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//! See [`CompilationFiles`].
use std::collections::HashMap;
use std::fmt;
use std::hash::{Hash, Hasher};
use std::path::{Path, PathBuf};
use std::sync::Arc;
use lazycell::LazyCell;
use tracing::debug;
use super::{BuildContext, CompileKind, Context, FileFlavor, Layout};
use crate::core::compiler::{CompileMode, CompileTarget, CrateType, FileType, Unit};
use crate::core::{Target, TargetKind, Workspace};
use crate::util::{self, CargoResult, StableHasher};
/// This is a generic version number that can be changed to make
/// backwards-incompatible changes to any file structures in the output
/// directory. For example, the fingerprint files or the build-script
/// output files.
///
/// Normally cargo updates ship with rustc updates which will
/// cause a new hash due to the rustc version changing, but this allows
/// cargo to be extra careful to deal with different versions of cargo that
/// use the same rustc version.
const METADATA_VERSION: u8 = 2;
/// The `Metadata` is a hash used to make unique file names for each unit in a
/// build. It is also used for symbol mangling.
///
/// For example:
/// - A project may depend on crate `A` and crate `B`, so the package name must be in the file name.
/// - Similarly a project may depend on two versions of `A`, so the version must be in the file name.
///
/// In general this must include all things that need to be distinguished in different parts of
/// the same build. This is absolutely required or we override things before
/// we get chance to use them.
///
/// It is also used for symbol mangling, because if you have two versions of
/// the same crate linked together, their symbols need to be differentiated.
///
/// We use a hash because it is an easy way to guarantee
/// that all the inputs can be converted to a valid path.
///
/// This also acts as the main layer of caching provided by Cargo.
/// For example, we want to cache `cargo build` and `cargo doc` separately, so that running one
/// does not invalidate the artifacts for the other. We do this by including [`CompileMode`] in the
/// hash, thus the artifacts go in different folders and do not override each other.
/// If we don't add something that we should have, for this reason, we get the
/// correct output but rebuild more than is needed.
///
/// Some things that need to be tracked to ensure the correct output should definitely *not*
/// go in the `Metadata`. For example, the modification time of a file, should be tracked to make a
/// rebuild when the file changes. However, it would be wasteful to include in the `Metadata`. The
/// old artifacts are never going to be needed again. We can save space by just overwriting them.
/// If we add something that we should not have, for this reason, we get the correct output but take
/// more space than needed. This makes not including something in `Metadata`
/// a form of cache invalidation.
///
/// You should also avoid anything that would interfere with reproducible
/// builds. For example, *any* absolute path should be avoided. This is one
/// reason that `RUSTFLAGS` is not in `Metadata`, because it often has
/// absolute paths (like `--remap-path-prefix` which is fundamentally used for
/// reproducible builds and has absolute paths in it). Also, in some cases the
/// mangled symbols need to be stable between different builds with different
/// settings. For example, profile-guided optimizations need to swap
/// `RUSTFLAGS` between runs, but needs to keep the same symbol names.
///
/// Note that the `Fingerprint` is in charge of tracking everything needed to determine if a
/// rebuild is needed.
#[derive(Copy, Clone, Hash, Eq, PartialEq, Ord, PartialOrd)]
pub struct Metadata(u64);
impl fmt::Display for Metadata {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{:016x}", self.0)
}
}
impl fmt::Debug for Metadata {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "Metadata({:016x})", self.0)
}
}
/// Information about the metadata hashes used for a `Unit`.
struct MetaInfo {
/// The symbol hash to use.
meta_hash: Metadata,
/// Whether or not the `-C extra-filename` flag is used to generate unique
/// output filenames for this `Unit`.
///
/// If this is `true`, the `meta_hash` is used for the filename.
use_extra_filename: bool,
}
/// Collection of information about the files emitted by the compiler, and the
/// output directory structure.
pub struct CompilationFiles<'a, 'cfg> {
/// The target directory layout for the host (and target if it is the same as host).
pub(super) host: Layout,
/// The target directory layout for the target (if different from then host).
pub(super) target: HashMap<CompileTarget, Layout>,
/// Additional directory to include a copy of the outputs.
export_dir: Option<PathBuf>,
/// The root targets requested by the user on the command line (does not
/// include dependencies).
roots: Vec<Unit>,
ws: &'a Workspace<'cfg>,
/// Metadata hash to use for each unit.
metas: HashMap<Unit, MetaInfo>,
/// For each Unit, a list all files produced.
outputs: HashMap<Unit, LazyCell<Arc<Vec<OutputFile>>>>,
}
/// Info about a single file emitted by the compiler.
