Enable passthrough by specifying environment variable name in NVAR_PA…

…SSTHROUGH

lib/nvar.rb

@@ -4,6 +4,7 @@
 require "nvar/environment_variable"
 require "nvar/engine" if defined?(Rails)
 require "active_support/core_ext/module/attribute_accessors"
+require "active_support/core_ext/hash/reverse_merge"
 
 # Centralized configuration for required environment variables in your Ruby app.
 module Nvar
@@ -62,7 +63,6 @@ def filter_from_vcr_cassettes(config)
 
     def all
       variables.map do |variable_name, config|
-        # TODO: Passthrough from environment behaviour might need to go here?
         EnvironmentVariable.new(**(config || {}).merge(name: variable_name))
       end.partition(&:set?)
     end

lib/nvar/environment_variable.rb

@@ -16,7 +16,7 @@ def initialize(name:, type: "String", filter_from_requests: nil, **args)
       @type = type
       @required = args[:required].nil? ? true : args[:required]
       @filter_from_requests = filter_from_requests.yield_self { |f| [true, false].include?(f) ? f : f&.to_sym }
-      @value = fetch_value(**args.slice(:passthrough, :default_value))
+      @value = fetch_value(**args.slice(:passthrough, :default_value).with_defaults(passthrough: ENV.fetch("NVAR_PASSTHROUGH", "").split(",").include?(name)))
       @defined = true
     rescue KeyError
       @value = args[:default_value]

spec/nvar/environment_variable_spec.rb

@@ -132,5 +132,65 @@
 
       it { is_expected.to eq("passthrough_value") }
     end
+
+    context "when passthrough is unset in the environment and a default value is not provided" do
+      let(:args) { base_args.except(:passthrough).merge(default_value: nil) }
+
+      it { is_expected.to eq(environment_variable.name) }
+    end
+
+    context "when passthrough is unset in the environment and a default value is provided" do
+      let(:args) { base_args.except(:passthrough).merge(default_value: "default_value") }
+
+      it { is_expected.to eq("default_value") }
+    end
+
+    context "when passthrough is enabled through the environment and a default value is provided" do
+      around { |example| ClimateControl.modify(NVAR_PASSTHROUGH: "SOME_OTHER_VAR,#{base_args[:name]}") { example.run } }
+
+      let(:args) { base_args.except(:passthrough).merge(default_value: "default_value") }
+
+      it { is_expected.to eq("passthrough_value") }
+    end
+
+    context "when passthrough is enabled through the environment and a default value is not provided" do
+      around { |example| ClimateControl.modify(NVAR_PASSTHROUGH: "SOME_OTHER_VAR,#{base_args[:name]}") { example.run } }
+
+      let(:args) { base_args.except(:passthrough).merge(default_value: nil) }
+
+      it { is_expected.to eq("passthrough_value") }
+    end
+
+    context "when passthrough is enabled through the environment, but is overridden by the config" do
+      around { |example| ClimateControl.modify(NVAR_PASSTHROUGH: "SOME_OTHER_VAR,#{base_args[:name]}") { example.run } }
+
+      let(:args) { base_args.merge(passthrough: false, default_value: nil) }
+
+      it { is_expected.to eq(environment_variable.name) }
+    end
+
+    context "when passthrough is disabled through the environment and a default value is provided" do
+      around { |example| ClimateControl.modify(NVAR_PASSTHROUGH: "SOME_OTHER_VAR") { example.run } }
+
+      let(:args) { base_args.except(:passthrough).merge(default_value: "default_value") }
+
+      it { is_expected.to eq("default_value") }
+    end
+
+    context "when passthrough is disabled through the environment and a default value is not provided" do
+      around { |example| ClimateControl.modify(NVAR_PASSTHROUGH: "false") { example.run } }
+
+      let(:args) { base_args.except(:passthrough).merge(default_value: nil) }
+
+      it { is_expected.to eq(environment_variable.name) }
+    end
+
+    context "when passthrough is disabled through the environment, but is overridden by the config" do
+      around { |example| ClimateControl.modify(NVAR_PASSTHROUGH: "SOME_OTHER_VAR") { example.run } }
+
+      let(:args) { base_args.merge(passthrough: true) }
+
+      it { is_expected.to eq("passthrough_value") }
+    end
   end
 end

spec/nvar_spec.rb

@@ -77,6 +77,8 @@
 
     context "when the env file exists and an optional environment variable is unset" do
       let!(:env) { base_env.except(:OPTIONAL_ENV_VAR) }
+
+      it { is_expected.to be_empty }
     end
 
     context "when the env file exists and an environment variable with a default value is unset" do