Fix linemap translation when an atomic token is at the end of a line.

Previously, if you entered an atomic token (like a tab) on an empty line it would not position the cursor after the token. This commit fixes that.

If the last screen line token is atomic, and screenLine.translateColumn's sourceColumn parameter is greater than the start position of the atomic token, then the translated column should be the end position of the atomic token.

spec/app/screen-line-spec.coffee

@@ -6,8 +6,8 @@ describe "ScreenLine", ->
   [editSession, buffer, tabText, screenLine, tokenizedBuffer] = []
 
   beforeEach ->
-    tabText = '  '
-    editSession = fixturesProject.buildEditSessionForPath('sample.js')
+    tabText = '••'
+    editSession = fixturesProject.buildEditSessionForPath('sample.js', { tabText } )
     { buffer, tokenizedBuffer } = editSession
     screenLine = tokenizedBuffer.lineForScreenRow(3)
 
@@ -81,8 +81,7 @@ describe "ScreenLine", ->
 
   describe ".translateColumn(sourceDeltaType, targetDeltaType, sourceColumn, skipAtomicTokens: false)", ->
     beforeEach ->
-      buffer.insert([0, 13], '\t')
-      buffer.insert([0, 0], '\t\t')
+      buffer.setText("\t\t-")
       screenLine = tokenizedBuffer.lineForScreenRow(0)
 
     describe "when translating from buffer to screen coordinates", ->
@@ -91,8 +90,11 @@ describe "ScreenLine", ->
         expect(screenLine.translateColumn('bufferDelta', 'screenDelta', 1)).toBe 2
         expect(screenLine.translateColumn('bufferDelta', 'screenDelta', 2)).toBe 4
         expect(screenLine.translateColumn('bufferDelta', 'screenDelta', 3)).toBe 5
-        expect(screenLine.translateColumn('bufferDelta', 'screenDelta', 15)).toBe 17
-        expect(screenLine.translateColumn('bufferDelta', 'screenDelta', 16)).toBe 19
+
+      describe "when an atomic token is at the end of the line (regression)", ->
+        it "translates a buffer position correctly", ->
+          buffer.setText("\t")
+          expect(tokenizedBuffer.lineForScreenRow(0).translateColumn('bufferDelta', 'screenDelta', 1)).toBe 2
 
     describe "when translating from screen coordinates to buffer coordinates", ->
       describe "when skipAtomicTokens is false (the default)", ->

src/app/screen-line.coffee

@@ -61,16 +61,19 @@ class ScreenLine
 
     currentSourceColumn = 0
     currentTargetColumn = 0
+    isSourceColumnBeforeLastToken = false
     for token in @tokens
       tokenStartTargetColumn = currentTargetColumn
       tokenStartSourceColumn = currentSourceColumn
       tokenEndSourceColumn = currentSourceColumn + token[sourceDeltaType]
       tokenEndTargetColumn = currentTargetColumn + token[targetDeltaType]
-      break if tokenEndSourceColumn > sourceColumn
+      if tokenEndSourceColumn > sourceColumn
+        isSourceColumnBeforeLastToken = true
+        break
       currentSourceColumn = tokenEndSourceColumn
       currentTargetColumn = tokenEndTargetColumn
 
-    if token?.isAtomic
+    if isSourceColumnBeforeLastToken and token?.isAtomic
       if skipAtomicTokens and sourceColumn > tokenStartSourceColumn
         tokenEndTargetColumn
       else