2 files changed, 334 insertions, 0 deletions

diff --git a/crates/flycheck/Cargo.toml b/crates/flycheck/Cargo.toml
new file mode 100644
index 000000000..bea485694
--- /dev/null
+++ b/crates/flycheck/Cargo.toml
@@ -0,0 +1,17 @@
+[package]
+edition = "2018"
+name = "flycheck"
+version = "0.1.0"
+authors = ["rust-analyzer developers"]
+license = "MIT OR Apache-2.0"
+
+[lib]
+doctest = false
+
+[dependencies]
+crossbeam-channel = "0.4.0"
+log = "0.4.8"
+cargo_metadata = "0.10.0"
+serde_json = "1.0.48"
+jod-thread = "0.1.1"
+ra_toolchain = { path = "../ra_toolchain" }
diff --git a/crates/flycheck/src/lib.rs b/crates/flycheck/src/lib.rs
new file mode 100644
index 000000000..6804d9bda
--- /dev/null
+++ b/crates/flycheck/src/lib.rs
@@ -0,0 +1,317 @@
+//! cargo_check provides the functionality needed to run `cargo check` or
+//! another compatible command (f.x. clippy) in a background thread and provide
+//! LSP diagnostics based on the output of the command.
+
+use std::{
+    fmt,
+    io::{self, BufReader},
+    ops,
+    path::PathBuf,
+    process::{self, Command, Stdio},
+    time::Duration,
+};
+
+use crossbeam_channel::{never, select, unbounded, Receiver, Sender};
+
+pub use cargo_metadata::diagnostic::{
+    Applicability, Diagnostic, DiagnosticCode, DiagnosticLevel, DiagnosticSpan,
+    DiagnosticSpanMacroExpansion,
+};
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum FlycheckConfig {
+    CargoCommand {
+        command: String,
+        all_targets: bool,
+        all_features: bool,
+        features: Vec<String>,
+        extra_args: Vec<String>,
+    },
+    CustomCommand {
+        command: String,
+        args: Vec<String>,
+    },
+}
+
+impl fmt::Display for FlycheckConfig {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            FlycheckConfig::CargoCommand { command, .. } => write!(f, "cargo {}", command),
+            FlycheckConfig::CustomCommand { command, args } => {
+                write!(f, "{} {}", command, args.join(" "))
+            }
+        }
+    }
+}
+
+/// Flycheck wraps the shared state and communication machinery used for
+/// running `cargo check` (or other compatible command) and providing
+/// diagnostics based on the output.
+/// The spawned thread is shut down when this struct is dropped.
+#[derive(Debug)]
+pub struct FlycheckHandle {
+    // XXX: drop order is significant
+    sender: Sender<Restart>,
+    thread: jod_thread::JoinHandle,
+}
+
+impl FlycheckHandle {
+    pub fn spawn(
+        sender: Box<dyn Fn(Message) + Send>,
+        config: FlycheckConfig,
+        workspace_root: PathBuf,
+    ) -> FlycheckHandle {
+        let actor = FlycheckActor::new(sender, config, workspace_root);
+        let (sender, receiver) = unbounded::<Restart>();
+        let thread = jod_thread::spawn(move || actor.run(receiver));
+        FlycheckHandle { sender, thread }
+    }
+
+    /// Schedule a re-start of the cargo check worker.
+    pub fn update(&self) {
+        self.sender.send(Restart).unwrap();
+    }
+}
+
+#[derive(Debug)]
+pub enum Message {
+    /// Request adding a diagnostic with fixes included to a file
+    AddDiagnostic { workspace_root: PathBuf, diagnostic: Diagnostic },
+
+    /// Request check progress notification to client
+    Progress(Progress),
+}
+
+#[derive(Debug)]
+pub enum Progress {
+    DidStart,
+    DidCheckCrate(String),
+    DidFinish(io::Result<()>),
+    DidCancel,
+}
+
+struct Restart;
+
+struct FlycheckActor {
+    sender: Box<dyn Fn(Message) + Send>,
+    config: FlycheckConfig,
+    workspace_root: PathBuf,
+    /// WatchThread exists to wrap around the communication needed to be able to
+    /// run `cargo check` without blocking. Currently the Rust standard library
+    /// doesn't provide a way to read sub-process output without blocking, so we
+    /// have to wrap sub-processes output handling in a thread and pass messages
+    /// back over a channel.
+    cargo_handle: Option<CargoHandle>,
+}
+
+enum Event {
+    Restart(Restart),
+    CheckEvent(Option<cargo_metadata::Message>),
+}
+
+impl FlycheckActor {
+    fn new(
+        sender: Box<dyn Fn(Message) + Send>,
+        config: FlycheckConfig,
+        workspace_root: PathBuf,
+    ) -> FlycheckActor {
+        FlycheckActor { sender, config, workspace_root, cargo_handle: None }
+    }
+    fn next_event(&self, inbox: &Receiver<Restart>) -> Option<Event> {
+        let check_chan = self.cargo_handle.as_ref().map(|cargo| &cargo.receiver);
+        select! {
+            recv(inbox) -> msg => msg.ok().map(Event::Restart),
+            recv(check_chan.unwrap_or(&never())) -> msg => Some(Event::CheckEvent(msg.ok())),
+        }
+    }
+    fn run(mut self, inbox: Receiver<Restart>) {
+        while let Some(event) = self.next_event(&inbox) {
+            match event {
+                Event::Restart(Restart) => {
+                    while let Ok(Restart) = inbox.recv_timeout(Duration::from_millis(50)) {}
+
+                    self.cancel_check_process();
+
+                    let mut command = self.check_command();
+                    log::info!("restart flycheck {:?}", command);
+                    command.stdout(Stdio::piped()).stderr(Stdio::null()).stdin(Stdio::null());
+                    if let Ok(child) = command.spawn().map(JodChild) {
+                        self.cargo_handle = Some(CargoHandle::spawn(child));
+                        self.send(Message::Progress(Progress::DidStart));
+                    }
+                }
+                Event::CheckEvent(None) => {
+                    // Watcher finished, replace it with a never channel to
+                    // avoid busy-waiting.
+                    let cargo_handle = self.cargo_handle.take().unwrap();
+                    let res = cargo_handle.join();
+                    self.send(Message::Progress(Progress::DidFinish(res)));
+                }
+                Event::CheckEvent(Some(message)) => match message {
+                    cargo_metadata::Message::CompilerArtifact(msg) => {
+                        self.send(Message::Progress(Progress::DidCheckCrate(msg.target.name)));
+                    }
+
+                    cargo_metadata::Message::CompilerMessage(msg) => {
+                        self.send(Message::AddDiagnostic {
+                            workspace_root: self.workspace_root.clone(),
+                            diagnostic: msg.message,
+                        });
+                    }
+
+                    cargo_metadata::Message::BuildScriptExecuted(_)
+                    | cargo_metadata::Message::BuildFinished(_)
+                    | cargo_metadata::Message::TextLine(_)
+                    | cargo_metadata::Message::Unknown => {}
+                },
+            }
+        }
+        // If we rerun the thread, we need to discard the previous check results first
+        self.cancel_check_process();
+    }
+    fn cancel_check_process(&mut self) {
+        if self.cargo_handle.take().is_some() {
+            self.send(Message::Progress(Progress::DidCancel));
+        }
+    }
+    fn check_command(&self) -> Command {
+        let mut cmd = match &self.config {
+            FlycheckConfig::CargoCommand {
+                command,
+                all_targets,
+                all_features,
+                extra_args,
+                features,
+            } => {
+                let mut cmd = Command::new(ra_toolchain::cargo());
+                cmd.arg(command);
+                cmd.args(&["--workspace", "--message-format=json", "--manifest-path"])
+                    .arg(self.workspace_root.join("Cargo.toml"));
+                if *all_targets {
+                    cmd.arg("--all-targets");
+                }
+                if *all_features {
+                    cmd.arg("--all-features");
+                } else if !features.is_empty() {
+                    cmd.arg("--features");
+                    cmd.arg(features.join(" "));
