graph_traverse_generators_test.cc

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/*
                          Aleph_w
 
  Data structures & Algorithms
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
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  of this software and associated documentation files (the "Software"), to deal
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*/
 
#include <set>
#include <stdexcept>
#include <type_traits>
#include <vector>
 
#include <gtest/gtest.h>
 
#include <graph-traverse-generators.H>
#include <graph-traverse.H>
#include <tpl_graph.H>
 
using namespace Aleph;
 
namespace
{
using TestGraph = List_Graph<Graph_Node<int>, Graph_Arc<double>>;
using TestDigraph = List_Digraph<Graph_Node<int>, Graph_Arc<double>>;
using Itor = Node_Arc_Iterator<TestGraph>;
using DigraphItor = Node_Arc_Iterator<TestDigraph>;
 
template <class GT>
std::vector<int> node_keys(const std::vector<typename GT::Node *> &nodes)
{
  std::vector<int> keys;
  keys.reserve(nodes.size());
  for (typename GT::Node *n : nodes)
    keys.push_back(n->get_info());
  return keys;
}
 
// Diamond-shaped connected graph:
//     0 --- 1
//     |     |
//     2 --- 3 --- 4
TestGraph build_diamond(std::vector<TestGraph::Node *> &nodes)
{
  TestGraph g;
  for (int i = 0; i < 5; ++i)
    nodes.push_back(g.insert_node(i));
  g.insert_arc(nodes[0], nodes[1], 1.0);
  g.insert_arc(nodes[0], nodes[2], 2.0);
  g.insert_arc(nodes[1], nodes[3], 3.0);
  g.insert_arc(nodes[2], nodes[3], 4.0);
  g.insert_arc(nodes[3], nodes[4], 5.0);
  return g;
}
}  // namespace
 
// Compile-time regression: traverse() is &-ref-qualified specifically so
// that calling it on a temporary traverser — the dangerous one-liner
// `Graph_Traverse_BFS_Generator<GT,Itor>(g).traverse(start)`, whose
// coroutine frame would otherwise read a dangling `this` on first resume —
// is a compile error instead of undefined behavior. `std::is_invocable_v`
// (not a bare `requires{...}` expression: a ref-qualifier mismatch is a
// hard error, not a SFINAE-friendly substitution failure, so it would
// abort the whole translation unit instead of just making the requirement
// unsatisfied) checks this without ever attempting the invalid call.
using BfsGen = Graph_Traverse_BFS_Generator<TestGraph, Itor>;
static_assert(
  not std::is_invocable_v<decltype(&BfsGen::traverse), BfsGen, TestGraph::Node *>,
  "Graph_Traverse_Generator::traverse() must reject rvalue (temporary) receivers");
static_assert(
  std::is_invocable_v<decltype(&BfsGen::traverse), BfsGen &, TestGraph::Node *>,
  "Graph_Traverse_Generator::traverse() must still accept lvalue receivers");
 
TEST(GraphTraverseGenerators, SingleNodeGraph)
{
  TestGraph g;
  TestGraph::Node *n = g.insert_node(42);
 
  Graph_Traverse_BFS_Generator<TestGraph, Itor> bfs(g);
  std::vector<int> seen;
  for (TestGraph::Node *v : bfs.traverse(n))
    seen.push_back(v->get_info());
  EXPECT_EQ(seen, (std::vector<int>{42}));
}
 
TEST(GraphTraverseGenerators, NullStartThrowsInvalidArgument)
{
  TestGraph g;
 
  Graph_Traverse_BFS_Generator<TestGraph, Itor> bfs(g);
  EXPECT_THROW(
    {
      for (TestGraph::Node *v : bfs.traverse(nullptr))
        (void) v;
    },
    std::invalid_argument);
}
 
TEST(GraphTraverseGenerators, BfsVisitsAllReachableNodesExactlyOnce)
{
  std::vector<TestGraph::Node *> nodes;
  TestGraph g = build_diamond(nodes);
 
