java-topology/defects/bazel/unit/BazelFeatureSelectionAlgorithmTest.java

package unit;

import java.util.*;

/**
 * Models Bazel FeatureSelection.run() provides-conflict check.
 *
 * SLOW: O(P×S×L) — ImmutableList.contains() O(L) per selectable in P×S nested loops.
 * FAST: O(P×S)   — HashSet built once from enabledList; O(1) per lookup.
 *
 * CWE-407: src/main/java/com/google/devtools/build/lib/rules/cpp/FeatureSelection.java:159
 */
public class BazelFeatureSelectionAlgorithmTest {

    // -------------------------------------------------------------------------
    // Slow — ImmutableList.contains() O(L) per lookup
    // -------------------------------------------------------------------------

    static class SlowFeatureSelection {
        long cmpOps = 0;

        boolean listContains(List<String> list, String val) {
            for (String s : list) {
                cmpOps++;
                if (s.equals(val)) return true;
            }
            return false;
        }

        /**
         * O(P × S × L): for each provide × selectable, check enabledList membership.
         * Returns count of conflict checks performed.
         */
        int run(List<String> enabledList,
                Map<String, List<String>> providesMap) {
            int conflicts = 0;
            for (Map.Entry<String, List<String>> entry : providesMap.entrySet()) {
                for (String selectable : entry.getValue()) {
                    if (listContains(enabledList, selectable)) {
                        conflicts++;
                    }
                }
            }
            return conflicts;
        }

        long ops(List<String> enabledList, Map<String, List<String>> providesMap) {
            cmpOps = 0;
            run(enabledList, providesMap);
            return cmpOps;
        }
    }

    // -------------------------------------------------------------------------
    // Fast — HashSet built once before loop
    // -------------------------------------------------------------------------

    static class FastFeatureSelection {
        long cmpOps = 0;

        int run(List<String> enabledList,
                Map<String, List<String>> providesMap) {
            Set<String> enabledSet = new HashSet<>(enabledList);
            cmpOps += enabledList.size(); // build cost
            int conflicts = 0;
            for (Map.Entry<String, List<String>> entry : providesMap.entrySet()) {
                for (String selectable : entry.getValue()) {
                    cmpOps++;
                    if (enabledSet.contains(selectable)) {
                        conflicts++;
                    }
                }
            }
            return conflicts;
        }

        long ops(List<String> enabledList, Map<String, List<String>> providesMap) {
            cmpOps = 0;
            run(enabledList, providesMap);
            return cmpOps;
        }
    }

    // -------------------------------------------------------------------------
    // Build test data
    // -------------------------------------------------------------------------

    static List<String> makeEnabledList(int l) {
        List<String> list = new ArrayList<>();
        for (int i = 0; i < l; i++) list.add("feature_" + i);
        return list;
    }

    static Map<String, List<String>> makeProvidesMap(int p, int s, int overlapStart) {
        Map<String, List<String>> map = new LinkedHashMap<>();
        for (int i = 0; i < p; i++) {
            List<String> sels = new ArrayList<>();
            for (int j = 0; j < s; j++) {
                // Some selectables are in enabledList (conflicts), some not
                sels.add("feature_" + (overlapStart + i * s + j));
            }
            map.put("provide_" + i, sels);
        }
        return map;
    }

    public static void main(String[] args) {
        SlowFeatureSelection slow = new SlowFeatureSelection();
        FastFeatureSelection fast = new FastFeatureSelection();

        int passed = 0, total = 0;

        System.out.println("=== bazel-0003: FeatureSelection ImmutableList.contains O(P×S×L) ===");

        // (L, P, S) configurations matching realistic Bazel C++ toolchain sizes
        int[][] configs = {
            {50,  7, 6},   // small toolchain
            {80,  7, 6},   // realistic (agent's estimate)
            {150, 10, 8},  // large toolchain
            {300, 15, 10}  // extreme
        };
        for (int[] cfg : configs) {
            int l = cfg[0], p = cfg[1], s = cfg[2];
            List<String> enabled = makeEnabledList(l);
            Map<String, List<String>> provides = makeProvidesMap(p, s, 0);

            long sv = slow.ops(enabled, provides);
            long fv = fast.ops(enabled, provides);
            double ratio = (double) sv / Math.max(fv, 1);

            total++;
            boolean ok = sv > fv && ratio >= 5.0;
            System.out.printf("L=%3d P=%2d S=%2d  slow=%7d fast=%5d ratio=%6.1fx  %s%n",
                l, p, s, sv, fv, ratio, ok ? "PASS" : "FAIL");
            if (ok) passed++;
        }

        // Correctness: both count same conflicts
        List<String> enabled = makeEnabledList(80);
        Map<String, List<String>> provides = makeProvidesMap(7, 6, 0);
        int sc = slow.run(enabled, provides);
        int fc = fast.run(enabled, provides);
        total++;
        boolean correct = sc == fc;
        System.out.printf("conflict count matches (%d): %s%n", sc, correct ? "PASS" : "FAIL");
        if (correct) passed++;

        System.out.printf("%n%d/%d PASS%n", passed, total);
        if (passed < total) System.exit(1);
    }
}