+                }
+                cmd.args(extra_args);
+                cmd
+            }
+            FlycheckConfig::CustomCommand { command, args } => {
+                let mut cmd = Command::new(command);
+                cmd.args(args);
+                cmd
+            }
+        };
+        cmd.current_dir(&self.workspace_root);
+        cmd
+    }
+
+    fn send(&self, check_task: Message) {
+        (self.sender)(check_task)
+    }
+}
+
+struct CargoHandle {
+    child: JodChild,
+    #[allow(unused)]
+    thread: jod_thread::JoinHandle<io::Result<bool>>,
+    receiver: Receiver<cargo_metadata::Message>,
+}
+
+impl CargoHandle {
+    fn spawn(mut child: JodChild) -> CargoHandle {
+        let child_stdout = child.stdout.take().unwrap();
+        let (sender, receiver) = unbounded();
+        let actor = CargoActor::new(child_stdout, sender);
+        let thread = jod_thread::spawn(move || actor.run());
+        CargoHandle { child, thread, receiver }
+    }
+    fn join(mut self) -> io::Result<()> {
+        // It is okay to ignore the result, as it only errors if the process is already dead
+        let _ = self.child.kill();
+        let exit_status = self.child.wait()?;
+        let read_at_least_one_message = self.thread.join()?;
+        if !exit_status.success() && !read_at_least_one_message {
+            // FIXME: Read the stderr to display the reason, see `read2()` reference in PR comment:
+            // https://github.com/rust-analyzer/rust-analyzer/pull/3632#discussion_r395605298
+            return Err(io::Error::new(
+                io::ErrorKind::Other,
+                format!(
+                    "Cargo watcher failed,the command produced no valid metadata (exit code: {:?})",
+                    exit_status
+                ),
+            ));
+        }
+        Ok(())
+    }
+}
+
+struct CargoActor {
+    child_stdout: process::ChildStdout,
+    sender: Sender<cargo_metadata::Message>,
+}
+
+impl CargoActor {
+    fn new(
+        child_stdout: process::ChildStdout,
+        sender: Sender<cargo_metadata::Message>,
+    ) -> CargoActor {
+        CargoActor { child_stdout, sender }
+    }
+    fn run(self) -> io::Result<bool> {
+        // We manually read a line at a time, instead of using serde's
+        // stream deserializers, because the deserializer cannot recover
+        // from an error, resulting in it getting stuck, because we try to
+        // be resilient against failures.
+        //
+        // Because cargo only outputs one JSON object per line, we can
+        // simply skip a line if it doesn't parse, which just ignores any
+        // erroneus output.
+        let stdout = BufReader::new(self.child_stdout);
+        let mut read_at_least_one_message = false;
+        for message in cargo_metadata::Message::parse_stream(stdout) {
+            let message = match message {
+                Ok(message) => message,
+                Err(err) => {
+                    log::error!("Invalid json from cargo check, ignoring ({})", err);
+                    continue;
+                }
+            };
+
+            read_at_least_one_message = true;
+
+            // Skip certain kinds of messages to only spend time on what's useful
+            match &message {
+                cargo_metadata::Message::CompilerArtifact(artifact) if artifact.fresh => (),
+                cargo_metadata::Message::BuildScriptExecuted(_)
+                | cargo_metadata::Message::Unknown => (),
+                _ => self.sender.send(message).unwrap(),
+            }
+        }
+        Ok(read_at_least_one_message)
+    }
+}
+
+struct JodChild(process::Child);
+
+impl ops::Deref for JodChild {
+    type Target = process::Child;
+    fn deref(&self) -> &process::Child {
+        &self.0
+    }
+}
+
+impl ops::DerefMut for JodChild {
+    fn deref_mut(&mut self) -> &mut process::Child {
+        &mut self.0
+    }
+}
+
+impl Drop for JodChild {
+    fn drop(&mut self) {
+        let _ = self.0.kill();
+    }
+}