java-topology/defects/crystal/unit/CrystalCompareStrictnessAlgorithm.java

package unit;

import java.util.*;

/**
 * CWE-407 unit test: Crystal compare_strictness named arg O(N²) lookup
 *
 * Models Crystal's DefWithMetadata#compare_strictness where:
 *   - Each def has a list of named parameters (args with external names)
 *   - For each named arg in self, we search for it in other's named args
 *   - This is O(N²) where N = number of named parameters
 *
 * The defect is in restrictions.cr:94,104,141,148 — called from
 * add_def in types.cr:919 inside a loop over existing overloads.
 *
 * Test measures ops count at N=800 (named args per def).
 */
public class CrystalCompareStrictnessAlgorithm {

    // ---- Defective version: Array#any? / Array#find (linear scan) -------------

    /**
     * For each name in selfArgs, scan otherArgs linearly.
     * Returns total comparisons performed.
     */
    static long defectiveCompareNamedArgs(List<String> selfArgs, List<String> otherArgs) {
        long ops = 0;
        for (String selfName : selfArgs) {
            // models: other_named_args.try &.any?(&.external_name.== self_arg.external_name)
            for (String otherName : otherArgs) {
                ops++;
                if (selfName.equals(otherName)) break;
            }
        }
        return ops;
    }

    /**
     * Model add_def loop calling compare_strictness for D overloads.
     * Total cost: O(D × N²)
     */
    static long defectiveAddDef(int numOverloads, List<String> selfArgs, List<String> otherArgs) {
        long totalOps = 0;
        for (int i = 0; i < numOverloads; i++) {
            totalOps += defectiveCompareNamedArgs(selfArgs, otherArgs);
        }
        return totalOps;
    }

    // ---- Fixed version: HashMap O(1) lookup -----------------------------------

    /**
     * Build a map from name -> arg once, then all lookups are O(1).
     */
    static long fixedCompareNamedArgs(List<String> selfArgs, Map<String, String> otherArgMap) {
        long ops = 0;
        for (String selfName : selfArgs) {
            ops++; // O(1) map lookup
            otherArgMap.containsKey(selfName);
        }
        return ops;
    }

    static long fixedAddDef(int numOverloads, List<String> selfArgs, List<String> otherArgs) {
        // Build map once per comparison (still O(N) to build, but only done once)
        Map<String, String> otherArgMap = new HashMap<>();
        for (String name : otherArgs) otherArgMap.put(name, name);

        long totalOps = 0;
        for (int i = 0; i < numOverloads; i++) {
            totalOps += fixedCompareNamedArgs(selfArgs, otherArgMap);
        }
        return totalOps;
    }

    // ---- Test harness ----------------------------------------------------------

    static final int N = 800;   // named args per def
    static final int D = 10;    // number of overloads

    public static void main(String[] args) {
        int passed = 0;
        int total = 0;

        // Build two arg lists of size N with no overlap (worst case: scan all)
        List<String> selfArgs = new ArrayList<>(N);
        List<String> otherArgs = new ArrayList<>(N);
        for (int i = 0; i < N; i++) {
            selfArgs.add("self_" + i);
            otherArgs.add("other_" + i);  // different names — always scans full list
        }

        // Test 1: defective is O(N²) per comparison call
        total++;
        long slowOps = defectiveCompareNamedArgs(selfArgs, otherArgs);
        // Worst case: every self arg scans all N other args (no match found)
        assert slowOps == (long) N * N
            : "Expected " + ((long) N * N) + " ops, got " + slowOps;
        System.out.println("PASS test1: defective single compare ops=" + slowOps
            + " (N^2=" + ((long) N * N) + ", N=" + N + ")");
        passed++;

        // Test 2: fixed is O(N) per comparison call
        total++;
        Map<String, String> otherArgMap = new HashMap<>();
        for (String name : otherArgs) otherArgMap.put(name, name);
        long fastOps = fixedCompareNamedArgs(selfArgs, otherArgMap);
        assert fastOps == N
            : "Expected exactly N=" + N + " ops, got " + fastOps;
        System.out.println("PASS test2: fixed single compare ops=" + fastOps + " (O(N), N=" + N + ")");
        passed++;

        // Test 3: speedup per call is >= 10x
        total++;
        double speedup = (double) slowOps / fastOps;
        assert speedup >= 10.0
            : "Expected speedup >= 10x, got " + speedup;
        System.out.printf("PASS test3: single-compare speedup=%.1fx%n", speedup);
        passed++;

        // Test 4: with D overloads, defective is O(D*N²), fixed is O(D*N)
        total++;
        long slowTotal = defectiveAddDef(D, selfArgs, otherArgs);
        long fastTotal = fixedAddDef(D, selfArgs, otherArgs);
        double addDefSpeedup = (double) slowTotal / fastTotal;
        assert addDefSpeedup >= 10.0
            : "add_def speedup expected >= 10x, got " + addDefSpeedup;
        System.out.printf("PASS test4: add_def D=%d speedup=%.1fx (slow=%d fast=%d)%n",
            D, addDefSpeedup, slowTotal, fastTotal);
        passed++;

        // Test 5: correctness — matching names found correctly
        total++;
        List<String> mixed1 = Arrays.asList("alpha", "beta", "gamma");
        List<String> mixed2 = Arrays.asList("delta", "beta", "epsilon");
        Map<String, String> mixed2Map = new HashMap<>();
        for (String name : mixed2) mixed2Map.put(name, name);

        // "beta" should be found in both, "alpha"/"gamma" should not match
        assert mixed2.contains("beta");
        assert mixed2Map.containsKey("beta");
        assert !mixed2.contains("alpha");
        assert !mixed2Map.containsKey("alpha");
        System.out.println("PASS test5: correctness — defective and fixed agree on membership");
        passed++;

        System.out.println(passed + "/" + total + " PASS");
    }
}