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    //! High-level overview of how `fix` works:
    //!
    //! The main goal is to run `cargo check` to get rustc to emit JSON
    //! diagnostics with suggested fixes that can be applied to the files on the
    //! filesystem, and validate that those changes didn't break anything.
    //!
    //! Cargo begins by launching a `LockServer` thread in the background to
    //! listen for network connections to coordinate locking when multiple targets
    //! are built simultaneously. It ensures each package has only one fix running
    //! at once.
    //!
    //! The `RustfixDiagnosticServer` is launched in a background thread (in
    //! `JobQueue`) to listen for network connections to coordinate displaying
    //! messages to the user on the console (so that multiple processes don't try
    //! to print at the same time).
    //!
    //! Cargo begins a normal `cargo check` operation with itself set as a proxy
    //! for rustc by setting `primary_unit_rustc` in the build config. When
    //! cargo launches rustc to check a crate, it is actually launching itself.
    //! The `FIX_ENV_INTERNAL` environment variable is set so that cargo knows it is in
    //! fix-proxy-mode.
    //!
    //! Each proxied cargo-as-rustc detects it is in fix-proxy-mode (via `FIX_ENV_INTERNAL`
    //! environment variable in `main`) and does the following:
    //!
    //! - Acquire a lock from the `LockServer` from the master cargo process.
    //! - Launches the real rustc (`rustfix_and_fix`), looking at the JSON output
    //!   for suggested fixes.
    //! - Uses the `rustfix` crate to apply the suggestions to the files on the
    //!   file system.
    //! - If rustfix fails to apply any suggestions (for example, they are
    //!   overlapping), but at least some suggestions succeeded, it will try the
    //!   previous two steps up to 4 times as long as some suggestions succeed.
    //! - Assuming there's at least one suggestion applied, and the suggestions
    //!   applied cleanly, rustc is run again to verify the suggestions didn't
    //!   break anything. The change will be backed out if it fails (unless
    //!   `--broken-code` is used).

    use std::collections::{BTreeSet, HashMap, HashSet};
    use std::ffi::OsString;
    use std::io::Write;
    use std::path::{Path, PathBuf};
    use std::process::{self, ExitStatus, Output};
    use std::{env, fs, str};

    use anyhow::{bail, Context as _};
    use cargo_util::{exit_status_to_string, is_simple_exit_code, paths, ProcessBuilder};
    use rustfix::diagnostics::Diagnostic;
    use rustfix::CodeFix;
    use semver::Version;
    use tracing::{debug, trace, warn};

    use crate::core::compiler::RustcTargetData;
    use crate::core::resolver::features::{DiffMap, FeatureOpts, FeatureResolver, FeaturesFor};
    use crate::core::resolver::{HasDevUnits, Resolve, ResolveBehavior};
    use crate::core::{Edition, MaybePackage, PackageId, Workspace};
    use crate::ops::resolve::WorkspaceResolve;
    use crate::ops::{self, CompileOptions};
    use crate::util::diagnostic_server::{Message, RustfixDiagnosticServer};
    use crate::util::errors::CargoResult;
    use crate::util::GlobalContext;
    use crate::util::{existing_vcs_repo, LockServer, LockServerClient};
    use crate::{drop_eprint, drop_eprintln};

    /// **Internal only.**
    /// Indicates Cargo is in fix-proxy-mode if presents.
    /// The value of it is the socket address of the [`LockServer`] being used.
    /// See the [module-level documentation](mod@super::fix) for more.
    const FIX_ENV_INTERNAL: &str = "__CARGO_FIX_PLZ";
    /// **Internal only.**
    /// For passing [`FixOptions::broken_code`] through to cargo running in proxy mode.
    const BROKEN_CODE_ENV_INTERNAL: &str = "__CARGO_FIX_BROKEN_CODE";
    /// **Internal only.**
    /// For passing [`FixOptions::edition`] through to cargo running in proxy mode.
    const EDITION_ENV_INTERNAL: &str = "__CARGO_FIX_EDITION";
    /// **Internal only.**
    /// For passing [`FixOptions::idioms`] through to cargo running in proxy mode.
    const IDIOMS_ENV_INTERNAL: &str = "__CARGO_FIX_IDIOMS";

    pub struct FixOptions {
        pub edition: bool,
        pub idioms: bool,
        pub compile_opts: CompileOptions,
        pub allow_dirty: bool,
        pub allow_no_vcs: bool,
        pub allow_staged: bool,
        pub broken_code: bool,
    }

    pub fn fix(ws: &Workspace<'_>, opts: &mut FixOptions) -> CargoResult<()> {
        check_version_control(ws.gctx(), opts)?;
        if opts.edition {
            check_resolver_change(ws, opts)?;
        }

        // Spin up our lock server, which our subprocesses will use to synchronize fixes.
        let lock_server = LockServer::new()?;
        let mut wrapper = ProcessBuilder::new(env::current_exe()?);
        wrapper.env(FIX_ENV_INTERNAL, lock_server.addr().to_string());
        let _started = lock_server.start()?;

        opts.compile_opts.build_config.force_rebuild = true;

        if opts.broken_code {
            wrapper.env(BROKEN_CODE_ENV_INTERNAL, "1");
        }

        if opts.edition {
            wrapper.env(EDITION_ENV_INTERNAL, "1");
        }
        if opts.idioms {
            wrapper.env(IDIOMS_ENV_INTERNAL, "1");
        }

        *opts
            .compile_opts
            .build_config
            .rustfix_diagnostic_server
            .borrow_mut() = Some(RustfixDiagnosticServer::new()?);

        if let Some(server) = opts
            .compile_opts
            .build_config
            .rustfix_diagnostic_server
            .borrow()
            .as_ref()
        {
            server.configure(&mut wrapper);
        }

        let rustc = ws.gctx().load_global_rustc(Some(ws))?;
        wrapper.arg(&rustc.path);
        // This is calling rustc in cargo fix-proxy-mode, so it also need to retry.
        // The argfile handling are located at `FixArgs::from_args`.
        wrapper.retry_with_argfile(true);

        // primary crates are compiled using a cargo subprocess to do extra work of applying fixes and
        // repeating build until there are no more changes to be applied
        opts.compile_opts.build_config.primary_unit_rustc = Some(wrapper);

        ops::compile(ws, &opts.compile_opts)?;
        Ok(())
    }

    fn check_version_control(gctx: &GlobalContext, opts: &FixOptions) -> CargoResult<()> {
        if opts.allow_no_vcs {
            return Ok(());
        }
        if !existing_vcs_repo(gctx.cwd(), gctx.cwd()) {
            bail!(
                "no VCS found for this package and `cargo fix` can potentially \
                 perform destructive changes; if you'd like to suppress this \
                 error pass `--allow-no-vcs`"
            )
        }

        if opts.allow_dirty && opts.allow_staged {
            return Ok(());
        }

        let mut dirty_files = Vec::new();
        let mut staged_files = Vec::new();
        if let Ok(repo) = git2::Repository::discover(gctx.cwd()) {
            let mut repo_opts = git2::StatusOptions::new();
            repo_opts.include_ignored(false);
            repo_opts.include_untracked(true);
            for status in repo.statuses(Some(&mut repo_opts))?.iter() {
                if let Some(path) = status.path() {
                    match status.status() {
                        git2::Status::CURRENT => (),
                        git2::Status::INDEX_NEW
                        | git2::Status::INDEX_MODIFIED
                        | git2::Status::INDEX_DELETED
                        | git2::Status::INDEX_RENAMED
                        | git2::Status::INDEX_TYPECHANGE => {
                            if !opts.allow_staged {
                                staged_files.push(path.to_string())
                            }
                        }
                        _ => {
                            if !opts.allow_dirty {
                                dirty_files.push(path.to_string())
                            }
                        }
                    };
                }
            }
        }

        if dirty_files.is_empty() && staged_files.is_empty() {
            return Ok(());
        }

        let mut files_list = String::new();
        for file in dirty_files {
            files_list.push_str("  * ");
            files_list.push_str(&file);
            files_list.push_str(" (dirty)\n");
        }
        for file in staged_files {
            files_list.push_str("  * ");
            files_list.push_str(&file);
            files_list.push_str(" (staged)\n");
        }

        bail!(
            "the working directory of this package has uncommitted changes, and \
             `cargo fix` can potentially perform destructive changes; if you'd \
             like to suppress this error pass `--allow-dirty`, `--allow-staged`, \
             or commit the changes to these files:\n\
             \n\
             {}\n\
             ",
            files_list
        );
    }

    fn check_resolver_change(ws: &Workspace<'_>, opts: &FixOptions) -> CargoResult<()> {
        let root = ws.root_maybe();
        match root {
            MaybePackage::Package(root_pkg) => {
                if root_pkg.manifest().resolve_behavior().is_some() {
                    // If explicitly specified by the user, no need to check.
                    return Ok(());
                }
                // Only trigger if updating the root package from 2018.
                let pkgs = opts.compile_opts.spec.get_packages(ws)?;
                if !pkgs.iter().any(|&pkg| pkg == root_pkg) {
                    // The root is not being migrated.
                    return Ok(());
                }
                if root_pkg.manifest().edition() != Edition::Edition2018 {
                    // V1 to V2 only happens on 2018 to 2021.
                    return Ok(());
                }
            }
            MaybePackage::Virtual(_vm) => {
                // Virtual workspaces don't have a global edition to set (yet).
                return Ok(());
            }
        }
        // 2018 without `resolver` set must be V1
        assert_eq!(ws.resolve_behavior(), ResolveBehavior::V1);
        let specs = opts.compile_opts.spec.to_package_id_specs(ws)?;
        let mut target_data =
            RustcTargetData::new(ws, &opts.compile_opts.build_config.requested_kinds)?;
        let mut resolve_differences = |has_dev_units| -> CargoResult<(WorkspaceResolve<'_>, DiffMap)> {
            let ws_resolve = ops::resolve_ws_with_opts(
                ws,
                &mut target_data,
                &opts.compile_opts.build_config.requested_kinds,
                &opts.compile_opts.cli_features,
                &specs,
                has_dev_units,
                crate::core::resolver::features::ForceAllTargets::No,
            )?;

            let feature_opts = FeatureOpts::new_behavior(ResolveBehavior::V2, has_dev_units);
            let v2_features = FeatureResolver::resolve(
                ws,
                &mut target_data,
                &ws_resolve.targeted_resolve,
                &ws_resolve.pkg_set,
                &opts.compile_opts.cli_features,
                &specs,
                &opts.compile_opts.build_config.requested_kinds,
                feature_opts,
            )?;

            let diffs = v2_features.compare_legacy(&ws_resolve.resolved_features);
            Ok((ws_resolve, diffs))
        };
        let (_, without_dev_diffs) = resolve_differences(HasDevUnits::No)?;
        let (ws_resolve, mut with_dev_diffs) = resolve_differences(HasDevUnits::Yes)?;
        if without_dev_diffs.is_empty() && with_dev_diffs.is_empty() {
            // Nothing is different, nothing to report.
            return Ok(());
        }
        // Only display unique changes with dev-dependencies.
        with_dev_diffs.retain(|k, vals| without_dev_diffs.get(k) != Some(vals));
        let gctx = ws.gctx();
        gctx.shell().note(
            "Switching to Edition 2021 will enable the use of the version 2 feature resolver in Cargo.",
        )?;
        drop_eprintln!(
            gctx,
            "This may cause some dependencies to be built with fewer features enabled than previously."
        );
        drop_eprintln!(
            gctx,
            "More information about the resolver changes may be found \
             at https://doc.rust-lang.org/nightly/edition-guide/rust-2021/default-cargo-resolver.html"
        );
        drop_eprintln!(
            gctx,
            "When building the following dependencies, \
             the given features will no longer be used:\n"
        );
        let show_diffs = |differences: DiffMap| {
            for ((pkg_id, features_for), removed) in differences {
                drop_eprint!(gctx, "  {}", pkg_id);
                if let FeaturesFor::HostDep = features_for {
                    drop_eprint!(gctx, " (as host dependency)");
                }
                drop_eprint!(gctx, " removed features: ");
                let joined: Vec<_> = removed.iter().map(|s| s.as_str()).collect();
                drop_eprintln!(gctx, "{}", joined.join(", "));
            }
            drop_eprint!(gctx, "\n");
        };
        if !without_dev_diffs.is_empty() {
            show_diffs(without_dev_diffs);
        }
        if !with_dev_diffs.is_empty() {
            drop_eprintln!(
                gctx,
                "The following differences only apply when building with dev-dependencies:\n"
            );
            show_diffs(with_dev_diffs);
        }
        report_maybe_diesel(gctx, &ws_resolve.targeted_resolve)?;
        Ok(())
    }

    fn report_maybe_diesel(gctx: &GlobalContext, resolve: &Resolve) -> CargoResult<()> {
        fn is_broken_diesel(pid: PackageId) -> bool {
            pid.name() == "diesel" && pid.version() < &Version::new(1, 4, 8)
        }

        fn is_broken_diesel_migration(pid: PackageId) -> bool {
            pid.name() == "diesel_migrations" && pid.version().major <= 1
        }

        if resolve.iter().any(is_broken_diesel) && resolve.iter().any(is_broken_diesel_migration) {
            gctx.shell().note(
                "\
    This project appears to use both diesel and diesel_migrations. These packages have
    a known issue where the build may fail due to the version 2 resolver preventing
    feature unification between those two packages. Please update to at least diesel 1.4.8
    to prevent this issue from happening.
    ",
            )?;
        }
        Ok(())
    }

    /// Provide the lock address when running in proxy mode
    ///
    /// Returns `None` if `fix` is not being run (not in proxy mode). Returns
    /// `Some(...)` if in `fix` proxy mode
    pub fn fix_get_proxy_lock_addr() -> Option<String> {
        // ALLOWED: For the internal mechanism of `cargo fix` only.
        // Shouldn't be set directly by anyone.
        #[allow(clippy::disallowed_methods)]
        env::var(FIX_ENV_INTERNAL).ok()
    }

