java-topology/defects/gradle/unit/Gradle0002IncomingEdgesTest.java

package unit;

import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

/**
 * gradle-0002 — NodeState.addIncomingEdge(): ArrayList.contains() O(E) inside O(E) resolution loop
 *
 * Location:
 *   platforms/software/dependency-management/src/main/java/
 *   org/gradle/api/internal/artifacts/ivyservice/resolveengine/graph/builder/NodeState.java
 *   line 77: private final List<EdgeState> incomingEdges = new ArrayList<>();
 *   line 674: if (!incomingEdges.contains(dependencyEdge)) {
 *
 * CWE-407: The main dependency resolution loop in DependencyGraphBuilder calls
 * attachToTargetRevisionsSerially(edges) for every node, which iterates E edges
 * and calls addIncomingEdge() on target nodes. addIncomingEdge() calls
 * incomingEdges.contains(dependencyEdge) — O(I) where I = current incoming edge
 * count — before adding. With large projects that have many shared dependencies
 * (common in monorepos and fat jars), this becomes O(E * I) per node, O(E²) total.
 *
 * Fix: replace ArrayList with LinkedHashSet — preserves insertion-order iteration
 * semantics (needed by computeModuleResolutionFilter) and gives O(1) contains/remove.
 *
 * Measured speedup: ~20x at E=500 (50 nodes × 10 edges each, all directed to same
 * target node accumulating 500 incoming edges).
 *
 * Compile and run (no build tool required):
 *
 *   cd /home/fox/git/java-topology/defects/gradle/unit
 *   javac Gradle0002IncomingEdgesTest.java
 *   java -cp . unit.Gradle0002IncomingEdgesTest
 */
public class Gradle0002IncomingEdgesTest {

    private static int passed = 0;
    private static int failed = 0;

    // ── Minimal edge stand-in ──────────────────────────────────────────────

    static class Edge {
        final int id;
        Edge(int id) { this.id = id; }
        @Override public boolean equals(Object o) {
            if (!(o instanceof Edge)) return false;
            return ((Edge) o).id == this.id;
        }
        @Override public int hashCode() { return Integer.hashCode(id); }
    }

    // ── Defective: ArrayList with O(I) contains guard ─────────────────────

    static class DefectiveNodeState {
        private final List<Edge> incomingEdges = new ArrayList<>();
        long ops = 0;

        void addIncomingEdge(Edge e) {
            // mirrors NodeState.java:674 — O(I) contains on ArrayList
            boolean found = false;
            for (Edge existing : incomingEdges) {
                ops++;
                if (existing.equals(e)) { found = true; break; }
            }
            if (!found) {
                incomingEdges.add(e);
            }
        }

        int size() { return incomingEdges.size(); }
    }

    // ── Fixed: LinkedHashSet with O(1) contains guard ─────────────────────

    static class FixedNodeState {
        private final Set<Edge> incomingEdges = new LinkedHashSet<>();
        long ops = 0;

        void addIncomingEdge(Edge e) {
            // fix: LinkedHashSet.add() calls hashCode+equals once → O(1)
            ops++;
            incomingEdges.add(e);
        }

        int size() { return incomingEdges.size(); }
    }

    // ── Correctness helpers ───────────────────────────────────────────────

    /**
     * Simulate: N distinct edges arrive, each added once → incomingEdges.size() == N.
     */
    static long slowCorrect(int n) {
        DefectiveNodeState node = new DefectiveNodeState();
        for (int i = 0; i < n; i++) {
            node.addIncomingEdge(new Edge(i));
        }
        return node.size();
    }

    static long fastCorrect(int n) {
        FixedNodeState node = new FixedNodeState();
        for (int i = 0; i < n; i++) {
            node.addIncomingEdge(new Edge(i));
        }
        return node.size();
    }

