tbstyle_given

src/_pytest/config/__init__.py

@@ -782,6 +782,7 @@ def __init__(self, pluginmanager, *, invocation_params=None) -> None:
             )
 
         self.option = argparse.Namespace()
+        self._nondefault_options = set()  # type: Set[str]
         self.invocation_params = invocation_params
 
         _a = FILE_OR_DIR
@@ -895,9 +896,10 @@ def _processopt(self, opt: "Argument") -> None:
         for name in opt._short_opts + opt._long_opts:
             self._opt2dest[name] = opt.dest
 
-        if hasattr(opt, "default"):
-            if not hasattr(self.option, opt.dest):
-                setattr(self.option, opt.dest, opt.default)
+        if hasattr(self.option, opt.dest):
+            self._nondefault_options.add(opt.dest)
+        elif hasattr(opt, "default"):
+            setattr(self.option, opt.dest, opt.default)
 
     @hookimpl(trylast=True)
     def pytest_load_initial_conftests(self, early_config):

src/_pytest/nodes.py

@@ -333,11 +333,11 @@ def _repr_failure_py(
             return excinfo.value.formatrepr()
 
         # XXX should excinfo.getrepr record all data and toterminal() process it?
-        # XXX: does not distinguish between default/unset and --tb=auto.
         tbstyle = self.config.option.tbstyle
         verbosity = self.config.option.verbose
         if fulltrace:
-            style = "long" if tbstyle == "auto" else tbstyle  # type: _TracebackStyle
+            tbstyle_given = "tbstyle" in self.config._nondefault_options
+            style = tbstyle if tbstyle_given else "long"  # type: _TracebackStyle
         else:
             if tbstyle == "auto":
                 if default_style is None: