1 //! This module defines a generic file format that allows to check if a given
2 //! file generated by incremental compilation was generated by a compatible
3 //! compiler version. This file format is used for the on-disk version of the
4 //! dependency graph and the exported metadata hashes.
6 //! In practice "compatible compiler version" means "exactly the same compiler
7 //! version", since the header encodes the git commit hash of the compiler.
8 //! Since we can always just ignore the incremental compilation cache and
9 //! compiler versions don't change frequently for the typical user, being
10 //! conservative here practically has no downside.
14 use std::io::{self, Read};
17 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
19 /// The first few bytes of files generated by incremental compilation.
20 const FILE_MAGIC: &[u8] = b"RSIC";
22 /// Change this if the header format changes.
23 const HEADER_FORMAT_VERSION: u16 = 0;
25 /// A version string that hopefully is always different for compiler versions
26 /// with different encodings of incremental compilation artifacts. Contains
27 /// the Git commit hash.
28 const RUSTC_VERSION: Option<&str> = option_env!("CFG_VERSION");
30 pub fn write_file_header(stream: &mut FileEncoder, nightly_build: bool) -> FileEncodeResult {
31 stream.emit_raw_bytes(FILE_MAGIC)?;
32 stream.emit_raw_bytes(&[
33 (HEADER_FORMAT_VERSION >> 0) as u8,
34 (HEADER_FORMAT_VERSION >> 8) as u8,
37 let rustc_version = rustc_version(nightly_build);
38 assert_eq!(rustc_version.len(), (rustc_version.len() as u8) as usize);
39 stream.emit_raw_bytes(&[rustc_version.len() as u8])?;
40 stream.emit_raw_bytes(rustc_version.as_bytes())
43 /// Reads the contents of a file with a file header as defined in this module.
45 /// - Returns `Ok(Some(data, pos))` if the file existed and was generated by a
46 /// compatible compiler version. `data` is the entire contents of the file
47 /// and `pos` points to the first byte after the header.
48 /// - Returns `Ok(None)` if the file did not exist or was generated by an
49 /// incompatible version of the compiler.
50 /// - Returns `Err(..)` if some kind of IO error occurred while reading the
53 report_incremental_info: bool,
56 ) -> io::Result<Option<(Vec<u8>, usize)>> {
57 let data = match fs::read(path) {
59 Err(err) if err.kind() == io::ErrorKind::NotFound => return Ok(None),
60 Err(err) => return Err(err),
63 let mut file = io::Cursor::new(data);
67 debug_assert!(FILE_MAGIC.len() == 4);
68 let mut file_magic = [0u8; 4];
69 file.read_exact(&mut file_magic)?;
70 if file_magic != FILE_MAGIC {
71 report_format_mismatch(report_incremental_info, path, "Wrong FILE_MAGIC");
76 // Check HEADER_FORMAT_VERSION
78 debug_assert!(::std::mem::size_of_val(&HEADER_FORMAT_VERSION) == 2);
79 let mut header_format_version = [0u8; 2];
80 file.read_exact(&mut header_format_version)?;
81 let header_format_version =
82 (header_format_version[0] as u16) | ((header_format_version[1] as u16) << 8);
84 if header_format_version != HEADER_FORMAT_VERSION {
85 report_format_mismatch(report_incremental_info, path, "Wrong HEADER_FORMAT_VERSION");
90 // Check RUSTC_VERSION
92 let mut rustc_version_str_len = [0u8; 1];
93 file.read_exact(&mut rustc_version_str_len)?;
94 let rustc_version_str_len = rustc_version_str_len[0] as usize;
95 let mut buffer = vec![0; rustc_version_str_len];
96 file.read_exact(&mut buffer)?;
98 if buffer != rustc_version(nightly_build).as_bytes() {
99 report_format_mismatch(report_incremental_info, path, "Different compiler version");
104 let post_header_start_pos = file.position() as usize;
105 Ok(Some((file.into_inner(), post_header_start_pos)))
108 fn report_format_mismatch(report_incremental_info: bool, file: &Path, message: &str) {
109 debug!("read_file: {}", message);
111 if report_incremental_info {
113 "[incremental] ignoring cache artifact `{}`: {}",
114 file.file_name().unwrap().to_string_lossy(),
120 fn rustc_version(nightly_build: bool) -> String {
122 if let Some(val) = env::var_os("RUSTC_FORCE_INCR_COMP_ARTIFACT_HEADER") {
123 return val.to_string_lossy().into_owned();
129 "Cannot use rustc without explicit version for \
130 incremental compilation",