Test firstLineRegex first when finding grammar

This is required for the property-list bundle to highlight
.plist files that maybe in XML or non-XML formats.

Also specify the cached buffer disk contents to grammarForFilePath
so fs.read doesn't need to be called again if the contents are
already read.

spec/app/syntax-spec.coffee

@@ -1,3 +1,5 @@
+fs = require 'fs'
+
 describe "the `syntax` global", ->
   describe ".grammarForFilePath(filePath)", ->
     it "uses the filePath's extension to load the correct grammar", ->
@@ -10,6 +12,13 @@ describe "the `syntax` global", ->
       filePath = require.resolve("fixtures/shebang")
       expect(syntax.grammarForFilePath(filePath).name).toBe "Ruby"
 
+    it "doesn't read the file when the file contents are specified", ->
+      filePath = require.resolve("fixtures/shebang")
+      filePathContents = fs.read(filePath)
+      spyOn(fs, 'read').andCallThrough()
+      expect(syntax.grammarForFilePath(filePath, filePathContents).name).toBe "Ruby"
+      expect(fs.read).not.toHaveBeenCalled()
+
     it "uses the grammar's fileType as a suffix of the full filePath if the grammar cannot be determined by shebang line", ->
       expect(syntax.grammarForFilePath("/tmp/.git/config").name).toBe "Git Config"
 

src/app/language-mode.coffee

@@ -48,10 +48,12 @@ class LanguageMode
         false
 
   reloadGrammar: ->
+    path = @buffer.getPath()
+    pathContents = @buffer.cachedDiskContents
     if @buffer.project?
-      @grammar = @buffer.project.grammarForFilePath(@buffer.getPath())
+      @grammar = @buffer.project.grammarForFilePath(path, pathContents)
     else
-      @grammar = syntax.grammarForFilePath(@buffer.getPath())
+      @grammar = syntax.grammarForFilePath(path, pathContents)
 
   isQuote: (string) ->
     /'|"/.test(string)

src/app/project.coffee

@@ -45,8 +45,8 @@ class Project
   grammarOverrideForPath: (path) ->
     syntax.grammarForScopeName(@grammarOverridesByPath[path])
 
-  grammarForFilePath: (path) ->
-    @grammarOverrideForPath(path) or syntax.grammarForFilePath(path)
+  grammarForFilePath: (path, contents) ->
+    @grammarOverrideForPath(path) or syntax.grammarForFilePath(path, contents)
 
   getPath: ->
     @rootDirectory?.path

src/app/syntax.coffee

@@ -20,15 +20,15 @@ class Syntax
       @grammarsByFileType[fileType] = grammar
       @grammarsByScopeName[grammar.scopeName] = grammar
 
-  grammarForFilePath: (filePath) ->
+  grammarForFilePath: (filePath, fileContents) ->
     return @grammarsByFileType["txt"] unless filePath
 
     extension = fs.extension(filePath)?[1..]
     if filePath and extension.length == 0
       extension = fs.base(filePath)
 
-    @grammarsByFileType[extension] or
-      @grammarByFirstLineRegex(filePath) or
+    @grammarByFirstLineRegex(filePath, fileContents) or
+      @grammarsByFileType[extension] or
       @grammarByFileTypeSuffix(filePath) or
       @grammarsByFileType["txt"]
 
@@ -36,9 +36,9 @@ class Syntax
     for fileType, grammar of @grammarsByFileType
       return grammar if _.endsWith(filePath, fileType)
 
-  grammarByFirstLineRegex: (filePath) ->
+  grammarByFirstLineRegex: (filePath, fileContents) ->
     try
-      fileContents = fs.read(filePath)
+      fileContents = fs.read(filePath) unless fileContents?
     catch e
       null