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};
18 use rustc_serialize::Encoder;
20 /// The first few bytes of files generated by incremental compilation.
21 const FILE_MAGIC: &[u8] = b"RSIC";
23 /// Change this if the header format changes.
24 const HEADER_FORMAT_VERSION: u16 = 0;
26 /// A version string that hopefully is always different for compiler versions
27 /// with different encodings of incremental compilation artifacts. Contains
28 /// the Git commit hash.
29 const RUSTC_VERSION: Option<&str> = option_env!("CFG_VERSION");
31 pub fn write_file_header(stream: &mut FileEncoder, nightly_build: bool) -> FileEncodeResult {
32 stream.emit_raw_bytes(FILE_MAGIC)?;
33 stream.emit_raw_bytes(&[
34 (HEADER_FORMAT_VERSION >> 0) as u8,
35 (HEADER_FORMAT_VERSION >> 8) as u8,
38 let rustc_version = rustc_version(nightly_build);
39 assert_eq!(rustc_version.len(), (rustc_version.len() as u8) as usize);
40 stream.emit_raw_bytes(&[rustc_version.len() as u8])?;
41 stream.emit_raw_bytes(rustc_version.as_bytes())
44 /// Reads the contents of a file with a file header as defined in this module.
46 /// - Returns `Ok(Some(data, pos))` if the file existed and was generated by a
47 /// compatible compiler version. `data` is the entire contents of the file
48 /// and `pos` points to the first byte after the header.
49 /// - Returns `Ok(None)` if the file did not exist or was generated by an
50 /// incompatible version of the compiler.
51 /// - Returns `Err(..)` if some kind of IO error occurred while reading the
54 report_incremental_info: bool,
57 ) -> io::Result<Option<(Vec<u8>, usize)>> {
58 let data = match fs::read(path) {
60 Err(err) if err.kind() == io::ErrorKind::NotFound => return Ok(None),
61 Err(err) => return Err(err),
64 let mut file = io::Cursor::new(data);
68 debug_assert!(FILE_MAGIC.len() == 4);
69 let mut file_magic = [0u8; 4];
70 file.read_exact(&mut file_magic)?;
71 if file_magic != FILE_MAGIC {
72 report_format_mismatch(report_incremental_info, path, "Wrong FILE_MAGIC");
77 // Check HEADER_FORMAT_VERSION
79 debug_assert!(::std::mem::size_of_val(&HEADER_FORMAT_VERSION) == 2);
80 let mut header_format_version = [0u8; 2];
81 file.read_exact(&mut header_format_version)?;
82 let header_format_version =
83 (header_format_version[0] as u16) | ((header_format_version[1] as u16) << 8);
85 if header_format_version != HEADER_FORMAT_VERSION {
86 report_format_mismatch(report_incremental_info, path, "Wrong HEADER_FORMAT_VERSION");
91 // Check RUSTC_VERSION
93 let mut rustc_version_str_len = [0u8; 1];
94 file.read_exact(&mut rustc_version_str_len)?;
95 let rustc_version_str_len = rustc_version_str_len[0] as usize;
96 let mut buffer = vec![0; rustc_version_str_len];
97 file.read_exact(&mut buffer)?;
99 if buffer != rustc_version(nightly_build).as_bytes() {
100 report_format_mismatch(report_incremental_info, path, "Different compiler version");
105 let post_header_start_pos = file.position() as usize;
106 Ok(Some((file.into_inner(), post_header_start_pos)))
109 fn report_format_mismatch(report_incremental_info: bool, file: &Path, message: &str) {
110 debug!("read_file: {}", message);
112 if report_incremental_info {
114 "[incremental] ignoring cache artifact `{}`: {}",
115 file.file_name().unwrap().to_string_lossy(),
121 fn rustc_version(nightly_build: bool) -> String {
123 if let Some(val) = env::var_os("RUSTC_FORCE_INCR_COMP_ARTIFACT_HEADER") {
124 return val.to_string_lossy().into_owned();
130 "Cannot use rustc without explicit version for \
131 incremental compilation",