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    //! This modules contains types storing information of target platforms.
    //!
    //! Normally, call [`RustcTargetData::new`] to construct all the target
    //! platform once, and then query info on your demand. For example,
    //!
    //! * [`RustcTargetData::dep_platform_activated`] to check if platform is activated.
    //! * [`RustcTargetData::info`] to get a [`TargetInfo`] for an in-depth query.
    //! * [`TargetInfo::rustc_outputs`] to get a list of supported file types.

    use crate::core::compiler::apply_env_config;
    use crate::core::compiler::{
        BuildOutput, BuildRunner, CompileKind, CompileMode, CompileTarget, CrateType,
    };
    use crate::core::{Dependency, Package, Target, TargetKind, Workspace};
    use crate::util::context::{GlobalContext, StringList, TargetConfig};
    use crate::util::interning::InternedString;
    use crate::util::{CargoResult, Rustc};
    use anyhow::Context as _;
    use cargo_platform::{Cfg, CfgExpr};
    use cargo_util::{paths, ProcessBuilder};
    use serde::{Deserialize, Serialize};
    use std::cell::RefCell;
    use std::collections::hash_map::{Entry, HashMap};
    use std::path::{Path, PathBuf};
    use std::str::{self, FromStr};

    /// Information about the platform target gleaned from querying rustc.
    ///
    /// [`RustcTargetData`] keeps several of these, one for the host and the others
    /// for other specified targets. If no target is specified, it uses a clone from
    /// the host.
    #[derive(Clone)]
    pub struct TargetInfo {
        /// A base process builder for discovering crate type information. In
        /// particular, this is used to determine the output filename prefix and
        /// suffix for a crate type.
        crate_type_process: ProcessBuilder,
        /// Cache of output filename prefixes and suffixes.
        ///
        /// The key is the crate type name (like `cdylib`) and the value is
        /// `Some((prefix, suffix))`, for example `libcargo.so` would be
        /// `Some(("lib", ".so"))`. The value is `None` if the crate type is not
        /// supported.
        crate_types: RefCell<HashMap<CrateType, Option<(String, String)>>>,
        /// `cfg` information extracted from `rustc --print=cfg`.
        cfg: Vec<Cfg>,
        /// Supported values for `-Csplit-debuginfo=` flag, queried from rustc
        support_split_debuginfo: Vec<String>,
        /// Path to the sysroot.
        pub sysroot: PathBuf,
        /// Path to the "lib" directory in the sysroot which rustc uses for linking
        /// target libraries.
        pub sysroot_target_libdir: PathBuf,
        /// Extra flags to pass to `rustc`, see [`extra_args`].
        pub rustflags: Vec<String>,
        /// Extra flags to pass to `rustdoc`, see [`extra_args`].
        pub rustdocflags: Vec<String>,
        /// Whether or not rustc (stably) supports the `--check-cfg` flag.
        ///
        /// Can be removed once the minimum supported rustc version of Cargo is
        /// at minimum 1.80.0.
        pub support_check_cfg: bool,
    }

    /// Kind of each file generated by a Unit, part of `FileType`.
    #[derive(Clone, PartialEq, Eq, Debug)]
    pub enum FileFlavor {
        /// Not a special file type.
        Normal,
        /// Like `Normal`, but not directly executable.
        /// For example, a `.wasm` file paired with the "normal" `.js` file.
        Auxiliary,
        /// Something you can link against (e.g., a library).
        Linkable,
        /// An `.rmeta` Rust metadata file.
        Rmeta,
        /// Piece of external debug information (e.g., `.dSYM`/`.pdb` file).
        DebugInfo,
    }

    /// Type of each file generated by a Unit.
    #[derive(Debug)]
    pub struct FileType {
        /// The kind of file.
        pub flavor: FileFlavor,
        /// The crate-type that generates this file.
        ///
        /// `None` for things that aren't associated with a specific crate type,
        /// for example `rmeta` files.
        pub crate_type: Option<CrateType>,
        /// The suffix for the file (for example, `.rlib`).
        /// This is an empty string for executables on Unix-like platforms.
        suffix: String,
        /// The prefix for the file (for example, `lib`).
        /// This is an empty string for things like executables.
        prefix: String,
        /// Flag to convert hyphen to underscore when uplifting.
        should_replace_hyphens: bool,
    }

    impl FileType {
        /// The filename for this FileType crated by rustc.
        pub fn output_filename(&self, target: &Target, metadata: Option<&str>) -> String {
            match metadata {
                Some(metadata) => format!(
                    "{}{}-{}{}",
                    self.prefix,
                    target.crate_name(),
                    metadata,
                    self.suffix
                ),
                None => format!("{}{}{}", self.prefix, target.crate_name(), self.suffix),
            }
        }

