[GitHub] [arrow] mqy edited a comment on pull request #8967: ARROW-10967: [Rust] Add functions for test data to mod arrow::util::test_util

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mqy edited a comment on pull request #8967:
URL: https://github.com/apache/arrow/pull/8967#issuecomment-749648137


   > I wonder if we can use a Cargo environment variable rather than calling out to git to find the appropriate paths. For example, I think env!("CARGO_MANIFEST_DIR") is the directory containing Cargo.toml.
   
   @alamb I [The Cargo Book :: Environment Variables](https://doc.rust-lang.org/cargo/reference/environment-variables.html) states that:
   ```
   CARGO_MANIFEST_DIR — The directory containing the manifest for **the package** being built (the package containing the build script). Also note that this is the value of the current working directory of the build script when it starts.
   ```
   I've verified with unit test in the "arrow" package, that `env!("CARGO_MANIFEST_DIR")` equals to `env::current_dir().unwrap().display().to_string()` -- the dir "rust/arrow".
   
   Actually, the most simplest implementation to get "git toplevel dir" is to append "../../" to current dir at present.
   
   I did tried various ways to get the `git top level dir`: 
   
   - find ".git" file or dir from parents of current dir
   - find  dir "rust" from parents of current dir
   - use `git` command 
   
   I prefer that `arrow_test_data()` and `parquet_test_dir()` SHOULD NOT depends on the actual dir structure: workspace dir "rust/" or any existing package dir ("parquet/" for example), or possible deeper nesting dirs. The major reason is: these data dirs are **defined (controlled)** by `git submodule` for all sub projects,  it's none of the business of underlying dir structures in "apache arrow".
   
   Thank you for your review and comments!


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