Bump version to 0.0.40

.pre-commit-config.yaml

@@ -1,5 +1,5 @@
 repos:
   - repo: https://github.com/charliermarsh/ruff
-    rev: v0.0.38
+    rev: v0.0.40
     hooks:
       - id: lint

Cargo.lock

@@ -1432,6 +1432,24 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "path-absolutize"
+version = "3.0.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d3de4b40bd9736640f14c438304c09538159802388febb02c8abaae0846c1f13"
+dependencies = [
+ "path-dedot",
+]
+
+[[package]]
+name = "path-dedot"
+version = "3.0.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d611d5291372b3738a34ebf0d1f849e58b1dcc1101032f76a346eaa1f8ddbb5b"
+dependencies = [
+ "once_cell",
+]
+
 [[package]]
 name = "percent-encoding"
 version = "2.1.0"
@@ -1783,7 +1801,7 @@ dependencies = [
 
 [[package]]
 name = "ruff"
-version = "0.0.38"
+version = "0.0.40"
 dependencies = [
  "anyhow",
  "bincode",
@@ -1802,6 +1820,7 @@ dependencies = [
  "log",
  "notify",
  "once_cell",
+ "path-absolutize",
  "rayon",
  "regex",
  "rustpython-parser",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ruff"
-version = "0.0.38"
+version = "0.0.40"
 edition = "2021"
 
 [lib]
@@ -23,6 +23,7 @@ itertools = "0.10.3"
 log = { version = "0.4.17" }
 notify = { version = "4.0.17" }
 once_cell = { version = "1.13.1" }
+path-absolutize = "3.0.13"
 rayon = { version = "1.5.3" }
 regex = { version = "1.6.0" }
 rustpython-parser = { features = ["lalrpop"], git = "https://github.com/charliermarsh/RustPython.git", rev = "7d21c6923a506e79cc041708d83cef925efd33f4" }

README.md

@@ -57,7 +57,7 @@ ruff also works with [Pre-Commit](https://pre-commit.com) (requires Cargo on sys
 ```yaml
 repos:
 - repo: https://github.com/charliermarsh/ruff
-  rev: v0.0.38
+  rev: v0.0.40
   hooks:
     - id: lint
 ```
@@ -86,7 +86,7 @@ ruff path/to/code/ --select F401 F403
 See `ruff --help` for more:
 
 ```shell
-ruff (v0.0.38)
+ruff (v0.0.40)
 An extremely fast Python linter.
 
 USAGE:
@@ -96,19 +96,42 @@ ARGS:
     <FILES>...
 
 OPTIONS:
-    -e, --exit-zero               Exit with status code "0", even upon detecting errors
-        --exclude <EXCLUDE>...    List of file and/or directory patterns to exclude from checks
-    -f, --fix                     Attempt to automatically fix lint errors
-    -h, --help                    Print help information
-        --ignore <IGNORE>...      List of error codes to ignore
-    -n, --no-cache                Disable cache reads
-    -q, --quiet                   Disable all logging (but still exit with status code "1" upon
-                                  detecting errors)
-        --select <SELECT>...      List of error codes to enable
-    -v, --verbose                 Enable verbose logging
-    -w, --watch                   Run in watch mode by re-running whenever files change
+    -e, --exit-zero
+            Exit with status code "0", even upon detecting errors
+        --exclude <EXCLUDE>...
+            List of paths, used to exclude files and/or directories from checks
+        --extend-exclude <EXTEND_EXCLUDE>...
+            Like --exclude, but adds additional files and directories on top of the excluded ones
+    -f, --fix
+            Attempt to automatically fix lint errors
+        --format <FORMAT>
+            Output serialization format for error messages [default: text] [possible values: text,
+            json]
+    -h, --help
+            Print help information
+        --ignore <IGNORE>...
