Add a `--check` subcommand

[juntyr]

First of all, thank you for creating this useful tool!

I've been experimenting with wit-deps for a while. At the moment, using it as a tightly integrated dependency manager for my wit deps from within my Rust deps doesn't quite work yet. Therefore, I'm trying to switch to just using wit-deps in CI for now to assert that my deps.lock file is accurate and my deps folder is up-to-date. At the moment, it seems that checking the deps folder requires running wit-deps update, which fully recreates the folder. In my usecase, this wont't work, unfortunately.

Would it be possible to add a wit-deps check subcommand? It should work almost identically to wit-deps update, but instead of overriding folders and files, it would check that their contents are the same. Crucially, it should follow symlinks.

Thanks for your help and feedback :)

[rvolosatovs]

Thank you for the report @juntyr!
Perhaps wit-deps lock --check could address your use case?
See example usage in CI e.g. here: https://github.com/WebAssembly/wasi-http/blob/a81c61fc584278f801393b22289840a439e51f50/.github/workflows/main.yml#L18

[juntyr]

Thanks for pointing me in the direction of wit-deps lock --check! It almost solves my usecase, but also seems to modify the wit/deps folder. Could the check variant ensure that no changes to the current files are made?

[rvolosatovs]

Thanks for pointing me in the direction of wit-deps lock --check! It almost solves my usecase, but also seems to modify the wit/deps folder. Could the check variant ensure that no changes to the current files are made?

That sounds like the right behavior actually (not doing any changes), but I don't have capacity to implement that any time soon. I suppose the way it would work for now would be failing fast if any of the paths specified in deps.toml are not in wit/deps and otherwise construct a tar (until we have #25), hash it and compare to what's in deps.lock.
It looks like the failfast is the only missing piece to allow for that, since I think right now it's probably just fetching everything missing and then hashing.

Would you be interested in contributing this change?

[juntyr]

I unfortunately also don't have the time at the moment, but I can share the code that I'm using (ignore my custom error types), which runs wit-deps in a tempdir and then compares the changes but also ignored deep dependencies since they will be flattened anyways:

use std::{
    fmt,
    fs::{self, File},
    hash::{BuildHasher, DefaultHasher, Hasher, RandomState},
    io::{self, BufReader},
    path::Path,
};

use core_error::LocationError;
use tempdir::TempDir;
use walkdir::{DirEntry, WalkDir};

pub type Result<T, E = LocationError<AnyError>> = std::result::Result<T, E>;

#[allow(clippy::too_many_lines)]
#[allow(clippy::missing_errors_doc)]
pub fn check_is_locked(wit: impl AsRef<Path>) -> Result<()> {
    let wit = wit.as_ref();

    let deps_file = fs::read_to_string(wit.join("deps.toml")).map_err(AnyError::new)?;
    let deps_lock = fs::read_to_string(wit.join("deps.lock")).map_err(AnyError::new)?;

    let deps = TempDir::new("deps").map_err(AnyError::new)?;

    let lock = wit_deps::lock(
        Some(&wit),
        deps_file,
        Some(deps_lock),
        deps.path().join("deps"),
    );
    let lock = tokio::runtime::Builder::new_current_thread()
        .enable_io()
        .enable_time()
        .build()
        .map_err(AnyError::new)?
        .block_on(lock)
        .map_err(AnyError::from)?;

    if lock.is_some() {
        return Err(AnyError::msg("lock file has changed").into());
    }

    let old_wit = wit.join("deps");
    let new_wit = deps.path().join("deps");

    let mut old_deps = WalkDir::new(&old_wit)
        .min_depth(1)
        .follow_links(true)
        .sort_by_file_name()
        .into_iter();
    let mut new_deps = WalkDir::new(&new_wit)
        .min_depth(1)
        .follow_links(true)
        .sort_by_file_name()
        .into_iter();

    let (mut old_dep, mut new_dep) = (
        old_deps.next().transpose().map_err(AnyError::new)?,
        new_deps.next().transpose().map_err(AnyError::new)?,
    );

    loop {
        // skip indirect dependency deps files, lock files, and directories,
        //  since indirect dependencies are flattened into the main dendencies
        let skip = |dep: &Option<DirEntry>| match dep {
            Some(dep) if dep.path().ends_with("deps") && dep.file_type().is_dir() => {
                Some(Skip::Directory)
            },
            Some(dep)
                if (dep.path().ends_with("deps.toml") && dep.file_type().is_file())
                    || (dep.path().ends_with("deps.lock") && dep.file_type().is_file()) =>
            {
                Some(Skip::File)
            },
            _ => None,
        };

