Add required support for reading path files (#301)

Soon these will have to be read to find linked worktrees, maybe?

Author: Byron

Cargo.lock

@@ -15,10 +15,11 @@ doctest = false
 
 [dependencies]
 git-sec = { version = "^0.1.0", path = "../git-sec", features = ["thiserror"] }
+git-path = { version = "^0.1.0", path = "../git-path" }
 git-ref = { version = "^0.12.1", path = "../git-ref" }
 git-hash = { version = "^0.9.3", path = "../git-hash" }
 
-bstr = { version = "0.2.13", default-features = false, features = ["std"]}
+bstr = { version = "0.2.13", default-features = false, features = ["std", "unicode"] }
 thiserror = "1.0.26"
 
 [dev-dependencies]

git-discover/Cargo.toml

@@ -1,4 +1,6 @@
-//! Find git repositories or search them upwards from a starting point.
+//! Find git repositories or search them upwards from a starting point, or determine if a directory looks like a git repository.
+//!
+//! Note that detection methods are educated guesses using the presence of files, without looking too much into the details.
 #![forbid(unsafe_code, rust_2018_idioms)]
 #![deny(missing_docs)]
 
@@ -100,3 +102,21 @@ pub use is::{bare as is_bare, git as is_git};
 ///
 pub mod upwards;
 pub use upwards::function::{discover as upwards, discover_opts as upwards_opts};
+
+///
+pub mod path {
+    use std::path::PathBuf;
+
+    /// Reads a plain path from a file that contains it as its only content, with trailing newlines trimmed.
+    pub fn from_plain_file(path: impl AsRef<std::path::Path>) -> Option<std::io::Result<PathBuf>> {
+        use bstr::ByteSlice;
+        let mut buf = match std::fs::read(path) {
+            Ok(buf) => buf,
+            Err(err) if err.kind() == std::io::ErrorKind::NotFound => return None,
+            Err(err) => return Some(Err(err)),
+        };
+        let trimmed_len = buf.trim_end().len();
+        buf.truncate(trimmed_len);
+        Some(Ok(git_path::from_bstring(buf)))
+    }
+}