Constrain scrollLeft based on computed clientWith and scrollWidth

spec/text-editor-presenter-spec.coffee

@@ -143,11 +143,30 @@ describe "TextEditorPresenter", ->
 
       describe ".scrollLeft", ->
         it "tracks the value of ::scrollLeft", ->
-          presenter = new TextEditorPresenter(model: editor, scrollLeft: 10, lineHeight: 10, lineOverdrawMargin: 1)
+          presenter = new TextEditorPresenter(model: editor, scrollLeft: 10, lineHeight: 10, baseCharacterWidth: 10, lineOverdrawMargin: 1, verticalScrollbarWidth: 10, contentFrameWidth: 500)
           expect(presenter.state.horizontalScrollbar.scrollLeft).toBe 10
           expectStateUpdate presenter, -> presenter.setScrollLeft(50)
           expect(presenter.state.horizontalScrollbar.scrollLeft).toBe 50
 
+        it "never exceeds the computed scrollWidth minus the computed clientWidth", ->
+          presenter = new TextEditorPresenter(model: editor, scrollLeft: 10, lineHeight: 10, baseCharacterWidth: 10, lineOverdrawMargin: 1, verticalScrollbarWidth: 10, contentFrameWidth: 500)
+          expectStateUpdate presenter, -> presenter.setScrollLeft(300)
+          expect(presenter.state.horizontalScrollbar.scrollLeft).toBe presenter.computeScrollWidth() - presenter.computeClientWidth()
+
+          expectStateUpdate presenter, -> presenter.setContentFrameWidth(600)
+          expect(presenter.state.horizontalScrollbar.scrollLeft).toBe presenter.computeScrollWidth() - presenter.computeClientWidth()
+
+          expectStateUpdate presenter, -> presenter.setVerticalScrollbarWidth(15)
+          expect(presenter.state.horizontalScrollbar.scrollLeft).toBe presenter.computeScrollWidth() - presenter.computeClientWidth()
+
+          expectStateUpdate presenter, -> editor.getBuffer().delete([[6, 0], [6, Infinity]])
+          expect(presenter.state.horizontalScrollbar.scrollLeft).toBe presenter.computeScrollWidth() - presenter.computeClientWidth()
+
+          # Scroll top only gets smaller when needed as dimensions change, never bigger
+          scrollLeftBefore = presenter.state.horizontalScrollbar.scrollLeft
+          expectStateUpdate presenter, -> editor.getBuffer().insert([6, 0], new Array(100).join('x'))
+          expect(presenter.state.horizontalScrollbar.scrollLeft).toBe scrollLeftBefore
+
     describe ".verticalScrollbar", ->
       describe ".visible", ->
         it "is true if the scrollHeight exceeds the computed client height", ->
@@ -228,7 +247,7 @@ describe "TextEditorPresenter", ->
           expectStateUpdate presenter, -> presenter.setScrollTop(50)
           expect(presenter.state.verticalScrollbar.scrollTop).toBe 50
 
-        it "never exceeds the computed scroll height minus the computed client height", ->
+        it "never exceeds the computed scrollHeight minus the computed clientHeight", ->
           presenter = new TextEditorPresenter(model: editor, scrollTop: 10, lineHeight: 10, height: 50, horizontalScrollbarHeight: 10)
           expectStateUpdate presenter, -> presenter.setScrollTop(100)
           expect(presenter.state.verticalScrollbar.scrollTop).toBe presenter.computeScrollHeight() - presenter.computeClientHeight()
@@ -366,13 +385,31 @@ describe "TextEditorPresenter", ->
           expectStateUpdate presenter, -> editor.getBuffer().insert([9, Infinity], '\n\n\n')
           expect(presenter.state.content.scrollTop).toBe scrollTopBefore
 
-      describe ".scrollLeft", ->
         it "tracks the value of ::scrollLeft", ->
-          presenter = new TextEditorPresenter(model: editor, scrollLeft: 10, lineHeight: 10, lineOverdrawMargin: 1)
+          presenter = new TextEditorPresenter(model: editor, scrollLeft: 10, lineHeight: 10, baseCharacterWidth: 10, lineOverdrawMargin: 1, verticalScrollbarWidth: 10, contentFrameWidth: 500)
           expect(presenter.state.content.scrollLeft).toBe 10
           expectStateUpdate presenter, -> presenter.setScrollLeft(50)
           expect(presenter.state.content.scrollLeft).toBe 50
 
+        it "never exceeds the computed scrollWidth minus the computed clientWidth", ->
+          presenter = new TextEditorPresenter(model: editor, scrollLeft: 10, lineHeight: 10, baseCharacterWidth: 10, lineOverdrawMargin: 1, verticalScrollbarWidth: 10, contentFrameWidth: 500)
+          expectStateUpdate presenter, -> presenter.setScrollLeft(300)
+          expect(presenter.state.content.scrollLeft).toBe presenter.computeScrollWidth() - presenter.computeClientWidth()
+
+          expectStateUpdate presenter, -> presenter.setContentFrameWidth(600)
+          expect(presenter.state.content.scrollLeft).toBe presenter.computeScrollWidth() - presenter.computeClientWidth()
+
+          expectStateUpdate presenter, -> presenter.setVerticalScrollbarWidth(15)
+          expect(presenter.state.content.scrollLeft).toBe presenter.computeScrollWidth() - presenter.computeClientWidth()
+
+          expectStateUpdate presenter, -> editor.getBuffer().delete([[6, 0], [6, Infinity]])
+          expect(presenter.state.content.scrollLeft).toBe presenter.computeScrollWidth() - presenter.computeClientWidth()
+
+          # Scroll top only gets smaller when needed as dimensions change, never bigger
+          scrollLeftBefore = presenter.state.content.scrollLeft
+          expectStateUpdate presenter, -> editor.getBuffer().insert([6, 0], new Array(100).join('x'))
+          expect(presenter.state.content.scrollLeft).toBe scrollLeftBefore
+
       describe ".indentGuidesVisible", ->
         it "is initialized based on the editor.showIndentGuide config setting", ->
           presenter = new TextEditorPresenter(model: editor)
@@ -1804,6 +1841,7 @@ describe "TextEditorPresenter", ->
 
     expectValidState = ->
       presenterParams.scrollTop = presenter.scrollTop
+      presenterParams.scrollLeft = presenter.scrollLeft
       actualState = presenter.state
       expectedState = new TextEditorPresenter(presenterParams).state
       delete actualState.content.scrollingVertically

src/text-editor-presenter.coffee

@@ -108,8 +108,9 @@ class TextEditorPresenter
     @state.content.scrollWidth = scrollWidth
     @state.horizontalScrollbar.scrollWidth = scrollWidth
 
-    @state.content.scrollLeft = @scrollLeft
-    @state.horizontalScrollbar.scrollLeft = @scrollLeft
+    scrollLeft = @computeScrollLeft()
+    @state.content.scrollLeft = scrollLeft
+    @state.horizontalScrollbar.scrollLeft = scrollLeft
 
     @emitter.emit 'did-update-state'
 
@@ -346,6 +347,9 @@ class TextEditorPresenter
   computeScrollTop: ->
     @scrollTop = Math.min(@scrollTop, @computeScrollHeight() - @computeClientHeight())
 
+  computeScrollLeft: ->
+    @scrollLeft = Math.min(@scrollLeft, @computeScrollWidth() - @computeClientWidth())
+
   computeHorizontalScrollbarHeight: ->
     contentWidth = @computeContentWidth()
     contentHeight = @computeContentHeight()