    /// Entry point for `cargo` running as a proxy for `rustc`.
    ///
    /// This is called every time `cargo` is run to check if it is in proxy mode.
    ///
    /// If there are warnings or errors, this does not return,
    /// and the process exits with the corresponding `rustc` exit code.
    ///
    /// See [`fix_get_proxy_lock_addr`]
    pub fn fix_exec_rustc(gctx: &GlobalContext, lock_addr: &str) -> CargoResult<()> {
        let args = FixArgs::get()?;
        trace!("cargo-fix as rustc got file {:?}", args.file);

        let workspace_rustc = gctx
            .get_env("RUSTC_WORKSPACE_WRAPPER")
            .map(PathBuf::from)
            .ok();
        let mut rustc = ProcessBuilder::new(&args.rustc).wrapped(workspace_rustc.as_ref());
        rustc.retry_with_argfile(true);
        rustc.env_remove(FIX_ENV_INTERNAL);
        args.apply(&mut rustc);
        // Removes `FD_CLOEXEC` set by `jobserver::Client` to ensure that the
        // compiler can access the jobserver.
        if let Some(client) = gctx.jobserver_from_env() {
            rustc.inherit_jobserver(client);
        }

        trace!("start rustfixing {:?}", args.file);
        let fixes = rustfix_crate(&lock_addr, &rustc, &args.file, &args, gctx)?;

        if fixes.last_output.status.success() {
            for (path, file) in fixes.files.iter() {
                Message::Fixed {
                    file: path.clone(),
                    fixes: file.fixes_applied,
                }
                .post(gctx)?;
            }
            // Display any remaining diagnostics.
            emit_output(&fixes.last_output)?;
            return Ok(());
        }

        let allow_broken_code = gctx.get_env_os(BROKEN_CODE_ENV_INTERNAL).is_some();

        // There was an error running rustc during the last run.
        //
        // Back out all of the changes unless --broken-code was used.
        if !allow_broken_code {
            for (path, file) in fixes.files.iter() {
                debug!("reverting {:?} due to errors", path);
                paths::write(path, &file.original_code)?;
            }
        }

        // If there were any fixes, let the user know that there was a failure
        // attempting to apply them, and to ask for a bug report.
        //
        // FIXME: The error message here is not correct with --broken-code.
        //        https://github.com/rust-lang/cargo/issues/10955
        if fixes.files.is_empty() {
            // No fixes were available. Display whatever errors happened.
            emit_output(&fixes.last_output)?;
            exit_with(fixes.last_output.status);
        } else {
            let krate = {
                let mut iter = rustc.get_args();
                let mut krate = None;
                while let Some(arg) = iter.next() {
                    if arg == "--crate-name" {
                        krate = iter.next().and_then(|s| s.to_owned().into_string().ok());
                    }
                }
                krate
            };
            log_failed_fix(
                gctx,
                krate,
                &fixes.last_output.stderr,
                fixes.last_output.status,
            )?;
            // Display the diagnostics that appeared at the start, before the
            // fixes failed. This can help with diagnosing which suggestions
            // caused the failure.
            emit_output(&fixes.first_output)?;
            // Exit with whatever exit code we initially started with. `cargo fix`
            // treats this as a warning, and shouldn't return a failure code
            // unless the code didn't compile in the first place.
            exit_with(fixes.first_output.status);
        }
    }

    fn emit_output(output: &Output) -> CargoResult<()> {
        // Unfortunately if there is output on stdout, this does not preserve the
        // order of output relative to stderr. In practice, rustc should never
        // print to stdout unless some proc-macro does it.
        std::io::stderr().write_all(&output.stderr)?;
        std::io::stdout().write_all(&output.stdout)?;
        Ok(())
    }

    struct FixedCrate {
        /// Map of file path to some information about modifications made to that file.
        files: HashMap<String, FixedFile>,
        /// The output from rustc from the first time it was called.
        ///
        /// This is needed when fixes fail to apply, so that it can display the
        /// original diagnostics to the user which can help with diagnosing which
        /// suggestions caused the failure.
        first_output: Output,
        /// The output from rustc from the last time it was called.
        ///
        /// This will be displayed to the user to show any remaining diagnostics
        /// or errors.
        last_output: Output,
    }

    #[derive(Debug)]
    struct FixedFile {
        errors_applying_fixes: Vec<String>,
        fixes_applied: u32,
        original_code: String,
    }

    /// Attempts to apply fixes to a single crate.
    ///
    /// This runs `rustc` (possibly multiple times) to gather suggestions from the
    /// compiler and applies them to the files on disk.
    fn rustfix_crate(
        lock_addr: &str,
        rustc: &ProcessBuilder,
        filename: &Path,
        args: &FixArgs,
        gctx: &GlobalContext,
    ) -> CargoResult<FixedCrate> {
        // First up, we want to make sure that each crate is only checked by one
        // process at a time. If two invocations concurrently check a crate then
        // it's likely to corrupt it.
        //
        // Historically this used per-source-file locking, then per-package
        // locking. It now uses a single, global lock as some users do things like
        // #[path] or include!() of shared files between packages. Serializing
        // makes it slower, but is the only safe way to prevent concurrent
        // modification.
        let _lock = LockServerClient::lock(&lock_addr.parse()?, "global")?;