#[derive(Debug)]
pub struct OutputFile {
/// Absolute path to the file that will be produced by the build process.
pub path: PathBuf,
/// If it should be linked into `target`, and what it should be called
/// (e.g., without metadata).
pub hardlink: Option<PathBuf>,
/// If `--out-dir` is specified, the absolute path to the exported file.
pub export_path: Option<PathBuf>,
/// Type of the file (library / debug symbol / else).
pub flavor: FileFlavor,
}
impl OutputFile {
/// Gets the hard link if present; otherwise, returns the path.
pub fn bin_dst(&self) -> &PathBuf {
match self.hardlink {
Some(ref link_dst) => link_dst,
None => &self.path,
}
}
}
impl<'a, 'cfg: 'a> CompilationFiles<'a, 'cfg> {
pub(super) fn new(
cx: &Context<'a, 'cfg>,
host: Layout,
target: HashMap<CompileTarget, Layout>,
) -> CompilationFiles<'a, 'cfg> {
let mut metas = HashMap::new();
for unit in &cx.bcx.roots {
metadata_of(unit, cx, &mut metas);
}
let outputs = metas
.keys()
.cloned()
.map(|unit| (unit, LazyCell::new()))
.collect();
CompilationFiles {
ws: cx.bcx.ws,
host,
target,
export_dir: cx.bcx.build_config.export_dir.clone(),
roots: cx.bcx.roots.clone(),
metas,
outputs,
}
}
/// Returns the appropriate directory layout for either a plugin or not.
pub fn layout(&self, kind: CompileKind) -> &Layout {
match kind {
CompileKind::Host => &self.host,
CompileKind::Target(target) => &self.target[&target],
}
}
/// Gets the metadata for the given unit.
///
/// See [`Metadata`] and [`fingerprint`] module for more.
///
/// [`fingerprint`]: ../../fingerprint/index.html#fingerprints-and-metadata
pub fn metadata(&self, unit: &Unit) -> Metadata {
self.metas[unit].meta_hash
}
/// Returns whether or not `-C extra-filename` is used to extend the
/// output filenames to make them unique.
pub fn use_extra_filename(&self, unit: &Unit) -> bool {
self.metas[unit].use_extra_filename
}
/// Gets the short hash based only on the `PackageId`.
/// Used for the metadata when `metadata` returns `None`.
pub fn target_short_hash(&self, unit: &Unit) -> String {
let hashable = unit.pkg.package_id().stable_hash(self.ws.root());
util::short_hash(&(METADATA_VERSION, hashable))
}
/// Returns the directory where the artifacts for the given unit are
/// initially created.
pub fn out_dir(&self, unit: &Unit) -> PathBuf {
// Docscrape units need to have doc/ set as the out_dir so sources for reverse-dependencies
// will be put into doc/ and not into deps/ where the *.examples files are stored.
if unit.mode.is_doc() || unit.mode.is_doc_scrape() {
self.layout(unit.kind).doc().to_path_buf()
} else if unit.mode.is_doc_test() {
panic!("doc tests do not have an out dir");
} else if unit.target.is_custom_build() {
self.build_script_dir(unit)
} else if unit.target.is_example() {
self.layout(unit.kind).examples().to_path_buf()
} else if unit.artifact.is_true() {
self.artifact_dir(unit)
} else {
self.deps_dir(unit).to_path_buf()
}
}
/// Additional export directory from `--out-dir`.
pub fn export_dir(&self) -> Option<PathBuf> {
self.export_dir.clone()
}
/// Directory name to use for a package in the form `NAME-HASH`.
