clang-tidy v. -Weffc++

Context

Recent versions of clang-tidy added readability-redundant-member-init: https://clang.llvm.org/extra/clang-tidy/checks/readability-redundant-member-init.html

This is handy! When a class member has a default initializer it is redundent to initialize it in the member list.

But, because some types don't have default initializers, forgetting to initialize them in the member list (or using c++11 initialization in the class definition) can lead to serious trouble like mapbox/wagyu#69 - refs mapbox/wagyu#70.

So, this is the reason, at https://github.com/mapbox/cpp/issues/37#issuecomment-336200744, that we recommend using g++ and the -Weffc++ flag because it can catch this (note, clang++ plus -Weffc++ cannot):

-Weffc++ - useful when building with g++ (does not do much with clang++). With g++ it can catch uninitialized class members and prevent crashes like mapbox/wagyu#69 - refs mapbox/wagyu#70

Problem

• -Weffc++ will warn on all class members not explicitly initialized in the initializer list
• clang-tidy will automatically remove variables from the initializer list that have default constructors

So, the two will fight: causing each other warnings. For this reason I think we should likely:

• let clang-tidy win
• recommend no longer using g++ with -Weffc++
• figure out what alternative way we can catch when members, without default initializers, are uninitialized (without needing to use -Weffc++). Maybe another clang-tidy check?

从 clang-tidy's readability-redundant-member-init 文档以及链接的 mapbox/cpp#37、wagyu#69 和 wagyu#70 讨论开始；未确定任何 repository 文件或测试。确定针对 -Weffc++、clang-tidy 指南以及检测未初始化成员的统一方案；完成条件是形成有文档记录的建议和配置。