Ignore leading whitespace when auto-indenting a newline

Refs atom/language-less#1

src/editor.coffee

@@ -373,10 +373,16 @@ class Editor extends Model
   #
   # bufferRow - A {Number} indicating the buffer row.
   # newLevel - A {Number} indicating the new indentation level.
-  setIndentationForBufferRow: (bufferRow, newLevel) ->
-    currentIndentLength = @lineForBufferRow(bufferRow).match(/^\s*/)[0].length
+  # options - An {Object} with the following keys:
+  #   :ignoreLeadingWhitespace - true to not replace any of the leading
+  #                              whitespace already on the line (default: false)
+  setIndentationForBufferRow: (bufferRow, newLevel, {ignoreLeadingWhitespace}={}) ->
+    if ignoreLeadingWhitespace
+      endColumn = 0
+    else
+      endColumn = @lineForBufferRow(bufferRow).match(/^\s*/)[0].length
     newIndentString = @buildIndentString(newLevel)
-    @buffer.change([[bufferRow, 0], [bufferRow, currentIndentLength]], newIndentString)
+    @buffer.change([[bufferRow, 0], [bufferRow, endColumn]], newIndentString)
 
   # Public: Get the indentation level of the given line of text.
   #

src/language-mode.coffee

@@ -265,10 +265,11 @@ class LanguageMode
 
   # Given a buffer row, this indents it.
   #
-  # bufferRow - The row {Number}
-  autoIndentBufferRow: (bufferRow) ->
+  # bufferRow - The row {Number}.
+  # options - An options {Object} to pass to {Editor::setIndentationForBufferRow}.
+  autoIndentBufferRow: (bufferRow, options) ->
     indentLevel = @suggestedIndentForBufferRow(bufferRow)
-    @editor.setIndentationForBufferRow(bufferRow, indentLevel)
+    @editor.setIndentationForBufferRow(bufferRow, indentLevel, options)
 
   # Given a buffer row, this decreases the indentation.
   #

src/selection.coffee

@@ -301,7 +301,7 @@ class Selection
     if options.autoIndent
       @editor.autoIndentBufferRow(row) for row in newBufferRange.getRows()
     else if options.autoIndentNewline and text == '\n'
-      @editor.autoIndentBufferRow(newBufferRange.end.row)
+      @editor.autoIndentBufferRow(newBufferRange.end.row, ignoreLeadingWhitespace: true)
     else if options.autoDecreaseIndent and /\S/.test text
       @editor.autoDecreaseIndentForBufferRow(newBufferRange.start.row)