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 have 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 -- this is current solution
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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