        /// The filename for this FileType that Cargo should use when "uplifting"
        /// it to the destination directory.
        pub fn uplift_filename(&self, target: &Target) -> String {
            let name = match target.binary_filename() {
                Some(name) => name,
                None => {
                    // For binary crate type, `should_replace_hyphens` will always be false.
                    if self.should_replace_hyphens {
                        target.crate_name()
                    } else {
                        target.name().to_string()
                    }
                }
            };

            format!("{}{}{}", self.prefix, name, self.suffix)
        }

        /// Creates a new instance representing a `.rmeta` file.
        pub fn new_rmeta() -> FileType {
            // Note that even binaries use the `lib` prefix.
            FileType {
                flavor: FileFlavor::Rmeta,
                crate_type: None,
                suffix: ".rmeta".to_string(),
                prefix: "lib".to_string(),
                should_replace_hyphens: true,
            }
        }
    }

    impl TargetInfo {
        /// Learns the information of target platform from `rustc` invocation(s).
        ///
        /// Generally, the first time calling this function is expensive, as it may
        /// query `rustc` several times. To reduce the cost, output of each `rustc`
        /// invocation is cached by [`Rustc::cached_output`].
        ///
        /// Search `Tricky` to learn why querying `rustc` several times is needed.
        #[tracing::instrument(skip_all)]
        pub fn new(
            gctx: &GlobalContext,
            requested_kinds: &[CompileKind],
            rustc: &Rustc,
            kind: CompileKind,
        ) -> CargoResult<TargetInfo> {
            let mut rustflags =
                extra_args(gctx, requested_kinds, &rustc.host, None, kind, Flags::Rust)?;
            let mut turn = 0;
            loop {
                let extra_fingerprint = kind.fingerprint_hash();

                // Query rustc for several kinds of info from each line of output:
                // 0) file-names (to determine output file prefix/suffix for given crate type)
                // 1) sysroot
                // 2) split-debuginfo
                // 3) cfg
                //
                // Search `--print` to see what we query so far.
                let mut process = rustc.workspace_process();
                apply_env_config(gctx, &mut process)?;
                process
                    .arg("-")
                    .arg("--crate-name")
                    .arg("___")
                    .arg("--print=file-names")
                    .args(&rustflags)
                    .env_remove("RUSTC_LOG");

                // Removes `FD_CLOEXEC` set by `jobserver::Client` to pass jobserver
                // as environment variables specify.
                if let Some(client) = gctx.jobserver_from_env() {
                    process.inherit_jobserver(client);
                }

                if let CompileKind::Target(target) = kind {
                    process.arg("--target").arg(target.rustc_target());
                }

                let crate_type_process = process.clone();
                const KNOWN_CRATE_TYPES: &[CrateType] = &[
                    CrateType::Bin,
                    CrateType::Rlib,
                    CrateType::Dylib,
                    CrateType::Cdylib,
                    CrateType::Staticlib,
                    CrateType::ProcMacro,
                ];
                for crate_type in KNOWN_CRATE_TYPES.iter() {
                    process.arg("--crate-type").arg(crate_type.as_str());
                }

                let support_check_cfg = rustc
                    .cached_output(
                        process.clone().arg("--check-cfg").arg("cfg()"),
                        extra_fingerprint,
                    )
                    .is_ok();

                process.arg("--print=sysroot");
                process.arg("--print=split-debuginfo");
                process.arg("--print=crate-name"); // `___` as a delimiter.
                process.arg("--print=cfg");

                let (output, error) = rustc
                    .cached_output(&process, extra_fingerprint)
                    .with_context(|| {
                        "failed to run `rustc` to learn about target-specific information"
                    })?;

                let mut lines = output.lines();
                let mut map = HashMap::new();
                for crate_type in KNOWN_CRATE_TYPES {
                    let out = parse_crate_type(crate_type, &process, &output, &error, &mut lines)?;
                    map.insert(crate_type.clone(), out);
                }

                let Some(line) = lines.next() else {
                    return error_missing_print_output("sysroot", &process, &output, &error);
                };
                let sysroot = PathBuf::from(line);
                let sysroot_target_libdir = {
                    let mut libdir = sysroot.clone();
                    libdir.push("lib");
                    libdir.push("rustlib");
                    libdir.push(match &kind {
                        CompileKind::Host => rustc.host.as_str(),
                        CompileKind::Target(target) => target.short_name(),
                    });
                    libdir.push("lib");
                    libdir
                };

                let support_split_debuginfo = {
                    // HACK: abuse `--print=crate-name` to use `___` as a delimiter.
                    let mut res = Vec::new();
                    loop {
                        match lines.next() {
                            Some(line) if line == "___" => break,
                            Some(line) => res.push(line.into()),
                            None => {
                                return error_missing_print_output(
                                    "split-debuginfo",
                                    &process,
                                    &output,
                                    &error,
                                )
                            }
                        }
                    }
                    res
                };

                let cfg = lines
                    .map(|line| Ok(Cfg::from_str(line)?))
                    .filter(TargetInfo::not_user_specific_cfg)
                    .collect::<CargoResult<Vec<_>>>()
                    .with_context(|| {
                        format!(
                            "failed to parse the cfg from `rustc --print=cfg`, got:\n{}",
                            output
                        )
                    })?;

                // recalculate `rustflags` from above now that we have `cfg`
                // information
                let new_flags = extra_args(
                    gctx,
                    requested_kinds,
                    &rustc.host,
                    Some(&cfg),
                    kind,
                    Flags::Rust,
                )?;

