Change syntax.selectGrammar to choose the highest-scoring grammar

This sets us up to switch to a grammar when it is loaded if it is a
better match for the current file.

src/app/null-grammar.coffee

@@ -5,5 +5,7 @@ class NullGrammar
   name: 'Null Grammar'
   scopeName: 'text.plain.null-grammar'
 
+  getScore: -> 0
+
   tokenizeLine: (line) ->
     { tokens: [new Token(value: line, scopes: ['null-grammar.text.plain'])] }

src/app/syntax.coffee

@@ -5,8 +5,6 @@ Specificity = require 'specificity'
 fsUtils = require 'fs-utils'
 EventEmitter = require 'event-emitter'
 NullGrammar = require 'null-grammar'
-nodePath = require 'path'
-pathSplitRegex = new RegExp("[#{nodePath.sep}.]")
 
 module.exports =
 class Syntax
@@ -18,13 +16,13 @@ class Syntax
     syntax
 
   constructor: ->
-    @grammars = []
+    @nullGrammar = new NullGrammar
+    @grammars = [@nullGrammar]
     @grammarsByFileType = {}
     @grammarsByScopeName = {}
     @grammarOverridesByPath = {}
     @scopedPropertiesIndex = 0
     @scopedProperties = []
-    @nullGrammar = new NullGrammar
 
   serialize: ->
     { deserializer: @constructor.name, @grammarOverridesByPath }
@@ -50,51 +48,10 @@ class Syntax
     @grammarOverridesByPath = {}
 
   selectGrammar: (filePath, fileContents) ->
-
-    return @grammarsByFileType["txt"] ? @nullGrammar unless filePath
-
-    @grammarOverrideForPath(filePath) ?
-      @grammarByFirstLineRegex(filePath, fileContents) ?
-      @grammarByPath(filePath) ?
-      @grammarsByFileType["txt"] ?
-      @nullGrammar
+    _.max @grammars, (grammar) -> grammar.getScore(filePath, fileContents)
 
   grammarOverrideForPath: (path) ->
-    @grammarsByScopeName[@grammarOverridesByPath[path]]
-
-  grammarByPath: (path) ->
-    pathComponents = path.split(pathSplitRegex)
-    for fileType, grammar of @grammarsByFileType
-      fileTypeComponents = fileType.split(pathSplitRegex)
-      pathSuffix = pathComponents[-fileTypeComponents.length..-1]
-      return grammar if _.isEqual(pathSuffix, fileTypeComponents)
-
-  grammarByFirstLineRegex: (filePath, fileContents) ->
-    try
-      fileContents ?= fsUtils.read(filePath)
-    catch e
-      return
-
-    return unless fileContents
-
-    lines = fileContents.split('\n')
-    _.find @grammars, (grammar) ->
-      regex = grammar.firstLineRegex
-      return unless regex?
-
-      escaped = false
-      numberOfNewlinesInRegex = 0
-      for character in regex.source
-        switch character
-          when '\\'
-            escaped = !escaped
-          when 'n'
-            numberOfNewlinesInRegex++ if escaped
-            escaped = false
-          else
-            escaped = false
-
-      regex.test(lines[0..numberOfNewlinesInRegex].join('\n'))
+    @grammarOverridesByPath[path]
 
   grammarForScopeName: (scopeName) ->
     @grammarsByScopeName[scopeName]

src/app/text-mate-grammar.coffee

@@ -2,8 +2,9 @@ _ = require 'underscore'
 fsUtils = require 'fs-utils'
 plist = require 'plist'
 Token = require 'token'
-CSON = require 'cson'
 {OnigRegExp, OnigScanner} = require 'oniguruma'
+nodePath = require 'path'
+pathSplitRegex = new RegExp("[#{nodePath.sep}.]")
 
 module.exports =
 class TextMateGrammar
@@ -38,6 +39,48 @@ class TextMateGrammar
       data = {patterns: [data], tempName: name} if data.begin? or data.match?
       @repository[name] = new Rule(this, data)
 
+  getScore: (path, contents) ->
+    contents = fsUtils.read(path) if not contents? and fsUtils.isFile(path)
+
+    if syntax.grammarOverrideForPath(path) is @scopeName
+      Infinity
+    else if @matchesContents(contents)
+      3
+    else if @matchesPath(path)
+      2
+    else if @isTextGrammar()
+      1
+    else
+      -1
+
+  matchesContents: (contents) ->
+    return false unless contents? and @firstLineRegex?
+
+    escaped = false
+    numberOfNewlinesInRegex = 0
+    for character in @firstLineRegex.source
+      switch character
+        when '\\'
+          escaped = !escaped
+        when 'n'
+          numberOfNewlinesInRegex++ if escaped
+          escaped = false
+        else
+          escaped = false
+    lines = contents.split('\n')
+    @firstLineRegex.test(lines[0..numberOfNewlinesInRegex].join('\n'))
+
+  matchesPath: (path) ->
+    return false unless path?
+    pathComponents = path.split(pathSplitRegex)
+    _.find @fileTypes, (fileType) ->
+      fileTypeComponents = fileType.split(pathSplitRegex)
+      pathSuffix = pathComponents[-fileTypeComponents.length..-1]
+      _.isEqual(pathSuffix, fileTypeComponents)
+
+  isTextGrammar: ->
+    @scopeName is 'text.plain'
+
   tokenizeLine: (line, ruleStack=[@initialRule], firstLine=false) ->
     originalRuleStack = ruleStack
     ruleStack = new Array(ruleStack...) # clone ruleStack