Allow classifier to run on symlinks as usual (#3948)

* Fixups for symlink detection, incl. test

* assert the heuristics return none for symlink

test/test_heuristics.rb

@@ -13,8 +13,9 @@ class TestHeuristics < Minitest::Test
   end
 
   def all_fixtures(language_name, file="*")
-    Dir.glob("#{samples_path}/#{language_name}/#{file}") -
-      ["#{samples_path}/#{language_name}/filenames"]
+    fixs = Dir.glob("#{samples_path}/#{language_name}/#{file}") -
+             ["#{samples_path}/#{language_name}/filenames"]
+    fixs.reject { |f| File.symlink?(f) }
   end
 
   def test_no_match
@@ -23,6 +24,10 @@ class TestHeuristics < Minitest::Test
     assert_equal [], results
   end
 
+  def test_symlink_empty
+    assert_equal [], Heuristics.call(file_blob("Markdown/symlink.md"), [Language["Markdown"]])
+  end
+
   def assert_heuristics(hash)
     candidates = hash.keys.map { |l| Language[l] }
 

test/test_language.rb

@@ -473,4 +473,10 @@ class TestLanguage < Minitest::Test
     assert_nil Language.find_by_name(',')
     assert_nil Language.find_by_alias(',')
   end
+
+  def test_detect_prefers_markdown_for_md
+    blob = Linguist::FileBlob.new(File.join(samples_path, "Markdown/symlink.md"))
+    match = Linguist.detect(blob)
+    assert_equal Language["Markdown"], match
+  end
 end