                // Tricky: `RUSTFLAGS` defines the set of active `cfg` flags, active
                // `cfg` flags define which `.cargo/config` sections apply, and they
                // in turn can affect `RUSTFLAGS`! This is a bona fide mutual
                // dependency, and it can even diverge (see `cfg_paradox` test).
                //
                // So what we do here is running at most *two* iterations of
                // fixed-point iteration, which should be enough to cover
                // practically useful cases, and warn if that's not enough for
                // convergence.
                let reached_fixed_point = new_flags == rustflags;
                if !reached_fixed_point && turn == 0 {
                    turn += 1;
                    rustflags = new_flags;
                    continue;
                }
                if !reached_fixed_point {
                    gctx.shell().warn("non-trivial mutual dependency between target-specific configuration and RUSTFLAGS")?;
                }

                return Ok(TargetInfo {
                    crate_type_process,
                    crate_types: RefCell::new(map),
                    sysroot,
                    sysroot_target_libdir,
                    rustflags,
                    rustdocflags: extra_args(
                        gctx,
                        requested_kinds,
                        &rustc.host,
                        Some(&cfg),
                        kind,
                        Flags::Rustdoc,
                    )?,
                    cfg,
                    support_split_debuginfo,
                    support_check_cfg,
                });
            }
        }

        fn not_user_specific_cfg(cfg: &CargoResult<Cfg>) -> bool {
            if let Ok(Cfg::Name(cfg_name)) = cfg {
                // This should also include "debug_assertions", but it causes
                // regressions. Maybe some day in the distant future it can be
                // added (and possibly change the warning to an error).
                if cfg_name == "proc_macro" {
                    return false;
                }
            }
            true
        }

        /// All the target [`Cfg`] settings.
        pub fn cfg(&self) -> &[Cfg] {
            &self.cfg
        }

        /// Returns the list of file types generated by the given crate type.
        ///
        /// Returns `None` if the target does not support the given crate type.
        fn file_types(
            &self,
            crate_type: &CrateType,
            flavor: FileFlavor,
            target_triple: &str,
        ) -> CargoResult<Option<Vec<FileType>>> {
            let crate_type = if *crate_type == CrateType::Lib {
                CrateType::Rlib
            } else {
                crate_type.clone()
            };

            let mut crate_types = self.crate_types.borrow_mut();
            let entry = crate_types.entry(crate_type.clone());
            let crate_type_info = match entry {
                Entry::Occupied(o) => &*o.into_mut(),
                Entry::Vacant(v) => {
                    let value = self.discover_crate_type(v.key())?;
                    &*v.insert(value)
                }
            };
            let Some((prefix, suffix)) = crate_type_info else {
                return Ok(None);
            };
            let mut ret = vec![FileType {
                suffix: suffix.clone(),
                prefix: prefix.clone(),
                flavor,
                crate_type: Some(crate_type.clone()),
                should_replace_hyphens: crate_type != CrateType::Bin,
            }];

            // Window shared library import/export files.
            if crate_type.is_dynamic() {
                // Note: Custom JSON specs can alter the suffix. For now, we'll
                // just ignore non-DLL suffixes.
                if target_triple.ends_with("-windows-msvc") && suffix == ".dll" {
                    // See https://docs.microsoft.com/en-us/cpp/build/reference/working-with-import-libraries-and-export-files
                    // for more information about DLL import/export files.
                    ret.push(FileType {
                        suffix: ".dll.lib".to_string(),
                        prefix: prefix.clone(),
                        flavor: FileFlavor::Auxiliary,
                        crate_type: Some(crate_type.clone()),
                        should_replace_hyphens: true,
                    });
                    // NOTE: lld does not produce these
                    ret.push(FileType {
                        suffix: ".dll.exp".to_string(),
                        prefix: prefix.clone(),
                        flavor: FileFlavor::Auxiliary,
                        crate_type: Some(crate_type.clone()),
                        should_replace_hyphens: true,
                    });
                } else if target_triple.ends_with("windows-gnu") && suffix == ".dll" {
                    // See https://cygwin.com/cygwin-ug-net/dll.html for more
                    // information about GNU import libraries.
                    // LD can link DLL directly, but LLD requires the import library.
                    ret.push(FileType {
                        suffix: ".dll.a".to_string(),
                        prefix: "lib".to_string(),
                        flavor: FileFlavor::Auxiliary,
                        crate_type: Some(crate_type.clone()),
                        should_replace_hyphens: true,
                    })
                }
            }

            if target_triple.starts_with("wasm32-") && crate_type == CrateType::Bin && suffix == ".js" {
                // emscripten binaries generate a .js file, which loads a .wasm
                // file.
                ret.push(FileType {
                    suffix: ".wasm".to_string(),
                    prefix: prefix.clone(),
                    flavor: FileFlavor::Auxiliary,
                    crate_type: Some(crate_type.clone()),
                    // Name `foo-bar` will generate a `foo_bar.js` and
                    // `foo_bar.wasm`. Cargo will translate the underscore and
                    // copy `foo_bar.js` to `foo-bar.js`. However, the wasm
                    // filename is embedded in the .js file with an underscore, so
                    // it should not contain hyphens.
                    should_replace_hyphens: true,
                });
                // And a map file for debugging. This is only emitted with debug=2
                // (-g4 for emcc).
                ret.push(FileType {
                    suffix: ".wasm.map".to_string(),
                    prefix: prefix.clone(),
                    flavor: FileFlavor::DebugInfo,
                    crate_type: Some(crate_type.clone()),
                    should_replace_hyphens: true,
                });
            }