+            List of error codes to ignore
+    -n, --no-cache
+            Disable cache reads
+    -q, --quiet
+            Disable all logging (but still exit with status code "1" upon detecting errors)
+        --select <SELECT>...
+            List of error codes to enable
+    -v, --verbose
+            Enable verbose logging
+    -w, --watch
+            Run in watch mode by re-running whenever files change
 ```
 
+Exclusions are based on globs, and can be either:
+
+- Single-path patterns, like `.mypy_cache` (to exclude any directory named `.mypy_cache` in the
+  tree), `foo.py` (to exclude any file named `foo.py`), or `foo_*.py` (to exclude any file matching
+  `foo_*.py` ).
+- Relative patterns, like `./directory/foo.py` (to exclude that specific file) or `./directory/*.py`
+  (to exclude any Python files in `./directory`). Note that these paths are relative to the
+  directory from which you execute `ruff`, and _not_ the directory of the `pyproject.toml`.
+
 ### Compatibility with Black
 
 ruff is intended to be compatible with [Black](https://github.com/psf/black), and should be
@@ -221,28 +244,28 @@ Add this `pyproject.toml` to the CPython directory:
 [tool.ruff]
 line-length = 88
 exclude = [
-    "Lib/lib2to3/tests/data/bom.py",
-    "Lib/lib2to3/tests/data/crlf.py",
-    "Lib/lib2to3/tests/data/different_encoding.py",
-    "Lib/lib2to3/tests/data/false_encoding.py",
-    "Lib/lib2to3/tests/data/py2_test_grammar.py",
-    "Lib/test/bad_coding2.py",
-    "Lib/test/badsyntax_3131.py",
-    "Lib/test/badsyntax_pep3120.py",
-    "Lib/test/encoded_modules/module_iso_8859_1.py",
-    "Lib/test/encoded_modules/module_koi8_r.py",
-    "Lib/test/test_fstring.py",
-    "Lib/test/test_grammar.py",
-    "Lib/test/test_importlib/test_util.py",
-    "Lib/test/test_named_expressions.py",
-    "Lib/test/test_patma.py",
-    "Lib/test/test_source_encoding.py",
-    "Tools/c-analyzer/c_parser/parser/_delim.py",
-    "Tools/i18n/pygettext.py",
-    "Tools/test2to3/maintest.py",
-    "Tools/test2to3/setup.py",
-    "Tools/test2to3/test/test_foo.py",
-    "Tools/test2to3/test2to3/hello.py",
+    "./resources/test/cpython/Lib/lib2to3/tests/data/bom.py",
+    "./resources/test/cpython/Lib/lib2to3/tests/data/crlf.py",
+    "./resources/test/cpython/Lib/lib2to3/tests/data/different_encoding.py",
+    "./resources/test/cpython/Lib/lib2to3/tests/data/false_encoding.py",
+    "./resources/test/cpython/Lib/lib2to3/tests/data/py2_test_grammar.py",
+    "./resources/test/cpython/Lib/test/bad_coding2.py",
+    "./resources/test/cpython/Lib/test/badsyntax_3131.py",
+    "./resources/test/cpython/Lib/test/badsyntax_pep3120.py",
+    "./resources/test/cpython/Lib/test/encoded_modules/module_iso_8859_1.py",
+    "./resources/test/cpython/Lib/test/encoded_modules/module_koi8_r.py",
+    "./resources/test/cpython/Lib/test/test_fstring.py",
+    "./resources/test/cpython/Lib/test/test_grammar.py",
+    "./resources/test/cpython/Lib/test/test_importlib/test_util.py",
+    "./resources/test/cpython/Lib/test/test_named_expressions.py",
+    "./resources/test/cpython/Lib/test/test_patma.py",
+    "./resources/test/cpython/Lib/test/test_source_encoding.py",
+    "./resources/test/cpython/Tools/c-analyzer/c_parser/parser/_delim.py",
+    "./resources/test/cpython/Tools/i18n/pygettext.py",
+    "./resources/test/cpython/Tools/test2to3/maintest.py",
+    "./resources/test/cpython/Tools/test2to3/setup.py",
+    "./resources/test/cpython/Tools/test2to3/test/test_foo.py",
