java-topology/defects/meson/unit/MesonLinkWholeDiamondTest.java

import java.util.*;

/**
 * CWE-407 unit test for Meson get_internal_static_libraries_recurse diamond recursion.
 *
 * Simulates the defective and fixed versions of the link_whole traversal.
 *
 * Defect: link_whole_targets branch recurses without checking `t not in result`,
 * causing O(2^D) traversal on diamond link_whole graphs.
 *
 * Fix: add the same guard used for link_targets to link_whole_targets.
 */
public class MesonLinkWholeDiamondTest {

    static int defectiveVisitCount;

    /** Simulates defective get_internal_static_libraries_recurse */
    static void defectiveRecurse(Map<String, List<String>> linkWholeGraph,
                                  String target, Set<String> result) {
        defectiveVisitCount++;
        List<String> children = linkWholeGraph.getOrDefault(target, Collections.emptyList());
        for (String child : children) {
            // Defect: no guard — always recurses even if child already in result
            defectiveRecurse(linkWholeGraph, child, result);
        }
        result.add(target);
    }

    static int fixedVisitCount;

    /** Simulates fixed get_internal_static_libraries_recurse */
    static void fixedRecurse(Map<String, List<String>> linkWholeGraph,
                              String target, Set<String> result) {
        fixedVisitCount++;
        List<String> children = linkWholeGraph.getOrDefault(target, Collections.emptyList());
        for (String child : children) {
            // Fix: check result before recursing
            if (!result.contains(child)) {
                result.add(child);
                fixedRecurse(linkWholeGraph, child, result);
            }
        }
    }

    /**
     * Build a chained diamond link_whole graph of depth D:
     *
     *   n0 link_whole [n0L, n0R]
     *   n0L link_whole [n1]
     *   n0R link_whole [n1]
     *   n1 link_whole [n1L, n1R]
     *   n1L link_whole [n2]
     *   n1R link_whole [n2]
     *   ...
     *   n(D) is a leaf
     */
    static Map<String, List<String>> buildDiamond(int depth) {
        Map<String, List<String>> graph = new HashMap<>();
        for (int d = 0; d < depth; d++) {
            String node = "n" + d;
            String left = "n" + d + "L";
            String right = "n" + d + "R";
            String next = "n" + (d + 1);
            graph.put(node, Arrays.asList(left, right));
            graph.put(left, Arrays.asList(next));
            graph.put(right, Arrays.asList(next));
        }
        // n(depth) is a leaf
        return graph;
    }

    public static void main(String[] args) {
        System.out.println("=== Meson link_whole Diamond Recursion CWE-407 ===");
        System.out.println("get_internal_static_libraries_recurse: link_whole_targets missing guard");
        System.out.println();
        System.out.printf("%-6s %-12s %-10s %-8s%n", "Depth", "Defective", "Fixed", "Ratio");
        System.out.println("--------------------------------------");

        boolean allPass = true;

        for (int depth : new int[]{1, 2, 3, 5, 7, 10}) {
            Map<String, List<String>> graph = buildDiamond(depth);

            defectiveVisitCount = 0;
            Set<String> defectiveResult = new HashSet<>();
            defectiveRecurse(graph, "n0", defectiveResult);

            fixedVisitCount = 0;
            Set<String> fixedResult = new HashSet<>();
            fixedResult.add("n0");
            fixedRecurse(graph, "n0", fixedResult);

            double ratio = (double) defectiveVisitCount / fixedVisitCount;

            System.out.printf("D=%-4d %-12d %-10d %-8.1fx%n",
                depth, defectiveVisitCount, fixedVisitCount, ratio);

            // Both should find the same closure
            // Note: defective adds nodes bottom-up; fixed adds them on descent
            // Results should contain same set of nodes
            Set<String> allNodes = new HashSet<>();
            for (int d = 0; d <= depth; d++) {
                allNodes.add("n" + d);
                if (d < depth) {
                    allNodes.add("n" + d + "L");
                    allNodes.add("n" + d + "R");
                }
            }
            // defectiveResult includes all nodes visited (including n0 itself)
            // fixedResult includes n0 plus all children
            // The important thing: fixed finds all shared descendants
            for (int d = 1; d <= depth; d++) {
                String bottom = "n" + d;
                if (!fixedResult.contains(bottom)) {
                    System.err.println("FAIL: fixed result missing " + bottom + " at depth " + depth);
                    allPass = false;
                }
            }

            if (depth >= 5 && ratio < 5.0) {
                System.err.println("FAIL: expected >5x ratio at depth " + depth + ", got " + ratio);
                allPass = false;
            }
        }

        System.out.println();

        // Edge case: linear chain (no diamond) — both should visit same count
        {
            Map<String, List<String>> linear = new HashMap<>();
            linear.put("A", Arrays.asList("B"));
            linear.put("B", Arrays.asList("C"));
            // C is a leaf

            defectiveVisitCount = 0;
            Set<String> dr = new HashSet<>();
            defectiveRecurse(linear, "A", dr);

            fixedVisitCount = 0;
            Set<String> fr = new HashSet<>();
            fr.add("A");
            fixedRecurse(linear, "A", fr);

            System.out.println("Linear chain (no diamond): defective=" + defectiveVisitCount
                + " fixed=" + fixedVisitCount + " — PASS (no blowup expected)");
        }

        System.out.println();
        if (allPass) {
            System.out.println("PASS — exponential blowup in link_whole confirmed and fixed");
        } else {
            System.exit(1);
        }
    }
}