Basic Vim modeline detection strategy

lib/linguist/language.rb

@@ -11,6 +11,7 @@ require 'linguist/samples'
 require 'linguist/file_blob'
 require 'linguist/blob_helper'
 require 'linguist/strategy/filename'
+require 'linguist/strategy/modeline'
 require 'linguist/shebang'
 
 module Linguist
@@ -95,6 +96,7 @@ module Linguist
 
     STRATEGIES = [
       Linguist::Strategy::Filename,
+      Linguist::Strategy::Modeline,
       Linguist::Shebang,
       Linguist::Heuristics,
       Linguist::Classifier

lib/linguist/strategy/modeline.rb

@@ -0,0 +1,31 @@
+module Linguist
+  module Strategy
+    class Modeline
+      # Public: Detects language based on Vim and Emacs modelines
+      #
+      # blob               - An object that quacks like a blob.
+      #
+      # Examples
+      #
+      #   Modeline.call(FileBlob.new("path/to/file"))
+      #
+      # Returns an Array with one Language if the blob has a shebang with a valid
+      # interpreter, or empty if there is no shebang.
+      def self.call(blob, _ = nil)
+        if language = Language.find_by_alias(modeline(blob.data))
+          return [language]
+        else
+          return []
+        end
+      end
+
+      # Public: Get the modeline from the first n-lines of the file
+      #
+      # Returns a String or nil
+      def self.modeline(data)
+        data.lines.first(5).any? { |l| l.match(/\W(?:filetype|ft)=\s*(\w+)/) }
+        lang = $1
+      end
+    end
+  end
+end