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    //! A small TCP server to handle collection of diagnostics information in a
    //! cross-platform way for the `cargo fix` command.

    use std::collections::HashSet;
    use std::io::{BufReader, Read, Write};
    use std::net::{Shutdown, SocketAddr, TcpListener, TcpStream};
    use std::path::PathBuf;
    use std::sync::atomic::{AtomicBool, Ordering};
    use std::sync::Arc;
    use std::thread::{self, JoinHandle};

    use anyhow::{Context as _, Error};
    use cargo_util::ProcessBuilder;
    use serde::{Deserialize, Serialize};
    use tracing::warn;

    use crate::core::Edition;
    use crate::util::errors::CargoResult;
    use crate::util::network::LOCALHOST;
    use crate::util::GlobalContext;

    const DIAGNOSTICS_SERVER_VAR: &str = "__CARGO_FIX_DIAGNOSTICS_SERVER";

    #[derive(Deserialize, Serialize, Hash, Eq, PartialEq, Clone)]
    pub enum Message {
        Migrating {
            file: String,
            from_edition: Edition,
            to_edition: Edition,
        },
        Fixing {
            file: String,
        },
        Fixed {
            file: String,
            fixes: u32,
        },
        FixFailed {
            files: Vec<String>,
            krate: Option<String>,
            errors: Vec<String>,
            abnormal_exit: Option<String>,
        },
        ReplaceFailed {
            file: String,
            message: String,
        },
        EditionAlreadyEnabled {
            message: String,
            edition: Edition,
        },
    }

    impl Message {
        pub fn post(&self, gctx: &GlobalContext) -> Result<(), Error> {
            let addr = gctx
                .get_env(DIAGNOSTICS_SERVER_VAR)
                .context("diagnostics collector misconfigured")?;
            let mut client =
                TcpStream::connect(&addr).context("failed to connect to parent diagnostics target")?;

            let s = serde_json::to_string(self).context("failed to serialize message")?;
            client
                .write_all(s.as_bytes())
                .context("failed to write message to diagnostics target")?;
            client
                .shutdown(Shutdown::Write)
                .context("failed to shutdown")?;

            client
                .read_to_end(&mut Vec::new())
                .context("failed to receive a disconnect")?;

            Ok(())
        }
    }

    /// A printer that will print diagnostics messages to the shell.
    pub struct DiagnosticPrinter<'a> {
        /// The context to get the shell to print to.
        gctx: &'a GlobalContext,
        /// An optional wrapper to be used in addition to `rustc.wrapper` for workspace crates.
        /// This is used to get the correct bug report URL. For instance,
        /// if `clippy-driver` is set as the value for the wrapper,
        /// then the correct bug report URL for `clippy` can be obtained.
        workspace_wrapper: &'a Option<PathBuf>,
        // A set of messages that have already been printed.
        dedupe: HashSet<Message>,
    }

    impl<'a> DiagnosticPrinter<'a> {
        pub fn new(
            gctx: &'a GlobalContext,
            workspace_wrapper: &'a Option<PathBuf>,
        ) -> DiagnosticPrinter<'a> {
            DiagnosticPrinter {
                gctx,
                workspace_wrapper,
                dedupe: HashSet::new(),
            }
        }

        pub fn print(&mut self, msg: &Message) -> CargoResult<()> {
            match msg {
                Message::Migrating {
                    file,
                    from_edition,
                    to_edition,
                } => {
                    if !self.dedupe.insert(msg.clone()) {
                        return Ok(());
                    }
                    self.gctx.shell().status(
                        "Migrating",
                        &format!("{} from {} edition to {}", file, from_edition, to_edition),
                    )
                }
                Message::Fixing { file } => self
                    .gctx
                    .shell()
                    .verbose(|shell| shell.status("Fixing", file)),
                Message::Fixed { file, fixes } => {
                    let msg = if *fixes == 1 { "fix" } else { "fixes" };
                    let msg = format!("{} ({} {})", file, fixes, msg);
                    self.gctx.shell().status("Fixed", msg)
                }
                Message::ReplaceFailed { file, message } => {
                    let msg = format!("error applying suggestions to `{}`\n", file);
                    self.gctx.shell().warn(&msg)?;
                    write!(
                        self.gctx.shell().err(),
                        "The full error message was:\n\n> {}\n\n",
                        message,
                    )?;
                    let issue_link = get_bug_report_url(self.workspace_wrapper);
                    write!(
                        self.gctx.shell().err(),
                        "{}",
                        gen_please_report_this_bug_text(issue_link)
                    )?;
                    Ok(())
                }
                Message::FixFailed {
                    files,
                    krate,
                    errors,
                    abnormal_exit,
                } => {
                    if let Some(ref krate) = *krate {
                        self.gctx.shell().warn(&format!(
                            "failed to automatically apply fixes suggested by rustc \
                             to crate `{}`",
                            krate,
                        ))?;
                    } else {
                        self.gctx
                            .shell()
                            .warn("failed to automatically apply fixes suggested by rustc")?;
                    }
                    if !files.is_empty() {
                        writeln!(
                            self.gctx.shell().err(),
                            "\nafter fixes were automatically applied the compiler \
                             reported errors within these files:\n"
                        )?;
                        for file in files {
                            writeln!(self.gctx.shell().err(), "  * {}", file)?;
                        }
                        writeln!(self.gctx.shell().err())?;
                    }
                    let issue_link = get_bug_report_url(self.workspace_wrapper);
                    write!(
                        self.gctx.shell().err(),
                        "{}",
                        gen_please_report_this_bug_text(issue_link)
                    )?;
                    if !errors.is_empty() {
                        writeln!(
                            self.gctx.shell().err(),
                            "The following errors were reported:"
                        )?;
                        for error in errors {
                            write!(self.gctx.shell().err(), "{}", error)?;
                            if !error.ends_with('\n') {
                                writeln!(self.gctx.shell().err())?;
                            }
                        }
                    }
                    if let Some(exit) = abnormal_exit {
                        writeln!(self.gctx.shell().err(), "rustc exited abnormally: {}", exit)?;
                    }
                    writeln!(
                        self.gctx.shell().err(),
                        "Original diagnostics will follow.\n"
                    )?;
                    Ok(())
                }
                Message::EditionAlreadyEnabled { message, edition } => {
                    if !self.dedupe.insert(msg.clone()) {
                        return Ok(());
                    }
                    // Don't give a really verbose warning if it has already been issued.
                    if self.dedupe.insert(Message::EditionAlreadyEnabled {
                        message: "".to_string(), // Dummy, so that this only long-warns once.
                        edition: *edition,
                    }) {
                        self.gctx.shell().warn(&format!("\
    {}