///
/// Note that some units may share the same directory, so care should be
/// taken in those cases!
fn pkg_dir(&self, unit: &Unit) -> String {
let name = unit.pkg.package_id().name();
let meta = &self.metas[unit];
if meta.use_extra_filename {
format!("{}-{}", name, meta.meta_hash)
} else {
format!("{}-{}", name, self.target_short_hash(unit))
}
}
/// Returns the final artifact path for the host (`/…/target/debug`)
pub fn host_dest(&self) -> &Path {
self.host.dest()
}
/// Returns the root of the build output tree for the host (`/…/target`)
pub fn host_root(&self) -> &Path {
self.host.root()
}
/// Returns the host `deps` directory path.
pub fn host_deps(&self) -> &Path {
self.host.deps()
}
/// Returns the directories where Rust crate dependencies are found for the
/// specified unit.
pub fn deps_dir(&self, unit: &Unit) -> &Path {
self.layout(unit.kind).deps()
}
/// Directory where the fingerprint for the given unit should go.
pub fn fingerprint_dir(&self, unit: &Unit) -> PathBuf {
let dir = self.pkg_dir(unit);
self.layout(unit.kind).fingerprint().join(dir)
}
/// Returns the path for a file in the fingerprint directory.
///
/// The "prefix" should be something to distinguish the file from other
/// files in the fingerprint directory.
pub fn fingerprint_file_path(&self, unit: &Unit, prefix: &str) -> PathBuf {
// Different targets need to be distinguished in the
let kind = unit.target.kind().description();
let flavor = if unit.mode.is_any_test() {
"test-"
} else if unit.mode.is_doc() {
"doc-"
} else if unit.mode.is_run_custom_build() {
"run-"
} else {
""
};
let name = format!("{}{}{}-{}", prefix, flavor, kind, unit.target.name());
self.fingerprint_dir(unit).join(name)
}
/// Path where compiler output is cached.
pub fn message_cache_path(&self, unit: &Unit) -> PathBuf {
self.fingerprint_file_path(unit, "output-")
}
/// Returns the directory where a compiled build script is stored.
/// `/path/to/target/{debug,release}/build/PKG-HASH`
pub fn build_script_dir(&self, unit: &Unit) -> PathBuf {
assert!(unit.target.is_custom_build());
assert!(!unit.mode.is_run_custom_build());
assert!(self.metas.contains_key(unit));
let dir = self.pkg_dir(unit);
self.layout(CompileKind::Host).build().join(dir)
}
/// Returns the directory for compiled artifacts files.
/// `/path/to/target/{debug,release}/deps/artifact/KIND/PKG-HASH`
fn artifact_dir(&self, unit: &Unit) -> PathBuf {
assert!(self.metas.contains_key(unit));
assert!(unit.artifact.is_true());
let dir = self.pkg_dir(unit);
let kind = match unit.target.kind() {
TargetKind::Bin => "bin",
TargetKind::Lib(lib_kinds) => match lib_kinds.as_slice() {
&[CrateType::Cdylib] => "cdylib",
&[CrateType::Staticlib] => "staticlib",
invalid => unreachable!(
"BUG: unexpected artifact library type(s): {:?} - these should have been split",
invalid
),
},
invalid => unreachable!(
"BUG: {:?} are not supposed to be used as artifacts",
invalid
),
};
self.layout(unit.kind).artifact().join(dir).join(kind)
}
/// Returns the directory where information about running a build script
/// is stored.
/// `/path/to/target/{debug,release}/build/PKG-HASH`
pub fn build_script_run_dir(&self, unit: &Unit) -> PathBuf {
assert!(unit.target.is_custom_build());
assert!(unit.mode.is_run_custom_build());
let dir = self.pkg_dir(unit);
self.layout(unit.kind).build().join(dir)
}
/// Returns the "OUT_DIR" directory for running a build script.
/// `/path/to/target/{debug,release}/build/PKG-HASH/out`
pub fn build_script_out_dir(&self, unit: &Unit) -> PathBuf {
self.build_script_run_dir(unit).join("out")
}
/// Returns the path to the executable binary for the given bin target.
///
/// This should only to be used when a `Unit` is not available.
pub fn bin_link_for_target(
&self,
target: &Target,
kind: CompileKind,
bcx: &BuildContext<'_, '_>,
) -> CargoResult<PathBuf> {
assert!(target.is_bin());
let dest = self.layout(kind).dest();
let info = bcx.target_data.info(kind);
let (file_types, _) = info
.rustc_outputs(
CompileMode::Build,
&TargetKind::Bin,
bcx.target_data.short_name(&kind),
)
.expect("target must support `bin`");
let file_type = file_types
.iter()
.find(|file_type| file_type.flavor == FileFlavor::Normal)
.expect("target must support `bin`");
Ok(dest.join(file_type.uplift_filename(target)))
}
/// Returns the filenames that the given unit will generate.