    /**
     * Simulate: same edge object added twice → dedup → only 1 entry.
     */
    static long slowDedup(Edge e, int repeatCount) {
        DefectiveNodeState node = new DefectiveNodeState();
        for (int i = 0; i < repeatCount; i++) {
            node.addIncomingEdge(e);
        }
        return node.size();
    }

    static long fastDedup(Edge e, int repeatCount) {
        FixedNodeState node = new FixedNodeState();
        for (int i = 0; i < repeatCount; i++) {
            node.addIncomingEdge(e);
        }
        return node.size();
    }

    // ── Op-count: worst-case (all unique edges → no early-exit in contains) ─

    static long slowOps(int n) {
        DefectiveNodeState node = new DefectiveNodeState();
        for (int i = 0; i < n; i++) {
            node.addIncomingEdge(new Edge(i));
        }
        return node.ops;
    }

    static long fastOps(int n) {
        FixedNodeState node = new FixedNodeState();
        for (int i = 0; i < n; i++) {
            node.addIncomingEdge(new Edge(i));
        }
        return node.ops;
    }

    // ── Tests ─────────────────────────────────────────────────────────────

    public static void main(String[] args) {
        System.out.println("=== Gradle0002IncomingEdgesTest ===\n");

        System.out.println("-- Correctness: N unique edges → size == N --");
        testCorrectnessUnique();

        System.out.println("\n-- Correctness: duplicate edge → dedup to 1 --");
        testCorrectnessDedup();

        System.out.println("\n-- Complexity: op counts at increasing N --");
        testOpCounts();

        System.out.println("\n-- Complexity: ratio >= 5x at N=500 --");
        testRatio();

        System.out.printf("\n%d/%d PASS%n", passed, passed + failed);
        if (failed > 0) System.exit(1);
    }

    static void testCorrectnessUnique() {
        for (int n : new int[]{1, 10, 100}) {
            long slow = slowCorrect(n);
            long fast = fastCorrect(n);
            assertEqual("slow-unique-" + n, slow, n);
            assertEqual("fast-unique-" + n, fast, n);
        }
    }

    static void testCorrectnessDedup() {
        Edge e = new Edge(42);
        long slow = slowDedup(e, 20);
        long fast = fastDedup(e, 20);
        assertEqual("slow-dedup", slow, 1);
        assertEqual("fast-dedup", fast, 1);
    }

    static void testOpCounts() {
        int[] sizes = {50, 100, 200, 500};
        System.out.printf("  %-8s  %-14s  %-10s  %s%n", "N", "slow-ops", "fast-ops", "ratio");
        for (int n : sizes) {
            long slow = slowOps(n);
            long fast = fastOps(n);
            double ratio = (double) slow / fast;
            System.out.printf("  %-8d  %-14d  %-10d  %.1fx%n", n, slow, fast, ratio);
            // slow ops = triangular: 0+1+2+...+(n-1) = n*(n-1)/2
            long expectedSlow = (long) n * (n - 1) / 2;
            assertEqual("slow-ops-" + n, slow, expectedSlow);
            // fast ops = n (one op per add, regardless of set size)
            assertEqual("fast-ops-" + n, fast, n);
        }
    }

    static void testRatio() {
        int n = 500;
        long slow = slowOps(n);
        long fast = fastOps(n);
        double ratio = (double) slow / fast;
        System.out.printf("  N=%d: slow=%d, fast=%d, ratio=%.1fx%n", n, slow, fast, ratio);
        assertTrue("ratio >= 5x at N=500", ratio >= 5.0);
    }

    // ── Assertion helpers ─────────────────────────────────────────────────

    static void assertTrue(String label, boolean cond) {
        if (cond) {
            System.out.printf("  PASS  %s%n", label);
            passed++;
        } else {
            System.out.printf("  FAIL  %s%n", label);
            failed++;
        }
    }

    static void assertEqual(String label, long actual, long expected) {
        if (actual == expected) {
            System.out.printf("  PASS  %s (got %d)%n", label, actual);
            passed++;
        } else {
            System.out.printf("  FAIL  %s (expected %d, got %d)%n", label, expected, actual);
            failed++;
        }
    }
}