+    "./resources/test/cpython/Tools/test2to3/test2to3/hello.py",
 ]
 ```
 

resources/test/fixtures/F821.py

@@ -77,3 +77,8 @@ class Ticket:
 
     def set_status(self, status: Status):
         self.status = status
+
+
+def update_tomato():
+    print(TOMATO)
+    TOMATO = "cherry tomato"

resources/test/fixtures/__init__.py

@@ -0,0 +1,3 @@
+print(__path__)
+
+__all__ = ["a", "b", "c"]

resources/test/fixtures/directory/also_excluded.py

@@ -0,0 +1,9 @@
+a = "abc"
+b = f"ghi{'jkl'}"
+
+c = f"def"
+d = f"def" + "ghi"
+e = (
+    f"def" +
+    "ghi"
+)

resources/test/fixtures/pyproject.toml

@@ -1,6 +1,10 @@
 [tool.ruff]
 line-length = 88
-extend-exclude = ["excluded.py", "migrations"]
+extend-exclude = [
+    "excluded.py",
+    "migrations",
+    "./resources/test/fixtures/directory/also_excluded.py",
+]
 select = [
     "E402",
     "E501",

src/ast/types.rs

@@ -53,5 +53,7 @@ pub enum BindingKind {
 pub struct Binding {
     pub kind: BindingKind,
     pub location: Location,
-    pub used: Option<usize>,
+    /// Tuple of (scope index, location) indicating the scope and location at which the binding was
+    /// last used.
+    pub used: Option<(usize, Location)>,
 }

src/cache.rs

@@ -1,8 +1,10 @@
 use std::collections::hash_map::DefaultHasher;
-use std::fs::Metadata;
+use std::fs::{create_dir_all, File, Metadata};
 use std::hash::{Hash, Hasher};
+use std::io::Write;
 use std::path::Path;
 
+use anyhow::Result;
 use cacache::Error::EntryNotFound;
 use filetime::FileTime;
 use log::error;
@@ -83,6 +85,16 @@ fn cache_key(path: &Path, settings: &Settings, autofix: &fixer::Mode) -> String
     )
 }
 
+pub fn init() -> Result<()> {
+    let gitignore_path = Path::new(cache_dir()).join(".gitignore");
+    if gitignore_path.exists() {
+        return Ok(());
+    }
+    create_dir_all(cache_dir())?;
+    let mut file = File::create(gitignore_path)?;
+    file.write_all(b"*").map_err(|e| e.into())
+}
+
 pub fn get(
     path: &Path,
     metadata: &Metadata,

src/check_ast.rs

@@ -26,7 +26,7 @@ struct Checker<'a> {
     locator: SourceCodeLocator<'a>,
     settings: &'a Settings,
     autofix: &'a fixer::Mode,
-    path: &'a str,
+    path: &'a Path,
     // Computed checks.
     checks: Vec<Check>,
     // Retain all scopes and parent nodes, along with a stack of indexes to track which are active
@@ -55,7 +55,7 @@ impl<'a> Checker<'a> {
     pub fn new(
         settings: &'a Settings,
         autofix: &'a fixer::Mode,
-        path: &'a str,
+        path: &'a Path,
         content: &'a str,
     ) -> Checker<'a> {
         Checker {
@@ -184,7 +184,7 @@ where
                                 name.to_string(),
                                 Binding {
                                     kind: BindingKind::Assignment,
-                                    used: Some(global_scope_id),
+                                    used: Some((global_scope_id, stmt.location)),
                                     location: stmt.location,
                                 },
                             );
@@ -416,13 +416,14 @@ where
                             name,
                             Binding {
                                 kind: BindingKind::FutureImportation,
-                                used: Some(
+                                used: Some((
                                     self.scopes[*(self
                                         .scope_stack
                                         .last()
                                         .expect("No current scope found."))]
