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    use std::io::prelude::*;

    use crate::core::{resolver, Resolve, ResolveVersion, Workspace};
    use crate::util::errors::CargoResult;
    use crate::util::toml as cargo_toml;
    use crate::util::Filesystem;

    use anyhow::Context as _;

    pub fn load_pkg_lockfile(ws: &Workspace<'_>) -> CargoResult<Option<Resolve>> {
        let lock_root = lock_root(ws);
        if !lock_root.as_path_unlocked().join("Cargo.lock").exists() {
            return Ok(None);
        }

        let mut f = lock_root.open_ro("Cargo.lock", ws.config(), "Cargo.lock file")?;

        let mut s = String::new();
        f.read_to_string(&mut s)
            .with_context(|| format!("failed to read file: {}", f.path().display()))?;

        let resolve = (|| -> CargoResult<Option<Resolve>> {
            let resolve: toml::Table = cargo_toml::parse_document(&s, f.path(), ws.config())?;
            let v: resolver::EncodableResolve = resolve.try_into()?;
            Ok(Some(v.into_resolve(&s, ws)?))
        })()
        .with_context(|| format!("failed to parse lock file at: {}", f.path().display()))?;
        Ok(resolve)
    }

    /// Generate a toml String of Cargo.lock from a Resolve.
    pub fn resolve_to_string(ws: &Workspace<'_>, resolve: &mut Resolve) -> CargoResult<String> {
        let (_orig, out, _lock_root) = resolve_to_string_orig(ws, resolve);
        Ok(out)
    }

    pub fn write_pkg_lockfile(ws: &Workspace<'_>, resolve: &mut Resolve) -> CargoResult<()> {
        let (orig, mut out, lock_root) = resolve_to_string_orig(ws, resolve);

        // If the lock file contents haven't changed so don't rewrite it. This is
        // helpful on read-only filesystems.
        if let Some(orig) = &orig {
            if are_equal_lockfiles(orig, &out, ws) {
                return Ok(());
            }
        }

        if !ws.config().lock_update_allowed() {
            let flag = if ws.config().locked() {
                "--locked"
            } else {
                "--frozen"
            };
            anyhow::bail!(
                "the lock file {} needs to be updated but {} was passed to prevent this\n\
                 If you want to try to generate the lock file without accessing the network, \
                 remove the {} flag and use --offline instead.",
                lock_root.as_path_unlocked().join("Cargo.lock").display(),
                flag,
                flag
            );
        }

        // While we're updating the lock file anyway go ahead and update its
        // encoding to whatever the latest default is. That way we can slowly roll
        // out lock file updates as they're otherwise already updated, and changes
        // which don't touch dependencies won't seemingly spuriously update the lock
        // file.
        if resolve.version() < ResolveVersion::default() {
            resolve.set_version(ResolveVersion::default());
            out = serialize_resolve(resolve, orig.as_deref());
        } else if resolve.version() > ResolveVersion::default()
            && !ws.config().cli_unstable().next_lockfile_bump
        {
            // The next version hasn't yet stabilized.
            anyhow::bail!(
                "lock file version `{:?}` requires `-Znext-lockfile-bump`",
                resolve.version()
            )
        }

        // Ok, if that didn't work just write it out
        lock_root
            .open_rw("Cargo.lock", ws.config(), "Cargo.lock file")
            .and_then(|mut f| {
                f.file().set_len(0)?;
                f.write_all(out.as_bytes())?;
                Ok(())
            })
            .with_context(|| {
                format!(
                    "failed to write {}",
                    lock_root.as_path_unlocked().join("Cargo.lock").display()
                )
            })?;
        Ok(())
    }

    fn resolve_to_string_orig(
        ws: &Workspace<'_>,
        resolve: &mut Resolve,
    ) -> (Option<String>, String, Filesystem) {
        // Load the original lock file if it exists.
        let lock_root = lock_root(ws);
        let orig = lock_root.open_ro("Cargo.lock", ws.config(), "Cargo.lock file");
        let orig = orig.and_then(|mut f| {
            let mut s = String::new();
            f.read_to_string(&mut s)?;
            Ok(s)
        });
        let out = serialize_resolve(resolve, orig.as_deref().ok());
        (orig.ok(), out, lock_root)
    }

    fn serialize_resolve(resolve: &Resolve, orig: Option<&str>) -> String {
        let toml = toml::Table::try_from(resolve).unwrap();

        let mut out = String::new();