            // Handle separate debug files.
            let is_apple = target_triple.contains("-apple-");
            if matches!(
                crate_type,
                CrateType::Bin | CrateType::Dylib | CrateType::Cdylib | CrateType::ProcMacro
            ) {
                if is_apple {
                    let suffix = if crate_type == CrateType::Bin {
                        ".dSYM".to_string()
                    } else {
                        ".dylib.dSYM".to_string()
                    };
                    ret.push(FileType {
                        suffix,
                        prefix: prefix.clone(),
                        flavor: FileFlavor::DebugInfo,
                        crate_type: Some(crate_type),
                        // macOS tools like lldb use all sorts of magic to locate
                        // dSYM files. See https://lldb.llvm.org/use/symbols.html
                        // for some details. It seems like a `.dSYM` located next
                        // to the executable with the same name is one method. The
                        // dSYM should have the same hyphens as the executable for
                        // the names to match.
                        should_replace_hyphens: false,
                    })
                } else if target_triple.ends_with("-msvc") || target_triple.ends_with("-uefi") {
                    ret.push(FileType {
                        suffix: ".pdb".to_string(),
                        prefix: prefix.clone(),
                        flavor: FileFlavor::DebugInfo,
                        crate_type: Some(crate_type),
                        // The absolute path to the pdb file is embedded in the
                        // executable. If the exe/pdb pair is moved to another
                        // machine, then debuggers will look in the same directory
                        // of the exe with the original pdb filename. Since the
                        // original name contains underscores, they need to be
                        // preserved.
                        should_replace_hyphens: true,
                    })
                } else {
                    // Because DWARF Package (dwp) files are produced after the
                    // fact by another tool, there is nothing in the binary that
                    // provides a means to locate them. By convention, debuggers
                    // take the binary filename and append ".dwp" (including to
                    // binaries that already have an extension such as shared libs)
                    // to find the dwp.
                    ret.push(FileType {
                        // It is important to preserve the existing suffix for
                        // e.g. shared libraries, where the dwp for libfoo.so is
                        // expected to be at libfoo.so.dwp.
                        suffix: format!("{suffix}.dwp"),
                        prefix: prefix.clone(),
                        flavor: FileFlavor::DebugInfo,
                        crate_type: Some(crate_type.clone()),
                        // Likewise, the dwp needs to match the primary artifact's
                        // hyphenation exactly.
                        should_replace_hyphens: crate_type != CrateType::Bin,
                    })
                }
            }

            Ok(Some(ret))
        }

        fn discover_crate_type(&self, crate_type: &CrateType) -> CargoResult<Option<(String, String)>> {
            let mut process = self.crate_type_process.clone();

            process.arg("--crate-type").arg(crate_type.as_str());

            let output = process.exec_with_output().with_context(|| {
                format!(
                    "failed to run `rustc` to learn about crate-type {} information",
                    crate_type
                )
            })?;

            let error = str::from_utf8(&output.stderr).unwrap();
            let output = str::from_utf8(&output.stdout).unwrap();
            parse_crate_type(crate_type, &process, output, error, &mut output.lines())
        }

        /// Returns all the file types generated by rustc for the given mode/target_kind.
        ///
        /// The first value is a Vec of file types generated, the second value is
        /// a list of CrateTypes that are not supported by the given target.
        pub fn rustc_outputs(
            &self,
            mode: CompileMode,
            target_kind: &TargetKind,
            target_triple: &str,
        ) -> CargoResult<(Vec<FileType>, Vec<CrateType>)> {
            match mode {
                CompileMode::Build => self.calc_rustc_outputs(target_kind, target_triple),
                CompileMode::Test | CompileMode::Bench => {
                    match self.file_types(&CrateType::Bin, FileFlavor::Normal, target_triple)? {
                        Some(fts) => Ok((fts, Vec::new())),
                        None => Ok((Vec::new(), vec![CrateType::Bin])),
                    }
                }
                CompileMode::Check { .. } => Ok((vec![FileType::new_rmeta()], Vec::new())),
                CompileMode::Doc { .. }
                | CompileMode::Doctest
                | CompileMode::Docscrape
                | CompileMode::RunCustomBuild => {
                    panic!("asked for rustc output for non-rustc mode")
                }
            }
        }

        fn calc_rustc_outputs(
            &self,
            target_kind: &TargetKind,
            target_triple: &str,
        ) -> CargoResult<(Vec<FileType>, Vec<CrateType>)> {
            let mut unsupported = Vec::new();
            let mut result = Vec::new();
            let crate_types = target_kind.rustc_crate_types();
            for crate_type in &crate_types {
                let flavor = if crate_type.is_linkable() {
                    FileFlavor::Linkable
                } else {
                    FileFlavor::Normal
                };
                let file_types = self.file_types(crate_type, flavor, target_triple)?;
                match file_types {
                    Some(types) => {
                        result.extend(types);
                    }
                    None => {
                        unsupported.push(crate_type.clone());
                    }
                }
            }
            if !result.is_empty() && !crate_types.iter().any(|ct| ct.requires_upstream_objects()) {
                // Only add rmeta if pipelining.
                result.push(FileType::new_rmeta());
            }
            Ok((result, unsupported))
        }

