Show Python Script source code in tracebacks (#65)

Expose a __loader__ in globals so that linecache module is able to use
it to display the source code.

This requires changing the "filename" used when compiling function,
because linecache uses code.co_filename as a cache key, so it's
necessary that each python script use a different filename.

Author: perrinjerome

CHANGES.rst

@@ -10,6 +10,8 @@ Changelog
 
 - Drop support for Python 3.7.
 
+- Show Python Scripts source code in tracebacks.
+  `#64 <https://github.com/zopefoundation/Products.PythonScripts/issues/64>`_
 
 5.0 (2023-02-01)
 ----------------

src/Products/PythonScripts/PythonScript.py

@@ -16,7 +16,9 @@
 Python code.
 """
 
+import importlib.abc
 import importlib.util
+import linecache
 import marshal
 import os
 import re
@@ -56,7 +58,7 @@
 Python_magic = importlib.util.MAGIC_NUMBER
 
 # This should only be incremented to force recompilation.
-Script_magic = 4
+Script_magic = 5
 _log_complaint = (
     'Some of your Scripts have stale code cached.  Since Zope cannot'
     ' use this code, startup will be slightly slower until these Scripts'
@@ -97,6 +99,17 @@ def manage_addPythonScript(self, id, title='', file=None, REQUEST=None,
     return ''
 
 
+class PythonScriptLoader(importlib.abc.Loader):
+    """PEP302 loader to display source code in tracebacks
+    """
+
+    def __init__(self, source):
+        self._source = source
+
+    def get_source(self, name):
+        return self._source
+
+
 class PythonScript(Script, Historical, Cacheable):
     """Web-callable scripts written in a safe subset of Python.
 
@@ -234,7 +247,7 @@ def _compile(self):
             self._params,
             body=self._body or 'pass',
             name=self.id,
-            filename=self.meta_type,
+            filename=getattr(self, '_filepath', None) or self.get_filepath(),
             globalize=bind_names)
 
         code = compile_result.code
@@ -261,6 +274,7 @@ def _compile(self):
                                fc.co_argcount)
         self.Python_magic = Python_magic
         self.Script_magic = Script_magic
+        linecache.clearcache()
         self._v_change = 0
 
     def _newfun(self, code):
@@ -331,6 +345,8 @@ def _exec(self, bound_names, args, kw):
             PythonScriptTracebackSupplement, self, -1)
         safe_globals['__file__'] = getattr(
             self, '_filepath', None) or self.get_filepath()
+        safe_globals['__loader__'] = PythonScriptLoader(self._body)
+
         function = types.FunctionType(
             function_code, safe_globals, None, function_argument_definitions)
 

src/Products/PythonScripts/tests/testPythonScript.py

@@ -15,6 +15,7 @@
 import io
 import os
 import sys
+import traceback
 import unittest
 import warnings
 from urllib.error import HTTPError
@@ -241,7 +242,8 @@ def test_manage_DAVget(self):
         self.assertEqual(ps.read(), ps.manage_DAVget())
 
     def test_PUT_native_string(self):
-        ps = makerequest(self._filePS('complete'))
+        container = DummyFolder('container')
+        ps = makerequest(self._filePS('complete').__of__(container))
         self.assertEqual(ps.title, 'This is a title')
         self.assertEqual(ps.body(), 'print(foo+bar+baz)\nreturn printed\n')
         self.assertEqual(ps.params(), 'foo, bar, baz=1')
@@ -265,7 +267,8 @@ def test_PUT_native_string(self):
         self.assertEqual(ps.params(), 'oops')
 
     def test_PUT_bytes(self):
-        ps = makerequest(self._filePS('complete'))
+        container = DummyFolder('container')
+        ps = makerequest(self._filePS('complete').__of__(container))
         self.assertEqual(ps.title, 'This is a title')
         self.assertEqual(ps.body(), 'print(foo+bar+baz)\nreturn printed\n')
         self.assertEqual(ps.params(), 'foo, bar, baz=1')
@@ -588,3 +591,46 @@ def test_PythonScript_proxyroles_nonmanager(self):
 
         # Cleanup
         noSecurityManager()
+
+
+class TestTraceback(FunctionalTestCase, PythonScriptTestBase):
+
+    def _format_exception(self):
+        return "".join(traceback.format_exception(*sys.exc_info()))
+
+    def test_source_code_in_traceback(self):
+        ps = self._newPS("1 / 0")
+        try:
+            ps()
+        except ZeroDivisionError:
+            formatted_exception = self._format_exception()
+        self.assertIn("1 / 0", formatted_exception)
+
+        ps.write("2 / 0")
+        try:
+            ps()
+        except ZeroDivisionError:
+            formatted_exception = self._format_exception()
+        self.assertIn("2 / 0", formatted_exception)
+
+    def test_multiple_scripts_in_traceback(self):
+        from Products.PythonScripts.PythonScript import manage_addPythonScript
+
+        script1_body = "container.script2()"
+        manage_addPythonScript(
+            self.folder,
+            "script1",
+            file=script1_body,
+        )
+        script2_body = "1 / 0"
+        manage_addPythonScript(
+            self.folder,
+            "script2",
+            file=script2_body,
+        )
+        try:
+            self.folder.script1()
+        except ZeroDivisionError:
+            formatted_exception = self._format_exception()
+        self.assertIn(script1_body, formatted_exception)
+        self.assertIn(script2_body, formatted_exception)