Better handling for unpickle failure (#160)

When we pickle the object, also store its repr. If we fail to unpickle,
include the repr in the error message.

Also, add the info to the error using `add_node`. This requires Python 3.11
so I bumped the requires_python.

This requires Pytest 8 for the test to work, so I needed to merge #161 first.

Author: hoodmane

pyproject.toml

@@ -15,7 +15,7 @@ classifiers = [
     "Framework :: Pytest"
 ]
 dynamic = ["version"]
-requires-python = ">=3.10"
+requires-python = ">=3.11"
 dependencies = [
   "pexpect",
   "pytest",
@@ -49,7 +49,7 @@ Changelog = "https://github.com/pyodide/pytest-pyodide/blob/main/CHANGELOG.md"
 source = "vcs"
 
 [tool.mypy]
-python_version = "3.10"
+python_version = "3.11"
 show_error_codes = true
 warn_unreachable = true
 enable_error_code = ["ignore-without-code", "redundant-expr", "truthy-bool"]

pytest_pyodide/_decorator_in_pyodide.py

@@ -97,7 +97,7 @@ def decode(x: str) -> Any:
 
 async def run_in_pyodide_main(
     mod64: str, args64: str, module_filename: str, func_name: str, async_func: bool
-) -> tuple[int, str]:
+) -> tuple[int, str, str]:
     """
     This actually runs the code for run_in_pyodide.
     """
@@ -119,7 +119,7 @@ async def run_in_pyodide_main(
         result = d[func_name](None, *args)
         if async_func:
             result = await result
-        return (0, encode(result))
+        return (0, encode(result), repr(result))
     except BaseException as e:
         try:
             # If tblib is present, we can show much better tracebacks.
@@ -141,7 +141,7 @@ def get_locals(frame):
 
         except ImportError:
             pass
-        return (1, encode(e))
+        return (1, encode(e), repr(e))
 
 
 __all__ = ["PyodideHandle", "encode"]

pytest_pyodide/decorator.py

@@ -100,15 +100,19 @@ def _encode(obj: Any) -> str:
     return b64encode(b.getvalue()).decode()
 
 
-def _decode(result: str, selenium: SeleniumType) -> Any:
+def _decode(selenium: SeleniumType, result, status, repr) -> Any:
+    if status:
+        thing = "exception raised"
+    else:
+        thing = "value returned"
     try:
         return Unpickler(BytesIO(b64decode(result)), selenium).load()
-    except ModuleNotFoundError as exc:
-        raise ModuleNotFoundError(
-            f"There was a problem with unpickling the return value/exception from your pyodide environment. "
-            f"This usually means the type of the return value/exception does not exist in your host environment. "
-            f"The original message is: {exc}."
-        ) from None
+    except Exception as e:
+        e.add_note(
+            f"The error occurred while unpickling the {thing} from pyodide.\n"
+            f"The repr of the object we failed to unpickle was '{repr}'"
+        )
+        raise
 
 
 def all_args(funcdef: MaybeAsyncFuncDef) -> list[ast.arg]:
@@ -450,9 +454,9 @@ def _run(self, selenium: SeleniumType, args: tuple[Any, ...]):
             selenium.load_package(self._pkgs)
 
         r = selenium.run_async(code)
-        [status, result] = r
+        [status, result, repr] = r
 
-        result = _decode(result, selenium)
+        result = _decode(selenium, result, status, repr)
         if status:
             raise result
         else:

tests/test_decorator.py

@@ -86,7 +86,7 @@ def inner_function(selenium):
         inner_function(selenium)
 
 
-def test_not_unpickable_return_value(selenium):
+def test_unpickleable_return_value(selenium):
     @run_in_pyodide
     async def inner_function(selenium):
         with open("some_module.py", "w") as fp:
@@ -96,10 +96,37 @@ async def inner_function(selenium):
 
         return Test()
 
-    with pytest.raises(
-        ModuleNotFoundError,
-        match="There was a problem with unpickling the return.*",
-    ):
+    regex = "\n".join(
+        [
+            r"No module named 'some_module'",
+            r"The error occurred while unpickling the value returned from pyodide.",
+            r"The repr of the object we failed to unpickle was '<some_module.Test object at 0x[0-9a-f]*>'",
+        ]
+    )
+
+    with pytest.raises(ModuleNotFoundError, match=regex):
+        inner_function(selenium)
+
+
+def test_unpickleable_exception(selenium):
+    @run_in_pyodide
+    async def inner_function(selenium):
+        with open("some_module2.py", "w") as fp:
+            fp.write("class TestException(Exception): pass\n")
+
+        from some_module2 import TestException
+
+        raise TestException
+
+    regex = "\n".join(
+        [
+            r"No module named 'some_module2'",
+            r"The error occurred while unpickling the exception raised from pyodide.",
+            r"The repr of the object we failed to unpickle was 'TestException\(\)'",
+        ]
+    )
+
+    with pytest.raises(ModuleNotFoundError, match=regex):
         inner_function(selenium)