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    //! Management of the directory layout of a build
    //!
    //! The directory layout is a little tricky at times, hence a separate file to
    //! house this logic. The current layout looks like this:
    //!
    //! ```text
    //! # This is the root directory for all output, the top-level package
    //! # places all of its output here.
    //! target/
    //!
    //!     # Cache of `rustc -Vv` output for performance.
    //!     .rustc-info.json
    //!
    //!     # All final artifacts are linked into this directory from `deps`.
    //!     # Note that named profiles will soon be included as separate directories
    //!     # here. They have a restricted format, similar to Rust identifiers, so
    //!     # Cargo-specific directories added in the future should use some prefix
    //!     # like `.` to avoid name collisions.
    //!     debug/  # or release/
    //!
    //!         # File used to lock the directory to prevent multiple cargo processes
    //!         # from using it at the same time.
    //!         .cargo-lock
    //!
    //!         # Hidden directory that holds all of the fingerprint files for all
    //!         # packages
    //!         .fingerprint/
    //!             # Each package is in a separate directory.
    //!             # Note that different target kinds have different filename prefixes.
    //!             $pkgname-$META/
    //!                 # Set of source filenames for this package.
    //!                 dep-lib-$targetname
    //!                 # Timestamp when this package was last built.
    //!                 invoked.timestamp
    //!                 # The fingerprint hash.
    //!                 lib-$targetname
    //!                 # Detailed information used for logging the reason why
    //!                 # something is being recompiled.
    //!                 lib-$targetname.json
    //!                 # The console output from the compiler. This is cached
    //!                 # so that warnings can be redisplayed for "fresh" units.
    //!                 output-lib-$targetname
    //!
    //!         # This is the root directory for all rustc artifacts except build
    //!         # scripts, examples, and test and bench executables. Almost every
    //!         # artifact should have a metadata hash added to its filename to
    //!         # prevent collisions. One notable exception is dynamic libraries.
    //!         deps/
    //!
    //!             # Each artifact dependency gets in its own directory.
    //!             /artifact/$pkgname-$META/$kind
    //!
    //!         # Root directory for all compiled examples.
    //!         examples/
    //!
    //!         # Directory used to store incremental data for the compiler (when
    //!         # incremental is enabled.
    //!         incremental/
    //!
    //!         # This is the location at which the output of all custom build
    //!         # commands are rooted.
    //!         build/
    //!
    //!             # Each package gets its own directory where its build script and
    //!             # script output are placed
    //!             $pkgname-$META/    # For the build script itself.
    //!                 # The build script executable (name may be changed by user).
    //!                 build-script-build-$META
    //!                 # Hard link to build-script-build-$META.
    //!                 build-script-build
    //!                 # Dependency information generated by rustc.
    //!                 build-script-build-$META.d
    //!                 # Debug information, depending on platform and profile
    //!                 # settings.
    //!                 <debug symbols>
    //!
    //!             # The package shows up twice with two different metadata hashes.
    //!             $pkgname-$META/  # For the output of the build script.
    //!                 # Timestamp when the build script was last executed.
    //!                 invoked.timestamp
    //!                 # Directory where script can output files ($OUT_DIR).
    //!                 out/
    //!                 # Output from the build script.
    //!                 output
    //!                 # Path to `out`, used to help when the target directory is
    //!                 # moved.
    //!                 root-output
    //!                 # Stderr output from the build script.
    //!                 stderr
    //!
    //!     # Output from rustdoc
    //!     doc/
    //!
    //!     # Used by `cargo package` and `cargo publish` to build a `.crate` file.
    //!     package/
    //!
    //!     # Experimental feature for generated build scripts.
    //!     .metabuild/
    //! ```
    //!
    //! When cross-compiling, the layout is the same, except it appears in
    //! `target/$TRIPLE`.

    use crate::core::compiler::CompileTarget;
    use crate::core::Workspace;
    use crate::util::{CargoResult, FileLock};
    use cargo_util::paths;
    use std::path::{Path, PathBuf};