        // Map of files that have been modified.
        let mut files = HashMap::new();

        if !args.can_run_rustfix(gctx)? {
            // This fix should not be run. Skipping...
            // We still need to run rustc at least once to make sure any potential
            // rmeta gets generated, and diagnostics get displayed.
            debug!("can't fix {filename:?}, running rustc: {rustc}");
            let last_output = rustc.output()?;
            let fixes = FixedCrate {
                files,
                first_output: last_output.clone(),
                last_output,
            };
            return Ok(fixes);
        }

        // Next up, this is a bit suspicious, but we *iteratively* execute rustc and
        // collect suggestions to feed to rustfix. Once we hit our limit of times to
        // execute rustc or we appear to be reaching a fixed point we stop running
        // rustc.
        //
        // This is currently done to handle code like:
        //
        //      ::foo::<::Bar>();
        //
        // where there are two fixes to happen here: `crate::foo::<crate::Bar>()`.
        // The spans for these two suggestions are overlapping and its difficult in
        // the compiler to **not** have overlapping spans here. As a result, a naive
        // implementation would feed the two compiler suggestions for the above fix
        // into `rustfix`, but one would be rejected because it overlaps with the
        // other.
        //
        // In this case though, both suggestions are valid and can be automatically
        // applied! To handle this case we execute rustc multiple times, collecting
        // fixes each time we do so. Along the way we discard any suggestions that
        // failed to apply, assuming that they can be fixed the next time we run
        // rustc.
        //
        // Naturally, we want a few protections in place here though to avoid looping
        // forever or otherwise losing data. To that end we have a few termination
        // conditions:
        //
        // * Do this whole process a fixed number of times. In theory we probably
        //   need an infinite number of times to apply fixes, but we're not gonna
        //   sit around waiting for that.
        // * If it looks like a fix genuinely can't be applied we need to bail out.
        //   Detect this when a fix fails to get applied *and* no suggestions
        //   successfully applied to the same file. In that case looks like we
        //   definitely can't make progress, so bail out.
        let max_iterations = gctx
            .get_env("CARGO_FIX_MAX_RETRIES")
            .ok()
            .and_then(|n| n.parse().ok())
            .unwrap_or(4);
        let mut last_output;
        let mut last_made_changes;
        let mut first_output = None;
        let mut current_iteration = 0;
        loop {
            for file in files.values_mut() {
                // We'll generate new errors below.
                file.errors_applying_fixes.clear();
            }
            (last_output, last_made_changes) = rustfix_and_fix(&mut files, rustc, filename, gctx)?;
            if current_iteration == 0 {
                first_output = Some(last_output.clone());
            }
            let mut progress_yet_to_be_made = false;
            for (path, file) in files.iter_mut() {
                if file.errors_applying_fixes.is_empty() {
                    continue;
                }
                debug!("had rustfix apply errors in {path:?} {file:?}");
                // If anything was successfully fixed *and* there's at least one
                // error, then assume the error was spurious and we'll try again on
                // the next iteration.
                if last_made_changes {
                    progress_yet_to_be_made = true;
                }
            }
            if !progress_yet_to_be_made {
                break;
            }
            current_iteration += 1;
            if current_iteration >= max_iterations {
                break;
            }
        }
        if last_made_changes {
            debug!("calling rustc one last time for final results: {rustc}");
            last_output = rustc.output()?;
        }

        // Any errors still remaining at this point need to be reported as probably
        // bugs in Cargo and/or rustfix.
        for (path, file) in files.iter_mut() {
            for error in file.errors_applying_fixes.drain(..) {
                Message::ReplaceFailed {
                    file: path.clone(),
                    message: error,
                }
                .post(gctx)?;
            }
        }

        Ok(FixedCrate {
            files,
            first_output: first_output.expect("at least one iteration"),
            last_output,
        })
    }

    /// Executes `rustc` to apply one round of suggestions to the crate in question.
    ///
    /// This will fill in the `fixes` map with original code, suggestions applied,
    /// and any errors encountered while fixing files.
    fn rustfix_and_fix(
        files: &mut HashMap<String, FixedFile>,
        rustc: &ProcessBuilder,
        filename: &Path,
        gctx: &GlobalContext,
    ) -> CargoResult<(Output, bool)> {
        // If not empty, filter by these lints.
        // TODO: implement a way to specify this.
        let only = HashSet::new();

        debug!("calling rustc to collect suggestions and validate previous fixes: {rustc}");
        let output = rustc.output()?;

