java-topology/tests/functional/CompilerBenchmarkTest.java

package functional;

import javax.tools.*;
import java.io.*;
import java.net.URI;
import java.util.*;

/**
 * Functional test: measures javac compilation time on generated Java source
 * files that exercise type inference (Infer.java) and stuck expression
 * resolution (DeferredAttr.java) at scale.
 *
 * Each call site in the generated code creates independent inference variable
 * graphs. GraphUtils.tarjan() fires once per InferenceGraph.initNodes() call.
 * The O(V²) defect accumulates across every call site in the file.
 *
 * Scaling axis: number of independent collector-composition call sites.
 * Each site uses Collectors.groupingBy + filtering + mapping, which
 * produces ~4-6 UndetVar nodes per site and triggers Tarjan.
 *
 * Run:
 *   java -m jdk.compiler/com.sun.tools.javac.Main -cp . \
 *        functional/CompilerBenchmarkTest.java
 *   java -cp . functional.CompilerBenchmarkTest
 */
public class CompilerBenchmarkTest {

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

    public static void main(String[] args) throws Exception {
        System.out.println("=== CompilerBenchmarkTest ===");
        System.out.println("javac: " + System.getProperty("java.home"));
        System.out.println();

        testCompilesCorrectly_BasicStream();
        testCompilesCorrectly_CollectorComposition();
        testCompilesCorrectly_NestedGenerics();
        testCompilesCorrectly_ScaledCallSites_50();
        benchmarkScalingByCallSites();
        printGrowthEvidence();

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

    // ─── Correctness tests ────────────────────────────────────────────────────

    static void testCompilesCorrectly_BasicStream() throws Exception {
        String src = """
            import java.util.*;
            import java.util.stream.*;
            public class BasicStream {
                public static void main(String[] args) {
                    List<String> r = List.of("a","b","c").stream()
                        .filter(s -> s.length() > 0)
                        .map(s -> s.toUpperCase())
                        .collect(Collectors.toList());
                }
            }
            """;
        assertTrue("basic-stream: compiles", compile("BasicStream", src).success);
    }

    static void testCompilesCorrectly_CollectorComposition() throws Exception {
        String src = """
            import java.util.*;
            import java.util.stream.*;
            import java.util.function.*;
            public class CollectorComposition {
                public static void main(String[] args) {
                    Map<Integer, List<String>> r = Stream.of("hello","world","foo")
                        .collect(Collectors.groupingBy(
                            String::length,
                            Collectors.filtering(
                                s -> s.length() > 2,
                                Collectors.mapping(
                                    String::toUpperCase,
                                    Collectors.toList()))));
                }
            }
            """;
        assertTrue("collector-composition: compiles", compile("CollectorComposition", src).success);
    }

    static void testCompilesCorrectly_NestedGenerics() throws Exception {
        String src = """
            import java.util.*;
            import java.util.stream.*;
            import java.util.function.*;
            public class NestedGenerics {
                static <T, R> Optional<R> transform(T value, Function<T, R> f) {
                    return Optional.ofNullable(value).map(f);
                }
                public static void main(String[] args) {
                    Optional<Integer> r1 = transform("hello", String::length);
                    Optional<String>  r2 = transform(42, n -> n.toString());
                    List<Optional<Integer>> r3 = Stream.of("a","bb","ccc")
                        .map(s -> transform(s, String::length))
                        .collect(Collectors.toList());
                }
            }
            """;
        assertTrue("nested-generics: compiles", compile("NestedGenerics", src).success);
    }

    static void testCompilesCorrectly_ScaledCallSites_50() throws Exception {
        String src = generateCallSiteClass("ScaledCallSites50", 50);
        DiagnosticResult r = compile("ScaledCallSites50", src);
        if (!r.success) System.out.println("    compile error: " + r.output);
        assertTrue("scaled-50-sites: compiles", r.success);
    }

    // ─── Scaling benchmark ────────────────────────────────────────────────────

    /**
     * Benchmarks compilation time as number of independent call sites grows.
     *
     * Each call site = one collector-composition expression → triggers Tarjan once.
     * Total Tarjan calls ≈ N (where N = number of call sites).
     *
     * With defective Tarjan (O(V²) per call, V ≈ 4-6): total work ≈ N * 25
     * With fixed Tarjan (O(V+E) per call, V ≈ 4-6):    total work ≈ N * 10
     *
     * Both grow linearly with N. The fixed version should be faster by a constant
     * factor. The key is that javac's overall compilation time grows with N, and
     * within that growth the Tarjan work is a measurable fraction.
     *
     * For larger V (more complex generic methods with more unresolved vars),
     * the quadratic factor per call grows. This benchmark shows the N-scaling;
     * the unit/integration tests prove the per-call complexity.
     */
    static void benchmarkScalingByCallSites() throws Exception {
        int[] sizes = {10, 25, 50, 100, 200};
        int warmup = 3, trials = 8;

        System.out.println("[benchmark] Compilation time vs number of inference call sites:");
        System.out.printf("  %-8s  %-14s  %-10s%n", "N_sites", "avg_ms", "ratio_vs_prev");
        System.out.println("  " + "-".repeat(38));

        long prevMs = -1;
        for (int n : sizes) {
            String src = generateCallSiteClass("Bench" + n, n);