///
/// Note: It is not guaranteed that all of the files will be generated.
pub(super) fn outputs(
&self,
unit: &Unit,
bcx: &BuildContext<'a, 'cfg>,
) -> CargoResult<Arc<Vec<OutputFile>>> {
self.outputs[unit]
.try_borrow_with(|| self.calc_outputs(unit, bcx))
.map(Arc::clone)
}
/// Returns the path where the output for the given unit and FileType
/// should be uplifted to.
///
/// Returns `None` if the unit shouldn't be uplifted (for example, a
/// dependent rlib).
fn uplift_to(&self, unit: &Unit, file_type: &FileType, from_path: &Path) -> Option<PathBuf> {
// Tests, check, doc, etc. should not be uplifted.
if unit.mode != CompileMode::Build || file_type.flavor == FileFlavor::Rmeta {
return None;
}
// Artifact dependencies are never uplifted.
if unit.artifact.is_true() {
return None;
}
// - Binaries: The user always wants to see these, even if they are
// implicitly built (for example for integration tests).
// - dylibs: This ensures that the dynamic linker pulls in all the
// latest copies (even if the dylib was built from a previous cargo
// build). There are complex reasons for this, see #8139, #6167, #6162.
// - Things directly requested from the command-line (the "roots").
// This one is a little questionable for rlibs (see #6131), but is
// historically how Cargo has operated. This is primarily useful to
// give the user access to staticlibs and cdylibs.
if !unit.target.is_bin()
&& !unit.target.is_custom_build()
&& file_type.crate_type != Some(CrateType::Dylib)
&& !self.roots.contains(unit)
{
return None;
}
let filename = file_type.uplift_filename(&unit.target);
let uplift_path = if unit.target.is_example() {
// Examples live in their own little world.
self.layout(unit.kind).examples().join(filename)
} else if unit.target.is_custom_build() {
self.build_script_dir(unit).join(filename)
} else {
self.layout(unit.kind).dest().join(filename)
};
if from_path == uplift_path {
// This can happen with things like examples that reside in the
// same directory, do not have a metadata hash (like on Windows),
// and do not have hyphens.
return None;
}
Some(uplift_path)
}
/// Calculates the filenames that the given unit will generate.
/// Should use [`CompilationFiles::outputs`] instead
/// as it caches the result of this function.
fn calc_outputs(
&self,
unit: &Unit,
bcx: &BuildContext<'a, 'cfg>,
) -> CargoResult<Arc<Vec<OutputFile>>> {
let ret = match unit.mode {
CompileMode::Doc { .. } => {
let path = self
.out_dir(unit)
.join(unit.target.crate_name())
.join("index.html");
vec![OutputFile {
path,
hardlink: None,
export_path: None,
flavor: FileFlavor::Normal,
}]
}
CompileMode::RunCustomBuild => {
// At this time, this code path does not handle build script
// outputs.
vec![]
}
CompileMode::Doctest => {
// Doctests are built in a temporary directory and then
// deleted. There is the `--persist-doctests` unstable flag,
// but Cargo does not know about that.
vec![]
}
CompileMode::Docscrape => {
// The file name needs to be stable across Cargo sessions.
// This originally used unit.buildkey(), but that isn't stable,
// so we use metadata instead (prefixed with name for debugging).
let file_name = format!("{}-{}.examples", unit.pkg.name(), self.metadata(unit));
let path = self.deps_dir(unit).join(file_name);
vec![OutputFile {
path,
hardlink: None,
export_path: None,
flavor: FileFlavor::Normal,
}]
}
CompileMode::Test
| CompileMode::Build
| CompileMode::Bench
| CompileMode::Check { .. } => self.calc_outputs_rustc(unit, bcx)?,
};
debug!("Target filenames: {:?}", ret);
Ok(Arc::new(ret))
}
/// Computes the actual, full pathnames for all the files generated by rustc.