        // If rustc didn't succeed for whatever reasons then we're very likely to be
        // looking at otherwise broken code. Let's not make things accidentally
        // worse by applying fixes where a bug could cause *more* broken code.
        // Instead, punt upwards which will reexec rustc over the original code,
        // displaying pretty versions of the diagnostics we just read out.
        if !output.status.success() && gctx.get_env_os(BROKEN_CODE_ENV_INTERNAL).is_none() {
            debug!(
                "rustfixing `{:?}` failed, rustc exited with {:?}",
                filename,
                output.status.code()
            );
            return Ok((output, false));
        }

        let fix_mode = gctx
            .get_env_os("__CARGO_FIX_YOLO")
            .map(|_| rustfix::Filter::Everything)
            .unwrap_or(rustfix::Filter::MachineApplicableOnly);

        // Sift through the output of the compiler to look for JSON messages.
        // indicating fixes that we can apply.
        let stderr = str::from_utf8(&output.stderr).context("failed to parse rustc stderr as UTF-8")?;

        let suggestions = stderr
            .lines()
            .filter(|x| !x.is_empty())
            .inspect(|y| trace!("line: {}", y))
            // Parse each line of stderr, ignoring errors, as they may not all be JSON.
            .filter_map(|line| serde_json::from_str::<Diagnostic>(line).ok())
            // From each diagnostic, try to extract suggestions from rustc.
            .filter_map(|diag| rustfix::collect_suggestions(&diag, &only, fix_mode));

        // Collect suggestions by file so we can apply them one at a time later.
        let mut file_map = HashMap::new();
        let mut num_suggestion = 0;
        // It's safe since we won't read any content under home dir.
        let home_path = gctx.home().as_path_unlocked();
        for suggestion in suggestions {
            trace!("suggestion");
            // Make sure we've got a file associated with this suggestion and all
            // snippets point to the same file. Right now it's not clear what
            // we would do with multiple files.
            let file_names = suggestion
                .solutions
                .iter()
                .flat_map(|s| s.replacements.iter())
                .map(|r| &r.snippet.file_name);

            let file_name = if let Some(file_name) = file_names.clone().next() {
                file_name.clone()
            } else {
                trace!("rejecting as it has no solutions {:?}", suggestion);
                continue;
            };

            // Do not write into registry cache. See rust-lang/cargo#9857.
            if Path::new(&file_name).starts_with(home_path) {
                continue;
            }

            if !file_names.clone().all(|f| f == &file_name) {
                trace!("rejecting as it changes multiple files: {:?}", suggestion);
                continue;
            }

            trace!("adding suggestion for {:?}: {:?}", file_name, suggestion);
            file_map
                .entry(file_name)
                .or_insert_with(Vec::new)
                .push(suggestion);
            num_suggestion += 1;
        }

        debug!(
            "collected {} suggestions for `{}`",
            num_suggestion,
            filename.display(),
        );

        let mut made_changes = false;
        for (file, suggestions) in file_map {
            // Attempt to read the source code for this file. If this fails then
            // that'd be pretty surprising, so log a message and otherwise keep
            // going.
            let code = match paths::read(file.as_ref()) {
                Ok(s) => s,
                Err(e) => {
                    warn!("failed to read `{}`: {}", file, e);
                    continue;
                }
            };
            let num_suggestions = suggestions.len();
            debug!("applying {} fixes to {}", num_suggestions, file);

            // If this file doesn't already exist then we just read the original
            // code, so save it. If the file already exists then the original code
            // doesn't need to be updated as we've just read an interim state with
            // some fixes but perhaps not all.
            let fixed_file = files.entry(file.clone()).or_insert_with(|| FixedFile {
                errors_applying_fixes: Vec::new(),
                fixes_applied: 0,
                original_code: code.clone(),
            });
            let mut fixed = CodeFix::new(&code);

            // As mentioned above in `rustfix_crate`, we don't immediately warn
            // about suggestions that fail to apply here, and instead we save them
            // off for later processing.
            for suggestion in suggestions.iter().rev() {
                match fixed.apply(suggestion) {
                    Ok(()) => fixed_file.fixes_applied += 1,
                    Err(e) => fixed_file.errors_applying_fixes.push(e.to_string()),
                }
            }
            if fixed.modified() {
                made_changes = true;
                let new_code = fixed.finish()?;
                paths::write(&file, new_code)?;
            }
        }