                                     .id,
-                                ),
+                                    stmt.location,
+                                )),
                                 location: stmt.location,
                             },
                         );
@@ -1108,7 +1109,7 @@ impl<'a> Checker<'a> {
                     }
                 }
                 if let Some(binding) = scope.values.get_mut(id) {
-                    binding.used = Some(scope_id);
+                    binding.used = Some((scope_id, expr.location));
                     return;
                 }
 
@@ -1117,6 +1118,10 @@ impl<'a> Checker<'a> {
             }
 
             if self.settings.select.contains(&CheckCode::F821) {
+                // Allow __path__.
+                if self.path.ends_with("__init__.py") && id == "__path__" {
+                    return;
+                }
                 self.checks.push(Check::new(
                     CheckKind::UndefinedName(id.clone()),
                     expr.location,
@@ -1136,17 +1141,14 @@ impl<'a> Checker<'a> {
             {
                 for scope in self.scopes.iter().rev().skip(1) {
                     if matches!(scope.kind, ScopeKind::Function | ScopeKind::Module) {
-                        let used = scope
-                            .values
-                            .get(id)
-                            .map(|binding| binding.used)
-                            .unwrap_or_default();
-                        if let Some(scope_id) = used {
-                            if scope_id == current.id {
-                                self.checks.push(Check::new(
-                                    CheckKind::UndefinedLocal(id.clone()),
-                                    expr.location,
-                                ));
+                        if let Some(binding) = scope.values.get(id) {
+                            if let Some((scope_id, location)) = binding.used {
+                                if scope_id == current.id {
+                                    self.checks.push(Check::new(
+                                        CheckKind::UndefinedLocal(id.clone()),
+                                        location,
+                                    ));
+                                }
                             }
                         }
                     }
@@ -1240,12 +1242,12 @@ impl<'a> Checker<'a> {
         }
     }
 
-    fn check_deferred_string_annotations<'b>(&mut self, path: &str, allocator: &'b mut Vec<Expr>)
+    fn check_deferred_string_annotations<'b>(&mut self, allocator: &'b mut Vec<Expr>)
     where
         'b: 'a,
     {
         while let Some((location, expression)) = self.deferred_string_annotations.pop() {
-            if let Ok(mut expr) = parser::parse_expression(expression, path) {
+            if let Ok(mut expr) = parser::parse_expression(expression, "<filename>") {
                 relocate_expr(&mut expr, location);
                 allocator.push(expr);
             } else if self.settings.select.contains(&CheckCode::F722) {
@@ -1328,7 +1330,7 @@ impl<'a> Checker<'a> {
             });
 
             if self.settings.select.contains(&CheckCode::F822)
-                && !Path::new(self.path).ends_with("__init__.py")
+                && !self.path.ends_with("__init__.py")
             {
                 if let Some(binding) = all_binding {
                     if let Some(names) = all_names {
@@ -1374,7 +1376,7 @@ pub fn check_ast(
     content: &str,
     settings: &Settings,
     autofix: &fixer::Mode,
-    path: &str,
+    path: &Path,
 ) -> Vec<Check> {
     let mut checker = Checker::new(settings, autofix, path, content);
     checker.push_scope(Scope::new(ScopeKind::Module));
@@ -1391,7 +1393,7 @@ pub fn check_ast(
     checker.check_deferred_assignments();
     checker.check_deferred_annotations();
     let mut allocator = vec![];
-    checker.check_deferred_string_annotations(path, &mut allocator);
+    checker.check_deferred_string_annotations(&mut allocator);
 
     // Reset the scope to module-level, and check all consumed scopes.
