Replace .env* with .kamal/env*

By default look for the env file in .kamal/env to avoid clashes with
other tools using .env.

For now we'll still load .env and issue a deprecation warning, but in
future we'll stop reading those.

test/cli/main_test.rb

@@ -447,9 +447,9 @@ class CliMainTest < CliTestCase
   end
 
   test "envify" do
-    with_test_dotenv(".env.erb": "HELLO=<%= 'world' %>") do
+    with_test_env_files("env.erb": "HELLO=<%= 'world' %>") do
       run_command("envify")
-      assert_equal("HELLO=world", File.read(".env"))
+      assert_equal("HELLO=world", File.read(".kamal/env"))
     end
   end
 
@@ -461,32 +461,32 @@ class CliMainTest < CliTestCase
       <% end  -%>
     EOF
 
-    with_test_dotenv(".env.erb": file) do
+    with_test_env_files("env.erb": file) do
       run_command("envify")
-      assert_equal("HELLO=world\nKEY=value\n", File.read(".env"))
+      assert_equal("HELLO=world\nKEY=value\n", File.read(".kamal/env"))
     end
   end
 
   test "envify with destination" do
-    with_test_dotenv(".env.world.erb": "HELLO=<%= 'world' %>") do
+    with_test_env_files("env.world.erb": "HELLO=<%= 'world' %>") do
       run_command("envify", "-d", "world", config_file: "deploy_for_dest")
-      assert_equal "HELLO=world", File.read(".env.world")
+      assert_equal "HELLO=world", File.read(".kamal/env.world")
     end
   end
 
   test "envify with skip_push" do
-    Pathname.any_instance.expects(:exist?).returns(true).times(1)
-    File.expects(:read).with(".env.erb").returns("HELLO=<%= 'world' %>")
-    File.expects(:write).with(".env", "HELLO=world", perm: 0600)
+    Pathname.any_instance.expects(:exist?).returns(true).times(2)
+    File.expects(:read).with(".kamal/env.erb").returns("HELLO=<%= 'world' %>")
+    File.expects(:write).with(".kamal/env", "HELLO=world", perm: 0600)
 
     Kamal::Cli::Main.any_instance.expects(:invoke).with("kamal:cli:env:push").never
     run_command("envify", "--skip-push")
   end
 
   test "envify with clean env" do
-    with_test_dotenv(".env": "HELLO=already", ".env.erb": "HELLO=<%= ENV.fetch 'HELLO', 'never' %>") do
+    with_test_env_files("env": "HELLO=already", "env.erb": "HELLO=<%= ENV.fetch 'HELLO', 'never' %>") do
       run_command("envify", "--skip-push")
-      assert_equal "HELLO=never", File.read(".env")
+      assert_equal "HELLO=never", File.read(".kamal/env")
     end
   end
 
@@ -542,15 +542,18 @@ class CliMainTest < CliTestCase
       stdouted { Kamal::Cli::Main.start([ *command, "-c", "test/fixtures/#{config_file}.yml" ]) }
     end
 
-    def with_test_dotenv(**files)
+    def with_test_env_files(**files)
       Dir.mktmpdir do |dir|
         fixtures_dup = File.join(dir, "test")
         FileUtils.mkdir_p(fixtures_dup)
         FileUtils.cp_r("test/fixtures/", fixtures_dup)
 
         Dir.chdir(dir) do
-          files.each do |filename, contents|
-            File.binwrite(filename.to_s, contents)
+          FileUtils.mkdir_p(".kamal")
+          Dir.chdir(".kamal") do
+            files.each do |filename, contents|
+              File.binwrite(filename.to_s, contents)
+            end
           end
           yield
         end

test/integration/main_test.rb

@@ -97,7 +97,7 @@ class MainTest < IntegrationTest
 
   private
     def assert_local_env_file(contents)
-      assert_equal contents, deployer_exec("cat .env", capture: true)
+      assert_equal contents, deployer_exec("cat .kamal/env", capture: true)
     end
 
     def assert_envs(version:)
@@ -127,7 +127,7 @@ class MainTest < IntegrationTest
     end
 
     def remove_local_env_file
-      deployer_exec("rm .env")
+      deployer_exec("rm .kamal/env")
     end
 
     def assert_remote_env_file(contents, vm:)