  Graph_Traverse_BFS_Generator<TestGraph, Itor> bfs(g);
  std::vector<int> seen;
  for (TestGraph::Node *v : bfs.traverse(nodes[0]))
    seen.push_back(v->get_info());
 
  ASSERT_EQ(seen.size(), 5u);
  EXPECT_EQ(std::set<int>(seen.begin(), seen.end()),
            (std::set<int>{0, 1, 2, 3, 4}));
  EXPECT_EQ(seen[0], 0);  // start node is always first
}
 
TEST(GraphTraverseGenerators, BfsOrderMatchesEagerBfsOrder)
{
  std::vector<TestGraph::Node *> nodes;
  TestGraph g = build_diamond(nodes);
 
  Graph_Traverse_BFS_Generator<TestGraph, Itor> lazy_bfs(g);
  std::vector<int> lazy_seen;
  for (TestGraph::Node *v : lazy_bfs.traverse(nodes[0]))
    lazy_seen.push_back(v->get_info());
 
  Graph_Traverse_BFS<TestGraph, Itor> eager_bfs(g);
  std::vector<int> eager_seen;
  eager_bfs(nodes[0], [&](TestGraph::Node *v) {
    eager_seen.push_back(v->get_info());
    return true;
  });
 
  EXPECT_EQ(lazy_seen, eager_seen);
}
 
TEST(GraphTraverseGenerators, DfsOrderMatchesEagerDfsOrder)
{
  std::vector<TestGraph::Node *> nodes;
  TestGraph g = build_diamond(nodes);
 
  Graph_Traverse_DFS_Generator<TestGraph, Itor> lazy_dfs(g);
  std::vector<int> lazy_seen;
  for (TestGraph::Node *v : lazy_dfs.traverse(nodes[0]))
    lazy_seen.push_back(v->get_info());
 
  Graph_Traverse_DFS<TestGraph, Itor> eager_dfs(g);
  std::vector<int> eager_seen;
  eager_dfs(nodes[0], [&](TestGraph::Node *v) {
    eager_seen.push_back(v->get_info());
    return true;
  });
 
  EXPECT_EQ(lazy_seen, eager_seen);
}
 
TEST(GraphTraverseGenerators, DisconnectedGraphOnlyVisitsReachableComponent)
{
  // Component 1: 0 - 1 - 2      Component 2: 3 - 4
  TestGraph g;
  std::vector<TestGraph::Node *> nodes;
  for (int i = 0; i < 5; ++i)
    nodes.push_back(g.insert_node(i));
  g.insert_arc(nodes[0], nodes[1], 1.0);
  g.insert_arc(nodes[1], nodes[2], 2.0);
  g.insert_arc(nodes[3], nodes[4], 3.0);
 
  Graph_Traverse_BFS_Generator<TestGraph, Itor> bfs(g);
  std::vector<int> seen;
  for (TestGraph::Node *v : bfs.traverse(nodes[0]))
    seen.push_back(v->get_info());
 
  EXPECT_EQ(std::set<int>(seen.begin(), seen.end()), (std::set<int>{0, 1, 2}));
}
 
TEST(GraphTraverseGenerators, EarlyBreakStopsTraversal)
{
  std::vector<TestGraph::Node *> nodes;
  TestGraph g = build_diamond(nodes);
 
  Graph_Traverse_BFS_Generator<TestGraph, Itor> bfs(g);
  int visited = 0;
  for (TestGraph::Node *v : bfs.traverse(nodes[0]))
    {
      (void) v;
      if (++visited == 2)
        break;
    }
  EXPECT_EQ(visited, 2);  // stopped well before all 5 nodes were visited
}
 