///
/// The `OutputFile` also contains the paths where those files should be
/// "uplifted" to.
fn calc_outputs_rustc(
&self,
unit: &Unit,
bcx: &BuildContext<'a, 'cfg>,
) -> CargoResult<Vec<OutputFile>> {
let out_dir = self.out_dir(unit);
let info = bcx.target_data.info(unit.kind);
let triple = bcx.target_data.short_name(&unit.kind);
let (file_types, unsupported) =
info.rustc_outputs(unit.mode, unit.target.kind(), triple)?;
if file_types.is_empty() {
if !unsupported.is_empty() {
let unsupported_strs: Vec<_> = unsupported.iter().map(|ct| ct.as_str()).collect();
anyhow::bail!(
"cannot produce {} for `{}` as the target `{}` \
does not support these crate types",
unsupported_strs.join(", "),
unit.pkg,
triple,
)
}
anyhow::bail!(
"cannot compile `{}` as the target `{}` does not \
support any of the output crate types",
unit.pkg,
triple,
);
}
// Convert FileType to OutputFile.
let mut outputs = Vec::new();
for file_type in file_types {
let meta = &self.metas[unit];
let meta_opt = meta.use_extra_filename.then(|| meta.meta_hash.to_string());
let path = out_dir.join(file_type.output_filename(&unit.target, meta_opt.as_deref()));
// If, the `different_binary_name` feature is enabled, the name of the hardlink will
// be the name of the binary provided by the user in `Cargo.toml`.
let hardlink = self.uplift_to(unit, &file_type, &path);
let export_path = if unit.target.is_custom_build() {
None
} else {
self.export_dir.as_ref().and_then(|export_dir| {
hardlink
.as_ref()
.map(|hardlink| export_dir.join(hardlink.file_name().unwrap()))
})
};
outputs.push(OutputFile {
path,
hardlink,
export_path,
flavor: file_type.flavor,
});
}
Ok(outputs)
}
}
/// Gets the metadata hash for the given [`Unit`].
///
/// When a metadata hash doesn't exist for the given unit,
/// this calls itself recursively to compute metadata hashes of all its dependencies.
/// See [`compute_metadata`] for how a single metadata hash is computed.
fn metadata_of<'a>(
unit: &Unit,
cx: &Context<'_, '_>,
metas: &'a mut HashMap<Unit, MetaInfo>,
) -> &'a MetaInfo {
if !metas.contains_key(unit) {
let meta = compute_metadata(unit, cx, metas);
metas.insert(unit.clone(), meta);
for dep in cx.unit_deps(unit) {
metadata_of(&dep.unit, cx, metas);
}
}
&metas[unit]
}
/// Computes the metadata hash for the given [`Unit`].
fn compute_metadata(
unit: &Unit,
cx: &Context<'_, '_>,
metas: &mut HashMap<Unit, MetaInfo>,
) -> MetaInfo {
let bcx = &cx.bcx;
let mut hasher = StableHasher::new();
METADATA_VERSION.hash(&mut hasher);
// Unique metadata per (name, source, version) triple. This'll allow us
// to pull crates from anywhere without worrying about conflicts.
unit.pkg
.package_id()
.stable_hash(bcx.ws.root())
.hash(&mut hasher);
// Also mix in enabled features to our metadata. This'll ensure that
// when changing feature sets each lib is separately cached.
unit.features.hash(&mut hasher);
// Mix in the target-metadata of all the dependencies of this target.
let mut deps_metadata = cx
.unit_deps(unit)
.iter()
.map(|dep| metadata_of(&dep.unit, cx, metas).meta_hash)
.collect::<Vec<_>>();
deps_metadata.sort();
deps_metadata.hash(&mut hasher);
// Throw in the profile we're compiling with. This helps caching
// `panic=abort` and `panic=unwind` artifacts, additionally with various
// settings like debuginfo and whatnot.
unit.profile.hash(&mut hasher);
unit.mode.hash(&mut hasher);
cx.lto[unit].hash(&mut hasher);
// Artifacts compiled for the host should have a different
// metadata piece than those compiled for the target, so make sure
// we throw in the unit's `kind` as well. Use `fingerprint_hash`
// so that the StableHash doesn't change based on the pathnames
// of the custom target JSON spec files.
unit.kind.fingerprint_hash().hash(&mut hasher);
// Finally throw in the target name/kind. This ensures that concurrent
// compiles of targets in the same crate don't collide.
unit.target.name().hash(&mut hasher);
unit.target.kind().hash(&mut hasher);
hash_rustc_version(bcx, &mut hasher);
if cx.bcx.ws.is_member(&unit.pkg) {
// This is primarily here for clippy. This ensures that the clippy
// artifacts are separate from the `check` ones.
if let Some(path) = &cx.bcx.rustc().workspace_wrapper {
path.hash(&mut hasher);
}
}
// Seed the contents of `__CARGO_DEFAULT_LIB_METADATA` to the hasher if present.
