Merge branch 'detect-prolog' of https://github.com/tautologico/linguist into tautologico-detect-prolog

Conflicts:
	lib/linguist/blob_helper.rb
	test/test_blob.rb

lib/linguist/blob_helper.rb

@@ -281,6 +281,9 @@ module Linguist
         # If it's a .m file, try to guess the language
         m_language ||
 
+        # If it's a .pl file, try to guess the language
+        pl_language ||
+
         # If it's a .r file, try to guess the language
         r_language ||
 
@@ -347,6 +350,26 @@ module Linguist
       end
     end
 
+    # Internal: Guess language of .pl files
+    #
+    # Returns a Language.
+    def pl_language
+      return unless extname == '.pl'
+
+      # The rules for disambiguation are:
+      #
+      # 1. Many perl files begin with a shebang
+      # 2. Most Prolog source files have a rule somewhere (marked by the :- operator)
+      # 3. Default to Perl, because it is more popular
+      if shebang_script == 'perl'
+        Language['Perl']
+      elsif lines.grep(/:-/).any?
+        Language['Prolog']
+      else
+        Language['Perl']
+      end
+    end
+
     # Internal: Guess language of .r files.
     #
     # Returns a Language.

lib/linguist/languages.yml

@@ -590,6 +590,12 @@ Perl:
   - .perl
   - .psgi
 
+Prolog:
+  major: true
+  extensions:
+  - .pro
+  - .prolog
+
 Pure Data:
   major: true
   lexer: Text only