     checker.scope_stack = vec![GLOBAL_SCOPE_INDEX];

src/fs.rs

@@ -1,3 +1,4 @@
+use std::env;
 use std::fs::File;
 use std::io::{BufReader, Read};
 use std::path::{Path, PathBuf};
@@ -5,9 +6,11 @@ use std::path::{Path, PathBuf};
 use anyhow::Result;
 use glob::Pattern;
 use log::debug;
+use path_absolutize::Absolutize;
 use walkdir::{DirEntry, WalkDir};
 
 fn is_excluded(path: &Path, exclude: &[Pattern]) -> bool {
+    // Check the basename.
     if let Some(file_name) = path.file_name() {
         if let Some(file_name) = file_name.to_str() {
             for pattern in exclude {
@@ -15,13 +18,19 @@ fn is_excluded(path: &Path, exclude: &[Pattern]) -> bool {
                     return true;
                 }
             }
-            false
-        } else {
-            false
         }
-    } else {
-        false
     }
+
+    // Check the complete path.
+    if let Some(file_name) = path.to_str() {
+        for pattern in exclude {
+            if pattern.matches(file_name) {
+                return true;
+            }
+        }
+    }
+
+    false
 }
 
 fn is_included(path: &Path) -> bool {
@@ -34,7 +43,7 @@ pub fn iter_python_files<'a>(
     exclude: &'a [Pattern],
     extend_exclude: &'a [Pattern],
 ) -> impl Iterator<Item = DirEntry> + 'a {
-    WalkDir::new(path)
+    WalkDir::new(normalize_path(path))
         .follow_links(true)
         .into_iter()
         .filter_entry(|entry| {
@@ -60,6 +69,20 @@ pub fn iter_python_files<'a>(
         })
 }
 
+pub fn normalize_path(path: &PathBuf) -> PathBuf {
+    if path == Path::new(".") || path == Path::new("..") {
+        return path.clone();
+    }
+    if let Ok(path) = path.absolutize() {
+        if let Ok(root) = env::current_dir() {
+            if let Ok(path) = path.strip_prefix(root) {
+                return Path::new(".").join(path);
+            }
+        }
+    }
+    path.clone()
+}
+
 pub fn read_file(path: &Path) -> Result<String> {
     let file = File::open(path)?;
     let mut buf_reader = BufReader::new(file);
@@ -105,6 +128,18 @@ mod tests {
         let exclude = vec![Pattern::new("baz.py").unwrap()];
         assert!(is_excluded(path, &exclude));
 
+        let path = Path::new("foo/bar");
+        let exclude = vec![Pattern::new("foo/bar").unwrap()];
+        assert!(is_excluded(path, &exclude));
+
+        let path = Path::new("foo/bar/baz.py");
+        let exclude = vec![Pattern::new("foo/bar/baz.py").unwrap()];
+        assert!(is_excluded(path, &exclude));
+
+        let path = Path::new("foo/bar/baz.py");
+        let exclude = vec![Pattern::new("foo/bar/*.py").unwrap()];
+        assert!(is_excluded(path, &exclude));
+
         let path = Path::new("foo/bar/baz.py");
         let exclude = vec![Pattern::new("baz").unwrap()];
         assert!(!is_excluded(path, &exclude));

src/lib.rs

@@ -2,7 +2,7 @@ extern crate core;
 
 mod ast;
 mod autofix;
-mod cache;
+pub mod cache;
 pub mod check_ast;
 mod check_lines;
 pub mod checks;
@@ -10,6 +10,7 @@ pub mod fs;
 pub mod linter;
 pub mod logging;
 pub mod message;
+pub mod printer;
 mod pyproject;
 mod python;
 pub mod settings;

src/linter.rs

@@ -13,10 +13,12 @@ use crate::message::Message;
 use crate::settings::Settings;
 use crate::{cache, fs};
 
-fn check_path(path: &Path, settings: &Settings, autofix: &fixer::Mode) -> Result<Vec<Check>> {
-    // Read the file from disk.