        /// Checks if the debuginfo-split value is supported by this target
        pub fn supports_debuginfo_split(&self, split: InternedString) -> bool {
            self.support_split_debuginfo
                .iter()
                .any(|sup| sup.as_str() == split.as_str())
        }
    }

    /// Takes rustc output (using specialized command line args), and calculates the file prefix and
    /// suffix for the given crate type, or returns `None` if the type is not supported. (e.g., for a
    /// Rust library like `libcargo.rlib`, we have prefix "lib" and suffix "rlib").
    ///
    /// The caller needs to ensure that the lines object is at the correct line for the given crate
    /// type: this is not checked.
    ///
    /// This function can not handle more than one file per type (with wasm32-unknown-emscripten, there
    /// are two files for bin (`.wasm` and `.js`)).
    fn parse_crate_type(
        crate_type: &CrateType,
        cmd: &ProcessBuilder,
        output: &str,
        error: &str,
        lines: &mut str::Lines<'_>,
    ) -> CargoResult<Option<(String, String)>> {
        let not_supported = error.lines().any(|line| {
            (line.contains("unsupported crate type") || line.contains("unknown crate type"))
                && line.contains(&format!("crate type `{}`", crate_type))
        });
        if not_supported {
            return Ok(None);
        }
        let Some(line) = lines.next() else {
            anyhow::bail!(
                "malformed output when learning about crate-type {} information\n{}",
                crate_type,
                output_err_info(cmd, output, error)
            )
        };
        let mut parts = line.trim().split("___");
        let prefix = parts.next().unwrap();
        let Some(suffix) = parts.next() else {
            return error_missing_print_output("file-names", cmd, output, error);
        };

        Ok(Some((prefix.to_string(), suffix.to_string())))
    }

    /// Helper for creating an error message for missing output from a certain `--print` request.
    fn error_missing_print_output<T>(
        request: &str,
        cmd: &ProcessBuilder,
        stdout: &str,
        stderr: &str,
    ) -> CargoResult<T> {
        let err_info = output_err_info(cmd, stdout, stderr);
        anyhow::bail!(
            "output of --print={request} missing when learning about \
         target-specific information from rustc\n{err_info}",
        )
    }

    /// Helper for creating an error message when parsing rustc output fails.
    fn output_err_info(cmd: &ProcessBuilder, stdout: &str, stderr: &str) -> String {
        let mut result = format!("command was: {}\n", cmd);
        if !stdout.is_empty() {
            result.push_str("\n--- stdout\n");
            result.push_str(stdout);
        }
        if !stderr.is_empty() {
            result.push_str("\n--- stderr\n");
            result.push_str(stderr);
        }
        if stdout.is_empty() && stderr.is_empty() {
            result.push_str("(no output received)");
        }
        result
    }

    /// Compiler flags for either rustc or rustdoc.
    #[derive(Debug, Copy, Clone)]
    enum Flags {
        Rust,
        Rustdoc,
    }

    impl Flags {
        fn as_key(self) -> &'static str {
            match self {
                Flags::Rust => "rustflags",
                Flags::Rustdoc => "rustdocflags",
            }
        }

        fn as_env(self) -> &'static str {
            match self {
                Flags::Rust => "RUSTFLAGS",
                Flags::Rustdoc => "RUSTDOCFLAGS",
            }
        }
    }

    /// Acquire extra flags to pass to the compiler from various locations.
    ///
    /// The locations are:
    ///
    ///  - the `CARGO_ENCODED_RUSTFLAGS` environment variable
    ///  - the `RUSTFLAGS` environment variable
    ///
    /// then if none of those were found
    ///
    ///  - `target.*.rustflags` from the config (.cargo/config)
    ///  - `target.cfg(..).rustflags` from the config
    ///  - `host.*.rustflags` from the config if compiling a host artifact or without `--target`
    ///     (requires `-Zhost-config`)
    ///
    /// then if none of those were found
    ///
    ///  - `build.rustflags` from the config
    ///
    /// The behavior differs slightly when cross-compiling (or, specifically, when `--target` is
    /// provided) for artifacts that are always built for the host (plugins, build scripts, ...).
    /// For those artifacts, _only_ `host.*.rustflags` is respected, and no other configuration
    /// sources, _regardless of the value of `target-applies-to-host`_. This is counterintuitive, but
    /// necessary to retain backwards compatibility with older versions of Cargo.
    ///
    /// Rules above also applies to rustdoc. Just the key would be `rustdocflags`/`RUSTDOCFLAGS`.
    fn extra_args(
        gctx: &GlobalContext,
        requested_kinds: &[CompileKind],
        host_triple: &str,
        target_cfg: Option<&[Cfg]>,
        kind: CompileKind,
        flags: Flags,
    ) -> CargoResult<Vec<String>> {
        let target_applies_to_host = gctx.target_applies_to_host()?;

