31. Gradle: build.gradle を1行ずつ読む

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

// build.gradle の dependencies ブロックの模型。
// 「どの configuration(implementation など)に書いたか」で、その依存がどのクラスパスに入るかが決まる。
// 継承の関係は Gradle 9.7.1 の java プラグインの表どおり(testImplementation extends implementation など)。
// Gradle の実装ではなく、表を読むための模型。
class Main {
    // 宣言用の configuration -> 継承元
    static final Map<String, List<String>> EXTENDS = new LinkedHashMap<>();
    // タスクが使うクラスパス -> 取り込む configuration と、使うタスク
    static final Map<String, List<String>> CLASSPATHS = new LinkedHashMap<>();
    static final Map<String, String> USED_BY = new LinkedHashMap<>();
    // build.gradle に書いた依存
    static final Map<String, List<String>> declared = new LinkedHashMap<>();

    static void dep(String configuration, String coordinates) {
        declared.computeIfAbsent(configuration, k -> new ArrayList<>()).add(coordinates);
    }

    // configuration 自身に書かれた依存と、継承元の依存を集める
    static Set<String> collect(String configuration) {
        Set<String> result = new LinkedHashSet<>(declared.getOrDefault(configuration, List.of()));
        for (String parent : EXTENDS.getOrDefault(configuration, List.of())) {
            result.addAll(collect(parent));
        }
        return result;
    }

    public static void main(String[] args) {
        EXTENDS.put("implementation", List.of());
        EXTENDS.put("compileOnly", List.of());
        EXTENDS.put("runtimeOnly", List.of());
        EXTENDS.put("testImplementation", List.of("implementation"));
        EXTENDS.put("testCompileOnly", List.of());
        EXTENDS.put("testRuntimeOnly", List.of("runtimeOnly"));

        CLASSPATHS.put("compileClasspath", List.of("compileOnly", "implementation"));
        USED_BY.put("compileClasspath", "compileJava");
        CLASSPATHS.put("runtimeClasspath", List.of("runtimeOnly", "implementation"));
        USED_BY.put("runtimeClasspath", "bootJar (BOOT-INF/lib), bootRun");
        CLASSPATHS.put("testCompileClasspath", List.of("testCompileOnly", "testImplementation"));
        USED_BY.put("testCompileClasspath", "compileTestJava");
        CLASSPATHS.put("testRuntimeClasspath", List.of("testRuntimeOnly", "testImplementation"));
        USED_BY.put("testRuntimeClasspath", "test");

        // start.spring.io の雛形の build.gradle に書いてある 3 行
        dep("implementation", "spring-boot-starter-webmvc");
        dep("testImplementation", "spring-boot-starter-webmvc-test");
        dep("testRuntimeOnly", "junit-platform-launcher");
        // 雛形には無いが、規則を見せるために 1 本足す(実行時だけ要るもの)
        dep("runtimeOnly", "(not in the template) a-jdbc-driver");

        for (String classpath : CLASSPATHS.keySet()) {
            Set<String> jars = new LinkedHashSet<>();
            for (String configuration : CLASSPATHS.get(classpath)) {
                jars.addAll(collect(configuration));
            }
            System.out.println(classpath + "  (used by " + USED_BY.get(classpath) + ")");
            for (String jar : jars) {
                System.out.println("    " + jar);
            }
        }
        System.out.println();
        System.out.println("implementation is on every classpath; runtimeOnly never reaches compileJava;");
        System.out.println("testImplementation stays out of the main jar. Versions are missing on purpose: the BOM fills them in.");
    }
}

// 出力(JDK 22 で実行)
//   compileClasspath  (used by compileJava)
//       spring-boot-starter-webmvc
//   runtimeClasspath  (used by bootJar (BOOT-INF/lib), bootRun)
//       (not in the template) a-jdbc-driver
//       spring-boot-starter-webmvc
//   testCompileClasspath  (used by compileTestJava)
//       spring-boot-starter-webmvc-test
//       spring-boot-starter-webmvc
//   testRuntimeClasspath  (used by test)
//       junit-platform-launcher
//       (not in the template) a-jdbc-driver
//       spring-boot-starter-webmvc-test
//       spring-boot-starter-webmvc
//   ...