-    let contents = fs::read_file(path)?;
-
+fn check_path(
+    path: &Path,
+    contents: &str,
+    settings: &Settings,
+    autofix: &fixer::Mode,
+) -> Result<Vec<Check>> {
     // Aggregate all checks.
     let mut checks: Vec<Check> = vec![];
 
@@ -26,13 +28,12 @@ fn check_path(path: &Path, settings: &Settings, autofix: &fixer::Mode) -> Result
         .iter()
         .any(|check_code| matches!(check_code.lint_source(), LintSource::AST))
     {
-        let path = path.to_string_lossy();
-        let python_ast = parser::parse_program(&contents, &path)?;
-        checks.extend(check_ast(&python_ast, &contents, settings, autofix, &path));
+        let python_ast = parser::parse_program(contents, "<filename>")?;
+        checks.extend(check_ast(&python_ast, contents, settings, autofix, path));
     }
 
     // Run the lines-based checks.
-    check_lines(&mut checks, &contents, settings);
+    check_lines(&mut checks, contents, settings);
 
     Ok(checks)
 }
@@ -55,7 +56,7 @@ pub fn lint_path(
     let contents = fs::read_file(path)?;
 
     // Generate checks.
-    let mut checks = check_path(path, settings, autofix)?;
+    let mut checks = check_path(path, &contents, settings, autofix)?;
 
     // Apply autofix.
     if matches!(autofix, fixer::Mode::Apply) {
@@ -85,10 +86,20 @@ mod tests {
     use anyhow::Result;
 
     use crate::autofix::fixer;
-    use crate::checks::CheckCode;
-    use crate::linter::check_path;
+    use crate::checks::{Check, CheckCode};
+    use crate::fs;
+    use crate::linter;
     use crate::settings;
 
+    fn check_path(
+        path: &Path,
+        settings: &settings::Settings,
+        autofix: &fixer::Mode,
+    ) -> Result<Vec<Check>> {
+        let contents = fs::read_file(path)?;
+        linter::check_path(path, &contents, settings, autofix)
+    }
+
     #[test]
     fn e402() -> Result<()> {
         let mut checks = check_path(
@@ -752,6 +763,23 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn init() -> Result<()> {
+        let mut checks = check_path(
+            Path::new("./resources/test/fixtures/__init__.py"),
+            &settings::Settings {
+                line_length: 88,
+                exclude: vec![],
+                extend_exclude: vec![],
+                select: BTreeSet::from([CheckCode::F821, CheckCode::F822]),
+            },
+            &fixer::Mode::Generate,
+        )?;
+        checks.sort_by_key(|check| check.location);
+        insta::assert_yaml_snapshot!(checks);
+        Ok(())
+    }
+
     #[test]
     fn future_annotations() -> Result<()> {
         let mut checks = check_path(

src/main.rs

@@ -12,12 +12,14 @@ use notify::{raw_watcher, RecursiveMode, Watcher};
 use rayon::prelude::*;
 use walkdir::DirEntry;
 
+use ::ruff::cache;
 use ::ruff::checks::CheckCode;
 use ::ruff::checks::CheckKind;
 use ::ruff::fs::iter_python_files;
 use ::ruff::linter::lint_path;
 use ::ruff::logging::set_up_logging;
 use ::ruff::message::Message;
+use ::ruff::printer::{Printer, SerializationFormat};
 use ::ruff::settings::Settings;
 use ::ruff::tell_user;
 
@@ -60,6 +62,9 @@ struct Cli {
     /// Like --exclude, but adds additional files and directories on top of the excluded ones.
     #[clap(long, multiple = true)]
     extend_exclude: Vec<Pattern>,
+    /// Output serialization format for error messages.