        // Host artifacts should not generally pick up rustflags from anywhere except [host].
        //
        // The one exception to this is if `target-applies-to-host = true`, which opts into a
        // particular (inconsistent) past Cargo behavior where host artifacts _do_ pick up rustflags
        // set elsewhere when `--target` isn't passed.
        if kind.is_host() {
            if target_applies_to_host && requested_kinds == [CompileKind::Host] {
                // This is the past Cargo behavior where we fall back to the same logic as for other
                // artifacts without --target.
            } else {
                // In all other cases, host artifacts just get flags from [host], regardless of
                // --target. Or, phrased differently, no `--target` behaves the same as `--target
                // <host>`, and host artifacts are always "special" (they don't pick up `RUSTFLAGS` for
                // example).
                return Ok(rustflags_from_host(gctx, flags, host_triple)?.unwrap_or_else(Vec::new));
            }
        }

        // All other artifacts pick up the RUSTFLAGS, [target.*], and [build], in that order.
        // NOTE: It is impossible to have a [host] section and reach this logic with kind.is_host(),
        // since [host] implies `target-applies-to-host = false`, which always early-returns above.

        if let Some(rustflags) = rustflags_from_env(gctx, flags) {
            Ok(rustflags)
        } else if let Some(rustflags) =
            rustflags_from_target(gctx, host_triple, target_cfg, kind, flags)?
        {
            Ok(rustflags)
        } else if let Some(rustflags) = rustflags_from_build(gctx, flags)? {
            Ok(rustflags)
        } else {
            Ok(Vec::new())
        }
    }

    /// Gets compiler flags from environment variables.
    /// See [`extra_args`] for more.
    fn rustflags_from_env(gctx: &GlobalContext, flags: Flags) -> Option<Vec<String>> {
        // First try CARGO_ENCODED_RUSTFLAGS from the environment.
        // Prefer this over RUSTFLAGS since it's less prone to encoding errors.
        if let Ok(a) = gctx.get_env(format!("CARGO_ENCODED_{}", flags.as_env())) {
            if a.is_empty() {
                return Some(Vec::new());
            }
            return Some(a.split('\x1f').map(str::to_string).collect());
        }

        // Then try RUSTFLAGS from the environment
        if let Ok(a) = gctx.get_env(flags.as_env()) {
            let args = a
                .split(' ')
                .map(str::trim)
                .filter(|s| !s.is_empty())
                .map(str::to_string);
            return Some(args.collect());
        }

        // No rustflags to be collected from the environment
        None
    }

    /// Gets compiler flags from `[target]` section in the config.
    /// See [`extra_args`] for more.
    fn rustflags_from_target(
        gctx: &GlobalContext,
        host_triple: &str,
        target_cfg: Option<&[Cfg]>,
        kind: CompileKind,
        flag: Flags,
    ) -> CargoResult<Option<Vec<String>>> {
        let mut rustflags = Vec::new();

        // Then the target.*.rustflags value...
        let target = match &kind {
            CompileKind::Host => host_triple,
            CompileKind::Target(target) => target.short_name(),
        };
        let key = format!("target.{}.{}", target, flag.as_key());
        if let Some(args) = gctx.get::<Option<StringList>>(&key)? {
            rustflags.extend(args.as_slice().iter().cloned());
        }
        // ...including target.'cfg(...)'.rustflags
        if let Some(target_cfg) = target_cfg {
            gctx.target_cfgs()?
                .iter()
                .filter_map(|(key, cfg)| {
                    match flag {
                        Flags::Rust => cfg
                            .rustflags
                            .as_ref()
                            .map(|rustflags| (key, &rustflags.val)),
                        // `target.cfg(…).rustdocflags` is currently not supported.
                        Flags::Rustdoc => None,
                    }
                })
                .filter(|(key, _rustflags)| CfgExpr::matches_key(key, target_cfg))
                .for_each(|(_key, cfg_rustflags)| {
                    rustflags.extend(cfg_rustflags.as_slice().iter().cloned());
                });
        }

        if rustflags.is_empty() {
            Ok(None)
        } else {
            Ok(Some(rustflags))
        }
    }

    /// Gets compiler flags from `[host]` section in the config.
    /// See [`extra_args`] for more.
    fn rustflags_from_host(
        gctx: &GlobalContext,
        flag: Flags,
        host_triple: &str,
    ) -> CargoResult<Option<Vec<String>>> {
        let target_cfg = gctx.host_cfg_triple(host_triple)?;
        let list = match flag {
            Flags::Rust => &target_cfg.rustflags,
            Flags::Rustdoc => {
                // host.rustdocflags is not a thing, since it does not make sense
                return Ok(None);
            }
        };
        Ok(list.as_ref().map(|l| l.val.as_slice().to_vec()))
    }

