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    //! Support for [future-incompatible warning reporting][1].
    //!
    //! Here is an overview of how Cargo handles future-incompatible reports.
    //!
    //! ## Receive reports from the compiler
    //!
    //! When receiving a compiler message during a build, if it is effectively
    //! a [`FutureIncompatReport`], Cargo gathers and forwards it as a
    //! `Message::FutureIncompatReport` to the main thread.
    //!
    //! To have the correct layout of strucutures for deserializing a report
    //! emitted by the compiler, most of structure definitions, for example
    //! [`FutureIncompatReport`], are copied either partially or entirely from
    //! [compiler/rustc_errors/src/json.rs][2] in rust-lang/rust repository.
    //!
    //! ## Persist reports on disk
    //!
    //! When a build comes to an end, by calling [`save_and_display_report`]
    //! Cargo saves the report on disk, and displays it directly if requested
    //! via command line or configuration. The information of the on-disk file can
    //! be found in [`FUTURE_INCOMPAT_FILE`].
    //!
    //! During the persistent process, Cargo will attempt to query the source of
    //! each package emitting the report, for the sake of providing an upgrade
    //! information as a solution to fix the incompatibility.
    //!
    //! ## Display reports to users
    //!
    //! Users can run `cargo report future-incompat` to retrieve a report. This is
    //! done by [`OnDiskReports::load`]. Cargo simply prints reports to the
    //! standard output.
    //!
    //! [1]: https://doc.rust-lang.org/nightly/cargo/reference/future-incompat-report.html
    //! [2]: https://github.com/rust-lang/rust/blob/9bb6e60d1f1360234aae90c97964c0fa5524f141/compiler/rustc_errors/src/json.rs#L312-L315

    use crate::core::compiler::BuildContext;
    use crate::core::{Dependency, PackageId, Workspace};
    use crate::sources::source::QueryKind;
    use crate::sources::SourceConfigMap;
    use crate::util::cache_lock::CacheLockMode;
    use crate::util::CargoResult;
    use anyhow::{bail, format_err, Context};
    use serde::{Deserialize, Serialize};
    use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
    use std::fmt::Write as _;
    use std::io::{Read, Write};
    use std::task::Poll;

    pub const REPORT_PREAMBLE: &str = "\
    The following warnings were discovered during the build. These warnings are an
    indication that the packages contain code that will become an error in a
    future release of Rust. These warnings typically cover changes to close
    soundness problems, unintended or undocumented behavior, or critical problems
    that cannot be fixed in a backwards-compatible fashion, and are not expected
    to be in wide use.

    Each warning should contain a link for more information on what the warning
    means and how to resolve it.
    ";

    /// Current version of the on-disk format.
    const ON_DISK_VERSION: u32 = 0;

    /// The future incompatibility report, emitted by the compiler as a JSON message.
    #[derive(serde::Deserialize)]
    pub struct FutureIncompatReport {
        pub future_incompat_report: Vec<FutureBreakageItem>,
    }

    /// Structure used for collecting reports in-memory.
    pub struct FutureIncompatReportPackage {
        pub package_id: PackageId,
        pub items: Vec<FutureBreakageItem>,
    }

    /// A single future-incompatible warning emitted by rustc.
    #[derive(Serialize, Deserialize)]
    pub struct FutureBreakageItem {
        /// The date at which this lint will become an error.
        /// Currently unused
        pub future_breakage_date: Option<String>,
        /// The original diagnostic emitted by the compiler
        pub diagnostic: Diagnostic,
    }

    /// A diagnostic emitted by the compiler as a JSON message.
    /// We only care about the 'rendered' field
    #[derive(Serialize, Deserialize)]
    pub struct Diagnostic {
        pub rendered: String,
        pub level: String,
    }

    /// The filename in the top-level `target` directory where we store
    /// the report
    const FUTURE_INCOMPAT_FILE: &str = ".future-incompat-report.json";
    /// Max number of reports to save on disk.
    const MAX_REPORTS: usize = 5;