        Ok((output, made_changes))
    }

    fn exit_with(status: ExitStatus) -> ! {
        #[cfg(unix)]
        {
            use std::os::unix::prelude::*;
            if let Some(signal) = status.signal() {
                drop(writeln!(
                    std::io::stderr().lock(),
                    "child failed with signal `{}`",
                    signal
                ));
                process::exit(2);
            }
        }
        process::exit(status.code().unwrap_or(3));
    }

    fn log_failed_fix(
        gctx: &GlobalContext,
        krate: Option<String>,
        stderr: &[u8],
        status: ExitStatus,
    ) -> CargoResult<()> {
        let stderr = str::from_utf8(stderr).context("failed to parse rustc stderr as utf-8")?;

        let diagnostics = stderr
            .lines()
            .filter(|x| !x.is_empty())
            .filter_map(|line| serde_json::from_str::<Diagnostic>(line).ok());
        let mut files = BTreeSet::new();
        let mut errors = Vec::new();
        for diagnostic in diagnostics {
            errors.push(diagnostic.rendered.unwrap_or(diagnostic.message));
            for span in diagnostic.spans.into_iter() {
                files.insert(span.file_name);
            }
        }
        // Include any abnormal messages (like an ICE or whatever).
        errors.extend(
            stderr
                .lines()
                .filter(|x| !x.starts_with('{'))
                .map(|x| x.to_string()),
        );

        let files = files.into_iter().collect();
        let abnormal_exit = if status.code().map_or(false, is_simple_exit_code) {
            None
        } else {
            Some(exit_status_to_string(status))
        };
        Message::FixFailed {
            files,
            krate,
            errors,
            abnormal_exit,
        }
        .post(gctx)?;

        Ok(())
    }

    /// Various command-line options and settings used when `cargo` is running as
    /// a proxy for `rustc` during the fix operation.
    struct FixArgs {
        /// This is the `.rs` file that is being fixed.
        file: PathBuf,
        /// If `--edition` is used to migrate to the next edition, this is the
        /// edition we are migrating towards.
        prepare_for_edition: Option<Edition>,
        /// `true` if `--edition-idioms` is enabled.
        idioms: bool,
        /// The current edition.
        ///
        /// `None` if on 2015.
        enabled_edition: Option<Edition>,
        /// Other command-line arguments not reflected by other fields in
        /// `FixArgs`.
        other: Vec<OsString>,
        /// Path to the `rustc` executable.
        rustc: PathBuf,
    }

    impl FixArgs {
        fn get() -> CargoResult<FixArgs> {
            Self::from_args(env::args_os())
        }

        // This is a separate function so that we can use it in tests.
        fn from_args(argv: impl IntoIterator<Item = OsString>) -> CargoResult<Self> {
            let mut argv = argv.into_iter();
            let mut rustc = argv
                .nth(1)
                .map(PathBuf::from)
                .ok_or_else(|| anyhow::anyhow!("expected rustc or `@path` as first argument"))?;
            let mut file = None;
            let mut enabled_edition = None;
            let mut other = Vec::new();

            let mut handle_arg = |arg: OsString| -> CargoResult<()> {
                let path = PathBuf::from(arg);
                if path.extension().and_then(|s| s.to_str()) == Some("rs") && path.exists() {
                    file = Some(path);
                    return Ok(());
                }
                if let Some(s) = path.to_str() {
                    if let Some(edition) = s.strip_prefix("--edition=") {
                        enabled_edition = Some(edition.parse()?);
                        return Ok(());
                    }
                }
                other.push(path.into());
                Ok(())
            };

            if let Some(argfile_path) = rustc.to_str().unwrap_or_default().strip_prefix("@") {
                // Because cargo in fix-proxy-mode might hit the command line size limit,
                // cargo fix need handle `@path` argfile for this special case.
                if argv.next().is_some() {
                    bail!("argfile `@path` cannot be combined with other arguments");
                }
                let contents = fs::read_to_string(argfile_path)
                    .with_context(|| format!("failed to read argfile at `{argfile_path}`"))?;
                let mut iter = contents.lines().map(OsString::from);
                rustc = iter
                    .next()
                    .map(PathBuf::from)
                    .ok_or_else(|| anyhow::anyhow!("expected rustc as first argument"))?;
                for arg in iter {
                    handle_arg(arg)?;
                }
            } else {
                for arg in argv {
                    handle_arg(arg)?;
                }
            }

            let file = file.ok_or_else(|| anyhow::anyhow!("could not find .rs file in rustc args"))?;
            // ALLOWED: For the internal mechanism of `cargo fix` only.
            // Shouldn't be set directly by anyone.
            #[allow(clippy::disallowed_methods)]
            let idioms = env::var(IDIOMS_ENV_INTERNAL).is_ok();

            // ALLOWED: For the internal mechanism of `cargo fix` only.
            // Shouldn't be set directly by anyone.
            #[allow(clippy::disallowed_methods)]
            let prepare_for_edition = env::var(EDITION_ENV_INTERNAL).ok().map(|_| {
                enabled_edition
                    .unwrap_or(Edition::Edition2015)
                    .saturating_next()
            });