    /// Gets compiler flags from `[build]` section in the config.
    /// See [`extra_args`] for more.
    fn rustflags_from_build(gctx: &GlobalContext, flag: Flags) -> CargoResult<Option<Vec<String>>> {
        // Then the `build.rustflags` value.
        let build = gctx.build_config()?;
        let list = match flag {
            Flags::Rust => &build.rustflags,
            Flags::Rustdoc => &build.rustdocflags,
        };
        Ok(list.as_ref().map(|l| l.as_slice().to_vec()))
    }

    /// Collection of information about `rustc` and the host and target.
    pub struct RustcTargetData<'gctx> {
        /// Information about `rustc` itself.
        pub rustc: Rustc,

        /// Config
        pub gctx: &'gctx GlobalContext,
        requested_kinds: Vec<CompileKind>,

        /// Build information for the "host", which is information about when
        /// `rustc` is invoked without a `--target` flag. This is used for
        /// procedural macros, build scripts, etc.
        host_config: TargetConfig,
        /// Information about the host platform.
        host_info: TargetInfo,

        /// Build information for targets that we're building for.
        target_config: HashMap<CompileTarget, TargetConfig>,
        /// Information about the target platform that we're building for.
        target_info: HashMap<CompileTarget, TargetInfo>,
    }

    impl<'gctx> RustcTargetData<'gctx> {
        #[tracing::instrument(skip_all)]
        pub fn new(
            ws: &Workspace<'gctx>,
            requested_kinds: &[CompileKind],
        ) -> CargoResult<RustcTargetData<'gctx>> {
            let gctx = ws.gctx();
            let rustc = gctx.load_global_rustc(Some(ws))?;
            let mut target_config = HashMap::new();
            let mut target_info = HashMap::new();
            let target_applies_to_host = gctx.target_applies_to_host()?;
            let host_info = TargetInfo::new(gctx, requested_kinds, &rustc, CompileKind::Host)?;
            let host_config = if target_applies_to_host {
                gctx.target_cfg_triple(&rustc.host)?
            } else {
                gctx.host_cfg_triple(&rustc.host)?
            };

            // This is a hack. The unit_dependency graph builder "pretends" that
            // `CompileKind::Host` is `CompileKind::Target(host)` if the
            // `--target` flag is not specified. Since the unit_dependency code
            // needs access to the target config data, create a copy so that it
            // can be found. See `rebuild_unit_graph_shared` for why this is done.
            if requested_kinds.iter().any(CompileKind::is_host) {
                let ct = CompileTarget::new(&rustc.host)?;
                target_info.insert(ct, host_info.clone());
                target_config.insert(ct, gctx.target_cfg_triple(&rustc.host)?);
            };

            let mut res = RustcTargetData {
                rustc,
                gctx,
                requested_kinds: requested_kinds.into(),
                host_config,
                host_info,
                target_config,
                target_info,
            };

            // Get all kinds we currently know about.
            //
            // For now, targets can only ever come from the root workspace
            // units and artifact dependencies, so this
            // correctly represents all the kinds that can happen. When we have
            // other ways for targets to appear at places that are not the root units,
            // we may have to revisit this.
            fn artifact_targets(package: &Package) -> impl Iterator<Item = CompileKind> + '_ {
                package
                    .manifest()
                    .dependencies()
                    .iter()
                    .filter_map(|d| d.artifact()?.target()?.to_compile_kind())
            }
            let all_kinds = requested_kinds
                .iter()
                .copied()
                .chain(ws.members().flat_map(|p| {
                    p.manifest()
                        .default_kind()
                        .into_iter()
                        .chain(p.manifest().forced_kind())
                        .chain(artifact_targets(p))
                }));
            for kind in all_kinds {
                res.merge_compile_kind(kind)?;
            }

            Ok(res)
        }

        /// Insert `kind` into our `target_info` and `target_config` members if it isn't present yet.
        pub fn merge_compile_kind(&mut self, kind: CompileKind) -> CargoResult<()> {
            if let CompileKind::Target(target) = kind {
                if !self.target_config.contains_key(&target) {
                    self.target_config
                        .insert(target, self.gctx.target_cfg_triple(target.short_name())?);
                }
                if !self.target_info.contains_key(&target) {
                    self.target_info.insert(
                        target,
                        TargetInfo::new(self.gctx, &self.requested_kinds, &self.rustc, kind)?,
                    );
                }
            }
            Ok(())
        }

        /// Returns a "short" name for the given kind, suitable for keying off
        /// configuration in Cargo or presenting to users.
        pub fn short_name<'a>(&'a self, kind: &'a CompileKind) -> &'a str {
            match kind {
                CompileKind::Host => &self.rustc.host,
                CompileKind::Target(target) => target.short_name(),
            }
        }

        /// Whether a dependency should be compiled for the host or target platform,
        /// specified by `CompileKind`.
        pub fn dep_platform_activated(&self, dep: &Dependency, kind: CompileKind) -> bool {
            // If this dependency is only available for certain platforms,
            // make sure we're only enabling it for that platform.
            let Some(platform) = dep.platform() else {
                return true;
            };
            let name = self.short_name(&kind);
            platform.matches(name, self.cfg(kind))
        }

