Drop support for Terraform 0.8 and older

The support has been actually broken for year now, since PR #9.
Nobody has complained, so clean up the code base a bit.

Anyway, add a check and clear error message for old Terraform versions.

lib/yle_tf.rb

@@ -4,6 +4,8 @@
 require 'yle_tf/version'
 
 class YleTf
+  TERRAFORM_VERSION_REQUIREMENT = '>= 0.9'
+
   autoload :Action,  'yle_tf/action'
   autoload :Error,   'yle_tf/error'
   autoload :Plugin,  'yle_tf/plugin'

lib/yle_tf/action/terraform_init.rb

@@ -4,7 +4,6 @@
 require 'yle_tf/logger'
 require 'yle_tf/plugin'
 require 'yle_tf/system'
-require 'yle_tf/version_requirement'
 
 class YleTf
   module Action
@@ -27,31 +26,16 @@ def call(env)
         Logger.info('Initializing Terraform')
         Logger.debug("Backend configuration: #{backend}")
 
-        if VersionRequirement.pre_0_9?(env[:terraform_version])
-          init_pre_0_9(backend)
-        else
-          init(backend)
-        end
+        init(backend)
 
         @app.call(env)
       end
 
-      def init_pre_0_9(backend)
-        cli_args = backend.cli_args
-        if cli_args
-          YleTf::System.cmd('terraform', 'remote', 'config', *TF_CMD_ARGS, *cli_args, TF_CMD_OPTS)
-        end
-
-        Logger.debug('Fetching Terraform modules')
-        YleTf::System.cmd('terraform', 'get', *TF_CMD_ARGS, TF_CMD_OPTS)
-      end
-
       def init(backend)
-        Logger.debug('Generating the backend configuration')
-        backend.generate_config do
-          Logger.debug('Initializing Terraform')
-          YleTf::System.cmd('terraform', 'init', *TF_CMD_ARGS, TF_CMD_OPTS)
-        end
+        Logger.debug('Configuring the backend')
+        backend.generate_config
+        Logger.debug('Initializing Terraform')
+        YleTf::System.cmd('terraform', 'init', *TF_CMD_ARGS, TF_CMD_OPTS)
       end
 
       def backend_config(config)

lib/yle_tf/action/verify_terraform_version.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'yle_tf'
 require 'yle_tf/error'
 require 'yle_tf/logger'
 require 'yle_tf/system'
@@ -19,22 +20,32 @@ def call(env)
         raise(Error, 'Terraform not found') if !version
 
         Logger.debug("Terraform version: #{version}")
-        verify_version(env)
+
+        verify_version(version, requirement_by_yletf, required_by: 'YleTf')
+        verify_version(version, requirement_by_config(env), required_by: 'config')
 
         @app.call(env)
       end
 
       def terraform_version
         v = YleTf::System.read_cmd('terraform', 'version', error_handler: proc {})
-        Regexp.last_match(1) if v =~ /^Terraform v([^\s]+)/
+        m = /^Terraform v(?<version>[^\s]+)/.match(v)
+        m && m[:version]
       end
 
-      def verify_version(env)
-        version = env[:terraform_version]
+      def requirement_by_config(env)
         requirement = env[:config].fetch('terraform', 'version_requirement') { nil }
+        VersionRequirement.new(requirement)
+      end
+
+      def requirement_by_yletf
+        VersionRequirement.new(YleTf::TERRAFORM_VERSION_REQUIREMENT)
+      end
 
-        if !VersionRequirement.new(requirement).satisfied_by?(version)
-          raise Error, "Terraform version '#{requirement}' required, '#{version}' found"
+      def verify_version(version, requirement, **opts)
+        if !requirement.satisfied_by?(version)
+          raise Error, "Terraform version '#{requirement}' required by #{opts[:required_by]}, " \
+                       "'#{version}' found"
         end
       end
     end

lib/yle_tf/backend_config.rb

@@ -13,15 +13,6 @@ def initialize(type, config)
       @config = config
     end
 
-    # Returns an `Array` of CLI args for Terraform pre 0.9 `init` command
-    def cli_args
-      args = ["-backend=#{type}"]
-      config.each do |key, value|
-        args << "-backend-config=#{key}=#{value}"
-      end
-      args
-    end
-
     # Generate backend configuration file for Terraform v0.9+
     def generate_config
       data = {
@@ -30,7 +21,6 @@ def generate_config
         }]
       }
       File.write(BACKEND_CONFIG_FILE, JSON.pretty_generate(data))
-      yield if block_given?
     end
 
     # Returns the backend configuration as a `Hash` for Terraform v0.9+

lib/yle_tf/version_requirement.rb

@@ -5,11 +5,6 @@
 class YleTf
   # Helper class for comparing versions
   class VersionRequirement
-    # Checks if the specified Terrform version is older than 0.9
-    def self.pre_0_9?(terraform_version)
-      new('< 0.9.0-beta').satisfied_by?(terraform_version)
-    end
-
     attr_reader :requirement
 
     def initialize(requirement)

lib/yle_tf_plugins/backends/file/config.rb

@@ -7,11 +7,7 @@ module Backends
     module File
       class Config < YleTf::BackendConfig
         def generate_config
-          yield if block_given?
-        end
-
-        def cli_args
-          nil
+          # Do nothing, as the state file is just symlinked
         end
       end
     end