            Ok(FixArgs {
                file,
                prepare_for_edition,
                idioms,
                enabled_edition,
                other,
                rustc,
            })
        }

        fn apply(&self, cmd: &mut ProcessBuilder) {
            cmd.arg(&self.file);
            cmd.args(&self.other);
            if self.prepare_for_edition.is_some() {
                // When migrating an edition, we don't want to fix other lints as
                // they can sometimes add suggestions that fail to apply, causing
                // the entire migration to fail. But those lints aren't needed to
                // migrate.
                cmd.arg("--cap-lints=allow");
            } else {
                // This allows `cargo fix` to work even if the crate has #[deny(warnings)].
                cmd.arg("--cap-lints=warn");
            }
            if let Some(edition) = self.enabled_edition {
                cmd.arg("--edition").arg(edition.to_string());
                if self.idioms && edition.supports_idiom_lint() {
                    cmd.arg(format!("-Wrust-{}-idioms", edition));
                }
            }

            if let Some(edition) = self.prepare_for_edition {
                if edition.supports_compat_lint() {
                    cmd.arg("--force-warn")
                        .arg(format!("rust-{}-compatibility", edition));
                }
            }
        }

        /// Validates the edition, and sends a message indicating what is being
        /// done. Returns a flag indicating whether this fix should be run.
        fn can_run_rustfix(&self, gctx: &GlobalContext) -> CargoResult<bool> {
            let Some(to_edition) = self.prepare_for_edition else {
                return Message::Fixing {
                    file: self.file.display().to_string(),
                }
                .post(gctx)
                .and(Ok(true));
            };
            // Unfortunately determining which cargo targets are being built
            // isn't easy, and each target can be a different edition. The
            // cargo-as-rustc fix wrapper doesn't know anything about the
            // workspace, so it can't check for the `cargo-features` unstable
            // opt-in. As a compromise, this just restricts to the nightly
            // toolchain.
            //
            // Unfortunately this results in a pretty poor error message when
            // multiple jobs run in parallel (the error appears multiple
            // times). Hopefully this doesn't happen often in practice.
            if !to_edition.is_stable() && !gctx.nightly_features_allowed {
                let message = format!(
                    "`{file}` is on the latest edition, but trying to \
                     migrate to edition {to_edition}.\n\
                     Edition {to_edition} is unstable and not allowed in \
                     this release, consider trying the nightly release channel.",
                    file = self.file.display(),
                    to_edition = to_edition
                );
                return Message::EditionAlreadyEnabled {
                    message,
                    edition: to_edition.previous().unwrap(),
                }
                .post(gctx)
                .and(Ok(false)); // Do not run rustfix for this the edition.
            }
            let from_edition = self.enabled_edition.unwrap_or(Edition::Edition2015);
            if from_edition == to_edition {
                let message = format!(
                    "`{}` is already on the latest edition ({}), \
                     unable to migrate further",
                    self.file.display(),
                    to_edition
                );
                Message::EditionAlreadyEnabled {
                    message,
                    edition: to_edition,
                }
                .post(gctx)
            } else {
                Message::Migrating {
                    file: self.file.display().to_string(),
                    from_edition,
                    to_edition,
                }
                .post(gctx)
            }
            .and(Ok(true))
        }
    }

    #[cfg(test)]
    mod tests {
        use super::FixArgs;
        use std::ffi::OsString;
        use std::io::Write as _;
        use std::path::PathBuf;

        #[test]
        fn get_fix_args_from_argfile() {
            let mut temp = tempfile::Builder::new().tempfile().unwrap();
            let main_rs = tempfile::Builder::new().suffix(".rs").tempfile().unwrap();

            let content = format!("/path/to/rustc\n{}\nfoobar\n", main_rs.path().display());
            temp.write_all(content.as_bytes()).unwrap();

            let argfile = format!("@{}", temp.path().display());
            let args = ["cargo", &argfile];
            let fix_args = FixArgs::from_args(args.map(|x| x.into())).unwrap();
            assert_eq!(fix_args.rustc, PathBuf::from("/path/to/rustc"));
            assert_eq!(fix_args.file, main_rs.path());
            assert_eq!(fix_args.other, vec![OsString::from("foobar")]);
        }

        #[test]
        fn get_fix_args_from_argfile_with_extra_arg() {
            let mut temp = tempfile::Builder::new().tempfile().unwrap();
            let main_rs = tempfile::Builder::new().suffix(".rs").tempfile().unwrap();

            let content = format!("/path/to/rustc\n{}\nfoobar\n", main_rs.path().display());
            temp.write_all(content.as_bytes()).unwrap();

            let argfile = format!("@{}", temp.path().display());
            let args = ["cargo", &argfile, "boo!"];
            match FixArgs::from_args(args.map(|x| x.into())) {
                Err(e) => assert_eq!(
                    e.to_string(),
                    "argfile `@path` cannot be combined with other arguments"
                ),
                Ok(_) => panic!("should fail"),
            }
        }
    }