    If you are trying to migrate from the previous edition ({prev_edition}), the
    process requires following these steps:

    1. Start with `edition = \"{prev_edition}\"` in `Cargo.toml`
    2. Run `cargo fix --edition`
    3. Modify `Cargo.toml` to set `edition = \"{this_edition}\"`
    4. Run `cargo build` or `cargo test` to verify the fixes worked

    More details may be found at
    https://doc.rust-lang.org/edition-guide/editions/transitioning-an-existing-project-to-a-new-edition.html
    ",
                            message, this_edition=edition, prev_edition=edition.previous().unwrap()
                        ))
                    } else {
                        self.gctx.shell().warn(message)
                    }
                }
            }
        }
    }

    fn gen_please_report_this_bug_text(url: &str) -> String {
        format!(
            "This likely indicates a bug in either rustc or cargo itself,\n\
         and we would appreciate a bug report! You're likely to see\n\
         a number of compiler warnings after this message which cargo\n\
         attempted to fix but failed. If you could open an issue at\n\
         {}\n\
         quoting the full output of this command we'd be very appreciative!\n\
         Note that you may be able to make some more progress in the near-term\n\
         fixing code with the `--broken-code` flag\n\n\
         ",
            url
        )
    }

    fn get_bug_report_url(rustc_workspace_wrapper: &Option<PathBuf>) -> &str {
        let clippy = std::ffi::OsStr::new("clippy-driver");
        let issue_link = match rustc_workspace_wrapper.as_ref().and_then(|x| x.file_stem()) {
            Some(wrapper) if wrapper == clippy => "https://github.com/rust-lang/rust-clippy/issues",
            _ => "https://github.com/rust-lang/rust/issues",
        };

        issue_link
    }

    #[derive(Debug)]
    pub struct RustfixDiagnosticServer {
        listener: TcpListener,
        addr: SocketAddr,
    }

    pub struct StartedServer {
        addr: SocketAddr,
        done: Arc<AtomicBool>,
        thread: Option<JoinHandle<()>>,
    }

    impl RustfixDiagnosticServer {
        pub fn new() -> Result<Self, Error> {
            let listener = TcpListener::bind(&LOCALHOST[..])
                .with_context(|| "failed to bind TCP listener to manage locking")?;
            let addr = listener.local_addr()?;

            Ok(RustfixDiagnosticServer { listener, addr })
        }

        pub fn configure(&self, process: &mut ProcessBuilder) {
            process.env(DIAGNOSTICS_SERVER_VAR, self.addr.to_string());
        }

        pub fn start<F>(self, on_message: F) -> Result<StartedServer, Error>
        where
            F: Fn(Message) + Send + 'static,
        {
            let addr = self.addr;
            let done = Arc::new(AtomicBool::new(false));
            let done2 = done.clone();
            let thread = thread::spawn(move || {
                self.run(&on_message, &done2);
            });

            Ok(StartedServer {
                addr,
                thread: Some(thread),
                done,
            })
        }

        fn run(self, on_message: &dyn Fn(Message), done: &AtomicBool) {
            while let Ok((client, _)) = self.listener.accept() {
                if done.load(Ordering::SeqCst) {
                    break;
                }
                let mut client = BufReader::new(client);
                let mut s = String::new();
                if let Err(e) = client.read_to_string(&mut s) {
                    warn!("diagnostic server failed to read: {}", e);
                } else {
                    match serde_json::from_str(&s) {
                        Ok(message) => on_message(message),
                        Err(e) => warn!("invalid diagnostics message: {}", e),
                    }
                }
                // The client should be kept alive until after `on_message` is
                // called to ensure that the client doesn't exit too soon (and
                // Message::Finish getting posted before Message::FixDiagnostic).
                drop(client);
            }
        }
    }

    impl Drop for StartedServer {
        fn drop(&mut self) {
            self.done.store(true, Ordering::SeqCst);
            // Ignore errors here as this is largely best-effort
            if TcpStream::connect(&self.addr).is_err() {
                return;
            }
            drop(self.thread.take().unwrap().join());
        }
    }