2 files changed, 301 insertions, 0 deletions

diff --git a/crates/flycheck/Cargo.toml b/crates/flycheck/Cargo.toml
new file mode 100644
index 000000000..dc26b8ce7
--- /dev/null
+++ b/crates/flycheck/Cargo.toml
@@ -0,0 +1,16 @@
+[package]
+edition = "2018"
+name = "flycheck"
+version = "0.1.0"
+authors = ["rust-analyzer developers"]
+
+[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..92ec4f92e
--- /dev/null
+++ b/crates/flycheck/src/lib.rs
@@ -0,0 +1,285 @@
+//! 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},
+    path::PathBuf,
+    process::{Command, Stdio},
+    time::Duration,
+};
+
+use crossbeam_channel::{never, select, unbounded, Receiver, Sender};
+
+pub use cargo_metadata::diagnostic::{
+    Applicability, Diagnostic, 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
+    cmd_send: Sender<Restart>,
+    handle: jod_thread::JoinHandle,
+}
+
+impl FlycheckHandle {
+    pub fn spawn(
+        sender: Box<dyn Fn(Message) + Send>,
+        config: FlycheckConfig,
+        workspace_root: PathBuf,
+    ) -> FlycheckHandle {
+        let (cmd_send, cmd_recv) = unbounded::<Restart>();
+        let handle = jod_thread::spawn(move || {
+            FlycheckActor::new(sender, config, workspace_root).run(cmd_recv);
+        });
+        FlycheckHandle { cmd_send, handle }
+    }
+
+    /// Schedule a re-start of the cargo check worker.
+    pub fn update(&self) {
+        self.cmd_send.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,
+    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.
+    // XXX: drop order is significant
+    check_process: Option<(Receiver<cargo_metadata::Message>, jod_thread::JoinHandle)>,
+}
+
+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, check_process: None }
+    }
+    fn next_event(&self, inbox: &Receiver<Restart>) -> Option<Event> {
+        let check_chan = self.check_process.as_ref().map(|(chan, _thread)| chan);
+        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();
+                    self.check_process = Some(self.start_check_process());
+                    self.send(Message::Progress(Progress::DidStart));
+                }
+                Event::CheckEvent(None) => {
+                    // Watcher finished, replace it with a never channel to
+                    // avoid busy-waiting.
+                    assert!(self.check_process.take().is_some());
+                    self.send(Message::Progress(Progress::DidFinish));
+                }
+                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.check_process.take().is_some() {
+            self.send(Message::Progress(Progress::DidCancel));
+        }
+    }
+    fn start_check_process(&self) -> (Receiver<cargo_metadata::Message>, jod_thread::JoinHandle) {
+        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);
+
+        let (message_send, message_recv) = unbounded();
+        let thread = jod_thread::spawn(move || {
+            // If we trigger an error here, we will do so in the loop instead,
+            // which will break out of the loop, and continue the shutdown
+            let res = run_cargo(cmd, &mut |message| {
+                // Skip certain kinds of messages to only spend time on what's useful
+                match &message {
+                    cargo_metadata::Message::CompilerArtifact(artifact) if artifact.fresh => {
+                        return true
+                    }
+                    cargo_metadata::Message::BuildScriptExecuted(_)
+                    | cargo_metadata::Message::Unknown => return true,
+                    _ => {}
+                }
+
+                // if the send channel was closed, we want to shutdown
+                message_send.send(message).is_ok()
+            });
+
+            if let Err(err) = res {
+                // FIXME: make the `message_send` to be `Sender<Result<CheckEvent, CargoError>>`
+                // to display user-caused misconfiguration errors instead of just logging them here
+                log::error!("Cargo watcher failed {:?}", err);
+            }
+        });
+        (message_recv, thread)
+    }
+
+    fn send(&self, check_task: Message) {
+        (self.sender)(check_task)
+    }
+}
+
+fn run_cargo(
+    mut command: Command,
+    on_message: &mut dyn FnMut(cargo_metadata::Message) -> bool,
+) -> io::Result<()> {
+    let mut child =
+        command.stdout(Stdio::piped()).stderr(Stdio::null()).stdin(Stdio::null()).spawn()?;
+
+    // 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 resillient 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(child.stdout.take().unwrap());
+    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;
+
+        if !on_message(message) {
+            break;
+        }
+    }
+
+    // It is okay to ignore the result, as it only errors if the process is already dead
+    let _ = child.kill();
+
+    let exit_status = child.wait()?;
+    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!(
+                "the command produced no valid metadata (exit code: {:?}): {:?}",
+                exit_status, command
+            ),
+        ));
+    }
+
+    Ok(())
+}