New ExceptionInfo.getrepr 'chain' parameter to be able to suppress chained exceptions

src/_pytest/_code/code.py

@@ -451,13 +451,35 @@ class ExceptionInfo(object):
         tbfilter=True,
         funcargs=False,
         truncate_locals=True,
+        chain=True,
     ):
-        """ return str()able representation of this exception info.
-            showlocals: show locals per traceback entry
-            style: long|short|no|native traceback style
-            tbfilter: hide entries (where __tracebackhide__ is true)
+        """
+        Return str()able representation of this exception info.
 
-            in case of style==native, tbfilter and showlocals is ignored.
+        :param bool showlocals:
+            Show locals per traceback entry.
+            Ignored if ``style=="native"``.
+
+        :param str style: long|short|no|native traceback style
+
+        :param bool abspath:
+            If paths should be changed to absolute or left unchanged.
+
+        :param bool tbfilter:
+            Hide entries that contain a local variable ``__tracebackhide__==True``.
+            Ignored if ``style=="native"``.
+
+        :param bool funcargs:
+            Show fixtures ("funcargs" for legacy purposes) per traceback entry.
+
+        :param bool truncate_locals:
+            With ``showlocals==True``, make sure locals can be safely represented as strings.
+
+        :param bool chain: if chained exceptions in Python 3 should be shown.
+
+        .. versionchanged:: 3.9
+
+            Added the ``chain`` parameter.
         """
         if style == "native":
             return ReprExceptionInfo(
@@ -476,6 +498,7 @@ class ExceptionInfo(object):
             tbfilter=tbfilter,
             funcargs=funcargs,
             truncate_locals=truncate_locals,
+            chain=chain,
         )
         return fmt.repr_excinfo(self)
 
@@ -516,6 +539,7 @@ class FormattedExcinfo(object):
     tbfilter = attr.ib(default=True)
     funcargs = attr.ib(default=False)
     truncate_locals = attr.ib(default=True)
+    chain = attr.ib(default=True)
     astcache = attr.ib(default=attr.Factory(dict), init=False, repr=False)
 
     def _getindent(self, source):
@@ -735,7 +759,7 @@ class FormattedExcinfo(object):
                     reprcrash = None
 
                 repr_chain += [(reprtraceback, reprcrash, descr)]
-                if e.__cause__ is not None:
+                if e.__cause__ is not None and self.chain:
                     e = e.__cause__
                     excinfo = (
                         ExceptionInfo((type(e), e, e.__traceback__))
@@ -743,7 +767,11 @@ class FormattedExcinfo(object):
                         else None
                     )
                     descr = "The above exception was the direct cause of the following exception:"
-                elif e.__context__ is not None and not e.__suppress_context__:
+                elif (
+                    e.__context__ is not None
+                    and not e.__suppress_context__
+                    and self.chain
+                ):
                     e = e.__context__
                     excinfo = (
                         ExceptionInfo((type(e), e, e.__traceback__))

testing/code/test_excinfo.py

@@ -1184,20 +1184,28 @@ raise ValueError()
         assert tw.lines[47] == ":15: AttributeError"
 
     @pytest.mark.skipif("sys.version_info[0] < 3")
-    def test_exc_repr_with_raise_from_none_chain_suppression(self, importasmod):
+    @pytest.mark.parametrize("mode", ["from_none", "explicit_suppress"])
+    def test_exc_repr_chain_suppression(self, importasmod, mode):
+        """Check that exc repr does not show chained exceptions in Python 3.
+        - When the exception is raised with "from None"
+        - Explicitly suppressed with "chain=False" to ExceptionInfo.getrepr().
+        """
+        raise_suffix = " from None" if mode == "from_none" else ""
         mod = importasmod(
             """
             def f():
                 try:
                     g()
                 except Exception:
-                    raise AttributeError() from None
+                    raise AttributeError(){raise_suffix}
             def g():
                 raise ValueError()
-        """
+        """.format(
+                raise_suffix=raise_suffix
+            )
         )
         excinfo = pytest.raises(AttributeError, mod.f)
-        r = excinfo.getrepr(style="long")
+        r = excinfo.getrepr(style="long", chain=mode != "explicit_suppress")
         tw = TWMock()
         r.toterminal(tw)
         for line in tw.lines:
@@ -1207,7 +1215,9 @@ raise ValueError()
         assert tw.lines[2] == "        try:"
         assert tw.lines[3] == "            g()"
         assert tw.lines[4] == "        except Exception:"
-        assert tw.lines[5] == ">           raise AttributeError() from None"
+        assert tw.lines[5] == ">           raise AttributeError(){}".format(
+            raise_suffix
+        )
         assert tw.lines[6] == "E           AttributeError"
         assert tw.lines[7] == ""
         line = tw.get_write_msg(8)