Serialize/deserialize chained exceptions

Fix #5786

changelog/5786.bugfix.rst

@@ -0,0 +1,2 @@
+Chained exceptions in test and collection reports are now correctly serialized, allowing plugins like
+``pytest-xdist`` to display them properly.

src/_pytest/reports.py

@@ -3,6 +3,7 @@ from typing import Optional
 
 import py
 
+from _pytest._code.code import ExceptionChainRepr
 from _pytest._code.code import ExceptionInfo
 from _pytest._code.code import ReprEntry
 from _pytest._code.code import ReprEntryNative
@@ -160,7 +161,7 @@ class BaseReport:
 
         Experimental method.
         """
-        return _test_report_to_json(self)
+        return _report_to_json(self)
 
     @classmethod
     def _from_json(cls, reportdict):
@@ -172,7 +173,7 @@ class BaseReport:
 
         Experimental method.
         """
-        kwargs = _test_report_kwargs_from_json(reportdict)
+        kwargs = _report_kwargs_from_json(reportdict)
         return cls(**kwargs)
 
 
@@ -340,7 +341,7 @@ def pytest_report_from_serializable(data):
         )
 
 
-def _test_report_to_json(test_report):
+def _report_to_json(report):
     """
     This was originally the serialize_report() function from xdist (ca03269).
 
@@ -366,22 +367,35 @@ def _test_report_to_json(test_report):
         return reprcrash.__dict__.copy()
 
     def serialize_longrepr(rep):
-        return {
+        result = {
             "reprcrash": serialize_repr_crash(rep.longrepr.reprcrash),
             "reprtraceback": serialize_repr_traceback(rep.longrepr.reprtraceback),
             "sections": rep.longrepr.sections,
         }
+        if isinstance(rep.longrepr, ExceptionChainRepr):
+            result["chain"] = []
+            for repr_traceback, repr_crash, description in rep.longrepr.chain:
+                result["chain"].append(
+                    (
+                        serialize_repr_traceback(repr_traceback),
+                        serialize_repr_crash(repr_crash),
+                        description,
+                    )
+                )
+        else:
+            result["chain"] = None
+        return result
 
-    d = test_report.__dict__.copy()
-    if hasattr(test_report.longrepr, "toterminal"):
-        if hasattr(test_report.longrepr, "reprtraceback") and hasattr(
-            test_report.longrepr, "reprcrash"
+    d = report.__dict__.copy()
+    if hasattr(report.longrepr, "toterminal"):
+        if hasattr(report.longrepr, "reprtraceback") and hasattr(
+            report.longrepr, "reprcrash"
         ):
-            d["longrepr"] = serialize_longrepr(test_report)
+            d["longrepr"] = serialize_longrepr(report)
         else:
-            d["longrepr"] = str(test_report.longrepr)
+            d["longrepr"] = str(report.longrepr)
     else:
-        d["longrepr"] = test_report.longrepr
+        d["longrepr"] = report.longrepr
     for name in d:
         if isinstance(d[name], (py.path.local, Path)):
             d[name] = str(d[name])
@@ -390,12 +404,11 @@ def _test_report_to_json(test_report):
     return d
 
 
-def _test_report_kwargs_from_json(reportdict):
+def _report_kwargs_from_json(reportdict):
     """
     This was originally the serialize_report() function from xdist (ca03269).
 
-    Factory method that returns either a TestReport or CollectReport, depending on the calling
-    class. It's the callers responsibility to know which class to pass here.
+    Returns **kwargs that can be used to construct a TestReport or CollectReport instance.
     """
 
