Do not update RBS file if the signature nothing changed

At present, steep detect the file change via its timestamp. To avoid
unnecessary type check, this adds FileWriter class which updates the RBS
file only if its content has changed.

ref: pocke/rbs_rails#346

Author: tk0miya

.vscode/settings.json

@@ -22,7 +22,8 @@
         "readlines",
         "rmtree",
         "rubocop",
-        "Takeshi"
+        "Takeshi",
+        "utime"
     ],
     "rbs-helper.rbs-inline-on-save": true,
     "rbs-helper.rbs-inline-signature-directory": "sig/"

lib/ruby_lsp/rbs_rails/addon.rb

@@ -3,6 +3,7 @@
 require "language_server-protocol"
 require "ruby_lsp/addon"
 
+require_relative "file_writer"
 require_relative "logger"
 
 module RubyLsp
@@ -125,7 +126,7 @@ def generate_path_helpers_signature #: void
         rbs_path.dirname.mkpath
 
         sig = ::RbsRails::PathHelpers.generate
-        rbs_path.write sig
+        FileWriter.new(rbs_path).write sig
         logger.info("Updated RBS signature: #{rbs_path}")
       end
 
@@ -139,7 +140,7 @@ def generate_signature0(klass) #: void
         rbs_path.dirname.mkpath
 
         sig = ::RbsRails::ActiveRecord.class_to_rbs(klass)
-        rbs_path.write sig
+        FileWriter.new(rbs_path).write sig
         logger.info("Updated RBS signature: #{rbs_path}")
       end
 

lib/ruby_lsp/rbs_rails/file_writer.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+module RubyLsp
+  module RbsRails
+    # To avoid unnecessary type reloading by type checkers and other utilities,
+    # FileWriter modifies the target file only if its content has been changed.
+    #
+    # See https://github.com/pocke/rbs_rails/pull/346
+    class FileWriter
+      attr_reader :path #: Pathname
+
+      # @rbs path: Pathname
+      def initialize(path) #: void
+        @path = path
+      end
+
+      def write(content) #: void
+        original_content = begin
+          path.read
+        rescue StandardError
+          nil
+        end
+
+        return unless original_content != content
+
+        path.write(content)
+      end
+    end
+  end
+end

sig/ruby_lsp/rbs_rails/file_writer.rbs

@@ -0,0 +1,18 @@
+# Generated from lib/ruby_lsp/rbs_rails/file_writer.rb with RBS::Inline
+
+module RubyLsp
+  module RbsRails
+    # To avoid unnecessary type reloading by type checkers and other utilities,
+    # FileWriter modifies the target file only if its content has been changed.
+    #
+    # See https://github.com/pocke/rbs_rails/pull/346
+    class FileWriter
+      attr_reader path: Pathname
+
+      # @rbs path: Pathname
+      def initialize: (Pathname path) -> void
+
+      def write: (untyped content) -> void
+    end
+  end
+end

spec/rbs_rails/file_writer_spec.rb

@@ -0,0 +1,57 @@
+RSpec.describe RubyLsp::RbsRails::FileWriter do
+  describe "#write" do
+    subject { file_writer.write(content) }
+
+    after do
+      tmpdir.rmtree
+    end
+
+    let(:file_writer) { RubyLsp::RbsRails::FileWriter.new(path) }
+    let(:path) { tmpdir / "test_file.rbs" }
+    let(:tmpdir) { Pathname.new(Dir.mktmpdir("file_writer_test")) }
+
+    context "when the file does not exist" do
+      it "creates the file with the given content" do
+        expect(path).not_to exist
+
+        file_writer.write("class NewClass; end")
+
+        expect(path).to exist
+        expect(path.read).to eq("class NewClass; end")
+      end
+    end
+
+    context "when the file exists" do
+      before do
+        path.write(old_content)
+      end
+
+      let(:old_content) { "class ExistingClass; end" }
+
+      context "when the content is different" do
+        it "updates the file with the new content" do
+          file_writer.write("class NewClass; end")
+
+          expect(path).to exist
+          expect(path.read).to eq("class NewClass; end")
+        end
+      end
+
+      context "when the content is the same" do
+        before do
+          path.utime(mtime, mtime)
+        end
+
+        let(:mtime) { Time.now - 60 }
+
+        it "does not modify the file" do
+          file_writer.write(old_content)
+
+          expect(path).to exist
+          expect(path.read).to eq(old_content)
+          expect(path.mtime).to eq(mtime)
+        end
+      end
+    end
+  end
+end