incr.comp.: Add test case for cache artifact file headers.

src/librustc_incremental/persist/file_format.rs

@@ -22,6 +22,9 @@
 use std::io::{self, Read};
 use std::path::Path;
 use std::fs::File;
+use std::env;
+
+use rustc::session::config::nightly_options;
 
 /// The first few bytes of files generated by incremental compilation
 const FILE_MAGIC: &'static [u8] = b"RSIC";
@@ -38,9 +41,11 @@ pub fn write_file_header<W: io::Write>(stream: &mut W) -> io::Result<()> {
     stream.write_all(FILE_MAGIC)?;
     stream.write_all(&[(HEADER_FORMAT_VERSION >> 0) as u8,
                        (HEADER_FORMAT_VERSION >> 8) as u8])?;
-    assert_eq!(RUSTC_VERSION.len(), (RUSTC_VERSION.len() as u8) as usize);
-    stream.write_all(&[RUSTC_VERSION.len() as u8])?;
-    stream.write_all(RUSTC_VERSION.as_bytes())?;
+
+    let rustc_version = rustc_version();
+    assert_eq!(rustc_version.len(), (rustc_version.len() as u8) as usize);
+    stream.write_all(&[rustc_version.len() as u8])?;
+    stream.write_all(rustc_version.as_bytes())?;
 
     Ok(())
 }
@@ -103,3 +108,13 @@ pub fn read_file(path: &Path) -> io::Result<Option<Vec<u8>>> {
 
     Ok(Some(data))
 }
+
+fn rustc_version() -> String {
+    if nightly_options::is_nightly_build() {
+        if let Some(val) = env::var_os("RUSTC_FORCE_INCR_COMP_ARTIFACT_HEADER") {
+            return val.to_string_lossy().into_owned()
+        }
+    }
+
+    RUSTC_VERSION.to_string()
+}

src/test/incremental/cache_file_headers.rs

@@ -0,0 +1,29 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// This test case makes sure that the compiler does not try to re-use anything
+// from the incremental compilation cache if the cache was produced by a
+// different compiler version. This is tested by artificially forcing the
+// emission of a different compiler version in the header of rpass1 artifacts,
+// and then making sure that the only object file of the test program gets
+// re-translated although the program stays unchanged.
+
+// The `l33t haxx0r` Rust compiler is known to produce incr. comp. artifacts
+// that are outrageously incompatible with just about anything, even itself:
+//[rpass1] rustc-env:RUSTC_FORCE_INCR_COMP_ARTIFACT_HEADER="l33t haxx0r rustc 2.1 LTS"
+
+// revisions:rpass1 rpass2
+
+#![feature(rustc_attrs)]
+#![rustc_partition_translated(module="cache_file_headers", cfg="rpass2")]
+
+fn main() {
+    // empty
+}