// This should be the release channel, to get a different hash for each channel.
if let Ok(ref channel) = cx.bcx.config.get_env("__CARGO_DEFAULT_LIB_METADATA") {
channel.hash(&mut hasher);
}
// std units need to be kept separate from user dependencies. std crates
// are differentiated in the Unit with `is_std` (for things like
// `-Zforce-unstable-if-unmarked`), so they are always built separately.
// This isn't strictly necessary for build dependencies which probably
// don't need unstable support. A future experiment might be to set
// `is_std` to false for build dependencies so that they can be shared
// with user dependencies.
unit.is_std.hash(&mut hasher);
MetaInfo {
meta_hash: Metadata(hasher.finish()),
use_extra_filename: should_use_metadata(bcx, unit),
}
}
/// Hash the version of rustc being used during the build process.
fn hash_rustc_version(bcx: &BuildContext<'_, '_>, hasher: &mut StableHasher) {
let vers = &bcx.rustc().version;
if vers.pre.is_empty() || bcx.config.cli_unstable().separate_nightlies {
// For stable, keep the artifacts separate. This helps if someone is
// testing multiple versions, to avoid recompiles.
bcx.rustc().verbose_version.hash(hasher);
return;
}
// On "nightly"/"beta"/"dev"/etc, keep each "channel" separate. Don't hash
// the date/git information, so that whenever someone updates "nightly",
// they won't have a bunch of stale artifacts in the target directory.
//
// This assumes that the first segment is the important bit ("nightly",
// "beta", "dev", etc.). Skip other parts like the `.3` in `-beta.3`.
vers.pre.split('.').next().hash(hasher);
// Keep "host" since some people switch hosts to implicitly change
// targets, (like gnu vs musl or gnu vs msvc). In the future, we may want
// to consider hashing `unit.kind.short_name()` instead.
bcx.rustc().host.hash(hasher);
// None of the other lines are important. Currently they are:
// binary: rustc <-- or "rustdoc"
// commit-hash: 38114ff16e7856f98b2b4be7ab4cd29b38bed59a
// commit-date: 2020-03-21
// host: x86_64-apple-darwin
// release: 1.44.0-nightly
// LLVM version: 9.0
//
// The backend version ("LLVM version") might become more relevant in
// the future when cranelift sees more use, and people want to switch
// between different backends without recompiling.
}
/// Returns whether or not this unit should use a metadata hash.
fn should_use_metadata(bcx: &BuildContext<'_, '_>, unit: &Unit) -> bool {
if unit.mode.is_doc_test() || unit.mode.is_doc() {
// Doc tests do not have metadata.
return false;
}
if unit.mode.is_any_test() || unit.mode.is_check() {
// These always use metadata.
return true;
}
// No metadata in these cases:
//
// - dylibs:
// - if any dylib names are encoded in executables, so they can't be renamed.
// - TODO: Maybe use `-install-name` on macOS or `-soname` on other UNIX systems
// to specify the dylib name to be used by the linker instead of the filename.
// - Windows MSVC executables: The path to the PDB is embedded in the
// executable, and we don't want the PDB path to include the hash in it.
// - wasm32-unknown-emscripten executables: When using emscripten, the path to the
// .wasm file is embedded in the .js file, so we don't want the hash in there.
//
// This is only done for local packages, as we don't expect to export
// dependencies.
//
// The __CARGO_DEFAULT_LIB_METADATA env var is used to override this to
// force metadata in the hash. This is only used for building libstd. For
// example, if libstd is placed in a common location, we don't want a file
// named /usr/lib/libstd.so which could conflict with other rustc
// installs. In addition it prevents accidentally loading a libstd of a
// different compiler at runtime.
// See https://github.com/rust-lang/cargo/issues/3005
let short_name = bcx.target_data.short_name(&unit.kind);
if (unit.target.is_dylib()
|| unit.target.is_cdylib()
|| (unit.target.is_executable() && short_name == "wasm32-unknown-emscripten")
|| (unit.target.is_executable() && short_name.contains("msvc")))
&& unit.pkg.package_id().source_id().is_path()
&& bcx.config.get_env("__CARGO_DEFAULT_LIB_METADATA").is_err()
{
return false;
}
true
}