    /// The structure saved to disk containing the reports.
    #[derive(Serialize, Deserialize)]
    pub struct OnDiskReports {
        /// A schema version number, to handle older cargo's from trying to read
        /// something that they don't understand.
        version: u32,
        /// The report ID to use for the next report to save.
        next_id: u32,
        /// Available reports.
        reports: Vec<OnDiskReport>,
    }

    /// A single report for a given compilation session.
    #[derive(Serialize, Deserialize)]
    struct OnDiskReport {
        /// Unique reference to the report for the `--id` CLI flag.
        id: u32,
        /// A message describing suggestions for fixing the
        /// reported issues
        suggestion_message: String,
        /// Report, suitable for printing to the console.
        /// Maps package names to the corresponding report
        /// We use a `BTreeMap` so that the iteration order
        /// is stable across multiple runs of `cargo`
        per_package: BTreeMap<String, String>,
    }

    impl Default for OnDiskReports {
        fn default() -> OnDiskReports {
            OnDiskReports {
                version: ON_DISK_VERSION,
                next_id: 1,
                reports: Vec::new(),
            }
        }
    }

    impl OnDiskReports {
        /// Saves a new report returning its id
        pub fn save_report(
            mut self,
            ws: &Workspace<'_>,
            suggestion_message: String,
            per_package_reports: &[FutureIncompatReportPackage],
        ) -> u32 {
            let per_package = render_report(per_package_reports);

            if let Some(existing_report) = self
                .reports
                .iter()
                .find(|existing| existing.per_package == per_package)
            {
                return existing_report.id;
            }

            let report = OnDiskReport {
                id: self.next_id,
                suggestion_message,
                per_package,
            };

            let saved_id = report.id;
            self.next_id += 1;
            self.reports.push(report);
            if self.reports.len() > MAX_REPORTS {
                self.reports.remove(0);
            }
            let on_disk = serde_json::to_vec(&self).unwrap();
            if let Err(e) = ws
                .target_dir()
                .open_rw_exclusive_create(
                    FUTURE_INCOMPAT_FILE,
                    ws.gctx(),
                    "Future incompatibility report",
                )
                .and_then(|file| {
                    let mut file = file.file();
                    file.set_len(0)?;
                    file.write_all(&on_disk)?;
                    Ok(())
                })
            {
                crate::display_warning_with_error(
                    "failed to write on-disk future incompatible report",
                    &e,
                    &mut ws.gctx().shell(),
                );
            }

            saved_id
        }

        /// Loads the on-disk reports.
        pub fn load(ws: &Workspace<'_>) -> CargoResult<OnDiskReports> {
            let report_file = match ws.target_dir().open_ro_shared(
                FUTURE_INCOMPAT_FILE,
                ws.gctx(),
                "Future incompatible report",
            ) {
                Ok(r) => r,
                Err(e) => {
                    if let Some(io_err) = e.downcast_ref::<std::io::Error>() {
                        if io_err.kind() == std::io::ErrorKind::NotFound {
                            bail!("no reports are currently available");
                        }
                    }
                    return Err(e);
                }
            };

            let mut file_contents = String::new();
            report_file
                .file()
                .read_to_string(&mut file_contents)
                .with_context(|| "failed to read report")?;
            let on_disk_reports: OnDiskReports =
                serde_json::from_str(&file_contents).with_context(|| "failed to load report")?;
            if on_disk_reports.version != ON_DISK_VERSION {
                bail!("unable to read reports; reports were saved from a future version of Cargo");
            }
            Ok(on_disk_reports)
        }

        /// Returns the most recent report ID.
        pub fn last_id(&self) -> u32 {
            self.reports.last().map(|r| r.id).unwrap()
        }

