Add use_relative_paths configuration option

By setting this to `true`, imports will be resolved relatively to the
file you are currently looking at, under these circumstances:

 - The file you are currently in is in the same lookup_path as the
   module you are trying to import
 - The module you are resolving is not a package.json dependency /
   located in node_modules
 - The module you are importing is not an alias.

I'm not too happy with how the JSModule constructor ended up after this
change, so I indent to follow up with some clean-up.

lib/import_js/configuration.rb

@@ -9,7 +9,8 @@ module ImportJS
     'declaration_keyword' => 'import',
     'excludes' => [],
     'lookup_paths' => ['.'],
-    'strip_file_extensions' => ['.js', '.jsx']
+    'strip_file_extensions' => ['.js', '.jsx'],
+    'use_relative_paths' => false
   }
 
   # Class that initializes configuration from a .importjs.json file

lib/import_js/importer.rb

@@ -241,11 +241,11 @@ def find_current_imports
     # @param variable_name [String]
     # @return [Array]
     def find_js_modules(variable_name)
+      path_to_current_file = @editor.path_to_current_file
       if alias_module = @config.resolve_alias(variable_name,
-                                              @editor.path_to_current_file)
+                                              path_to_current_file)
         return [alias_module]
       end
-
       egrep_command =
         "egrep -i \"(/|^)#{formatted_to_regex(variable_name)}(/index)?(/package)?\.js.*\""
       matched_modules = []
@@ -260,7 +260,11 @@ def find_js_modules(variable_name)
             js_module = ImportJS::JSModule.new(
               lookup_path: lookup_path,
               relative_file_path: f,
-              strip_file_extensions: @config.get('strip_file_extensions'))
+              strip_file_extensions: @config.get('strip_file_extensions'),
+              make_relative_to: @config.get('use_relative_paths') &&
+                                path_to_current_file
+            )
+
             next if js_module.skip
             js_module
           end.compact

lib/import_js/js_module.rb

@@ -1,3 +1,5 @@
+require 'pathname'
+
 module ImportJS
   # Class that represents a js module found in the file system
   class JSModule
@@ -13,9 +15,12 @@ class JSModule
     #   the project root.
     # @param strip_file_extensions [Array] a list of file extensions to strip,
     #   e.g. ['.js', '.jsx']
+    # @param make_relative_to [String|nil] a path to a different file which the
+    #   resulting import path should be relative to.
     def initialize(lookup_path:,
                    relative_file_path:,
-                   strip_file_extensions:)
+                   strip_file_extensions:,
+                   make_relative_to: nil)
       @lookup_path = lookup_path
       @file_path = relative_file_path
       if relative_file_path.end_with? '/package.json'
@@ -39,6 +44,21 @@ def initialize(lookup_path:,
 
       if lookup_path
         @import_path = @import_path.sub("#{@lookup_path}\/", '') # remove path prefix
+        if make_relative_to
+          make_relative_to = make_relative_to.sub(Dir.pwd + "\/", '')
+          if make_relative_to.start_with? @lookup_path
+            make_relative_to_folder = Pathname.new(File.dirname(
+              make_relative_to.sub("#{@lookup_path}\/", '')
+            ))
+            path = Pathname.new(@import_path).relative_path_from(
+              make_relative_to_folder
+            ).to_s
+            unless path.start_with?('.')
+              path = './' + path
+            end
+            @import_path = path
+          end
+        end
       end
     end
 

spec/import_js/importer_spec.rb

@@ -1281,6 +1281,54 @@ def self.current_selection=(index)
           end
         end
       end
+
+      context 'with `use_relative_paths=true`' do
+        let(:existing_files) { ['bar/foo.jsx'] }
+        let(:text) { <<-EOS.strip }
+foo
+        EOS
+
+        before do
+          allow_any_instance_of(ImportJS::VIMEditor)
+            .to receive(:path_to_current_file)
+            .and_return(path_to_current_file)
+        end
+
+        subject do
+          described_class.new.import
+          VIM::Buffer.current_buffer.to_s
+        end
+
+        let(:configuration) do
+          {
+            'use_relative_paths' => true
+          }
+        end
+
+        context 'when the current file is in the same lookup_path' do
+          let(:path_to_current_file) { File.join(@tmp_dir, 'bar/current.js') }
+
+          it 'uses a relative import path' do
+            expect(subject).to eq(<<-EOS.strip)
+import foo from './foo';
+
+foo
+            EOS
+          end
+        end
+
+        context 'when the current file is not in the same lookup_path' do
+          let(:path_to_current_file) { '/foo/bar/current.js' }
+
+          it 'does not use a relative import path' do
+            expect(subject).to eq(<<-EOS.strip)
+import foo from 'bar/foo';
+
+foo
+            EOS
+          end
+        end
+      end
     end
   end
 

spec/import_js/js_module_spec.rb

@@ -3,12 +3,15 @@
 describe ImportJS::JSModule do
   let(:lookup_path) { 'app' }
   let(:relative_file_path) { 'app/lib/foo.js' }
+  let(:make_relative_to) { nil }
+  let(:strip_file_extensions) { ['.js'] }
 
   subject do
     described_class.new(
       lookup_path: lookup_path,
       relative_file_path: relative_file_path,
-      strip_file_extensions: strip_file_extensions
+      strip_file_extensions: strip_file_extensions,
+      make_relative_to: make_relative_to
     )
   end
 
@@ -58,5 +61,47 @@
         end
       end
     end
+
+    context 'when asked to produce an import path relative to another file' do
+      context 'and the other file is in the same folder' do
+        let(:make_relative_to) { 'app/lib/bar.js' }
+
+        it 'produces a correct relative path' do
+          expect(subject.import_path).to eq('./foo')
+        end
+      end
+
+      context 'and the other file is in a parent folder' do
+        let(:make_relative_to) { 'app/bar.js' }
+
+        it 'produces a correct relative path' do
+          expect(subject.import_path).to eq('./lib/foo')
+        end
+      end
+
+      context 'and the other file is in a sibling folder' do
+        let(:make_relative_to) { 'app/foo/bar.js' }
+
+        it 'produces a correct relative path' do
+          expect(subject.import_path).to eq('../lib/foo')
+        end
+      end
+
+      context 'and the other file is in a child of a sibling folder' do
+        let(:make_relative_to) { 'app/foo/gas/bar.js' }
+
+        it 'produces a correct relative path' do
+          expect(subject.import_path).to eq('../../lib/foo')
+        end
+      end
+
+      context 'and the other file is in a different lookup_path' do
+        let(:make_relative_to) { 'spec/foo/gas/bar.js' }
+
+        it 'does not create a relative path' do
+          expect(subject.import_path).to eq('lib/foo')
+        end
+      end
+    end
   end
 end