Introduce boilerplate for checking Nix files

For now without any checks, but this makes introducing ones fairly easy

src/eval.rs

@@ -1,3 +1,4 @@
+use std::collections::BTreeMap;
 use std::path::{Path, PathBuf};
 use std::{env, fs, process};
 
@@ -156,7 +157,7 @@ pub fn check_values(
     nixpkgs_path: &Path,
     nix_file_store: &mut NixFileStore,
     package_names: &[String],
-) -> validation::Result<ratchet::Nixpkgs> {
+) -> validation::Result<BTreeMap<String, ratchet::Package>> {
     let work_dir = tempfile::Builder::new()
         .prefix("nixpkgs-vet")
         .tempdir()
@@ -255,9 +256,7 @@ pub fn check_values(
             .collect_vec()?,
     );
 
-    Ok(check_result.map(|elems| ratchet::Nixpkgs {
-        packages: elems.into_iter().collect(),
-    }))
+    Ok(check_result.map(|elems| elems.into_iter().collect()))
 }
 
 /// Handle the evaluation result for an attribute in `pkgs/by-name`, making it a validation result.

src/files.rs

@@ -0,0 +1,77 @@
+use relative_path::RelativePath;
+use relative_path::RelativePathBuf;
+use std::collections::BTreeMap;
+use std::path::Path;
+
+use crate::nix_file::NixFileStore;
+use crate::validation::ResultIteratorExt;
+use crate::validation::Validation::Success;
+use crate::{nix_file, ratchet, structure, validation};
+
+/// Runs check on all Nix files, returning a ratchet result for each
+pub fn check_files(
+    nixpkgs_path: &Path,
+    nix_file_store: &mut NixFileStore,
+) -> validation::Result<BTreeMap<RelativePathBuf, ratchet::File>> {
+    process_nix_files(nixpkgs_path, nix_file_store, |_nix_file| {
+        // Noop for now, only boilerplate to make it easier to add future file-based checks
+        Ok(Success(ratchet::File {}))
+    })
+}
+
+/// Processes all Nix files in a Nixpkgs directory according to a given function `f`, collecting the
+/// results into a mapping from each file to a ratchet value.
+fn process_nix_files(
+    nixpkgs_path: &Path,
+    nix_file_store: &mut NixFileStore,
+    f: impl Fn(&nix_file::NixFile) -> validation::Result<ratchet::File>,
+) -> validation::Result<BTreeMap<RelativePathBuf, ratchet::File>> {
+    // Get all Nix files
+    let files = {
+        let mut files = vec![];
+        collect_nix_files(nixpkgs_path, &RelativePathBuf::new(), &mut files)?;
+        files
+    };
+
+    let results = files
+        .into_iter()
+        .map(|path| {
+            // Get the (optionally-cached) parsed Nix file
+            let nix_file = nix_file_store.get(&path.to_path(nixpkgs_path))?;
+            let result = f(nix_file)?;
+            let val = result.map(|ratchet| (path, ratchet));
+            Ok::<_, anyhow::Error>(val)
+        })
+        .collect_vec()?;
+
+    Ok(validation::sequence(results).map(|entries| {
+        // Convert the Vec to a BTreeMap
+        entries.into_iter().collect()
+    }))
+}
+
+/// Recursively collects all Nix files in the relative `dir` within `base`
+/// into the `files` `Vec`.
+fn collect_nix_files(
+    base: &Path,
+    dir: &RelativePath,
+    files: &mut Vec<RelativePathBuf>,
+) -> anyhow::Result<()> {
+    for entry in structure::read_dir_sorted(&dir.to_path(base))? {
+        let mut relative_path = dir.to_relative_path_buf();
+        relative_path.push(entry.file_name().to_string_lossy().into_owned());
+
+        let absolute_path = entry.path();
+
+        // We'll get to every file based on directory recursion, no need to follow symlinks.
+        if absolute_path.is_symlink() {
+            continue;
+        }
+        if absolute_path.is_dir() {
+            collect_nix_files(base, &relative_path, files)?
+        } else if absolute_path.extension().is_some_and(|x| x == "nix") {
+            files.push(relative_path)
+        }
+    }
+    Ok(())
+}

