Moved enable_attributes keyword to extension: legacy_attrs.

If you have existing documents that use the legacy attributes format,
then you should enable the legacy_attrs extension for those documents.
Everyone is encouraged to use the attr_list extension going forward.
Closes #643. Work adapted from 0005d7a of the md3 branch.

4 files changed, 51 insertions, 41 deletions

diff --git a/markdown/core.py b/markdown/core.py
index f4111e4..0fcf71d 100644
--- a/markdown/core.py
+++ b/markdown/core.py
@@ -27,7 +27,6 @@ class Markdown(object):
 
     option_defaults = {
         'tab_length':            4,
-        'enable_attributes':     True,
         'smart_emphasis':        True,
         'lazy_ol':               True,
     }
@@ -53,7 +52,6 @@ class Markdown(object):
             * "xhtml": Outputs XHTML style tags. Default.
             * "html": Outputs HTML style tags.
         * tab_length: Length of tabs in the source. Default: 4
-        * enable_attributes: Enable the conversion of attributes. Default: True
         * smart_emphasis: Treat `_connected_words_` intelligently Default: True
         * lazy_ol: Ignore number of first item of ordered lists. Default: True
 
diff --git a/markdown/extensions/legacy_attrs.py b/markdown/extensions/legacy_attrs.py
new file mode 100644
index 0000000..280be07
--- /dev/null
+++ b/markdown/extensions/legacy_attrs.py
@@ -0,0 +1,49 @@
+"""
+Legacy Attributes Extension
+===========================
+
+An extension to Python Markdown which implements legacy attributes.
+
+Prior to Python-Markdown version 3.0, the Markdown class had an `enable_attributes`
+keyword which was on by default and provided for attributes to be defined for elements
+using the format `{@key=value}`. This extension is provided as a replacement for
+backward compatability. New documents should be authored using attr_lists. However,
+numerious documents exist which have been using the old attribute format for many
+years. This extension can be used to continue to render those documents correctly.
+"""
+
+import re
+from markdown.treeprocessors import Treeprocessor, isString
+from markdown.extensions import Extension
+
+
+ATTR_RE = re.compile("\{@([^\}]*)=([^\}]*)}")  # {@id=123}
+
+
+class LegacyAttrs(Treeprocessor):
+    def run(self, doc):
+        """Find and set values of attributes ({@key=value}). """
+        for el in doc.iter():
+            alt = el.get('alt', None)
+            if alt is not None:
+                el.set('alt', self.handleAttributes(el, alt))
+            if el.text and isString(el.text):
+                el.text = self.handleAttributes(el, el.text)
+            if el.tail and isString(el.tail):
+                el.tail = self.handleAttributes(el, el.tail)
+
+    def handleAttributes(self, el, txt):
+        """ Set attributes and return text without definitions. """
+        def attributeCallback(match):
+            el.set(match.group(1), match.group(2).replace('\n', ' '))
+        return ATTR_RE.sub(attributeCallback, txt)
+
+
+class LegacyAttrExtension(Extension):
+    def extendMarkdown(self, md, md_globals):
+        la = LegacyAttrs(md)
+        md.treeprocessors.add('legacyattrs', la, '>inline')
+
+
+def makeExtension(**kwargs):  # pragma: no cover
+    return LegacyAttrExtension(**kwargs)
diff --git a/markdown/inlinepatterns.py b/markdown/inlinepatterns.py
index 18da73b..d67ef1f 100644
--- a/markdown/inlinepatterns.py
+++ b/markdown/inlinepatterns.py
@@ -154,17 +154,6 @@ def dequote(string):
         return string
 
 
-ATTR_RE = re.compile(r"\{@([^\}]*)=([^\}]*)}")  # {@id=123}
-
-
-def handleAttributes(text, parent):
-    """Set values of an element based on attribute definitions ({@id=123})."""
-    def attributeCallback(match):
-        parent.set(match.group(1), match.group(2).replace('\n', ' '))
-        return ''
-    return ATTR_RE.sub(attributeCallback, text)
-
-
 """
 The pattern classes
 -----------------------------------------------------------------------------
@@ -601,12 +590,7 @@ class ImageInlineProcessor(LinkInlineProcessor):
         if title is not None:
             el.set("title", title)
 
-        if self.markdown.enable_attributes:
-            truealt = handleAttributes(text, el)
-        else:
-            truealt = text
-
-        el.set('alt', self.unescape(truealt))
+        el.set('alt', self.unescape(text))
         return el, m.start(0), index
 
 
@@ -676,10 +660,6 @@ class ImageReferenceInlineProcessor(ReferenceInlineProcessor):
         el.set("src", href)
         if title:
             el.set("title", title)
-
-        if self.markdown.enable_attributes:
-            text = handleAttributes(text, el)
-
         el.set("alt", self.unescape(text))
         return el
 
diff --git a/markdown/treeprocessors.py b/markdown/treeprocessors.py
index 7c37ae7..df5e748 100644
--- a/markdown/treeprocessors.py
+++ b/markdown/treeprocessors.py
@@ -366,26 +366,9 @@ class InlineProcessor(Treeprocessor):
                     stack.append((child, self.ancestors[:]))
 
             for element, lst in insertQueue:
-                if self.markdown.enable_attributes:
-                    if element.text and isString(element.text):
-                        element.text = inlinepatterns.handleAttributes(
-                            element.text, element
-                        )
-                i = 0
-                for obj in lst:
+                for i, obj in enumerate(lst):
                     newChild = obj[0]
-                    if self.markdown.enable_attributes:
-                        # Processing attributes
-                        if newChild.tail and isString(newChild.tail):
-                            newChild.tail = inlinepatterns.handleAttributes(
-                                newChild.tail, element
-                            )
-                        if newChild.text and isString(newChild.text):
-                            newChild.text = inlinepatterns.handleAttributes(
-                                newChild.text, newChild
-                            )
                     element.insert(i, newChild)
-                    i += 1
         return tree