     def deserialize_repr_entry(entry_data):
@@ -439,12 +452,26 @@ def _test_report_kwargs_from_json(reportdict):
         and "reprcrash" in reportdict["longrepr"]
         and "reprtraceback" in reportdict["longrepr"]
     ):
-        exception_info = ReprExceptionInfo(
-            reprtraceback=deserialize_repr_traceback(
+
+        reprtraceback = deserialize_repr_traceback(
             reportdict["longrepr"]["reprtraceback"]
-            ),
-            reprcrash=deserialize_repr_crash(reportdict["longrepr"]["reprcrash"]),
         )
+        reprcrash = deserialize_repr_crash(reportdict["longrepr"]["reprcrash"])
+        if reportdict["longrepr"]["chain"]:
+            chain = []
+            for repr_traceback_data, repr_crash_data, description in reportdict[
+                "longrepr"
+            ]["chain"]:
+                chain.append(
+                    (
+                        deserialize_repr_traceback(repr_traceback_data),
+                        deserialize_repr_crash(repr_crash_data),
+                        description,
+                    )
+                )
+            exception_info = ExceptionChainRepr(chain)
+        else:
+            exception_info = ReprExceptionInfo(reprtraceback, reprcrash)
 
         for section in reportdict["longrepr"]["sections"]:
             exception_info.addsection(*section)

testing/test_reports.py

@@ -1,4 +1,5 @@
 import pytest
+from _pytest._code.code import ExceptionChainRepr
 from _pytest.pathlib import Path
 from _pytest.reports import CollectReport
 from _pytest.reports import TestReport
@@ -220,8 +221,8 @@ class TestReportSerialization:
         assert data["path1"] == str(testdir.tmpdir)
         assert data["path2"] == str(testdir.tmpdir)
 
-    def test_unserialization_failure(self, testdir):
-        """Check handling of failure during unserialization of report types."""
+    def test_deserialization_failure(self, testdir):
+        """Check handling of failure during deserialization of report types."""
         testdir.makepyfile(
             """
             def test_a():
@@ -242,6 +243,75 @@ class TestReportSerialization:
         ):
             TestReport._from_json(data)
 
+    @pytest.mark.parametrize("report_class", [TestReport, CollectReport])
+    def test_chained_exceptions(self, testdir, tw_mock, report_class):
+        """Check serialization/deserialization of report objects containing chained exceptions (#5786)"""
+        testdir.makepyfile(
+            """
+            def foo():
+                raise ValueError('value error')
+            def test_a():
+                try:
+                    foo()
+                except ValueError as e:
+                    raise RuntimeError('runtime error') from e
+            if {error_during_import}:
+                test_a()
+        """.format(
+                error_during_import=report_class is CollectReport
+            )
+        )
+
+        reprec = testdir.inline_run()
+        if report_class is TestReport:
+            reports = reprec.getreports("pytest_runtest_logreport")
+            # we have 3 reports: setup/call/teardown
+            assert len(reports) == 3
+            # get the call report
+            report = reports[1]
+        else:
+            assert report_class is CollectReport
+            # two collection reports: session and test file
+            reports = reprec.getreports("pytest_collectreport")
+            assert len(reports) == 2
+            report = reports[1]
+
+        def check_longrepr(longrepr):
+            """Check the attributes of the given longrepr object according to the test file.
+
+            We can get away with testing both CollectReport and TestReport with this function because
+            the longrepr objects are very similar.
+            """
+            assert isinstance(longrepr, ExceptionChainRepr)
+            assert longrepr.sections == [("title", "contents", "=")]
+            assert len(longrepr.chain) == 2
+            entry1, entry2 = longrepr.chain
+            tb1, fileloc1, desc1 = entry1
+            tb2, fileloc2, desc2 = entry2
+
+            assert "ValueError('value error')" in str(tb1)
+            assert "RuntimeError('runtime error')" in str(tb2)
+
+            assert (
+                desc1
+                == "The above exception was the direct cause of the following exception:"
+            )
+            assert desc2 is None
+
+        assert report.failed
+        assert len(report.sections) == 0
+        report.longrepr.addsection("title", "contents", "=")
+        check_longrepr(report.longrepr)
+
+        data = report._to_json()
+        loaded_report = report_class._from_json(data)
+        check_longrepr(loaded_report.longrepr)
+
+        # make sure we don't blow up on ``toterminal`` call; we don't test the actual output because it is very
+        # brittle and hard to maintain, but we can assume it is correct because ``toterminal`` is already tested
+        # elsewhere and we do check the contents of the longrepr object after loading it.
+        loaded_report.longrepr.toterminal(tw_mock)
+
 
 class TestHooks:
     """Test that the hooks are working correctly for plugins"""