
     name: ruby/gem_rbs_collection
-    revision: 14112a82013860a7d2e5246b4c4f36fbb8c349dc
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
     remote: https://github.com/ruby/gem_rbs_collection.git
     repo_dir: gems
 - name: actionview
   version: '6.0'
   source:
     type: git
     name: ruby/gem_rbs_collection
-    revision: 14112a82013860a7d2e5246b4c4f36fbb8c349dc
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
     remote: https://github.com/ruby/gem_rbs_collection.git
     repo_dir: gems
 - name: activemodel
   version: '7.1'
   source:
     type: git
     name: ruby/gem_rbs_collection
-    revision: 14112a82013860a7d2e5246b4c4f36fbb8c349dc
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
     remote: https://github.com/ruby/gem_rbs_collection.git
     repo_dir: gems
 - name: activesupport
   version: '7.0'
   source:
     type: git
     name: ruby/gem_rbs_collection
-    revision: 14112a82013860a7d2e5246b4c4f36fbb8c349dc
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
     remote: https://github.com/ruby/gem_rbs_collection.git
     repo_dir: gems
 - name: ast
   version: '2.4'
   source:
     type: git
     name: ruby/gem_rbs_collection
-    revision: 9bf2eebb1c54b5d6f23f2acb65d4c36f195b4783
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
     remote: https://github.com/ruby/gem_rbs_collection.git
     repo_dir: gems
 - name: base64
@@ -50,19 +50,15 @@ gems:
   source:
     type: stdlib
 - name: bigdecimal
-  version: '3.1'
+  version: 4.1.2
   source:
-    type: git
-    name: ruby/gem_rbs_collection
-    revision: 14112a82013860a7d2e5246b4c4f36fbb8c349dc
-    remote: https://github.com/ruby/gem_rbs_collection.git
-    repo_dir: gems
+    type: rubygems
 - name: binding_of_caller
   version: '1.0'
   source:
     type: git
     name: ruby/gem_rbs_collection
-    revision: 9bf2eebb1c54b5d6f23f2acb65d4c36f195b4783
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
     remote: https://github.com/ruby/gem_rbs_collection.git
     repo_dir: gems
 - name: date
@@ -82,13 +78,17 @@ gems:
   source:
     type: git
     name: ruby/gem_rbs_collection
-    revision: 14112a82013860a7d2e5246b4c4f36fbb8c349dc
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
     remote: https://github.com/ruby/gem_rbs_collection.git
     repo_dir: gems
 - name: logger
-  version: '0'
+  version: '1.7'
   source:
-    type: stdlib
+    type: git
+    name: ruby/gem_rbs_collection
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
+    remote: https://github.com/ruby/gem_rbs_collection.git
+    repo_dir: gems
 - name: monitor
   version: '0'
   source:
@@ -102,15 +102,19 @@ gems:
   source:
     type: git
     name: ruby/gem_rbs_collection
-    revision: 9bf2eebb1c54b5d6f23f2acb65d4c36f195b4783
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
     remote: https://github.com/ruby/gem_rbs_collection.git
     repo_dir: gems
 - name: prism
   version: 1.9.0
   source:
     type: rubygems
+- name: random-formatter
+  version: '0'
+  source:
+    type: stdlib
 - name: rspec-parameterized-core
-  version: 2.0.1
+  version: 2.0.2
   source:
     type: rubygems
 - name: rspec-parameterized-table_syntax
@@ -142,7 +146,7 @@ gems:
   source:
     type: git
     name: ruby/gem_rbs_collection
-    revision: 14112a82013860a7d2e5246b4c4f36fbb8c349dc
+    revision: d7090c40bcea7011ad2ebaaa46bdd7d7ac3136a7
     remote: https://github.com/ruby/gem_rbs_collection.git
     repo_dir: gems
 - name: uri

rbs_collection.yaml

@@ -37,4 +37,3 @@ gems:
      ignore: true
    - name: diff-lcs
      ignore: true
-

sig/structured_params.rbs

@@ -2,6 +2,47 @@
 
 # Main module
 module StructuredParams
+  # Global configuration for StructuredParams.
+  #
+  # == Options
+  #
+  # +array_index_base+ (Integer, default: +0+)::
+  #   Controls how array indices are displayed in human attribute names and
+  #   error messages.
+  #
+  #   * +0+ – 0-based (raw Ruby index): "Hobbies 0 Name"
+  #   * +1+ – 1-based (human-friendly): "Hobbies 1 Name"
+  #
+  # This setting applies to both API param error messages and Form Object
+  # +full_messages+.
+  #
+  # == Example
+  #
+  #   # config/initializers/structured_params.rb
+  #   StructuredParams.configure do |config|
+  #     config.array_index_base = 1   # show "1st" instead of "0th" to users
+  #   end
+  class Configuration
+    attr_reader array_index_base: Integer
+
+    # : () -> void
+    def initialize: () -> void
+
+    # : (Integer) -> void
+    def array_index_base=: (Integer) -> void
+  end
+
+  self.@configuration: Configuration?
+
+  # : () -> Configuration
+  def self.configuration: () -> Configuration
+
+  # : () { (Configuration) -> void } -> void
+  def self.configure: () { (Configuration) -> void } -> void
+
+  # : () -> void
+  def self.reset_configuration!: () -> void
+
   # Helper method to register types
   # : () -> void
   def self.register_types: () -> void