compiler/rustc_incremental/src/persist/file_format.rs

   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.
   5 //!
   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.
  11
  12 use std::env;
  13 use std::fs;
  14 use std::io::{self, Read};
  15 use std::path::Path;
  16
  17 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
  18
  19 /// The first few bytes of files generated by incremental compilation.
  20 const FILE_MAGIC: &[u8] = b"RSIC";
  21
  22 /// Change this if the header format changes.
  23 const HEADER_FORMAT_VERSION: u16 = 0;
  24
  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");
  29
  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,
  35     ])?;
  36
  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())
  41 }
  42
  43 /// Reads the contents of a file with a file header as defined in this module.
  44 ///
  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
  51 ///   file.
  52 pub fn read_file(
  53     report_incremental_info: bool,
  54     path: &Path,
  55     nightly_build: bool,
  56 ) -> io::Result<Option<(Vec<u8>, usize)>> {
  57     let data = match fs::read(path) {
  58         Ok(data) => data,
  59         Err(err) if err.kind() == io::ErrorKind::NotFound => return Ok(None),
  60         Err(err) => return Err(err),
  61     };
  62
  63     let mut file = io::Cursor::new(data);
  64
  65     // Check FILE_MAGIC
  66     {
  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");
  72             return Ok(None);
  73         }
  74     }
  75
  76     // Check HEADER_FORMAT_VERSION
  77     {
  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);
  83
  84         if header_format_version != HEADER_FORMAT_VERSION {
  85             report_format_mismatch(report_incremental_info, path, "Wrong HEADER_FORMAT_VERSION");
  86             return Ok(None);
  87         }
  88     }
  89
  90     // Check RUSTC_VERSION
  91     {
  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)?;
  97
  98         if buffer != rustc_version(nightly_build).as_bytes() {
  99             report_format_mismatch(report_incremental_info, path, "Different compiler version");
 100             return Ok(None);
 101         }
 102     }
 103
 104     let post_header_start_pos = file.position() as usize;
 105     Ok(Some((file.into_inner(), post_header_start_pos)))
 106 }
 107
 108 fn report_format_mismatch(report_incremental_info: bool, file: &Path, message: &str) {
 109     debug!("read_file: {}", message);
 110
 111     if report_incremental_info {
 112         eprintln!(
 113             "[incremental] ignoring cache artifact `{}`: {}",
 114             file.file_name().unwrap().to_string_lossy(),
 115             message
 116         );
 117     }
 118 }
 119
 120 fn rustc_version(nightly_build: bool) -> String {
 121     if nightly_build {
 122         if let Some(val) = env::var_os("RUSTC_FORCE_INCR_COMP_ARTIFACT_HEADER") {
 123             return val.to_string_lossy().into_owned();
 124         }
 125     }
 126
 127     RUSTC_VERSION
 128         .expect(
 129             "Cannot use rustc without explicit version for \
 130                           incremental compilation",
 131         )
 132         .to_string()
 133 }