Add editor.softWrapAtPreferredLineLength config setting

This is used by the DisplayBuffer to use `editor.preferredLineLength`
as the soft wrap column instead of the editor size.

spec/display-buffer-spec.coffee

@@ -65,6 +65,21 @@ describe "DisplayBuffer", ->
       changeHandler.reset()
 
     describe "rendering of soft-wrapped lines", ->
+      describe "when editor.softWrapAtPreferredLineLength is set", ->
+        it "uses the preferred line length as the soft wrap column when it is less than the configured soft wrap column", ->
+          config.set('editor.preferredLineLength', 100)
+          config.set('editor.softWrapAtPreferredLineLength', true)
+          displayBuffer.updateWrappedScreenLines()
+          expect(displayBuffer.lineForRow(10).text).toBe '    return '
+
+          config.set('editor.preferredLineLength', 5)
+          displayBuffer.updateWrappedScreenLines()
+          expect(displayBuffer.lineForRow(10).text).toBe 'funct'
+
+          config.set('editor.softWrapAtPreferredLineLength', false)
+          displayBuffer.updateWrappedScreenLines()
+          expect(displayBuffer.lineForRow(10).text).toBe '    return '
+
       describe "when the line is shorter than the max line length", ->
         it "renders the line unchanged", ->
           expect(displayBuffer.lineForRow(0).text).toBe buffer.lineForRow(0)

src/display-buffer.coffee

@@ -415,6 +415,8 @@ class DisplayBuffer
   # Returns a {Number} representing the `line` position where the wrap would take place.
   # Returns `null` if a wrap wouldn't occur.
   findWrapColumn: (line, softWrapColumn=@getSoftWrapColumn()) ->
+    if config.get('editor.softWrapAtPreferredLineLength')
+      softWrapColumn = Math.min(softWrapColumn, config.getPositiveInt('editor.preferredLineLength', softWrapColumn))
     return unless @getSoftWrap()
     return unless line.length > softWrapColumn
 

src/editor.coffee

@@ -26,6 +26,7 @@ class Editor extends View
     tabLength: 2
     softWrap: false
     softTabs: true
+    softWrapAtPreferredLineLength: false
 
   @nextEditorId: 1