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//! Interface for injecting I/O-related functionality into tvix-eval.
//!
//! The Nix language contains several builtins (e.g. `builtins.readDir`), as
//! well as language feature (e.g. string-"coercion" of paths) that interact
//! with the filesystem.
//!
//! The language evaluator implemented by this crate does not depend on any
//! particular filesystem interaction model. Instead, this module provides a
//! trait that can be implemented by tvix-eval callers to provide the
//! functionality they desire.
//!
//! In theory this can be used to implement "mocked" filesystem interactions, or
//! interaction with remote filesystems, etc.
//!
//! In the context of Nix builds, callers also use this interface to determine
//! how store paths are opened and so on.
use std::path::PathBuf;
use crate::errors::ErrorKind;
/// Defines how filesystem interaction occurs inside of tvix-eval.
pub trait EvalIO {
/// Read the file at the specified path to a string.
fn read_to_string(&self, path: PathBuf) -> Result<String, ErrorKind>;
}
/// Implementation of [`EvalIO`] that simply uses the equivalent
/// standard library functions, i.e. does local file-IO.
struct StdIO;
impl EvalIO for StdIO {
fn read_to_string(&self, path: PathBuf) -> Result<String, ErrorKind> {
let path: PathBuf = path.into();
std::fs::read_to_string(&path).map_err(|e| ErrorKind::IO {
path: Some(path),
error: std::rc::Rc::new(e),
})
}
}
/// Dummy implementation of [`EvalIO`], can be used in contexts where
/// IO is not available but code should "pretend" that it is.
struct DummyIO;
impl EvalIO for DummyIO {
fn read_to_string(&self, _: PathBuf) -> Result<String, ErrorKind> {
Err(ErrorKind::NotImplemented(
"I/O methods are not implemented in DummyIO",
))
}
}
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