make use of locked markers in lock file version 2.1 and thereby avoid…

… `dependency walk failed`

src/poetry_plugin_export/exporter.py

@@ -11,6 +11,7 @@
 from poetry.repositories.http_repository import HTTPRepository
 
 from poetry_plugin_export.walker import get_project_dependency_packages
+from poetry_plugin_export.walker import get_project_dependency_packages2
 
 
 if TYPE_CHECKING:
@@ -89,17 +90,26 @@ def _export_generic_txt(
         content = ""
         dependency_lines = set()
 
-        root = self._poetry.package.with_dependency_groups(
-            list(self._groups), only=True
-        )
-
-        for dependency_package in get_project_dependency_packages(
-            self._poetry.locker,
-            project_requires=root.all_requires,
-            root_package_name=root.name,
-            project_python_marker=root.python_marker,
-            extras=self._extras,
-        ):
+        if self._poetry.locker.is_locked_groups_and_markers():
+            dependency_package_iterator = get_project_dependency_packages2(
+                self._poetry.locker,
+                project_python_marker=self._poetry.package.python_marker,
+                groups=set(self._groups),
+                extras=self._extras,
+            )
+        else:
+            root = self._poetry.package.with_dependency_groups(
+                list(self._groups), only=True
+            )
+            dependency_package_iterator = get_project_dependency_packages(
+                self._poetry.locker,
+                project_requires=root.all_requires,
+                root_package_name=root.name,
+                project_python_marker=root.python_marker,
+                extras=self._extras,
+            )
+
+        for dependency_package in dependency_package_iterator:
             line = ""
 
             if not with_extras:

src/poetry_plugin_export/walker.py

@@ -264,5 +264,27 @@ def get_locked_package(
     return next(iter(compatible_candidates), None)
 
 
+def get_project_dependency_packages2(
+    locker: Locker,
+    project_python_marker: BaseMarker | None = None,
+    groups: Collection[str] = (),
+    extras: Collection[NormalizedName] = (),
+) -> Iterator[DependencyPackage]:
+    for package, info in locker.locked_packages().items():
+        if not info.groups.intersection(groups):
+            continue
+
+        marker = info.get_marker(groups)
+        if not marker.validate({"extra": extras}):
+            continue
+
+        if project_python_marker:
+            marker = project_python_marker.intersect(marker)
+
+        package.marker = marker
+
+        yield DependencyPackage(dependency=package.to_dependency(), package=package)
+
+
 class DependencyWalkerError(Exception):
     pass