Adds the option fail_on_missing (default false) (#182)

Author: Yoshiji

CHANGELOG.md

@@ -4,7 +4,8 @@
 
 ### New features
 
-...
+* `Config#fail_on_missing` option (default `false`) to raise a `KeyError` exception when accessing a non-existing key
+* Add ability to test if a value was set for a given key with `key?` and `has_key?`
 
 ## 1.5.1
 

README.md

@@ -299,6 +299,49 @@ between the schema and your config.
 
 Check [dry-validation](https://github.com/dry-rb/dry-validation) for more details.
 
+### Missing keys
+
+For an example settings file:
+
+```yaml
+size: 1
+server: google.com
+```
+
+You can test if a value was set for a given key using `key?` and its alias `has_key?`:
+
+```ruby
+Settings.key?(:path)
+# => false
+Settings.key?(:server)
+# => true
+```
+
+By default, accessing to a missing key returns `nil`:
+
+```ruby
+Settings.key?(:path)
+# => false
+Settings.path
+# => nil
+```
+
+This is not "typo-safe". To solve this problem, you can configure the `fail_on_missing` option:
+
+```ruby
+Config.setup do |config|
+  config.fail_on_missing = true
+  # ...
+end
+```
+
+So it will raise a `KeyError` when accessing a non-existing key (similar to `Hash#fetch` behaviour):
+
+```ruby
+Settings.path
+# => raises KeyError: key not found: :path
+```
+
 ### Environment variables
 
 See section below for more details.

lib/config.rb

@@ -15,13 +15,15 @@ module Config
   # Ensures the setup only gets run once
   @@_ran_once = false
 
-  mattr_accessor :const_name, :use_env, :env_prefix, :env_separator, :env_converter, :env_parse_values
+  mattr_accessor :const_name, :use_env, :env_prefix, :env_separator,
+                 :env_converter, :env_parse_values, :fail_on_missing
   @@const_name = 'Settings'
   @@use_env    = false
   @@env_prefix = @@const_name
   @@env_separator = '.'
   @@env_converter = :downcase
   @@env_parse_values = true
+  @@fail_on_missing = false
 
   # deep_merge options
   mattr_accessor :knockout_prefix, :overwrite_arrays

lib/config/options.rb

@@ -153,6 +153,19 @@ def []=(param, value)
       end
     end
 
+    delegate :key?, :has_key?, to: :table
+
+    def method_missing(method_name, *args)
+      if Config.fail_on_missing && method_name !~ /.*(?==\z)/m
+        raise KeyError, "key not found: #{method_name.inspect}" unless key?(method_name)
+      end
+      super
+    end
+
+    def respond_to_missing?(*args)
+      super
+    end
+
     protected
 
     def descend_array(array)

spec/options_spec.rb

@@ -114,4 +114,66 @@
     end
   end
 
+  context 'when fail_on_missing option' do
+    before { Config.reset }
+
+    context 'is set to true' do
+      before { Config.setup { |cfg| cfg.fail_on_missing = true } }
+
+      it 'should raise an error when accessing a missing key' do
+        config = Config.load_files("#{fixture_path}/empty1.yml")
+
+        expect { config.not_existing_method }.to raise_error(KeyError)
+        expect { config[:not_existing_method] }.to raise_error(KeyError)
+      end
+
+      it 'should raise an error when accessing a removed key' do
+        config = Config.load_files("#{fixture_path}/empty1.yml")
+
+        config.tmp_existing = 1337
+        expect(config.tmp_existing).to eq(1337)
+
+        config.delete_field(:tmp_existing)
+        expect { config.tmp_existing }.to raise_error(KeyError)
+        expect { config[:tmp_existing] }.to raise_error(KeyError)
+      end
+    end
+
+    context 'is set to false' do
+      before { Config.setup { |cfg| cfg.fail_on_missing = false } }
+
+      it 'should return nil when accessing a missing key' do
+        config = Config.load_files("#{fixture_path}/empty1.yml")
+
+        expect(config.not_existing_method).to eq(nil)
+        expect(config[:not_existing_method]).to eq(nil)
+      end
+    end
+  end
+
+  context '#key? and #has_key? methods' do
+    let(:config) {
+      config = Config.load_files("#{fixture_path}/empty1.yml")
+      config.existing = nil
+      config.send('complex_value=', nil)
+      config.send('even_more_complex_value==', nil)
+      config.nested = Config.load_files("#{fixture_path}/empty2.yml")
+      config.nested.existing = nil
+      config
+    }
+
+    it 'should test if a value exists for a given key' do
+      expect(config.key?(:not_existing)).to eq(false)
+      expect(config.key?(:complex_value)).to eq(true)
+      expect(config.key?('even_more_complex_value='.to_sym)).to eq(true)
+      expect(config.key?(:nested)).to eq(true)
+      expect(config.nested.key?(:not_existing)).to eq(false)
+      expect(config.nested.key?(:existing)).to eq(true)
+    end
+
+    it 'should be sensible to key\'s class' do
+      expect(config.key?(:existing)).to eq(true)
+      expect(config.key?('existing')).to eq(false)
+    end
+  end
 end