+    #[clap(long, arg_enum, default_value_t=SerializationFormat::Text)]
+    format: SerializationFormat,
 }
 
 #[cfg(feature = "update-informer")]
@@ -142,60 +147,15 @@ fn run_once(
     Ok(messages)
 }
 
-fn report_once(messages: &[Message]) -> Result<()> {
-    let (fixed, outstanding): (Vec<&Message>, Vec<&Message>) =
-        messages.iter().partition(|message| message.fixed);
-    let num_fixable = outstanding
-        .iter()
-        .filter(|message| message.kind.fixable())
-        .count();
-
-    if !outstanding.is_empty() {
-        for message in &outstanding {
-            println!("{}", message);
-        }
-        println!();
-    }
-
-    if !fixed.is_empty() {
-        println!(
-            "Found {} error(s) ({} fixed).",
-            outstanding.len(),
-            fixed.len()
-        );
-    } else {
-        println!("Found {} error(s).", outstanding.len());
-    }
-
-    if num_fixable > 0 {
-        println!("{num_fixable} potentially fixable with the --fix option.");
-    }
-
-    Ok(())
-}
-
-fn report_continuously(messages: &[Message]) -> Result<()> {
-    tell_user!(
-        "Found {} error(s). Watching for file changes.",
-        messages.len(),
-    );
-
-    if !messages.is_empty() {
-        println!();
-        for message in messages {
-            println!("{}", message);
-        }
-    }
-
-    Ok(())
-}
-
 fn inner_main() -> Result<ExitCode> {
     let cli = Cli::parse();
 
     set_up_logging(cli.verbose)?;
 
     let mut settings = Settings::from_paths(&cli.files);
+
+    let mut printer = Printer::new(cli.format);
+
     if !cli.select.is_empty() {
         settings.select(cli.select);
     }
@@ -209,18 +169,24 @@ fn inner_main() -> Result<ExitCode> {
         settings.extend_exclude = cli.extend_exclude;
     }
 
+    cache::init()?;
+
     if cli.watch {
         if cli.fix {
-            println!("Warning: --fix is not enabled in watch mode.")
+            println!("Warning: --fix is not enabled in watch mode.");
+        }
+
+        if cli.format != SerializationFormat::Text {
+            println!("Warning: --format 'text' is used in watch mode.");
         }
 
         // Perform an initial run instantly.
-        clearscreen::clear()?;
+        printer.clear_screen()?;
         tell_user!("Starting linter in watch mode...\n");
 
         let messages = run_once(&cli.files, &settings, !cli.no_cache, false)?;
         if !cli.quiet {
-            report_continuously(&messages)?;
+            printer.write_continuously(&messages)?;
         }
 
         // Configure the file watcher.
@@ -235,12 +201,12 @@ fn inner_main() -> Result<ExitCode> {
                 Ok(e) => {
                     if let Some(path) = e.path {
                         if path.to_string_lossy().ends_with(".py") {
-                            clearscreen::clear()?;
+                            printer.clear_screen()?;
                             tell_user!("File change detected...\n");
 
                             let messages = run_once(&cli.files, &settings, !cli.no_cache, false)?;
                             if !cli.quiet {
-                                report_continuously(&messages)?;
+                                printer.write_continuously(&messages)?;
                             }
                         }
                     }
@@ -251,7 +217,7 @@ fn inner_main() -> Result<ExitCode> {
     } else {
         let messages = run_once(&cli.files, &settings, !cli.no_cache, cli.fix)?;
         if !cli.quiet {
-            report_once(&messages)?;
+            printer.write_once(&messages)?;
         }
 
         #[cfg(feature = "update-informer")]

src/printer.rs

@@ -0,0 +1,80 @@
+use colored::Colorize;
+
+use anyhow::Result;
+use clap::ValueEnum;
+
+use crate::message::Message;
+use crate::tell_user;
+
+#[derive(Clone, Copy, ValueEnum, PartialEq, Eq, Debug)]
+pub enum SerializationFormat {
+    Text,
+    Json,
+}
+
+pub struct Printer {
+    format: SerializationFormat,
+}
+
+impl Printer {
+    pub fn new(format: SerializationFormat) -> Self {
+        Self { format }
+    }
+
+    pub fn write_once(&mut self, messages: &[Message]) -> Result<()> {
+        let (fixed, outstanding): (Vec<&Message>, Vec<&Message>) =
+            messages.iter().partition(|message| message.fixed);
+        let num_fixable = outstanding
+            .iter()
+            .filter(|message| message.kind.fixable())
+            .count();
+
+        match self.format {
+            SerializationFormat::Json => {
+                println!("{}", serde_json::to_string_pretty(&messages)?)