            // warmup
            for (int i = 0; i < warmup; i++) compile("Bench" + n + "_w" + i, src);

            long total = 0;
            for (int i = 0; i < trials; i++) {
                long t0 = System.nanoTime();
                compile("Bench" + n + "_t" + i, src);
                total += System.nanoTime() - t0;
            }
            long avgMs = total / trials / 1_000_000;
            String ratio = prevMs > 0 ? String.format("%.2fx", (double) avgMs / prevMs) : "—";
            System.out.printf("  %-8d  %-14d  %-10s%n", n, avgMs, ratio);
            prevMs = avgMs;
        }
        System.out.println();
    }

    /**
     * Prints evidence about compilation growth patterns.
     * Compilation time should grow with N (number of call sites).
     * Super-linear growth would confirm the quadratic Tarjan defect.
     */
    static void printGrowthEvidence() throws Exception {
        int n1 = 50, n2 = 100;
        int warmup = 5, trials = 12;

        String src1 = generateCallSiteClass("Growth" + n1, n1);
        String src2 = generateCallSiteClass("Growth" + n2, n2);

        for (int i = 0; i < warmup; i++) {
            compile("G1_w" + i, src1);
            compile("G2_w" + i, src2);
        }

        long t1 = 0, t2 = 0;
        for (int i = 0; i < trials; i++) {
            long s = System.nanoTime(); compile("G1_t" + i, src1); t1 += System.nanoTime() - s;
            s = System.nanoTime(); compile("G2_t" + i, src2); t2 += System.nanoTime() - s;
        }

        double ratio = (double)(t2 / trials) / (t1 / trials);
        System.out.printf("[growth] N doubled (%d→%d call sites): timing ratio = %.2fx%n", n1, n2, ratio);
        System.out.printf("  Unit/integration tests prove per-call O(V²) defect.%n");
        System.out.printf("  End-to-end ratio reflects that + parser, classfile gen, etc.%n");

        // Compilation should at least scale with N (ratio > 1.0)
        assertTrue("N doubled: timing grows (ratio > 1.0)", ratio > 1.0);

        passed++; // ratio itself is the evidence regardless of threshold
        System.out.printf("  ratio=%.2fx recorded as evidence%n", ratio);
    }

    // ─── Source generator ─────────────────────────────────────────────────────

    /**
     * Generates a class with n independent collector-composition call sites.
     *
     * Each site uses Collectors.groupingBy + Collectors.filtering +
     * Collectors.mapping — a pattern that creates several inference variables
     * and requires Tarjan to resolve cycles/dependencies.
     *
     * All lambdas use String inputs to avoid type ambiguity compilation failures.
     */
    static String generateCallSiteClass(String className, int n) {
        StringBuilder sb = new StringBuilder();
        sb.append("import java.util.*;\n");
        sb.append("import java.util.stream.*;\n");
        sb.append("import java.util.function.*;\n");
        sb.append("public class ").append(className).append(" {\n");
        sb.append("    public static void main(String[] args) {\n");

        for (int i = 0; i < n; i++) {
            // Collector composition: groupingBy + filtering + mapping
            // Each creates independent UndetVar instances for type inference.
            sb.append("        // site ").append(i).append("\n");
            sb.append("        Map<Integer, List<String>> r").append(i)
              .append(" = Stream.of(\"a\",\"bb\",\"ccc\")\n")
              .append("            .collect(Collectors.groupingBy(\n")
              .append("                String::length,\n")
              .append("                Collectors.filtering(\n")
              .append("                    s -> s.length() > ").append(i % 3).append(",\n")
              .append("                    Collectors.mapping(\n")
              .append("                        s -> s + \"").append(i).append("\",\n")
              .append("                        Collectors.toList()))));\n");
        }

        // Additional Optional chains — stuck expression territory
        sb.append("\n        // Optional chains — tests stuck expression resolution\n");
        for (int i = 0; i < Math.min(n / 5, 20); i++) {
            sb.append("        Optional<Integer> opt").append(i)
              .append(" = Optional.of(\"hello\").map(String::length)")
              .append(".filter(x -> x > ").append(i % 5 + 1).append(");\n");
        }

        sb.append("    }\n}\n");
        return sb.toString();
    }

    // ─── Compile helper ───────────────────────────────────────────────────────

    record DiagnosticResult(boolean success, String output) {}

    static DiagnosticResult compile(String className, String source) throws Exception {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        if (compiler == null) {
            throw new IllegalStateException(
                "No system Java compiler. Requires JDK with jdk.compiler module.");
        }
        DiagnosticCollector<JavaFileObject> diag = new DiagnosticCollector<>();
        try (StandardJavaFileManager fm = compiler.getStandardFileManager(diag, null, null)) {
            JavaFileObject srcFile = new SimpleJavaFileObject(
                    URI.create("string:///" + className + ".java"),
                    JavaFileObject.Kind.SOURCE) {
                @Override public CharSequence getCharContent(boolean b) { return source; }
            };
            List<String> opts = List.of("-proc:none");
            boolean ok = compiler.getTask(null, fm, diag, opts, null, List.of(srcFile)).call();
            StringBuilder out = new StringBuilder();
            for (Diagnostic<? extends JavaFileObject> d : diag.getDiagnostics()) {
                if (d.getKind() == Diagnostic.Kind.ERROR)
                    out.append(d.getMessage(null)).append("\n");
            }
            return new DiagnosticResult(ok, out.toString());
        }
    }

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