Detect softTabs/hardTabs when an EditSession is created

spec/app/buffer-spec.coffee

@@ -628,3 +628,12 @@ describe 'Buffer', ->
         buffer.delete([[3, 0], [5, 0]])
         expect(destroyHandler).toHaveBeenCalled()
         expect(buffer.getAnchors().indexOf(anchor)).toBe -1
+
+  describe ".usesSoftTabs()", ->
+    it "returns true if the first indented line begins with tabs", ->
+      buffer.setText("function() {\n  foo();\n}")
+      expect(buffer.usesSoftTabs()).toBeTruthy()
+      buffer.setText("function() {\n\tfoo();\n}")
+      expect(buffer.usesSoftTabs()).toBeFalsy()
+      buffer.setText("")
+      expect(buffer.usesSoftTabs()).toBeUndefined()

spec/app/edit-session-spec.coffee

@@ -10,7 +10,6 @@ describe "EditSession", ->
     buffer.setText(buffer.getText().replace(/[ ]{2}/g, "\t"))
 
   beforeEach ->
-    buffer = new Buffer()
     editSession = fixturesProject.buildEditSessionForPath('sample.js', autoIndent: false)
     buffer = editSession.buffer
     lineLengths = buffer.getLines().map (line) -> line.length
@@ -1745,3 +1744,14 @@ describe "EditSession", ->
       editSession.setSelectedBufferRange([[0, 1], [0, 4]])
       editSession.transpose()
       expect(editSession.lineForBufferRow(0)).toBe 'xcbaz'
+
+  describe "soft-tabs detection", ->
+    it "assign soft / hard tabs based on the contents of the buffer, or uses the default if unknown", ->
+      editSession = fixturesProject.buildEditSessionForPath('sample.js', softTabs: false)
+      expect(editSession.softTabs).toBeTruthy()
+
+      editSession = fixturesProject.buildEditSessionForPath('sample-with-tabs.coffee', softTabs: true)
+      expect(editSession.softTabs).toBeFalsy()
+
+      editSession = fixturesProject.buildEditSessionForPath(null, softTabs: false)
+      expect(editSession.softTabs).toBeFalsy()

src/app/buffer.coffee

@@ -352,6 +352,12 @@ class Buffer
         return row unless @isRowBlank(row)
     null
 
+  usesSoftTabs: ->
+    for line in @getLines()
+      if match = line.match(/^\s/)
+        return match[0][0] != '\t'
+    undefined
+
   logLines: (start=0, end=@getLastRow())->
     for row in [start..end]
       line = @lineForRow(row)

src/app/edit-session.coffee

@@ -39,9 +39,9 @@ class EditSession
   softTabs: true
   softWrap: false
 
-  constructor: ({@project, @buffer, @tabLength, @autoIndent, @softTabs, @softWrap }) ->
+  constructor: ({@project, @buffer, @tabLength, @autoIndent, softTabs, @softWrap }) ->
     @id = @constructor.idCounter++
-    @softTabs ?= true
+    @softTabs = @buffer.usesSoftTabs() ? softTabs ? true
     @languageMode = new LanguageMode(this, @buffer.getExtension())
     @displayBuffer = new DisplayBuffer(@buffer, { @languageMode, @tabLength })
     @tokenizedBuffer = @displayBuffer.tokenizedBuffer