+            }
+            SerializationFormat::Text => {
+                if !fixed.is_empty() {
+                    println!(
+                        "Found {} error(s) ({} fixed).",
+                        outstanding.len(),
+                        fixed.len()
+                    )
+                } else {
+                    println!("Found {} error(s).", outstanding.len())
+                }
+
+                for message in outstanding {
+                    println!("{}", message)
+                }
+
+                if num_fixable > 0 {
+                    println!("{num_fixable} potentially fixable with the --fix option.")
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    pub fn write_continuously(&mut self, messages: &[Message]) -> Result<()> {
+        tell_user!(
+            "Found {} error(s). Watching for file changes.",
+            messages.len(),
+        );
+
+        if !messages.is_empty() {
+            println!();
+            for message in messages {
+                println!("{}", message)
+            }
+        }
+
+        Ok(())
+    }
+
+    pub fn clear_screen(&mut self) -> Result<()> {
+        clearscreen::clear()?;
+        Ok(())
+    }
+}

src/pyproject.rs

@@ -261,7 +261,8 @@ other-attribute = 1
                 exclude: None,
                 extend_exclude: Some(vec![
                     Path::new("excluded.py").to_path_buf(),
-                    Path::new("migrations").to_path_buf()
+                    Path::new("migrations").to_path_buf(),
+                    Path::new("./resources/test/fixtures/directory/also_excluded.py").to_path_buf()
                 ]),
                 select: Some(vec![
                     CheckCode::E402,

src/settings.rs

@@ -24,6 +24,7 @@ impl Hash for Settings {
         }
     }
 }
+
 static DEFAULT_EXCLUDE: Lazy<Vec<Pattern>> = Lazy::new(|| {
     vec![
         Pattern::new(".bzr").unwrap(),
@@ -34,6 +35,7 @@ static DEFAULT_EXCLUDE: Lazy<Vec<Pattern>> = Lazy::new(|| {
         Pattern::new(".mypy_cache").unwrap(),
         Pattern::new(".nox").unwrap(),
         Pattern::new(".pants.d").unwrap(),
+        Pattern::new(".ruff_cache").unwrap(),
         Pattern::new(".svn").unwrap(),
         Pattern::new(".tox").unwrap(),
         Pattern::new(".venv").unwrap(),
@@ -56,7 +58,7 @@ impl Settings {
                 .exclude
                 .map(|paths| {
                     paths
-                        .into_iter()
+                        .iter()
                         .map(|path| {
                             Pattern::new(&path.to_string_lossy()).expect("Invalid pattern.")
                         })
@@ -67,7 +69,7 @@ impl Settings {
                 .extend_exclude
                 .map(|paths| {
                     paths
-                        .into_iter()
+                        .iter()
                         .map(|path| {
                             Pattern::new(&path.to_string_lossy()).expect("Invalid pattern.")
                         })

src/snapshots/ruff__linter__tests__f821.snap

@@ -32,4 +32,10 @@ expression: checks
     row: 58
     column: 5
   fix: ~
+- kind:
+    UndefinedName: TOMATO
+  location:
+    row: 83
+    column: 11
+  fix: ~
 

src/snapshots/ruff__linter__tests__init.snap

@@ -0,0 +1,6 @@
+---
+source: src/linter.rs
+expression: checks
+---
+[]
+