Deprecate strongly_connected_components_recursive (networkx#6957)

* Deprecate strongly_connected_components_recursive.

* Add release note.

* Replace buggy recursive implementation with wrapper.

Author: rossbar

doc/developer/deprecations.rst

@@ -61,3 +61,5 @@ Version 3.4
 * Remove ``normalized`` kwarg from ``algorithms.s_metric``
 * Remove renamed function ``join()`` in ``algorithms/tree/operations.py`` and
   in ``doc/reference/algorithms/trees.rst``
+* Remove ``strongly_connected_components_recursive`` from
+  ``algorithms/components/strongly_connected.py``

doc/release/release_dev.rst

@@ -75,6 +75,9 @@ Deprecations
 - [`#6841 <https://github.com/networkx/pull/6841>`_]
   Deprecate the ``normalized`` keyword of the ``s_metric`` function. Ignore
   value of ``normalized`` for future compatibility.
+- [`#6957 <https://github.com/networkx/pull/6957>`_]
+  Deprecate ``strongly_connected_components_recursive`` function in favor of
+  the non-recursive implmentation ``strongly_connected_components``.
 
 Merged PRs
 ----------

networkx/algorithms/components/strongly_connected.py

@@ -178,6 +178,11 @@ def kosaraju_strongly_connected_components(G, source=None):
 def strongly_connected_components_recursive(G):
     """Generate nodes in strongly connected components of graph.
 
+    .. deprecated:: 3.2
+
+       This function is deprecated and will be removed in a future version of
+       NetworkX. Use `strongly_connected_components` instead.
+
     Recursive version of algorithm.
 
     Parameters
@@ -236,35 +241,18 @@ def strongly_connected_components_recursive(G):
        Information Processing Letters 49(1): 9-14, (1994)..
 
     """
+    import warnings
+
+    warnings.warn(
+        (
+            "\n\nstrongly_connected_components_recursive is deprecated and will be\n"
+            "removed in the future. Use strongly_connected_components instead."
+        ),
+        category=DeprecationWarning,
+        stacklevel=2,
+    )
 
-    def visit(v, cnt):
-        root[v] = cnt
-        visited[v] = cnt
-        cnt += 1
-        stack.append(v)
-        for w in G[v]:
-            if w not in visited:
-                yield from visit(w, cnt)
-            if w not in component:
-                root[v] = min(root[v], root[w])
-        if root[v] == visited[v]:
-            component[v] = root[v]
-            tmpc = {v}  # hold nodes in this component
-            while stack[-1] != v:
-                w = stack.pop()
-                component[w] = root[v]
-                tmpc.add(w)
-            stack.remove(v)
-            yield tmpc
-
-    visited = {}
-    component = {}
-    root = {}
-    cnt = 0
-    stack = []
-    for source in G:
-        if source not in visited:
-            yield from visit(source, cnt)
+    yield from strongly_connected_components(G)
 
 
 @not_implemented_for("undirected")

networkx/algorithms/components/tests/test_strongly_connected.py

@@ -63,7 +63,8 @@ def test_tarjan(self):
     def test_tarjan_recursive(self):
         scc = nx.strongly_connected_components_recursive
         for G, C in self.gc:
-            assert {frozenset(g) for g in scc(G)} == C
+            with pytest.deprecated_call():
+                assert {frozenset(g) for g in scc(G)} == C
 
     def test_kosaraju(self):
         scc = nx.kosaraju_strongly_connected_components
@@ -168,7 +169,8 @@ def test_null_graph(self):
         G = nx.DiGraph()
         assert list(nx.strongly_connected_components(G)) == []
         assert list(nx.kosaraju_strongly_connected_components(G)) == []
-        assert list(nx.strongly_connected_components_recursive(G)) == []
+        with pytest.deprecated_call():
+            assert list(nx.strongly_connected_components_recursive(G)) == []
         assert len(nx.condensation(G)) == 0
         pytest.raises(
             nx.NetworkXPointlessConcept, nx.is_strongly_connected, nx.DiGraph()
@@ -181,7 +183,8 @@ def test_connected_raise(self):
         with pytest.raises(NetworkXNotImplemented):
             next(nx.kosaraju_strongly_connected_components(G))
         with pytest.raises(NetworkXNotImplemented):
-            next(nx.strongly_connected_components_recursive(G))
+            with pytest.deprecated_call():
+                next(nx.strongly_connected_components_recursive(G))
         pytest.raises(NetworkXNotImplemented, nx.is_strongly_connected, G)
         pytest.raises(
             nx.NetworkXPointlessConcept, nx.is_strongly_connected, nx.DiGraph()
@@ -191,7 +194,6 @@ def test_connected_raise(self):
     strong_cc_methods = (
         nx.strongly_connected_components,
         nx.kosaraju_strongly_connected_components,
-        nx.strongly_connected_components_recursive,
     )
 
     @pytest.mark.parametrize("get_components", strong_cc_methods)

networkx/conftest.py

@@ -117,6 +117,11 @@ def set_warnings():
     warnings.filterwarnings(
         "ignore", category=DeprecationWarning, message="function `join` is deprecated"
     )
+    warnings.filterwarnings(
+        "ignore",
+        category=DeprecationWarning,
+        message="\n\nstrongly_connected_components_recursive",
+    )
 
 
 @pytest.fixture(autouse=True)