fix(config): 根治 TestDefaultConfigValues 非 hermetic 红测（#90/#107）

[NeverENG]

问题

TestDefaultConfigValues 调 NewGlobalConfig() 断言「纯默认值」，但 NewGlobalConfig 会先填默认、再用 config.json 覆盖。默认与 json 不一致的字段（MaxMemTableSize：默认 1024 vs json 10000）恒红；且测试结果依赖 config.json 是否被找到——非 hermetic。

修法（已与用户确认：抽纯默认构造 + 测试 hermetic）

• 抽出 defaultGlobalConfig()：返回纯代码默认值，不读文件、不解析命令行
• NewGlobalConfig() = defaultGlobalConfig() + Init()(文件覆盖) + ParseFlags()(命令行覆盖)
• TestDefaultConfigValues 改测 defaultGlobalConfig()——名副其实，且不再依赖外部文件

测试

go build ./... 通过；config 包全绿（此前唯一红点 MaxMemTableSize 消除），其余 config 测试无回归。

🤖 Generated with Claude Code

Summary by CodeRabbit

• Refactor

  • Improved configuration initialization structure for better maintainability.

• Tests

  • Enhanced configuration tests to better validate default values in isolation.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 4a4c999e-9289-40d1-b24b-e6930b3e3721

📥 Commits

Reviewing files that changed from the base of the PR and between c051e47 and 4d7bd34.

📒 Files selected for processing (2)

• config/global.go
• config/global_test.go

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📝 Walkthrough

Walkthrough

NewGlobalConfig() is refactored to delegate initial struct construction to a new internal defaultGlobalConfig() helper, which builds a GlobalConfig from code defaults including a derived log directory. TestDefaultConfigValues is updated to call defaultGlobalConfig() directly to avoid external config.json overwriting expected defaults.

Changes

Config default construction refactor

Layer / File(s)	Summary
defaultGlobalConfig helper and wiring config/global.go, config/global_test.go	Adds defaultGlobalConfig() that returns a fully populated GlobalConfig from code defaults (using defaultLogDir()). NewGlobalConfig() now calls it instead of constructing the literal inline. TestDefaultConfigValues switches from NewGlobalConfig() to defaultGlobalConfig() with comments noting the hermetic isolation from external file loading.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related issues

• config 单测非 hermetic：TestDefaultConfigValues 加载仓库内 config.json 导致默认值断言失败 #90: This PR implements exactly the "split constructor" solution proposed in that issue — introducing defaultGlobalConfig() to expose pure in-code defaults and updating TestDefaultConfigValues to use it for hermetic test behavior.

Poem

🐇 A config once tangled with files from afar,
Now defaults are pure, kept safe in a jar.
No config.json to muddy the test,
The rabbit extracted what's simply the best.
Clean defaults, clean code — what a hop! ✨

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/config-hermetic-defaults

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[github-actions]

🐯 BanGD 数据库内核评审

整体风险：🟢 低

变更总结：本 PR 在 config 包的配置初始化层引入配置构造的责任分离：从原有的 NewGlobalConfig()（默认值 → 文件覆盖 → 命令行覆盖 捆绑在一个函数内），拆分为 defaultGlobalConfig()（纯代码默认值，不涉及 I/O） + NewGlobalConfig()（在其上叠加 Init() 文件覆盖与 ParseFlags() 命令行覆盖）。动机是修复 TestDefaultConfigValues 的非 hermetic 问题——该测试调用 NewGlobalConfig() 断言纯默认值，但后者会读取 config.json 覆盖字段，导致测试结果依赖外部文件是否存在/内容。改动位于配置层的构造逻辑，不涉及底层的存储引擎、WAL、并发模型或内存管理。是测试可观测性/工程质量层面的改进，不改变任何运行时行为。

本评审不阻塞合入；架构级建议以 Issue 形式跟踪，普通问题在下方内联列出。

未发现需要从架构层面改进的问题。

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