// Regression test: a self-loop at the start node must not be yielded
// twice, and must not prevent other reachable nodes from being visited.
// The initial frontier-seeding loop used to unconditionally overwrite the
// target node's state to Processing, which for a self-loop (tgt == start)
// clobbered start's already-Processed state.
TEST(GraphTraverseGenerators, SelfLoopAtStartNodeYieldsOnce)
{
  TestGraph g;
  TestGraph::Node *a = g.insert_node(1);
  TestGraph::Node *b = g.insert_node(2);
  g.insert_arc(a, a, 0.0);  // self-loop at the start node
  g.insert_arc(a, b, 1.0);
 
  std::vector<int> bfs_seen;
  Graph_Traverse_BFS_Generator<TestGraph, Itor> bfs(g);
  for (TestGraph::Node *n : bfs.traverse(a))
    bfs_seen.push_back(n->get_info());
  EXPECT_EQ(bfs_seen, (std::vector<int>{1, 2}));
 
  std::vector<int> dfs_seen;
  Graph_Traverse_DFS_Generator<TestGraph, Itor> dfs(g);
  for (TestGraph::Node *n : dfs.traverse(a))
    dfs_seen.push_back(n->get_info());
  EXPECT_EQ(dfs_seen, (std::vector<int>{1, 2}));
}
 
// Same regression, but the self-loop is on a node discovered mid-traversal
// rather than on the start node itself (already handled correctly by the
// main loop's own guard; kept as a sibling test for symmetry/coverage).
TEST(GraphTraverseGenerators, SelfLoopMidTraversalYieldsOnce)
{
  TestGraph g;
  TestGraph::Node *a = g.insert_node(1);
  TestGraph::Node *b = g.insert_node(2);
  TestGraph::Node *c = g.insert_node(3);
  g.insert_arc(a, b, 1.0);
  g.insert_arc(b, b, 0.0);  // self-loop at a non-start node
  g.insert_arc(b, c, 1.0);
 
  std::vector<int> seen;
  Graph_Traverse_BFS_Generator<TestGraph, Itor> bfs(g);
  for (TestGraph::Node *n : bfs.traverse(a))
    seen.push_back(n->get_info());
  EXPECT_EQ(seen, (std::vector<int>{1, 2, 3}));
}
 
TEST(GraphTraverseGenerators, CyclicGraphTerminates)
{
  // 0 - 1 - 2 - 3 - 0 (cycle)
  TestGraph g;
  std::vector<TestGraph::Node *> nodes;
  for (int i = 0; i < 4; ++i)
    nodes.push_back(g.insert_node(i));
  g.insert_arc(nodes[0], nodes[1], 1.0);
  g.insert_arc(nodes[1], nodes[2], 2.0);
  g.insert_arc(nodes[2], nodes[3], 3.0);
  g.insert_arc(nodes[3], nodes[0], 4.0);
 
  Graph_Traverse_DFS_Generator<TestGraph, Itor> dfs(g);
  std::vector<int> seen;
  for (TestGraph::Node *v : dfs.traverse(nodes[0]))
    seen.push_back(v->get_info());
 
  ASSERT_EQ(seen.size(), 4u);
  EXPECT_EQ(std::set<int>(seen.begin(), seen.end()), (std::set<int>{0, 1, 2, 3}));
}
 
TEST(GraphTraverseGenerators, DigraphRespectsArcDirection)
{
  // 0 -> 1 -> 2 ; note: no arc back, and no arc from 2 anywhere.
  TestDigraph g;
  std::vector<TestDigraph::Node *> nodes;
  for (int i = 0; i < 3; ++i)
    nodes.push_back(g.insert_node(i));
  g.insert_arc(nodes[0], nodes[1], 1.0);
  g.insert_arc(nodes[1], nodes[2], 2.0);
 
  Graph_Traverse_BFS_Generator<TestDigraph, DigraphItor> bfs(g);
  std::vector<int> from0;
  for (TestDigraph::Node *v : bfs.traverse(nodes[0]))
    from0.push_back(v->get_info());
  EXPECT_EQ(from0, (std::vector<int>{0, 1, 2}));
 
  // Starting from node 2 (a sink), only node 2 itself is reachable.
  std::vector<int> from2;
  for (TestDigraph::Node *v : bfs.traverse(nodes[2]))
    from2.push_back(v->get_info());
  EXPECT_EQ(from2, (std::vector<int>{2}));
}