improve the symlink probing by simplifying it

Less IO operations, and less that can go wrong.

gix-fs/src/capabilities.rs

@@ -101,22 +101,13 @@ impl Capabilities {
  }
 
  fn probe_symlink(root: &Path) -> std::io::Result<bool> {
- let src_path = root.join("__link_src_file");
- std::fs::OpenOptions::new()
- .create_new(true)
- .write(true)
- .open(&src_path)?;
  let link_path = root.join("__file_link");
- if crate::symlink::create(&src_path, &link_path).is_err() {
- std::fs::remove_file(&src_path)?;
+ if crate::symlink::create("dangling".as_ref(), &link_path).is_err() {
  return Ok(false);
  }
 
  let res = std::fs::symlink_metadata(&link_path).map(|m| m.file_type().is_symlink());
-
- let cleanup = crate::symlink::remove(&link_path).or_else(|_| std::fs::remove_file(&link_path));
- std::fs::remove_file(&src_path).and(cleanup)?;
-
+ crate::symlink::remove(&link_path).or_else(|_| std::fs::remove_file(&link_path))?;
  res
  }
 }

gix-fs/src/symlink.rs

@@ -2,6 +2,8 @@ use std::{io, io::ErrorKind::AlreadyExists, path::Path};
 
 #[cfg(not(windows))]
 /// Create a new symlink at `link` which points to `original`.
+///
+/// Note that `original` doesn't have to exist.
 pub fn create(original: &Path, link: &Path) -> io::Result<()> {
  std::os::unix::fs::symlink(original, link)
 }

gix-fs/tests/capabilities/mod.rs

@@ -2,7 +2,7 @@
 fn probe() {
  let dir = tempfile::tempdir().unwrap();
  std::fs::File::create(dir.path().join("config")).unwrap();
- gix_fs::Capabilities::probe(dir.path());
+ let caps = gix_fs::Capabilities::probe(dir.path());
 
  let entries: Vec<_> = std::fs::read_dir(dir.path())
  .unwrap()
@@ -15,4 +15,8 @@ fn probe() {
  0,
  "there should be no left-over files after probing, found {entries:?}"
  );
+ if cfg!(unix) {
+ assert!(caps.symlink, "Unix should always be able to create symlinks");
+ assert!(caps.executable_bit, "Unix should always honor executable bits");
+ }
 }