Add bracket matcher that highlights pair

(), {}, and [] pairs are now highlighted when
after or before the cursor

src/app/edit-session.coffee

@@ -307,6 +307,9 @@ class EditSession
     fold.destroy()
     @setCursorBufferPosition([fold.startRow, 0])
 
+  isFoldedAtCursorRow: ->
+    @isFoldedAtScreenRow(@getCursorScreenRow())
+
   isFoldedAtBufferRow: (bufferRow) ->
     screenRow = @screenPositionForBufferPosition([bufferRow]).row
     @isFoldedAtScreenRow(screenRow)

src/app/editor.coffee

@@ -277,6 +277,7 @@ class Editor extends View
   destroyFoldsContainingBufferRow: (bufferRow) -> @activeEditSession.destroyFoldsContainingBufferRow(bufferRow)
   isFoldedAtScreenRow: (screenRow) -> @activeEditSession.isFoldedAtScreenRow(screenRow)
   isFoldedAtBufferRow: (bufferRow) -> @activeEditSession.isFoldedAtBufferRow(bufferRow)
+  isFoldedAtCursorRow: -> @activeEditSession.isFoldedAtCursorRow()
 
   lineForScreenRow: (screenRow) -> @activeEditSession.lineForScreenRow(screenRow)
   linesForScreenRows: (start, end) -> @activeEditSession.linesForScreenRows(start, end)

src/packages/bracket-matcher/index.coffee

@@ -0,0 +1,94 @@
+AtomPackage = require 'atom-package'
+_ = require 'underscore'
+{$$} = require 'space-pen'
+Range = require 'range'
+
+module.exports =
+class BracketMatcher extends AtomPackage
+  startPairMatches:
+    '(': ')'
+    '[': ']'
+    '{': '}'
+
+  endPairMatches:
+    ')': '('
+    ']': '['
+    '}': '{'
+
+  pairHighlighted: false
+
+  activate: (rootView) ->
+    rootView.eachEditor (editor) => @subscribeToEditor(editor) if editor.attached
+
+  subscribeToEditor: (editor) ->
+    editor.on 'cursor:moved', => @updateMatch(editor)
+
+  createView: (editor, bufferPosition) ->
+    pixelPosition = editor.pixelPositionForBufferPosition(bufferPosition)
+    view = $$ -> @div class: 'bracket-matcher'
+    view.css('top', pixelPosition.top).css('left', pixelPosition.left)
+    view.width(editor.charWidth).height(editor.charHeight)
+
+  findCurrentPair: (editor, buffer, matches) ->
+    position = editor.getCursorBufferPosition()
+    currentPair = buffer.getTextInRange(Range.fromPointWithDelta(position, 0, 1))
+    unless matches[currentPair]
+      position = position.translate([0, -1])
+      currentPair = buffer.getTextInRange(Range.fromPointWithDelta(position, 0, 1))
+    matchingPair = matches[currentPair]
+    if matchingPair
+      {position, currentPair, matchingPair}
+    else
+      {}
+
+  findMatchingEndPair: (buffer, startPairPosition, startPair, endPair) ->
+    scanRange = new Range(startPairPosition.translate([0, 1]), buffer.getEofPosition())
+    regex = new RegExp("[#{_.escapeRegExp(startPair + endPair)}]", 'g')
+    endPairPosition = null
+    unpairedCount = 0
+    buffer.scanInRange regex, scanRange, (match, range, {stop}) =>
+      if match[0] is startPair
+        unpairedCount++
+      else if match[0] is endPair
+        unpairedCount--
+        endPairPosition = range.start
+        stop() if unpairedCount < 0
+    endPairPosition
+
+  findMatchingStartPair: (buffer, endPairPosition, startPair, endPair) ->
+    scanRange = new Range([0, 0], endPairPosition)
+    regex = new RegExp("[#{_.escapeRegExp(startPair + endPair)}]", 'g')
+    startPairPosition = null
+    unpairedCount = 0
+    scanner = (match, range, {stop}) =>
+      if match[0] is endPair
+        unpairedCount++
+      else if match[0] is startPair
+        unpairedCount--
+        startPairPosition = range.start
+        stop() if unpairedCount < 0
+    buffer.scanInRange(regex, scanRange, scanner, true)
+    startPairPosition
+
+  updateMatch: (editor) ->
+    return unless underlayer = editor.pane()?.find('.underlayer')
+
+    underlayer.find('.bracket-matcher').remove() if @pairHighlighted
+    @pairHighlighted = false
+
+    return unless editor.getSelection().isEmpty()
+    return if editor.isFoldedAtCursorRow()
+
+    buffer = editor.getBuffer()
+    {position, currentPair, matchingPair} = @findCurrentPair(editor, buffer, @startPairMatches)
+    if position
+      matchPosition = @findMatchingEndPair(buffer, position, currentPair, matchingPair)
+    else
+      {position, currentPair, matchingPair} = @findCurrentPair(editor, buffer, @endPairMatches)
+      if position
+        matchPosition = @findMatchingStartPair(buffer, position, matchingPair, currentPair)
+
+    if position? and matchPosition?
+      underlayer.append(@createView(editor, position))
+      underlayer.append(@createView(editor, matchPosition))
+      @pairHighlighted = true

