Support linting input from stdin (#387)

Cargo.lock

@@ -64,6 +64,20 @@ dependencies = [
  "term",
 ]
 
+[[package]]
+name = "assert_cmd"
+version = "2.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "93ae1ddd39efd67689deb1979d80bad3bf7f2b09c6e6117c8d1f2443b5e2f83e"
+dependencies = [
+ "bstr",
+ "doc-comment",
+ "predicates",
+ "predicates-core",
+ "predicates-tree",
+ "wait-timeout",
+]
+
 [[package]]
 name = "async-channel"
 version = "1.7.1"
@@ -580,6 +594,12 @@ version = "0.1.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "56254986775e3233ffa9c4d7d3faaf6d36a2c09d30b20687e9f88bc8bafc16c8"
 
+[[package]]
+name = "difflib"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6184e33543162437515c2e2b48714794e37845ec9851711914eec9d308f6ebe8"
+
 [[package]]
 name = "digest"
 version = "0.8.1"
@@ -658,6 +678,12 @@ dependencies = [
  "winapi 0.3.9",
 ]
 
+[[package]]
+name = "doc-comment"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fea41bba32d969b513997752735605054bc0dfa92b4c56bf1189f2e174be7a10"
+
 [[package]]
 name = "either"
 version = "1.8.0"
@@ -1685,6 +1711,33 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "925383efa346730478fb4838dbe9137d2a47675ad789c546d150a6e1dd4ab31c"
 
+[[package]]
+name = "predicates"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a5aab5be6e4732b473071984b3164dbbfb7a3674d30ea5ff44410b6bcd960c3c"
+dependencies = [
+ "difflib",
+ "itertools",
+ "predicates-core",
+]
+
+[[package]]
+name = "predicates-core"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da1c2388b1513e1b605fcec39a95e0a9e8ef088f71443ef37099fa9ae6673fcb"
+
+[[package]]
+name = "predicates-tree"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4d86de6de25020a36c6d3643a86d9a6a9f552107c0559c60ea03551b5e16c032"
+dependencies = [
+ "predicates-core",
+ "termtree",
+]
+
 [[package]]
 name = "proc-macro-error"
 version = "1.0.4"
@@ -1910,6 +1963,7 @@ name = "ruff"
 version = "0.0.68"
 dependencies = [
  "anyhow",
+ "assert_cmd",
  "bincode",
  "cacache",
  "chrono",
@@ -2345,6 +2399,12 @@ dependencies = [
  "phf_codegen 0.8.0",
 ]
 
+[[package]]
+name = "termtree"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "507e9898683b6c43a9aa55b64259b721b52ba226e0f3779137e50ad114a4c90b"
+
 [[package]]
 name = "thiserror"
 version = "1.0.37"
@@ -2593,6 +2653,15 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8e76fae08f03f96e166d2dfda232190638c10e0383841252416f9cfe2ae60e6"
 
+[[package]]
+name = "wait-timeout"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f200f5b12eb75f8c1ed65abd4b2db8a6e1b138a20de009dacee265a2498f3f6"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "waker-fn"
 version = "1.1.0"

Cargo.toml

@@ -40,6 +40,7 @@ strum_macros = "0.24.3"
 num-bigint = "0.4.3"
 
 [dev-dependencies]
+assert_cmd = "2.0.4"
 insta = { version = "1.19.1", features = ["yaml"] }
 
 [features]

src/cli.rs

@@ -78,6 +78,9 @@ pub struct Cli {
     // TODO(charlie): This should be a sub-command.
     #[arg(long, hide = true)]
     pub autoformat: bool,
+    /// The name of the file when passing it through stdin.
+    #[arg(long)]
+    pub stdin_filename: Option<String>,
 }
 
 pub enum Warnable {

src/linter.rs

@@ -83,6 +83,36 @@ pub(crate) fn check_path(
     Ok(checks)
 }
 
+pub fn lint_stdin(path: &Path, stdin: &str, settings: &Settings) -> Result<Vec<Message>> {
+    // Tokenize once.
+    let tokens: Vec<LexResult> = tokenize(stdin);
+
+    // Determine the noqa line for every line in the source.
+    let noqa_line_for = noqa::extract_noqa_line_for(&tokens);
+
+    // Generate checks.
+    let checks = check_path(
+        path,
+        stdin,
+        tokens,
+        &noqa_line_for,
+        settings,
+        &fixer::Mode::None,
+    )?;
+
+    // Convert to messages.
+    Ok(checks
+        .into_iter()
+        .map(|check| Message {
+            kind: check.kind,
+            fixed: check.fix.map(|fix| fix.applied).unwrap_or_default(),
+            location: check.location,
+            end_location: check.end_location,
+            filename: path.to_string_lossy().to_string(),
+        })
+        .collect())
+}
+
 pub fn lint_path(
     path: &Path,
     settings: &Settings,

