feat(tvix/eval): Add a struct implementing NIX_PATH

Add a simple struct implementing both the string parsing and path
resolution rules of Nix's `NIX_PATH` environment variable, for use in
resolving `<...>`-style paths

Change-Id: Ife75f39aa5c12928278d81fe428fbadc98bac5cc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6917
Autosubmit: grfn <grfn@gws.fyi>
Reviewed-by: tazjin <tazjin@tvl.su>
Reviewed-by: Adam Joseph <adam@westernsemico.com>
Tested-by: BuildkiteCI
This commit is contained in:
Griffin Smith 2022-10-09 22:57:21 -04:00 committed by grfn
parent 0e9f5d6890
commit 5e2b44b416
2 changed files with 208 additions and 0 deletions

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@ -12,6 +12,7 @@ mod value;
mod vm;
mod warnings;
mod nix_path;
#[cfg(test)]
mod properties;
#[cfg(test)]

207
tvix/eval/src/nix_path.rs Normal file
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@ -0,0 +1,207 @@
use std::convert::Infallible;
use std::io;
use std::path::{Path, PathBuf};
use std::str::FromStr;
use crate::errors::ErrorKind;
#[derive(Debug, Clone, PartialEq, Eq)]
enum NixPathEntry {
/// Resolve subdirectories of this path within `<...>` brackets. This
/// corresponds to bare paths within the `NIX_PATH` environment variable
///
/// For example, with `NixPathEntry::Path("/example")` and the following
/// directory structure:
///
/// ```notrust
/// example
/// └── subdir
/// └── grandchild
/// ```
///
/// A Nix path literal `<subdir>` would resolve to `/example/subdir`, and a
/// Nix path literal `<subdir/grandchild>` would resolve to
/// `/example/subdir/grandchild`
Path(PathBuf),
/// Resolve paths starting with `prefix` as subdirectories of `path`. This
/// corresponds to `prefix=path` within the `NIX_PATH` environment variable.
///
/// For example, with `NixPathEntry::Prefix { prefix: "prefix", path:
/// "/example" }` and the following directory structure:
///
/// ```notrust
/// example
/// └── subdir
/// └── grandchild
/// ```
///
/// A Nix path literal `<prefix/subdir>` would resolve to `/example/subdir`,
/// and a Nix path literal `<prefix/subdir/grandchild>` would resolve to
/// `/example/subdir/grandchild`
Prefix { prefix: PathBuf, path: PathBuf },
}
impl NixPathEntry {
fn resolve(&self, lookup_path: &Path) -> io::Result<Option<PathBuf>> {
let resolve_in =
|parent: &Path, lookup_path: &Path| match parent.join(lookup_path).canonicalize() {
Ok(path) => Ok(Some(path)),
Err(e) if e.kind() == io::ErrorKind::NotFound => Ok(None),
Err(e) => Err(e),
};
match self {
NixPathEntry::Path(p) => resolve_in(p, lookup_path),
NixPathEntry::Prefix { prefix, path } => {
if let Ok(child_path) = lookup_path.strip_prefix(prefix) {
resolve_in(path, child_path)
} else {
Ok(None)
}
}
}
}
}
impl FromStr for NixPathEntry {
type Err = Infallible;
fn from_str(s: &str) -> Result<Self, Self::Err> {
match s.split_once('=') {
Some((prefix, path)) => Ok(Self::Prefix {
prefix: prefix.into(),
path: path.into(),
}),
None => Ok(Self::Path(s.into())),
}
}
}
/// Struct implementing the format and path resolution rules of the `NIX_PATH`
/// environment variable.
///
/// This struct can be constructed by parsing a string using the [`FromStr`]
/// impl, or via [`str::parse`]. Nix `<...>` paths can then be resolved using
/// [`NixPath::resolve`].
#[derive(Default, Debug, Clone, PartialEq, Eq)]
pub struct NixPath {
entries: Vec<NixPathEntry>,
}
impl NixPath {
/// Attempt to resolve the given `path` within this [`NixPath`] using the
/// path resolution rules for `<...>`-style paths
#[allow(dead_code)] // TODO(grfn)
pub fn resolve<P>(&self, path: P) -> Result<PathBuf, ErrorKind>
where
P: AsRef<Path>,
{
let path = path.as_ref();
for entry in &self.entries {
if let Some(p) = entry.resolve(path)? {
return Ok(p);
}
}
Err(ErrorKind::PathResolution(format!(
"path '{}' was not found in the Nix search path",
path.display()
)))
}
}
impl FromStr for NixPath {
type Err = Infallible;
fn from_str(s: &str) -> Result<Self, Self::Err> {
let entries = s
.split(':')
.map(|s| s.parse())
.collect::<Result<Vec<_>, _>>()?;
Ok(NixPath { entries })
}
}
#[cfg(test)]
mod tests {
use super::*;
mod parse {
use super::*;
#[test]
fn bare_paths() {
assert_eq!(
NixPath::from_str("/foo/bar:/baz").unwrap(),
NixPath {
entries: vec![
NixPathEntry::Path("/foo/bar".into()),
NixPathEntry::Path("/baz".into())
],
}
);
}
#[test]
fn mixed_prefix_and_paths() {
assert_eq!(
NixPath::from_str("nixpkgs=/my/nixpkgs:/etc/nixos").unwrap(),
NixPath {
entries: vec![
NixPathEntry::Prefix {
prefix: "nixpkgs".into(),
path: "/my/nixpkgs".into()
},
NixPathEntry::Path("/etc/nixos".into())
],
}
);
}
}
mod resolve {
use std::env::current_dir;
use path_clean::PathClean;
use super::*;
#[test]
fn simple_dir() {
let nix_path = NixPath::from_str("./.").unwrap();
let res = nix_path.resolve("src").unwrap();
assert_eq!(res, current_dir().unwrap().join("src").clean());
}
#[test]
fn failed_resolution() {
let nix_path = NixPath::from_str("./.").unwrap();
let err = nix_path.resolve("nope").unwrap_err();
assert!(
matches!(err, ErrorKind::PathResolution(..)),
"err = {err:?}"
);
}
#[test]
fn second_in_path() {
let nix_path = NixPath::from_str("./.:/").unwrap();
let res = nix_path.resolve("bin").unwrap();
assert_eq!(res, Path::new("/bin"));
}
#[test]
fn prefix() {
let nix_path = NixPath::from_str("/:tvix=.").unwrap();
let res = nix_path.resolve("tvix/src").unwrap();
assert_eq!(res, current_dir().unwrap().join("src").clean());
}
#[test]
fn matching_prefix() {
let nix_path = NixPath::from_str("/:tvix=.").unwrap();
let res = nix_path.resolve("tvix").unwrap();
assert_eq!(res, current_dir().unwrap().clean());
}
}
}