The contents of <textarea> tags will no longer be modified when the

  tree is prettified. [bug=1555829]

4 files changed, 34 insertions, 7 deletions

diff --git a/NEWS.txt b/NEWS.txt
index 691cf1f..472538a 100644
--- a/NEWS.txt
+++ b/NEWS.txt
@@ -2,6 +2,9 @@
 
 * Corrected handling of XML processing instructions. [bug=1504393]
 
+* The contents of <textarea> tags will no longer be modified when the
+  tree is prettified. [bug=1555829]
+
 * Fixed a Python 3 ByteWarning when a URL was passed in as though it
   were markup. Thanks to James Salter for a patch and
   test. [bug=1533762]
diff --git a/bs4/builder/__init__.py b/bs4/builder/__init__.py
index f444edd..601979b 100644
--- a/bs4/builder/__init__.py
+++ b/bs4/builder/__init__.py
@@ -7,6 +7,7 @@ import sys
 from bs4.element import (
     CharsetMetaAttributeValue,
     ContentMetaAttributeValue,
+    HTMLAwareEntitySubstitution,
     whitespace_re
     )
 
@@ -230,7 +231,7 @@ class HTMLTreeBuilder(TreeBuilder):
     Such as which tags are empty-element tags.
     """
 
-    preserve_whitespace_tags = set(['pre', 'textarea'])
+    preserve_whitespace_tags = HTMLAwareEntitySubstitution.preserve_whitespace_tags
     empty_element_tags = set(['br' , 'hr', 'input', 'img', 'meta',
                               'spacer', 'link', 'frame', 'base'])
 
diff --git a/bs4/element.py b/bs4/element.py
index 9e2bfec..955f0fc 100644
--- a/bs4/element.py
+++ b/bs4/element.py
@@ -101,6 +101,8 @@ class HTMLAwareEntitySubstitution(EntitySubstitution):
 
     preformatted_tags = set(["pre"])
 
+    preserve_whitespace_tags = set(['pre', 'textarea'])
+
     @classmethod
     def _substitute_if_appropriate(cls, ns, f):
         if (isinstance(ns, NavigableString)
@@ -1065,10 +1067,18 @@ class Tag(PageElement):
 
     def _should_pretty_print(self, indent_level):
         """Should this tag be pretty-printed?"""
+        if self.builder:
+            preserve_whitespace_tags = self.builder.preserve_whitespace_tags
+        else:
+            if self._is_xml:
+                preserve_whitespace_tags = []
+            else:
+                preserve_whitespace_tags = HTMLAwareEntitySubstitution.preserve_whitespace_tags
+
         return (
-            indent_level is not None and
-            (self.name not in HTMLAwareEntitySubstitution.preformatted_tags
-             or self._is_xml))
+            indent_level is not None
+            and self.name not in preserve_whitespace_tags
+        )
 
     def decode(self, indent_level=None,
                eventual_encoding=DEFAULT_OUTPUT_ENCODING,
diff --git a/bs4/testing.py b/bs4/testing.py
index 1e2cc9c..676d7b3 100644
--- a/bs4/testing.py
+++ b/bs4/testing.py
@@ -217,9 +217,22 @@ Hello, world!
         self.assertEqual(comment, baz.previous_element)
 
     def test_preserved_whitespace_in_pre_and_textarea(self):
-        """Whitespace must be preserved in <pre> and <textarea> tags."""
-        self.assertSoupEquals("<pre>   </pre>")
-        self.assertSoupEquals("<textarea> woo  </textarea>")
+        """Whitespace must be preserved in <pre> and <textarea> tags,
+        even if that would mean not prettifying the markup.
+        """
+        pre_markup = "<pre>   </pre>"
+        textarea_markup = "<textarea> woo\nwoo  </textarea>"
+        self.assertSoupEquals(pre_markup)
+        self.assertSoupEquals(textarea_markup)
+
+        soup = self.soup(pre_markup)
+        self.assertEqual(soup.pre.prettify(), pre_markup)
+
+        soup = self.soup(textarea_markup)
+        self.assertEqual(soup.textarea.prettify(), textarea_markup)
+
+        soup = self.soup("<textarea></textarea>")
+        self.assertEqual(soup.textarea.prettify(), "<textarea></textarea>")
 
     def test_nested_inline_elements(self):
         """Inline elements can be nested indefinitely."""