    /// Contains the paths of all target output locations.
    ///
    /// See module docs for more information.
    pub struct Layout {
        /// The root directory: `/path/to/target`.
        /// If cross compiling: `/path/to/target/$TRIPLE`.
        root: PathBuf,
        /// The final artifact destination: `$root/debug` (or `release`).
        dest: PathBuf,
        /// The directory with rustc artifacts: `$dest/deps`
        deps: PathBuf,
        /// The directory for build scripts: `$dest/build`
        build: PathBuf,
        /// The directory for artifacts, i.e. binaries, cdylibs, staticlibs: `$dest/deps/artifact`
        artifact: PathBuf,
        /// The directory for incremental files: `$dest/incremental`
        incremental: PathBuf,
        /// The directory for fingerprints: `$dest/.fingerprint`
        fingerprint: PathBuf,
        /// The directory for examples: `$dest/examples`
        examples: PathBuf,
        /// The directory for rustdoc output: `$root/doc`
        doc: PathBuf,
        /// The directory for temporary data of integration tests and benches: `$dest/tmp`
        tmp: PathBuf,
        /// The lockfile for a build (`.cargo-lock`). Will be unlocked when this
        /// struct is `drop`ped.
        _lock: FileLock,
    }

    impl Layout {
        /// Calculate the paths for build output, lock the build directory, and return as a Layout.
        ///
        /// This function will block if the directory is already locked.
        ///
        /// `dest` should be the final artifact directory name. Currently either
        /// "debug" or "release".
        pub fn new(
            ws: &Workspace<'_>,
            target: Option<CompileTarget>,
            dest: &str,
        ) -> CargoResult<Layout> {
            let mut root = ws.target_dir();
            if let Some(target) = target {
                root.push(target.short_name());
            }
            let dest = root.join(dest);
            // If the root directory doesn't already exist go ahead and create it
            // here. Use this opportunity to exclude it from backups as well if the
            // system supports it since this is a freshly created folder.
            //
            paths::create_dir_all_excluded_from_backups_atomic(root.as_path_unlocked())?;
            // Now that the excluded from backups target root is created we can create the
            // actual destination (sub)subdirectory.
            paths::create_dir_all(dest.as_path_unlocked())?;

            // For now we don't do any more finer-grained locking on the artifact
            // directory, so just lock the entire thing for the duration of this
            // compile.
            let lock = dest.open_rw_exclusive_create(".cargo-lock", ws.config(), "build directory")?;
            let root = root.into_path_unlocked();
            let dest = dest.into_path_unlocked();
            let deps = dest.join("deps");
            let artifact = deps.join("artifact");

            Ok(Layout {
                deps,
                build: dest.join("build"),
                artifact,
                incremental: dest.join("incremental"),
                fingerprint: dest.join(".fingerprint"),
                examples: dest.join("examples"),
                doc: root.join("doc"),
                tmp: root.join("tmp"),
                root,
                dest,
                _lock: lock,
            })
        }

        /// Makes sure all directories stored in the Layout exist on the filesystem.
        pub fn prepare(&mut self) -> CargoResult<()> {
            paths::create_dir_all(&self.deps)?;
            paths::create_dir_all(&self.incremental)?;
            paths::create_dir_all(&self.fingerprint)?;
            paths::create_dir_all(&self.examples)?;
            paths::create_dir_all(&self.build)?;

            Ok(())
        }

        /// Fetch the destination path for final artifacts  (`/…/target/debug`).
        pub fn dest(&self) -> &Path {
            &self.dest
        }
        /// Fetch the deps path.
        pub fn deps(&self) -> &Path {
            &self.deps
        }
        /// Fetch the examples path.
        pub fn examples(&self) -> &Path {
            &self.examples
        }
        /// Fetch the doc path.
        pub fn doc(&self) -> &Path {
            &self.doc
        }
        /// Fetch the root path (`/…/target`).
        pub fn root(&self) -> &Path {
            &self.root
        }
        /// Fetch the incremental path.
        pub fn incremental(&self) -> &Path {
            &self.incremental
        }
        /// Fetch the fingerprint path.
        pub fn fingerprint(&self) -> &Path {
            &self.fingerprint
        }
        /// Fetch the build script path.
        pub fn build(&self) -> &Path {
            &self.build
        }
        /// Fetch the artifact path.
        pub fn artifact(&self) -> &Path {
            &self.artifact
        }
        /// Create and return the tmp path.
        pub fn prepare_tmp(&self) -> CargoResult<&Path> {
            paths::create_dir_all(&self.tmp)?;
            Ok(&self.tmp)
        }
    }