feat: --trace-warnings

[mansonchor]

start ensure no stderr, so open --trace-warnings will helpful for debug

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@cb00441). Click here to learn what that means.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #53 +/- ##
=========================================
Coverage ? 99.60% =========================================
Files ? 6 Lines ? 253 Branches ? 50 =========================================
Hits ? 252 Misses ? 1 Partials ? 0 

Impacted Files	Coverage Δ
lib/cmd/start.js	99.23% <100.00%> (ø)
lib/cmd/stop.js	100.00% <100.00%> (ø)
lib/command.js	100.00% <100.00%> (ø)
lib/helper.js	100.00% <100.00%> (ø)

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[atian25]

@hyj1991 也瞅瞅，默认开的话，会不会有什么性能问题？

[hyj1991]

默认开的话，会不会有什么性能问题？

一般来说不会有额外的性能问题，这个 flag 实际上就是开启后会在 process.emitWarning 和 process.emitWarningSync 时将 捕获的 warning 堆栈打出来，如果已有的日志中在运行期内没有大量的 Use xxx to show where the warning xxx 内容的话就是安全的

[hyj1991]

+1

[mansonchor]

• egg-scripts@2.16.0

[fengmk2]

--trace-warnings 先关闭，MaxListenersExceededWarning: Possible EventEmitter memory leak 默认就会被打印，不需要添加 --trace-warnings ，添加了 --trace-warnings 反而让 ExperimentalWarning 输出到了 stderr。

Experimental 特性还是允许应用使用的。

[fengmk2]

--trace-warnings 先关闭，MaxListenersExceededWarning: Possible EventEmitter memory leak 默认就会被打印，不需要添加 --trace-warnings ，添加了 --trace-warnings 反而让 ExperimentalWarning 输出到了 stderr。

Experimental 特性还是允许应用使用的。

哦，不对，跟这个无关。。。忽略。