        // At the start of the file we notify the reader that the file is generated.
        // Specifically Phabricator ignores files containing "@generated", so we use that.
        let marker_line = "# This file is automatically @generated by Cargo.";
        let extra_line = "# It is not intended for manual editing.";
        out.push_str(marker_line);
        out.push('\n');
        out.push_str(extra_line);
        out.push('\n');
        // and preserve any other top comments
        if let Some(orig) = orig {
            let mut comments = orig.lines().take_while(|line| line.starts_with('#'));
            if let Some(first) = comments.next() {
                if first != marker_line {
                    out.push_str(first);
                    out.push('\n');
                }
                if let Some(second) = comments.next() {
                    if second != extra_line {
                        out.push_str(second);
                        out.push('\n');
                    }
                    for line in comments {
                        out.push_str(line);
                        out.push('\n');
                    }
                }
            }
        }

        if let Some(version) = toml.get("version") {
            out.push_str(&format!("version = {}\n\n", version));
        }

        let deps = toml["package"].as_array().unwrap();
        for dep in deps {
            let dep = dep.as_table().unwrap();

            out.push_str("[[package]]\n");
            emit_package(dep, &mut out);
        }

        if let Some(patch) = toml.get("patch") {
            let list = patch["unused"].as_array().unwrap();
            for entry in list {
                out.push_str("[[patch.unused]]\n");
                emit_package(entry.as_table().unwrap(), &mut out);
                out.push('\n');
            }
        }

        if let Some(meta) = toml.get("metadata") {
            // 1. We need to ensure we print the entire tree, not just the direct members of `metadata`
            //    (which `toml_edit::Table::to_string` only shows)
            // 2. We need to ensure all children tables have `metadata.` prefix
            let meta_table = meta
                .as_table()
                .expect("validation ensures this is a table")
                .clone();
            let mut meta_doc = toml::Table::new();
            meta_doc.insert("metadata".to_owned(), toml::Value::Table(meta_table));

            out.push_str(&meta_doc.to_string());
        }

        // Historical versions of Cargo in the old format accidentally left trailing
        // blank newlines at the end of files, so we just leave that as-is. For all
        // encodings going forward, though, we want to be sure that our encoded lock
        // file doesn't contain any trailing newlines so trim out the extra if
        // necessary.
        if resolve.version() >= ResolveVersion::V2 {
            while out.ends_with("\n\n") {
                out.pop();
            }
        }
        out
    }

    fn are_equal_lockfiles(orig: &str, current: &str, ws: &Workspace<'_>) -> bool {
        // If we want to try and avoid updating the lock file, parse both and
        // compare them; since this is somewhat expensive, don't do it in the
        // common case where we can update lock files.
        if !ws.config().lock_update_allowed() {
            let res: CargoResult<bool> = (|| {
                let old: resolver::EncodableResolve = toml::from_str(orig)?;
                let new: resolver::EncodableResolve = toml::from_str(current)?;
                Ok(old.into_resolve(orig, ws)? == new.into_resolve(current, ws)?)
            })();
            if let Ok(true) = res {
                return true;
            }
        }

        orig.lines().eq(current.lines())
    }

    fn emit_package(dep: &toml::Table, out: &mut String) {
        out.push_str(&format!("name = {}\n", &dep["name"]));
        out.push_str(&format!("version = {}\n", &dep["version"]));

        if dep.contains_key("source") {
            out.push_str(&format!("source = {}\n", &dep["source"]));
        }
        if dep.contains_key("checksum") {
            out.push_str(&format!("checksum = {}\n", &dep["checksum"]));
        }

        if let Some(s) = dep.get("dependencies") {
            let slice = s.as_array().unwrap();

            if !slice.is_empty() {
                out.push_str("dependencies = [\n");

                for child in slice.iter() {
                    out.push_str(&format!(" {},\n", child));
                }

                out.push_str("]\n");
            }
            out.push('\n');
        } else if dep.contains_key("replace") {
            out.push_str(&format!("replace = {}\n\n", &dep["replace"]));
        }
    }

    fn lock_root(ws: &Workspace<'_>) -> Filesystem {
        if ws.root_maybe().is_embedded() {
            ws.target_dir()
        } else {
            Filesystem::new(ws.root().to_owned())
        }
    }