        /// Gets the list of `cfg`s printed out from the compiler for the specified kind.
        pub fn cfg(&self, kind: CompileKind) -> &[Cfg] {
            self.info(kind).cfg()
        }

        /// Information about the given target platform, learned by querying rustc.
        ///
        /// # Panics
        ///
        /// Panics, if the target platform described by `kind` can't be found.
        /// See [`get_info`](Self::get_info) for a non-panicking alternative.
        pub fn info(&self, kind: CompileKind) -> &TargetInfo {
            self.get_info(kind).unwrap()
        }

        /// Information about the given target platform, learned by querying rustc.
        ///
        /// Returns `None` if the target platform described by `kind` can't be found.
        pub fn get_info(&self, kind: CompileKind) -> Option<&TargetInfo> {
            match kind {
                CompileKind::Host => Some(&self.host_info),
                CompileKind::Target(s) => self.target_info.get(&s),
            }
        }

        /// Gets the target configuration for a particular host or target.
        pub fn target_config(&self, kind: CompileKind) -> &TargetConfig {
            match kind {
                CompileKind::Host => &self.host_config,
                CompileKind::Target(s) => &self.target_config[&s],
            }
        }

        /// If a build script is overridden, this returns the `BuildOutput` to use.
        ///
        /// `lib_name` is the `links` library name and `kind` is whether it is for
        /// Host or Target.
        pub fn script_override(&self, lib_name: &str, kind: CompileKind) -> Option<&BuildOutput> {
            self.target_config(kind).links_overrides.get(lib_name)
        }
    }

    /// Structure used to deal with Rustdoc fingerprinting
    #[derive(Debug, Serialize, Deserialize)]
    pub struct RustDocFingerprint {
        pub rustc_vv: String,
    }

    impl RustDocFingerprint {
        /// This function checks whether the latest version of `Rustc` used to compile this
        /// `Workspace`'s docs was the same as the one is currently being used in this `cargo doc`
        /// call.
        ///
        /// In case it's not, it takes care of removing the `doc/` folder as well as overwriting
        /// the rustdoc fingerprint info in order to guarantee that we won't end up with mixed
        /// versions of the `js/html/css` files that `rustdoc` autogenerates which do not have
        /// any versioning.
        pub fn check_rustdoc_fingerprint(build_runner: &BuildRunner<'_, '_>) -> CargoResult<()> {
            if build_runner
                .bcx
                .gctx
                .cli_unstable()
                .skip_rustdoc_fingerprint
            {
                return Ok(());
            }
            let actual_rustdoc_target_data = RustDocFingerprint {
                rustc_vv: build_runner.bcx.rustc().verbose_version.clone(),
            };

            let fingerprint_path = build_runner
                .files()
                .host_root()
                .join(".rustdoc_fingerprint.json");
            let write_fingerprint = || -> CargoResult<()> {
                paths::write(
                    &fingerprint_path,
                    serde_json::to_string(&actual_rustdoc_target_data)?,
                )
            };
            let Ok(rustdoc_data) = paths::read(&fingerprint_path) else {
                // If the fingerprint does not exist, do not clear out the doc
                // directories. Otherwise this ran into problems where projects
                // like rustbuild were creating the doc directory before running
                // `cargo doc` in a way that deleting it would break it.
                return write_fingerprint();
            };
            match serde_json::from_str::<RustDocFingerprint>(&rustdoc_data) {
                Ok(fingerprint) => {
                    if fingerprint.rustc_vv == actual_rustdoc_target_data.rustc_vv {
                        return Ok(());
                    } else {
                        tracing::debug!(
                            "doc fingerprint changed:\noriginal:\n{}\nnew:\n{}",
                            fingerprint.rustc_vv,
                            actual_rustdoc_target_data.rustc_vv
                        );
                    }
                }
                Err(e) => {
                    tracing::debug!("could not deserialize {:?}: {}", fingerprint_path, e);
                }
            };
            // Fingerprint does not match, delete the doc directories and write a new fingerprint.
            tracing::debug!(
                "fingerprint {:?} mismatch, clearing doc directories",
                fingerprint_path
            );
            build_runner
                .bcx
                .all_kinds
                .iter()
                .map(|kind| build_runner.files().layout(*kind).doc())
                .filter(|path| path.exists())
                .try_for_each(|path| clean_doc(path))?;
            write_fingerprint()?;
            return Ok(());

            fn clean_doc(path: &Path) -> CargoResult<()> {
                let entries = path
                    .read_dir()
                    .with_context(|| format!("failed to read directory `{}`", path.display()))?;
                for entry in entries {
                    let entry = entry?;
                    // Don't remove hidden files. Rustdoc does not create them,
                    // but the user might have.
                    if entry
                        .file_name()
                        .to_str()
                        .map_or(false, |name| name.starts_with('.'))
                    {
                        continue;
                    }
                    let path = entry.path();
                    if entry.file_type()?.is_dir() {
                        paths::remove_dir_all(path)?;
                    } else {
                        paths::remove_file(path)?;
                    }
                }
                Ok(())
            }
        }
    }