Freemine.cmake.external.proj

[freemine]

Description

with the hope of clarifying building system of TDengine itself, to isolate source code, external project and building-binaries, so that further work, such as test-cases-running, rebuilding among branches, could be simplied and less error prone.

this is still in early stage, and /contrib directory is still containing both source-code and downloaded external projects and there-built-binaries. but it's believed easy to isolate them later on.

wish you guys might think this potentially useful, and looking forward to your comments.

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[freemine]

btw, currently, this PR only tested under linux, not including windows or macosx yet.

[freemine]

in order to make external project downloaded to be compiled within the main project of TDengine itself with ADD_SUBDIRECTORY, by setting CMAKE__XXX variable and option(YYY), is really not a good practice, because it ruins the global namespace.
SAY, if project A compiles with CMAKE_XXX set to TRUE, while project B compiles with CMAKE_XXX set FALSE，how ugly the directives in contrib/CMakeLists.txt would be?
with ExternalProject_ADD, you can isolate elegantly easy.

[freemine]

and

which means: no matter you build the TDengine with -DBUILD_CONTRIB:BOOL=ON or not, taosd likely link with /deps//rocksdb_static/librocksdb.a

this really smells bad.

[freemine]

comparison of built binary images

[guanshengliang]

These commits could be compiled successfully in my development environment, but there were compilation errors in the CI environment of TDengine. I will contact the maintainer of the CI to see how to handle it. Subsequently, I will carefully review these submissions. However, time is limited before the Spring Festival, so it may not be until February that they can be merged.

[freemine]

thx,but I am NOT in a hurry.
actually speaking, this PR is not supposed to be merged directly at the very beginning, it's there to make suggestions to you guys that if it's worth doing so or not.
btw, ci failure is supposed to happen.
there are still several steps to fully fulfill this.

[CLAassistant]

All committers have signed the CLA.

[guanshengliang]

@freemine
代码中对 CMake 脚本的修改思路确实很好。然而，PR 在 macOS 和 Windows 系统下编译链接时时都会遇到问题，我尝试进行了调试，但似乎无法通过简单的修改来解决。具体问题如下：

1. lz4 和 tz 的下载目录存在冲突，各平台都可能编译失败
2. rocksdb 的编译选项存在问题，导致在 macOS 和 Windows 系统下编译失败。
3. 删除 xxhash 文件后，TSZ 在 macOS 和 Windows 系统下编译失败。
4. 未开启 BUILD_TEST 选项，导致许多单元测试代码未被编译；而开启该选项后，部分单元测试会出现链接失败。

在大家远程交流不方便的情况下，建议不要一次性提交几十个文件（拆分为多个小的 PR），我们小步快跑，也能更快合并

cc @feici02

[freemine]

@guanshengliang
thx. and agree.

[freemine]

#29903 is now taking place