src/main.rs

@@ -1,4 +1,4 @@
-use std::io;
+use std::io::{self, Read};
 use std::path::{Path, PathBuf};
 use std::process::ExitCode;
 use std::sync::mpsc::channel;
@@ -19,7 +19,7 @@ use ruff::cli::{warn_on, Cli, Warnable};
 use ruff::fs::iter_python_files;
 use ruff::linter::add_noqa_to_path;
 use ruff::linter::autoformat_path;
-use ruff::linter::lint_path;
+use ruff::linter::{lint_path, lint_stdin};
 use ruff::logging::set_up_logging;
 use ruff::message::Message;
 use ruff::printer::{Printer, SerializationFormat};
@@ -75,6 +75,19 @@ fn show_files(files: &[PathBuf], settings: &Settings) {
     }
 }
 
+fn read_from_stdin() -> Result<String> {
+    let mut buffer = String::new();
+    io::stdin().lock().read_to_string(&mut buffer)?;
+    Ok(buffer)
+}
+
+fn run_once_stdin(settings: &Settings, filename: &Path) -> Result<Vec<Message>> {
+    let stdin = read_from_stdin()?;
+    let mut messages = lint_stdin(filename, &stdin, settings)?;
+    messages.sort_unstable();
+    Ok(messages)
+}
+
 fn run_once(
     files: &[PathBuf],
     settings: &Settings,
@@ -352,7 +365,17 @@ fn inner_main() -> Result<ExitCode> {
             println!("Formatted {modifications} files.");
         }
     } else {
-        let messages = run_once(&cli.files, &settings, !cli.no_cache, cli.fix)?;
+        let messages = if cli.files == vec![PathBuf::from("-")] {
+            if cli.fix {
+                eprintln!("Warning: --fix is not enabled when reading from stdin.");
+            }
+
+            let filename = cli.stdin_filename.unwrap_or_else(|| "-".to_string());
+            let path = Path::new(&filename);
+            run_once_stdin(&settings, path)?
+        } else {
+            run_once(&cli.files, &settings, !cli.no_cache, cli.fix)?
+        };
         if !cli.quiet {
             printer.write_once(&messages)?;
         }

tests/integration_test.rs

@@ -0,0 +1,47 @@
+use std::str;
+
+use anyhow::Result;
+use assert_cmd::{crate_name, Command};
+
+#[test]
+fn test_stdin_success() -> Result<()> {
+    let mut cmd = Command::cargo_bin(crate_name!())?;
+    cmd.args(&["-"]).write_stdin("").assert().success();
+    Ok(())
+}
+
+#[test]
+fn test_stdin_error() -> Result<()> {
+    let mut cmd = Command::cargo_bin(crate_name!())?;
+    let output = cmd
+        .args(&["-"])
+        .write_stdin("import os\n")
+        .assert()
+        .failure();
+    assert!(str::from_utf8(&output.get_output().stdout)?.contains("-:1:1: F401"));
+    Ok(())
+}
+
+#[test]
+fn test_stdin_filename() -> Result<()> {
+    let mut cmd = Command::cargo_bin(crate_name!())?;
+    let output = cmd
+        .args(&["-", "--stdin-filename", "F401.py"])
+        .write_stdin("import os\n")
+        .assert()
+        .failure();
+    assert!(str::from_utf8(&output.get_output().stdout)?.contains("F401.py:1:1: F401"));
+    Ok(())
+}
+
+#[test]
+fn test_stdin_autofix() -> Result<()> {
+    let mut cmd = Command::cargo_bin(crate_name!())?;
+    let output = cmd
+        .args(&["-", "--fix"])
+        .write_stdin("import os\n")
+        .assert()
+        .failure();
+    assert!(str::from_utf8(&output.get_output().stdout)?.contains("-:1:1: F401"));
+    Ok(())
+}