Selection.selectLine takes a row as an argument.

spec/atom/selection-spec.coffee

@@ -184,8 +184,8 @@ describe "Selection", ->
          selection.selectWord()
          expect(selection.getText()).toBe ''
 
-  describe ".selectLine()", ->
-    it "selects the entire line the cursor is on", ->
-       editor.setCursorPosition [1,2]
-       selection.selectLine()
+  describe ".selectLine(row)", ->
+    it "selects the entire line at given row", ->
+       editor.setCursorPosition [0,2]
+       selection.selectLine(1)
        expect(selection.getText()).toBe "  var sort = function(items) {"

src/atom/editor.coffee

@@ -86,7 +86,7 @@ class Editor extends Template
         else if clickCount == 2
           @selection.selectWord()
         else if clickCount >= 3
-          @selection.selectLine()
+          @selection.selectLine(@getCursorRow())
 
         @selectTextOnMouseMovement()
 

src/atom/selection.coffee

@@ -114,9 +114,9 @@ class Selection extends Template
       range = new Range([row, column + startOffset], [row, column + endOffset])
       @setRange range
 
-    selectLine: ->
-      row = @cursor.getRow()
-      @setRange new Range([row, 0], [row, @editor.getCurrentLine().length])
+    selectLine: (row) ->
+      rowLength = @editor.buffer.getLine(row).length
+      @setRange new Range([row, 0], [row, rowLength])
 
     selectRight: ->
       @modifySelection =>