Add support for a simple config file

README.md

@@ -19,6 +19,7 @@ It is built with only standard library dependencies. It additionally ships with
   - [json](#json)
   - [match](#match)
   - [write](#write)
+  - [Configuration](#configuration)
 - [Library](#library)
   - [SyntaxTree.read(filepath)](#syntaxtreereadfilepath)
   - [SyntaxTree.parse(source)](#syntaxtreeparsesource)
@@ -231,6 +232,19 @@ To change the print width that you are writing with, specify the `--print-width`
 stree write --print-width=100 path/to/file.rb
 ```
 
+### Configuration
+
+Any of the above CLI commands can also read configuration options from a `.streerc` file in the directory where the commands are executed.
+
+This should be a text file with each argument on a separate line.
+
+```txt
+--print-width=100
+--plugins=plugin/trailing_comma
+```
+
+If this file is present, it will _always_ be used for CLI commands. You can also pass options from the command line as in the examples above. The options in the `.streerc` file are passed to the CLI first, then the arguments from the command line. In the case of exclusive options (e.g. `--print-width`), this means that the command line options override what's in the config file. In the case of options that can take multiple inputs (e.g. `--plugins`), the effect is additive. That is, the plugins passed from the command line will be loaded _in addition to_ the plugins in the config file.
+
 ## Library
 
 Syntax Tree can be used as a library to access the syntax tree underlying Ruby source code.

lib/syntax_tree/cli.rb

@@ -4,6 +4,8 @@ module SyntaxTree
   # Syntax Tree ships with the `stree` CLI, which can be used to inspect and
   # manipulate Ruby code. This module is responsible for powering that CLI.
   module CLI
+    CONFIG_FILE = ".streerc"
+
     # A utility wrapper around colored strings in the output.
     class Color
       attr_reader :value, :code
@@ -269,6 +271,11 @@ def run(argv)
         name, *arguments = argv
         print_width = DEFAULT_PRINT_WIDTH
 
+        config_file = File.join(Dir.pwd, CONFIG_FILE)
+        if File.readable?(config_file)
+          arguments.unshift(*File.readlines(config_file, chomp: true))
+        end
+
         while arguments.first&.start_with?("--")
           case (argument = arguments.shift)
           when /^--plugins=(.+)$/

test/cli_test.rb

@@ -180,6 +180,77 @@ def test_language_server
       $stdout = prev_stdout
     end
 
+    def test_config_file
+      config_file = File.join(Dir.pwd, SyntaxTree::CLI::CONFIG_FILE)
+      config = <<~TXT
+      --print-width=100
+      --plugins=plugin
+      TXT
+      File.write(config_file, config)
+
+      Dir.mktmpdir do |directory|
+        Dir.mkdir(File.join(directory, "syntax_tree"))
+        $:.unshift(directory)
+
+        File.write(
+          File.join(directory, "syntax_tree", "plugin.rb"),
+          "puts 'Hello, world!'"
+        )
+
+        file = Tempfile.new(%w[test- .rb])
+        contents = "#{"a" * 40} + #{"b" * 40}\n"
+        file.write(contents)
+
+        result = run_cli("format", file: file)
+        assert_equal("Hello, world!\n#{contents}", result.stdio)
+      end
+    ensure
+      FileUtils.rm(config_file)
+    end
+
+    def test_print_width_args_with_config_file
+      config_file = File.join(Dir.pwd, SyntaxTree::CLI::CONFIG_FILE)
+      File.write(config_file, "--print-width=100")
+
+      contents = "#{"a" * 40} + #{"b" * 40}\n"
+
+      file = Tempfile.new(%w[test- .rb])
+      file.write(contents)
+      result = run_cli("check", file: file)
+      assert_includes(result.stdio, "match")
+
+      file = Tempfile.new(%w[test- .rb])
+      file.write(contents)
+      result = run_cli("check", "--print-width=82", file: file)
+      assert_includes(result.stderr, "expected")
+    ensure
+      FileUtils.rm(config_file)
+    end
+
+    def test_plugin_args_with_config_file
+      config_file = File.join(Dir.pwd, SyntaxTree::CLI::CONFIG_FILE)
+      File.write(config_file, "--plugins=hello_plugin")
+
+      Dir.mktmpdir do |directory|
+        Dir.mkdir(File.join(directory, "syntax_tree"))
+        $:.unshift(directory)
+
+        File.write(
+          File.join(directory, "syntax_tree", "hello_plugin.rb"),
+          "puts 'Hello, world!'"
+        )
+        File.write(
+          File.join(directory, "syntax_tree", "bye_plugin.rb"),
+          "puts 'Bye, world!'"
+        )
+
+        result = run_cli("format", "--plugins=bye_plugin")
+        assert_equal("Hello, world!\nBye, world!\ntest\n", result.stdio)
+      end
+    ensure
+      FileUtils.rm(config_file)
+    end
+
     private
 
     Result = Struct.new(:status, :stdio, :stderr, keyword_init: true)