Don't obscure the last line of the editor with the horizontal scrollbar

This assumes the scrollbar is 15px high, which is incorrect when using
overlay scrollbars or when the scrollbar is styled to have a different
height. We'll need to measure it in a subsequent commit.

spec/editor-component-spec.coffee

@@ -1,4 +1,4 @@
-{extend, flatten, toArray} = require 'underscore-plus'
+{extend, flatten, toArray, last} = require 'underscore-plus'
 ReactEditorView = require '../src/react-editor-view'
 nbsp = String.fromCharCode(160)
 
@@ -526,6 +526,25 @@ describe "EditorComponent", ->
 
       expect(editor.getScrollLeft()).toBe 100
 
+    it "does not obscure the last line with the horizontal scrollbar", ->
+      node.style.height = 4.5 * lineHeightInPixels + 'px'
+      node.style.width = 10 * charWidth + 'px'
+      component.measureHeightAndWidth()
+      editor.setScrollBottom(editor.getScrollHeight())
+      lastLineNode = last(node.querySelectorAll('.line'))
+      bottomOfLastLine = lastLineNode.getBoundingClientRect().bottom
+      topOfHorizontalScrollbar = horizontalScrollbarNode.getBoundingClientRect().top
+      expect(bottomOfLastLine).toBe topOfHorizontalScrollbar
+
+      # Render no space below the last line when there's no horizontal scrollbar
+      node.style.width = 100 * charWidth + 'px'
+      component.measureHeightAndWidth()
+      editor.setScrollBottom(editor.getScrollHeight())
+      lastLineNode = last(node.querySelectorAll('.line'))
+      bottomOfLastLine = lastLineNode.getBoundingClientRect().bottom
+      bottomOfEditor = node.getBoundingClientRect().bottom
+      expect(bottomOfLastLine).toBe bottomOfEditor
+
     describe "when a mousewheel event occurs on the editor", ->
       it "updates the horizontal or vertical scrollbar depending on which delta is greater (x or y)", ->
         node.style.height = 4.5 * lineHeightInPixels + 'px'

src/display-buffer.coffee

@@ -114,6 +114,17 @@ class DisplayBuffer extends Model
   getHeight: -> @height ? @getScrollHeight()
   setHeight: (@height) -> @height
 
+  getClientHeight: ->
+    if @horizontallyScrollable()
+      @getHeight() - @getHorizontalScrollbarHeight()
+    else
+      @getHeight()
+
+  horizontallyScrollable: ->
+    not @getSoftWrap() and @getScrollWidth() > @getWidth()
+
+  getHorizontalScrollbarHeight: -> 15
+
   getWidth: -> @width ? @getScrollWidth()
   setWidth: (newWidth) ->
     oldWidth = @width
@@ -124,13 +135,13 @@ class DisplayBuffer extends Model
   getScrollTop: -> @scrollTop
   setScrollTop: (scrollTop) ->
     if @manageScrollPosition
-      @scrollTop = Math.max(0, Math.min(@getScrollHeight() - @getHeight(), scrollTop))
+      @scrollTop = Math.max(0, Math.min(@getScrollHeight() - @getClientHeight(), scrollTop))
     else
       @scrollTop = scrollTop
 
   getScrollBottom: -> @scrollTop + @height
   setScrollBottom: (scrollBottom) ->
-    @setScrollTop(scrollBottom - @height)
+    @setScrollTop(scrollBottom - @getClientHeight())
     @getScrollBottom()
 
   getScrollLeft: -> @scrollLeft
@@ -184,7 +195,7 @@ class DisplayBuffer extends Model
     unless @getLineHeight() > 0
       throw new Error("You must assign a non-zero lineHeight before calling ::getVisibleRowRange()")
 
-    heightInLines = Math.ceil(@getHeight() / @getLineHeight()) + 1
+    heightInLines = Math.ceil(@getClientHeight() / @getLineHeight()) + 1
     startRow = Math.floor(@getScrollTop() / @getLineHeight())
     endRow = Math.min(@getLineCount(), Math.ceil(startRow + heightInLines))
     [startRow, endRow]