feat: filter out files from each repo's rustfmt.toml ignore list

Implement skipping logic just like rustfmt does. rustfmt would ignore
these files anyway so we can save some time and effort if we avoid
spawning a subprocess for files that we know rustfmt is going to ignore
anyway.

This saves a significant amount of time, especially for repositories
like r-l/rust which ignore a lot of files.

Author: ytmimi

check_diff/Cargo.lock

@@ -13,3 +13,5 @@ tempfile = "3"
 walkdir = "2.5.0"
 diffy = "0.4.0"
 crossbeam-channel = "0.5.15"
+ignore = "0.4.25"
+toml = "0.9.11"

check_diff/Cargo.toml

@@ -670,18 +670,79 @@ pub fn compile_rustfmt<T: AsRef<str>>(
     })
 }
 
-/// Searches for rust files in the particular path and returns an iterator to them.
-pub fn search_for_rs_files(repo: &Path) -> impl Iterator<Item = PathBuf> {
-    WalkDir::new(repo).into_iter().filter_map(|e| match e.ok() {
-        Some(entry) => {
-            let path = entry.path();
-            if path.is_file() && path.extension().is_some_and(|ext| ext == "rs") {
-                return Some(entry.into_path());
+fn read_rustfmt_ignore_list(rustfmt_toml_path: &Path) -> Vec<String> {
+    let Ok(file_content) = std::fs::read_to_string(rustfmt_toml_path) else {
+        return Vec::new();
+    };
+
+    let Ok(mut data) = file_content.parse::<toml::Table>() else {
+        return Vec::new();
+    };
+
+    let Some(toml::Value::Array(ignore_list)) = data.remove("ignore") else {
+        return Vec::new();
+    };
+
+    ignore_list
+        .into_iter()
+        .map(toml::Value::try_into)
+        .collect::<Result<_, _>>()
+        .unwrap_or_default()
+}
+
+// Iterator over all rust files in a directory.
+//
+// Ignores files list in the root `.rustfmt.toml` or `rustfmt.toml` configuration files.
+pub struct RustFmtFileFinder<'a, P> {
+    ignore_set: ignore::gitignore::Gitignore,
+    repo: &'a Repository<P>,
+}
+
+impl<'a, P> RustFmtFileFinder<'a, P>
+where
+    P: AsRef<Path>,
+{
+    pub fn from_repository(repo: &'a Repository<P>) -> Self {
+        let root = repo.path();
+        let mut ignore_builder = ignore::gitignore::GitignoreBuilder::new(root);
+
+        let repo_name = repo.name();
+        for rustfmt_config_file in [".rustfmt.toml", "rustfmt.toml"] {
+            let rustfmt_toml_path = root.join(rustfmt_config_file);
+            for ignore_path in read_rustfmt_ignore_list(&rustfmt_toml_path) {
+                debug!("Adding {ignore_path} to the set of ignored files for '{repo_name}'");
+                let _ = ignore_builder.add_line(None, &ignore_path);
             }
-            None
         }
-        None => None,
-    })
+
+        Self {
+            repo,
+            ignore_set: ignore_builder
+                .build()
+                .unwrap_or(ignore::gitignore::Gitignore::empty()),
+        }
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = PathBuf> + use<'_, P> {
+        WalkDir::new(self.repo.path())
+            .into_iter()
+            .filter_map(|e| match e.ok() {
+                Some(entry) => {
+                    let path = entry.path();
+                    if path.is_file()
+                        && path.extension().is_some_and(|ext| ext == "rs")
+                        && !self
+                            .ignore_set
+                            .matched_path_or_any_parents(path, false)
+                            .is_ignore()
+                    {
+                        return Some(entry.into_path());
+                    }
+                    None
+                }
+                None => None,
+            })
+    }
 }
 
 /// Encapsulate the logic used to clone repositories for the diff check
@@ -817,7 +878,8 @@ where
         for repo in repositories.iter() {
             let tx = tx.clone();
             s.spawn(move || {
-                for file in search_for_rs_files(repo.path()) {
+                let file_finder = RustFmtFileFinder::from_repository(repo);
+                for file in file_finder.iter() {
                     let _ = tx.send((file, repo));
                 }
             });

check_diff/src/lib.rs

@@ -1,6 +1,6 @@
 use check_diff::{
-    CheckDiffError, CheckDiffRunners, CodeFormatter, FormatCodeError, Repository, check_diff,
-    search_for_rs_files,
+    CheckDiffError, CheckDiffRunners, CodeFormatter, FormatCodeError, Repository,
+    RustFmtFileFinder, check_diff,
 };
 use std::fs::File;
 use tempfile::Builder;
@@ -29,10 +29,11 @@ fn search_for_files_correctly_non_nested() -> Result<(), Box<dyn std::error::Err
     let file_path = dir.path().join("test.rs");
     let _tmp_file = File::create(file_path)?;
 
-    let iter = search_for_rs_files(dir.path());
+    let repo = Repository::new("", dir.path());
+    let file_finder = RustFmtFileFinder::from_repository(&repo);
 
     let mut count = 0;
-    for _ in iter {
+    for _ in file_finder.iter() {
         count += 1;
     }
 
@@ -51,10 +52,11 @@ fn search_for_files_correctly_nested() -> Result<(), Box<dyn std::error::Error>>
     let nested_file_path = nested_dir.path().join("nested.rs");
     let _ = File::create(nested_file_path)?;
 
-    let iter = search_for_rs_files(dir.path());
+    let repo = Repository::new("", dir.path());
+    let file_finder = RustFmtFileFinder::from_repository(&repo);
 
     let mut count = 0;
-    for _ in iter {
+    for _ in file_finder.iter() {
         count += 1;
     }