异常与资源释放：失败也要有出口

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collections;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Set;
public class Main {
    record Trace(List<String> messages, boolean truncated) {}
    static Trace trace(Throwable root, int limit) {
        if (limit < 0) throw new IllegalArgumentException("limit");
        if (root == null) return new Trace(List.of(),false);
        Set<Throwable> seen = Collections.newSetFromMap(new IdentityHashMap<>());
        ArrayDeque<Throwable> queue = new ArrayDeque<>();
        List<String> output = new ArrayList<>();
        queue.add(root);
        while (!queue.isEmpty()) {
            Throwable current = queue.remove();
            if (!seen.add(current)) continue; // 共享或环只按对象身份处理一次。
            if (output.size() == limit) return new Trace(List.copyOf(output),true);
            output.add(String.valueOf(current.getMessage()));
            // cause 先入队，随后按原记录顺序加入关闭等次要失败。
            Throwable cause = current.getCause(); // 单次读取，避免可覆写访问器两次结果不同。
            if (cause != null) queue.add(cause);
            for (Throwable other : current.getSuppressed()) queue.add(other);
        }
        return new Trace(List.copyOf(output),false);
    }
    static void require(boolean condition) {
        if (!condition) throw new AssertionError();
    }
    public static void main(String[] args) {
        require(trace(null,0).equals(new Trace(List.of(),false)));
        Exception a = new Exception("a"), b = new Exception("b");
        a.initCause(b); b.initCause(a); // 间接环用于检验身份去重。
        require(trace(a,10).equals(new Trace(List.of("a","b"),false)));
        require(trace(a,1).equals(new Trace(List.of("a"),true)));
        Exception shared = new Exception("same");
        Exception top = new Exception("top",shared); top.addSuppressed(shared);
        require(trace(top,10).messages().equals(List.of("top","same")));
        Exception twins = new Exception("root");
        twins.addSuppressed(new Exception("same")); twins.addSuppressed(new Exception("same"));
        require(trace(twins,10).messages().equals(List.of("root","same","same")));
        // 真实 try-with-resources 验证业务失败与关闭失败同时被保留。
        try (AutoCloseable resource = () -> { throw new Exception("close"); }) {
            throw new Exception("body");
        } catch (Exception e) {
            require(trace(e,10).equals(new Trace(List.of("body","close"),false)));
        }
        Throwable changing = new Exception("changing") {
            private int reads;
            @Override public synchronized Throwable getCause() {
                return reads++ == 0 ? new Exception("child") : null;
            }
        };
        require(trace(changing,10).equals(new Trace(List.of("changing","child"),false)));
        System.out.println("PASS 7");
    }
}