        if let Some(old_skip) = skip(&old_dep) {
            if matches!(old_skip, Skip::Directory) {
                old_deps.skip_current_dir();
            }
            old_dep = old_deps.next().transpose().map_err(AnyError::new)?;
            continue;
        }
        if let Some(new_skip) = skip(&new_dep) {
            if matches!(new_skip, Skip::Directory) {
                new_deps.skip_current_dir();
            }
            new_dep = new_deps.next().transpose().map_err(AnyError::new)?;
            continue;
        }

        // check that both have the same number of files
        let (some_old_dep, some_new_dep) = match (old_dep, new_dep) {
            (Some(old_dep), Some(new_dep)) => (old_dep, new_dep),
            (None, None) => break,
            (Some(extra), None) => {
                return Err(AnyError::msg(format!(
                    "{} is extraneous in deps",
                    extra.path().display()
                ))
                .into())
            },
            (None, Some(missing)) => {
                return Err(AnyError::msg(format!(
                    "{} is missing from deps",
                    missing.path().display()
                ))
                .into())
            },
        };

        // strip the file path prefixes to make them comparable
        let old_dep_path = some_old_dep
            .path()
            .strip_prefix(&old_wit)
            .map_err(AnyError::new)?;
        let new_dep_path = some_new_dep
            .path()
            .strip_prefix(&new_wit)
            .map_err(AnyError::new)?;

        // check that the next file path and type match
        if old_dep_path != new_dep_path {
            return Err(AnyError::msg(format!(
                "file name mismatch between {} and {} in deps",
                old_dep_path.display(),
                new_dep_path.display(),
            ))
            .into());
        }
        if some_old_dep.file_type() != some_new_dep.file_type() {
            return Err(AnyError::msg(format!(
                "file type mismatch for {}",
                old_dep_path.display()
            ))
            .into());
        }

        // we can only compare the binary contents of files
        if !some_old_dep.file_type().is_file() {
            old_dep = old_deps.next().transpose().map_err(AnyError::new)?;
            new_dep = new_deps.next().transpose().map_err(AnyError::new)?;

            continue;
        }

        let mut old_file = BufReader::new(File::open(some_old_dep.path()).map_err(AnyError::new)?);
        let mut new_file = BufReader::new(File::open(some_new_dep.path()).map_err(AnyError::new)?);

        let rng = RandomState::new();
        let mut old_hasher = HashWriter {
            hasher: rng.build_hasher(),
        };
        let mut new_hasher = HashWriter {
            hasher: rng.build_hasher(),
        };

        // hash the file contents
        io::copy(&mut old_file, &mut old_hasher).map_err(AnyError::new)?;
        io::copy(&mut new_file, &mut new_hasher).map_err(AnyError::new)?;

        let (old_hash, new_hash) = (old_hasher.hasher.finish(), new_hasher.hasher.finish());

        // check that the file content hashes match
        if old_hash != new_hash {
            return Err(AnyError::msg(format!(
                "file hash mismatch for {}",
                old_dep_path.display()
            ))
            .into());
        }

        old_dep = old_deps.next().transpose().map_err(AnyError::new)?;
        new_dep = new_deps.next().transpose().map_err(AnyError::new)?;
    }

    deps.close().map_err(AnyError::new)?;

    Ok(())
}

#[derive(Debug, thiserror::Error)]
#[error(transparent)]
pub struct AnyError(#[from] anyhow::Error);

impl AnyError {
    pub fn new<E: 'static + std::error::Error + Send + Sync>(error: E) -> Self {
        Self(anyhow::Error::new(error))
    }

    pub fn msg<M: 'static + fmt::Display + fmt::Debug + Send + Sync>(message: M) -> Self {
        Self(anyhow::Error::msg(message))
    }
}

enum Skip {
    File,
    Directory,
}

struct HashWriter {
    hasher: DefaultHasher,
}

impl io::Write for HashWriter {
    fn write(&mut self, bytes: &[u8]) -> Result<usize, io::Error> {
        self.hasher.write(bytes);
        Ok(bytes.len())
    }

    fn flush(&mut self) -> Result<(), io::Error> {
        Ok(())
    }
}