src/main.rs

@@ -10,6 +10,7 @@
 // #![allow(clippy::missing_const_for_fn)]
 
 mod eval;
+mod files;
 mod location;
 mod nix_file;
 mod problem;
@@ -21,6 +22,7 @@ mod validation;
 
 use anyhow::Context as _;
 use clap::Parser;
+use std::collections::BTreeMap;
 use std::path::{Path, PathBuf};
 use std::process::ExitCode;
 use std::{panic, thread};
@@ -113,20 +115,30 @@ fn check_nixpkgs(nixpkgs_path: &Path) -> validation::Result<ratchet::Nixpkgs> {
         )
     })?;
 
-    if !nixpkgs_path.join(structure::BASE_SUBPATH).exists() {
-        // No pkgs/by-name directory, always valid
-        return Ok(Success(ratchet::Nixpkgs::default()));
-    }
-
     let mut nix_file_store = NixFileStore::default();
-    let structure = check_structure(&nixpkgs_path, &mut nix_file_store)?;
 
-    // Only if we could successfully parse the structure, we do the evaluation checks
-    let result = structure.result_map(|package_names| {
-        eval::check_values(&nixpkgs_path, &mut nix_file_store, package_names.as_slice())
-    })?;
+    let package_result = {
+        if !nixpkgs_path.join(structure::BASE_SUBPATH).exists() {
+            // No pkgs/by-name directory, always valid
+            Success(BTreeMap::new())
+        } else {
+            let structure = check_structure(&nixpkgs_path, &mut nix_file_store)?;
+
+            // Only if we could successfully parse the structure, we do the evaluation checks
+            structure.result_map(|package_names| {
+                eval::check_values(&nixpkgs_path, &mut nix_file_store, package_names.as_slice())
+            })?
+        }
+    };
+
+    let file_result = files::check_files(&nixpkgs_path, &mut nix_file_store)?;
 
-    Ok(result)
+    Ok(
+        package_result.and(file_result, |packages, files| ratchet::Nixpkgs {
+            packages,
+            files,
+        }),
+    )
 }
 
 #[cfg(test)]

src/ratchet.rs

@@ -2,6 +2,7 @@
 //!
 //! Each type has a `compare` method that validates the ratchet checks for that item.
 
+use relative_path::RelativePath;
 use std::collections::BTreeMap;
 
 use relative_path::RelativePathBuf;
@@ -15,6 +16,7 @@ use crate::validation::{self, Validation, Validation::Success};
 pub struct Nixpkgs {
     /// The ratchet values for all packages
     pub packages: BTreeMap<String, Package>,
+    pub files: BTreeMap<RelativePathBuf, File>,
 }
 
 impl Nixpkgs {
@@ -27,6 +29,9 @@ impl Nixpkgs {
                 .into_iter()
                 .map(|(name, pkg)| Package::compare(&name, from.packages.get(&name), &pkg)),
         )
+        .and_(validation::sequence_(to.files.into_iter().map(
+            |(name, file)| File::compare(&name, from.files.get(&name), &file),
+        )))
     }
 }
 
@@ -57,6 +62,19 @@ impl Package {
     }
 }
 
+pub struct File {}
+
+impl File {
+    /// Validates the ratchet checks for a top-level package
+    pub fn compare(
+        _name: &RelativePath,
+        _optional_from: Option<&Self>,
+        _to: &Self,
+    ) -> Validation<()> {
+        Success(())
+    }
+}
+
 /// The ratchet state of a generic ratchet check.
 pub enum RatchetState<Ratchet: ToProblem> {
     /// The ratchet is loose. It can be tightened more. In other words, this is the legacy state