Add yarn (#3432)

* add yarn.lock

* fix comment

* remove yarn test

* add test

* fix test

* try fix again

* try 3rd time

* check filename and firstline for yarn lockfile

lib/linguist/generated.rb

@@ -80,7 +80,8 @@ module Linguist
       generated_jflex? ||
       generated_grammarkit? ||
       generated_roxygen2? ||
-      generated_jison?
+      generated_jison? ||
+      generated_yarn_lock?
     end
 
     # Internal: Is the blob an Xcode file?
@@ -479,5 +480,13 @@ module Linguist
       return lines[0].start_with?("/* parser generated by jison ") ||
              lines[0].start_with?("/* generated by jison-lex ")
     end
+
+    # Internal: Is the blob a generated yarn lockfile?
+    #
+    # Returns true or false.
+    def generated_yarn_lock?
+      return false unless name.match(/yarn\.lock/)
+      return lines[0].include?("# THIS IS AN AUTOGENERATED FILE")
+    end
   end
 end

test/fixtures/Data/yarn.lock

@@ -0,0 +1,9 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+abab@^1.0.0:
+  version "1.0.3"
+  resolved "https://registry.yarnpkg.com/abab/-/abab-1.0.3.tgz#b81de5f7274ec4e756d797cd834f303642724e5d"
+
+abbrev@1, abbrev@1.0.x:
+  version "1.0.9"
+  resolved "https://registry.yarnpkg.com/abbrev/-/abbrev-1.0.9.tgz#91b4792588a7738c25f35dd6f63752a2f8776135"

test/test_generated.rb

@@ -79,6 +79,9 @@ class TestGenerated < Minitest::Test
     generated_fixture_loading_data("Data/sourcemap.v3.map")
     generated_fixture_loading_data("Data/sourcemap.v1.map")
 
+    # Yarn locfile
+    generated_fixture_loading_data("Data/yarn.lock")
+
     # Specflow
     generated_fixture_without_loading_data("Features/BindingCulture.feature.cs")