Support the Chameleon expression type structure

CHANGES.rst

@@ -26,6 +26,9 @@ https://github.com/zopefoundation/Zope/blob/4.x/CHANGES.rst
 - Fix ``Content-Disposition`` filename for clients without rfc6266 support.
   (`#1198 <https://github.com/zopefoundation/Zope/pull/1198>`_)
 
+- Support ``Chameleon`` ``structure`` expression type.
+  Fixes `#1077 <https://github.com/zopefoundation/Zope/issues/1077>`_.
+
 
 5.9 (2023-11-24)
 ----------------

src/Products/PageTemplates/Expressions.py

@@ -10,7 +10,7 @@
 # FOR A PARTICULAR PURPOSE
 #
 ##############################################################################
-"""Page Template Expression Engine
+"""Page Template Expression Engine based on ``zope.tales``.
 
 Page Template-specific implementation of TALES, with handlers
 for Python expressions, string literals, and paths.
@@ -19,6 +19,8 @@
 import logging
 import warnings
 
+from chameleon.tales import Markup
+
 import OFS.interfaces
 from AccessControl import safe_builtins
 from AccessControl.SecurityManagement import getSecurityManager
@@ -39,6 +41,7 @@
 from zope.tales.expressions import StringExpr
 from zope.tales.expressions import SubPathExpr
 from zope.tales.expressions import Undefs
+from zope.tales.interfaces import ITALESExpression
 from zope.tales.pythonexpr import PythonExpr
 from zope.tales.tales import Context
 from zope.tales.tales import ErrorInfo as BaseErrorInfo
@@ -238,6 +241,26 @@ class TrustedZopePathExpr(ZopePathExpr):
     SUBEXPR_FACTORY = TrustedSubPathExpr
 
 
+@implementer(ITALESExpression)
+class StructureExpr:
+    """
+    An expression that tells the template engine to
+    render the value as structure (i.e. with markup).
+
+    Note: will only work with ``chameleon`` template engine.
+    """
+
+    def __init__(self, name, expr, engine):
+        self._s = expr = expr.lstrip()
+        self._c = engine.compile(expr)
+
+    def __call__(self, econtext):
+        return Markup(econtext.evaluate(self._c))
+
+    def __repr__(self):
+        return '<StructureExpr %s>' % repr(self._s)
+
+
 class SafeMapping(MultiMapping):
     """Mapping with security declarations and limited method exposure.
 
@@ -482,6 +505,7 @@ def createZopeEngine(zpe=ZopePathExpr, untrusted=True):
     e.registerType('defer', DeferExpr)
     e.registerType('lazy', LazyExpr)
     e.registerType('provider', TALESProviderExpression)
+    e.registerType('structure', StructureExpr)
     e.registerBaseName('modules', SecureModuleImporter)
     e.untrusted = untrusted
     return e

src/Products/PageTemplates/expression.py

@@ -9,6 +9,7 @@
 from chameleon.codegen import template
 from chameleon.tales import NotExpr
 from chameleon.tales import StringExpr
+from chameleon.tales import StructureExpr
 
 from AccessControl.SecurityManagement import getSecurityManager
 from AccessControl.ZopeGuards import guarded_apply
@@ -226,7 +227,8 @@ def compile(self, expression):
     exists=ExistsExpr,
     path=PathExpr,
     provider=expressions.ProviderExpr,
-    nocall=NocallExpr)
+    nocall=NocallExpr,
+    structure=StructureExpr)
 
 
 def createChameleonEngine(types=types, untrusted=True, **overrides):

src/Products/PageTemplates/tests/structure.pt

@@ -0,0 +1 @@
+${structure:options/param}

src/Products/PageTemplates/tests/test_pagetemplate.py

@@ -3,6 +3,8 @@
 
 from Products.PageTemplates.PageTemplateFile import PageTemplateFile
 from Testing.ZopeTestCase import ZopeTestCase
+from zope.component import provideAdapter
+from zope.traversing.adapters import DefaultTraversable
 
 from .util import useChameleonEngine
 
@@ -14,6 +16,7 @@ class TestPageTemplateFile(ZopeTestCase):
 
     def afterSetUp(self):
         useChameleonEngine()
+        provideAdapter(DefaultTraversable, (None,))
 
     def _makeOne(self, name):
         return PageTemplateFile(os.path.join(path, name)).__of__(self.app)
@@ -81,6 +84,12 @@ def test_secure(self):
         result = template(soup=soup)
         self.assertTrue('<foo></bar>' in result)
 
+    def test_structure(self):
+        template = self._makeOne("structure.pt")
+        param = "<span>abc</span>"
+        result = template(param=param)
+        self.assertTrue(param in result)
+
 
 def test_suite():
     return unittest.defaultTestLoader.loadTestsFromTestCase(