Avoid more allocations in transformContent

src/tokenized-line.coffee

@@ -8,8 +8,26 @@ LeadingWhitespaceRegex = /^\s*/
 TrailingWhitespaceRegex = /\s*$/
 RepeatedSpaceRegex = /[ ]/g
 CommentScopeRegex = /(\b|\.)comment/
+TabCharCode = 9
+SpaceCharCode = 32
+SpaceString = ' '
+TabStringsByLength = {
+  1: ' '
+  2: '  '
+  3: '   '
+  4: '    '
+}
+
 idCounter = 1
 
+getTabString = (length) ->
+  TabStringsByLength[length] ?= buildTabString(length)
+
+buildTabString = (length) ->
+  string = SpaceString
+  string += SpaceString for i in [1...length] by 1
+  string
+
 module.exports =
 class TokenizedLine
   endOfLineInvisibles: null
@@ -53,18 +71,18 @@ class TokenizedLine
       # advance to next token tag
       tokenIndex++ while @tags[tokenIndex] < 0
 
-      character = @text[bufferColumn]
+      charCode = @text.charCodeAt(bufferColumn)
 
       # split out unicode surrogate pairs
       if isPairedCharacter(@text, bufferColumn)
         prefix = tokenOffset
         suffix = @tags[tokenIndex] - tokenOffset - 2
-        splitTokens = []
-        splitTokens.push(prefix) if prefix > 0
-        splitTokens.push(2)
-        splitTokens.push(suffix) if suffix > 0
 
-        @tags.splice(tokenIndex, 1, splitTokens...)
+        i = tokenIndex
+        @tags.splice(i, 1)
+        @tags.splice(i++, 0, prefix) if prefix > 0
+        @tags.splice(i++, 0, 2)
+        @tags.splice(i, 0, suffix) if suffix > 0
 
         firstNonWhitespaceColumn ?= screenColumn
         lastNonWhitespaceColumn = screenColumn + 1
@@ -79,7 +97,7 @@ class TokenizedLine
         tokenOffset = 0
 
       # split out leading soft tabs
-      else if character is ' '
+      else if charCode is SpaceCharCode
         if firstNonWhitespaceColumn?
           substringEnd += 1
         else
@@ -90,7 +108,8 @@ class TokenizedLine
             @tags.splice(tokenIndex + 1, 0, suffix) if suffix > 0
 
           if @invisibles?.space
-            text += @text.substring(substringStart, substringEnd) if substringEnd > substringStart
+            if substringEnd > substringStart
+              text += @text.substring(substringStart, substringEnd)
             substringStart = substringEnd
             text += @invisibles.space
             substringStart += 1
@@ -102,28 +121,29 @@ class TokenizedLine
         tokenOffset++
 
       # expand hard tabs to the next tab stop
-      else if character is '\t'
-        text += @text.substring(substringStart, substringEnd) if substringEnd > substringStart
+      else if charCode is TabCharCode
+        if substringEnd > substringStart
+          text += @text.substring(substringStart, substringEnd)
         substringStart = substringEnd
 
         tabLength = @tabLength - (screenColumn % @tabLength)
         if @invisibles?.tab
           text += @invisibles.tab
+          text += getTabString(tabLength - 1) if tabLength > 1
         else
-          text += ' '
-        text += ' ' for i in [1...tabLength] by 1
+          text += getTabString(tabLength)
 
         substringStart += 1
         substringEnd += 1
 
         prefix = tokenOffset
         suffix = @tags[tokenIndex] - tokenOffset - 1
-        splitTokens = []
-        splitTokens.push(prefix) if prefix > 0
-        splitTokens.push(tabLength)
-        splitTokens.push(suffix) if suffix > 0
 
-        @tags.splice(tokenIndex, 1, splitTokens...)
+        i = tokenIndex
+        @tags.splice(i, 1)
+        @tags.splice(i++, 0, prefix) if prefix > 0
+        @tags.splice(i++, 0, tabLength)
+        @tags.splice(i, 0, suffix) if suffix > 0
 
         screenColumn += tabLength
         bufferColumn++