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use crate::errors::{
FailedCreateEncodedMetadata, FailedCreateFile, FailedCreateTempdir, FailedWriteError,
};
use crate::{encode_metadata, EncodedMetadata};
use rustc_data_structures::temp_dir::MaybeTempDir;
use rustc_hir::def_id::LOCAL_CRATE;
use rustc_middle::ty::TyCtxt;
use rustc_session::config::OutputType;
use rustc_session::output::filename_for_metadata;
use rustc_session::{MetadataKind, Session};
use tempfile::Builder as TempFileBuilder;
use std::fs;
use std::path::{Path, PathBuf};
// FIXME(eddyb) maybe include the crate name in this?
pub const METADATA_FILENAME: &str = "lib.rmeta";
/// We use a temp directory here to avoid races between concurrent rustc processes,
/// such as builds in the same directory using the same filename for metadata while
/// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
/// directory being searched for `extern crate` (observing an incomplete file).
/// The returned path is the temporary file containing the complete metadata.
pub fn emit_wrapper_file(
sess: &Session,
data: &[u8],
tmpdir: &MaybeTempDir,
name: &str,
) -> PathBuf {
let out_filename = tmpdir.as_ref().join(name);
let result = fs::write(&out_filename, data);
if let Err(err) = result {
sess.emit_fatal(FailedWriteError { filename: out_filename, err });
}
out_filename
}
pub fn encode_and_write_metadata(tcx: TyCtxt<'_>) -> (EncodedMetadata, bool) {
let crate_name = tcx.crate_name(LOCAL_CRATE);
let out_filename = filename_for_metadata(tcx.sess, crate_name, tcx.output_filenames(()));
// To avoid races with another rustc process scanning the output directory,
// we need to write the file somewhere else and atomically move it to its
// final destination, with an `fs::rename` call. In order for the rename to
// always succeed, the temporary file needs to be on the same filesystem,
// which is why we create it inside the output directory specifically.
let metadata_tmpdir = TempFileBuilder::new()
.prefix("rmeta")
.tempdir_in(out_filename.parent().unwrap_or_else(|| Path::new("")))
.unwrap_or_else(|err| tcx.sess.emit_fatal(FailedCreateTempdir { err }));
let metadata_tmpdir = MaybeTempDir::new(metadata_tmpdir, tcx.sess.opts.cg.save_temps);
let metadata_filename = metadata_tmpdir.as_ref().join(METADATA_FILENAME);
// Always create a file at `metadata_filename`, even if we have nothing to write to it.
// This simplifies the creation of the output `out_filename` when requested.
let metadata_kind = tcx.sess.metadata_kind();
match metadata_kind {
MetadataKind::None => {
std::fs::File::create(&metadata_filename).unwrap_or_else(|err| {
tcx.sess.emit_fatal(FailedCreateFile { filename: &metadata_filename, err });
});
}
MetadataKind::Uncompressed | MetadataKind::Compressed => {
encode_metadata(tcx, &metadata_filename);
}
};
let _prof_timer = tcx.sess.prof.generic_activity("write_crate_metadata");
// If the user requests metadata as output, rename `metadata_filename`
// to the expected output `out_filename`. The match above should ensure
// this file always exists.
let need_metadata_file = tcx.sess.opts.output_types.contains_key(&OutputType::Metadata);
let (metadata_filename, metadata_tmpdir) = if need_metadata_file {
if let Err(err) = non_durable_rename(&metadata_filename, &out_filename) {
tcx.sess.emit_fatal(FailedWriteError { filename: out_filename, err });
}
if tcx.sess.opts.json_artifact_notifications {
tcx.sess
.parse_sess
.span_diagnostic
.emit_artifact_notification(&out_filename, "metadata");
}
(out_filename, None)
} else {
(metadata_filename, Some(metadata_tmpdir))
};
// Load metadata back to memory: codegen may need to include it in object files.
let metadata =
EncodedMetadata::from_path(metadata_filename, metadata_tmpdir).unwrap_or_else(|err| {
tcx.sess.emit_fatal(FailedCreateEncodedMetadata { err });
});
let need_metadata_module = metadata_kind == MetadataKind::Compressed;
(metadata, need_metadata_module)
}
#[cfg(not(target_os = "linux"))]
pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> {
std::fs::rename(src, dst)
}
/// This function attempts to bypass the auto_da_alloc heuristic implemented by some filesystems
/// such as btrfs and ext4. When renaming over a file that already exists then they will "helpfully"
/// write back the source file before committing the rename in case a developer forgot some of
/// the fsyncs in the open/write/fsync(file)/rename/fsync(dir) dance for atomic file updates.
///
/// To avoid triggering this heuristic we delete the destination first, if it exists.
/// The cost of an extra syscall is much lower than getting descheduled for the sync IO.
#[cfg(target_os = "linux")]
pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> {
let _ = std::fs::remove_file(dst);
std::fs::rename(src, dst)
}
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