        /// Returns an ANSI-styled report
        pub fn get_report(&self, id: u32, package: Option<&str>) -> CargoResult<String> {
            let report = self.reports.iter().find(|r| r.id == id).ok_or_else(|| {
                let available = itertools::join(self.reports.iter().map(|r| r.id), ", ");
                format_err!(
                    "could not find report with ID {}\n\
                     Available IDs are: {}",
                    id,
                    available
                )
            })?;

            let mut to_display = report.suggestion_message.clone();
            to_display += "\n";

            let package_report = if let Some(package) = package {
                report
                    .per_package
                    .get(package)
                    .ok_or_else(|| {
                        format_err!(
                            "could not find package with ID `{}`\n
                    Available packages are: {}\n
                    Omit the `--package` flag to display a report for all packages",
                            package,
                            itertools::join(report.per_package.keys(), ", ")
                        )
                    })?
                    .to_string()
            } else {
                report
                    .per_package
                    .values()
                    .cloned()
                    .collect::<Vec<_>>()
                    .join("\n")
            };
            to_display += &package_report;

            Ok(to_display)
        }
    }

    fn render_report(per_package_reports: &[FutureIncompatReportPackage]) -> BTreeMap<String, String> {
        let mut report: BTreeMap<String, String> = BTreeMap::new();
        for per_package in per_package_reports {
            let package_spec = format!(
                "{}@{}",
                per_package.package_id.name(),
                per_package.package_id.version()
            );
            let rendered = report.entry(package_spec).or_default();
            rendered.push_str(&format!(
                "The package `{}` currently triggers the following future incompatibility lints:\n",
                per_package.package_id
            ));
            for item in &per_package.items {
                rendered.extend(
                    item.diagnostic
                        .rendered
                        .lines()
                        .map(|l| format!("> {}\n", l)),
                );
            }
        }
        report
    }

    /// Returns a user-readable message explaining which of
    /// the packages in `package_ids` have updates available.
    /// This is best-effort - if an error occurs, `None` will be returned.
    fn get_updates(ws: &Workspace<'_>, package_ids: &BTreeSet<PackageId>) -> Option<String> {
        // This in general ignores all errors since this is opportunistic.
        let _lock = ws
            .gctx()
            .acquire_package_cache_lock(CacheLockMode::DownloadExclusive)
            .ok()?;
        // Create a set of updated registry sources.
        let map = SourceConfigMap::new(ws.gctx()).ok()?;
        let mut package_ids: BTreeSet<_> = package_ids
            .iter()
            .filter(|pkg_id| pkg_id.source_id().is_registry())
            .collect();
        let source_ids: HashSet<_> = package_ids
            .iter()
            .map(|pkg_id| pkg_id.source_id())
            .collect();
        let mut sources: HashMap<_, _> = source_ids
            .into_iter()
            .filter_map(|sid| {
                let source = map.load(sid, &HashSet::new()).ok()?;
                Some((sid, source))
            })
            .collect();

        // Query the sources for new versions, mapping `package_ids` into `summaries`.
        let mut summaries = Vec::new();
        while !package_ids.is_empty() {
            package_ids.retain(|&pkg_id| {
                let Some(source) = sources.get_mut(&pkg_id.source_id()) else {
                    return false;
                };
                let Ok(dep) = Dependency::parse(pkg_id.name(), None, pkg_id.source_id()) else {
                    return false;
                };
                match source.query_vec(&dep, QueryKind::Exact) {
                    Poll::Ready(Ok(sum)) => {
                        summaries.push((pkg_id, sum));
                        false
                    }
                    Poll::Ready(Err(_)) => false,
                    Poll::Pending => true,
                }
            });
            for (_, source) in sources.iter_mut() {
                source.block_until_ready().ok()?;
            }
        }

        let mut updates = String::new();
        for (pkg_id, summaries) in summaries {
            let mut updated_versions: Vec<_> = summaries
                .iter()
                .map(|summary| summary.as_summary().version())
                .filter(|version| *version > pkg_id.version())
                .collect();
            updated_versions.sort();

            if !updated_versions.is_empty() {
                let updated_versions = itertools::join(updated_versions, ", ");
                writeln!(
                    updates,
                    "{} has the following newer versions available: {}",
                    pkg_id, updated_versions
                )
                .unwrap();
            }
        }
        Some(updates)
    }

