[clang] Reset CodeGenOptions fields for clean module/PCH builds (PR #138256)

[Ayush Pareek via cfe-commits]

ayushpareek2003 wrote:

> Could you elaborate? Why `= {}` is better than `.clear()` ?

according to my understanding, Clang stores some build-specific data in CodeGenOptions like file paths and debug info. When generating modules or precompiled headers, this data can make the output different from build to build. To avoid that, we reset those fields.

I changed .clear() to = {} because, as I understand, = {} resets the entire field to its default value, not just empties it. This is helpful because it works safely across different types—not just std::string, but also for types like std::optional, smallString, or other structs that might be used in the future. Using = {} makes it easier to refactor or extend the structure later without having to update every .clear() call. It also communicates intent more clearly: we’re not just clearing content, we’re fully resetting the field. This reduces the risk of leaking build-specific paths or flags into the output, and helps make Clang’s module and PCH output more consistent and reproducible across different systems. I did this to make the code more future-proof, maintainable, and reliable.





https://github.com/llvm/llvm-project/pull/138256