src/packages/bracket-matcher/spec/bracket-matcher-spec.coffee

@@ -0,0 +1,60 @@
+RootView = require 'root-view'
+
+describe "bracket matching", ->
+  [rootView, editor] = []
+
+  beforeEach ->
+    rootView = new RootView(require.resolve('fixtures/sample.js'))
+    atom.loadPackage('bracket-matcher')
+    rootView.attachToDom()
+    editor = rootView.getActiveEditor()
+
+  afterEach ->
+    rootView.deactivate()
+
+  describe "when the cursor is before a starting pair", ->
+    it "highlights the starting pair and ending pair", ->
+      editor.moveCursorToEndOfLine()
+      editor.moveCursorLeft()
+      expect(editor.underlayer.find('.bracket-matcher').length).toBe 2
+      expect(editor.underlayer.find('.bracket-matcher:first').position()).toEqual editor.pixelPositionForBufferPosition([0,28])
+      expect(editor.underlayer.find('.bracket-matcher:last').position()).toEqual editor.pixelPositionForBufferPosition([12,0])
+
+  describe "when the cursor is after a starting pair", ->
+    it "highlights the starting pair and ending pair", ->
+      editor.moveCursorToEndOfLine()
+      expect(editor.underlayer.find('.bracket-matcher').length).toBe 2
+      expect(editor.underlayer.find('.bracket-matcher:first').position()).toEqual editor.pixelPositionForBufferPosition([0,28])
+      expect(editor.underlayer.find('.bracket-matcher:last').position()).toEqual editor.pixelPositionForBufferPosition([12,0])
+
+  describe "when the cursor is before an ending pair", ->
+    it "highlights the starting pair and ending pair", ->
+      editor.moveCursorToBottom()
+      editor.moveCursorLeft()
+      editor.moveCursorLeft()
+      expect(editor.underlayer.find('.bracket-matcher').length).toBe 2
+      expect(editor.underlayer.find('.bracket-matcher:first').position()).toEqual editor.pixelPositionForBufferPosition([12,0])
+      expect(editor.underlayer.find('.bracket-matcher:last').position()).toEqual editor.pixelPositionForBufferPosition([0,28])
+
+  describe "when the cursor is after an ending pair", ->
+    it "highlights the starting pair and ending pair", ->
+      editor.moveCursorToBottom()
+      editor.moveCursorLeft()
+      expect(editor.underlayer.find('.bracket-matcher').length).toBe 2
+      expect(editor.underlayer.find('.bracket-matcher:first').position()).toEqual editor.pixelPositionForBufferPosition([12,0])
+      expect(editor.underlayer.find('.bracket-matcher:last').position()).toEqual editor.pixelPositionForBufferPosition([0,28])
+
+  describe "when the cursor is moved off a pair", ->
+    it "removes the starting pair and ending pair highlights", ->
+      editor.moveCursorToEndOfLine()
+      expect(editor.underlayer.find('.bracket-matcher').length).toBe 2
+      editor.moveCursorToBeginningOfLine()
+      expect(editor.underlayer.find('.bracket-matcher').length).toBe 0
+
+  describe "pair balancing", ->
+    describe "when a second starting pair preceeds the first ending pair", ->
+      it "advances to the second ending pair", ->
+        editor.setCursorBufferPosition([8,42])
+        expect(editor.underlayer.find('.bracket-matcher').length).toBe 2
+        expect(editor.underlayer.find('.bracket-matcher:first').position()).toEqual editor.pixelPositionForBufferPosition([8,42])
+        expect(editor.underlayer.find('.bracket-matcher:last').position()).toEqual editor.pixelPositionForBufferPosition([8,54])

src/packages/bracket-matcher/stylesheets/bracket-matcher.css

@@ -0,0 +1,3 @@
+.bracket-matcher {
+  position: absolute;
+}

themes/atom-dark-ui/bracket-matcher.css

@@ -0,0 +1,5 @@
+.bracket-matcher {
+  border-bottom: 1px solid #f8de7e;
+  margin-top: -1px;
+  opacity: .7;
+}

themes/atom-dark-ui/package.json

@@ -8,6 +8,7 @@
     "status-bar.css",
     "markdown-preview.css",
     "command-panel.css",
-    "command-logger.css"
+    "command-logger.css",
+    "bracket-matcher.css"
   ]
 }

themes/atom-light-ui/bracket-matcher.css

@@ -0,0 +1,5 @@
+.bracket-matcher {
+  border-bottom: 1px solid #f8de7e;
+  margin-top: -1px;
+  opacity: .7;
+}

themes/atom-light-ui/package.json

@@ -8,6 +8,7 @@
     "status-bar.css",
     "markdown-preview.css",
     "command-panel.css",
-    "command-logger.css"
+    "command-logger.css",
+    "bracket-matcher.css"
   ]
 }