    /// Writes a future-incompat report to disk, using the per-package
    /// reports gathered during the build. If requested by the user,
    /// a message is also displayed in the build output.
    pub fn save_and_display_report(
        bcx: &BuildContext<'_, '_>,
        per_package_future_incompat_reports: &[FutureIncompatReportPackage],
    ) {
        let should_display_message = match bcx.gctx.future_incompat_config() {
            Ok(config) => config.should_display_message(),
            Err(e) => {
                crate::display_warning_with_error(
                    "failed to read future-incompat config from disk",
                    &e,
                    &mut bcx.gctx.shell(),
                );
                true
            }
        };

        if per_package_future_incompat_reports.is_empty() {
            // Explicitly passing a command-line flag overrides
            // `should_display_message` from the config file
            if bcx.build_config.future_incompat_report {
                drop(
                    bcx.gctx
                        .shell()
                        .note("0 dependencies had future-incompatible warnings"),
                );
            }
            return;
        }

        let current_reports = match OnDiskReports::load(bcx.ws) {
            Ok(r) => r,
            Err(e) => {
                tracing::debug!(
                    "saving future-incompatible reports failed to load current reports: {:?}",
                    e
                );
                OnDiskReports::default()
            }
        };
        let report_id = current_reports.next_id;

        // Get a list of unique and sorted package name/versions.
        let package_ids: BTreeSet<_> = per_package_future_incompat_reports
            .iter()
            .map(|r| r.package_id)
            .collect();
        let package_vers: Vec<_> = package_ids.iter().map(|pid| pid.to_string()).collect();

        if should_display_message || bcx.build_config.future_incompat_report {
            drop(bcx.gctx.shell().warn(&format!(
                "the following packages contain code that will be rejected by a future \
                 version of Rust: {}",
                package_vers.join(", ")
            )));
        }

        let updated_versions = get_updates(bcx.ws, &package_ids).unwrap_or(String::new());

        let update_message = if !updated_versions.is_empty() {
            format!(
                "
    - Some affected dependencies have newer versions available.
    You may want to consider updating them to a newer version to see if the issue has been fixed.

    {updated_versions}\n",
                updated_versions = updated_versions
            )
        } else {
            String::new()
        };

        let upstream_info = package_ids
            .iter()
            .map(|package_id| {
                let manifest = bcx.packages.get_one(*package_id).unwrap().manifest();
                format!(
                    "
      - {package_spec}
      - Repository: {url}
      - Detailed warning command: `cargo report future-incompatibilities --id {id} --package {package_spec}`",
                    package_spec = format!("{}@{}", package_id.name(), package_id.version()),
                    url = manifest
                        .metadata()
                        .repository
                        .as_deref()
                        .unwrap_or("<not found>"),
                    id = report_id,
                )
            })
            .collect::<Vec<_>>()
            .join("\n");

        let suggestion_message = format!(
            "
    To solve this problem, you can try the following approaches:

    {update_message}
    - If the issue is not solved by updating the dependencies, a fix has to be
    implemented by those dependencies. You can help with that by notifying the
    maintainers of this problem (e.g. by creating a bug report) or by proposing a
    fix to the maintainers (e.g. by creating a pull request):
    {upstream_info}

    - If waiting for an upstream fix is not an option, you can use the `[patch]`
    section in `Cargo.toml` to use your own version of the dependency. For more
    information, see:
    https://doc.rust-lang.org/cargo/reference/overriding-dependencies.html#the-patch-section
            ",
            upstream_info = upstream_info,
            update_message = update_message,
        );

        let saved_report_id = current_reports.save_report(
            bcx.ws,
            suggestion_message.clone(),
            per_package_future_incompat_reports,
        );

        if bcx.build_config.future_incompat_report {
            drop(bcx.gctx.shell().note(&suggestion_message));
            drop(bcx.gctx.shell().note(&format!(
                "this report can be shown with `cargo report \
                 future-incompatibilities --id {}`",
                saved_report_id
            )));
        } else if should_display_message {
            drop(bcx.gctx.shell().note(&format!(
                "to see what the problems were, use the option \
                 `--future-incompat-report`, or run `cargo report \
                 future-incompatibilities --id {}`",
                saved_report_id
            )));
        }
    }