Kontinuation opened a new pull request, #672:
URL: https://github.com/apache/sedona-db/pull/672
## Summary
Replace the C-based `dlopen`/`dlsym` dynamic PROJ loading
(`proj_dyn.c`/`proj_dyn.h`) with a pure Rust implementation using the
`libloading` crate. This eliminates the `cc` build dependency and ~250 lines of
C code while maintaining the same `ProjApi` struct-of-function-pointers
architecture used by all existing call sites.
## Changes
- **New**: `c/sedona-proj/src/dyn_load.rs` — Pure Rust dynamic symbol loader
with `load_fn!` macro and `load_proj_from_path()` function
- **Deleted**: `c/sedona-proj/build.rs`, `c/sedona-proj/src/proj_dyn.c`,
`c/sedona-proj/src/proj_dyn.h` — C-based loader and its build script
- **Modified**: `c/sedona-proj/src/proj.rs` — `ProjApi` struct now holds
`Option<Library>` to keep the shared library alive; `try_from_shared_library()`
calls the Rust loader; `Drop` relies on automatic `Library` drop instead of the
C `release` callback
- **Modified**: `c/sedona-proj/src/proj_dyn_bindgen.rs` — Removed `extern
"C" { proj_dyn_api_init }` block (no longer needed)
- **Modified**: `c/sedona-proj/Cargo.toml` — Replaced `cc` build-dependency
with `libloading` runtime dependency
- **Modified**: `Cargo.toml` — Added `libloading = "0.9"` to workspace
dependencies
## Approach
The `libloading` crate provides safe, cross-platform dynamic library loading
(`dlopen`/`LoadLibrary`). Each PROJ symbol is loaded via a `load_fn!` macro
that:
1. Loads the symbol as a raw `*const ()` pointer
2. Transmutes it to the expected function pointer type
3. Stores it in the existing `ProjApi` `#[repr(C)]` struct
The `Library` handle is stored as `_lib: Option<Library>` in the Rust
`ProjApi` wrapper — `Some` when loaded from a shared library, `None` when using
`proj-sys`. This ensures the library stays loaded for the lifetime of the
function pointers.
All 22 existing tests pass. No clippy warnings.
## Note
A similar PR for `sedona-gdal` will follow as a stacked PR.
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