Omit some arguments with paths from Rust hash calculation. Fixes cros…

…sbeam-rs#207

Some rustc arguments like --out-dir, -L, and --extern contain absolute paths
which make building the same crate (from crates.io) in different projects
unable to get cache hits despite being otherwise the same. This patch omits
those arguments from the hash calculation which makes sccache much more useful
for local development.

For additional safety we add the cwd to the hash key, since that winds up in
the rlib and otherwise this patch could result in some compiles returning invalid results from cache.

src/compiler/rust.rs

@@ -187,7 +187,7 @@ lazy_static! {
 }
 
 /// Version number for cache key.
-const CACHE_VERSION: &[u8] = b"2";
+const CACHE_VERSION: &[u8] = b"3";
 
 /// Get absolute paths for all source files listed in rustc's dep-info output.
 fn get_source_files<T>(creator: &T,
@@ -980,7 +980,18 @@ impl<T> CompilerHasher<T> for RustHasher
             // and append them to the rest of the arguments.
             let args = {
                 let (mut sortables, rest): (Vec<_>, Vec<_>) = os_string_arguments.iter()
-                    .partition(|&&(ref arg, _)| arg == "--extern" || arg == "-L" || arg == "--cfg");
+                // We exclude a few arguments from the hash:
+                //   -L, --extern, --out-dir
+                // These contain paths which aren't relevant to the output, and the compiler inputs
+                // in those paths (rlibs and static libs used in the compilation) are used as hash
+                // inputs below.
+                    .filter(|&&(ref arg, _)| {
+                        !(arg == "--extern" || arg == "-L" || arg == "--out-dir")
+                    })
+                // A few argument types were not passed in a deterministic order
+                // by older versions of cargo: --extern, -L, --cfg. We'll filter the rest of those
+                // out, sort them, and append them to the rest of the arguments.
+                    .partition(|&&(ref arg, _)| arg == "--cfg");
                 sortables.sort();
                 rest.into_iter()
                     .chain(sortables)
@@ -1020,6 +1031,8 @@ impl<T> CompilerHasher<T> for RustHasher
                     val.hash(&mut HashToDigest { digest: &mut m });
                 }
             }
+            // 8. The cwd of the compile. This will wind up in the rlib.
+            cwd.hash(&mut HashToDigest { digest: &mut m });
             // Turn arguments into a simple Vec<OsString> to calculate outputs.
             let flat_os_string_arguments: Vec<OsString> = os_string_arguments.into_iter()
                 .flat_map(|(arg, val)| iter::once(arg).into_iter().chain(val))
@@ -2019,12 +2032,12 @@ c:/foo/bar.rs:
             parsed_args: ParsedArguments {
                 arguments: vec![
                     Argument::Raw("a".into()),
-                    Argument::WithValue("--extern".into(),
-                                        ArgData::Extern(ArgExtern::process("xyz=/xyz".into()).unwrap()),
+                    Argument::WithValue("--cfg".into(),
+                                        ArgData::PassThrough("xyz".into()),
                                         ArgDisposition::Separated),
                     Argument::Raw("b".into()),
-                    Argument::WithValue("--extern".into(),
-                                        ArgData::Extern(ArgExtern::process("abc=/abc".into()).unwrap()),
+                    Argument::WithValue("--cfg".into(),
+                                        ArgData::PassThrough("abc".into()),
                                         ArgDisposition::Separated),
                 ],
                 output_dir: "foo/".into(),
@@ -2057,8 +2070,8 @@ c:/foo/bar.rs:
         m.update(CACHE_VERSION);
         // sysroot shlibs digests.
         m.update(FAKE_DIGEST.as_bytes());
-        // Arguments, with externs sorted at the end.
-        OsStr::new("ab--externabc=/abc--externxyz=/xyz").hash(&mut HashToDigest { digest: &mut m });
+        // Arguments, with cfgs sorted at the end.
+        OsStr::new("ab--cfgabc--cfgxyz").hash(&mut HashToDigest { digest: &mut m });
         // bar.rs (source file, from dep-info)
         m.update(empty_digest.as_bytes());
         // foo.rs (source file, from dep-info)
@@ -2074,18 +2087,18 @@ c:/foo/bar.rs:
         OsStr::new("CARGO_PKG_NAME").hash(&mut HashToDigest { digest: &mut m });
         m.update(b"=");
         OsStr::new("foo").hash(&mut HashToDigest { digest: &mut m });
+        f.tempdir.path().hash(&mut HashToDigest { digest: &mut m });
         let digest = m.finish();
         assert_eq!(res.key, digest);
         let mut out = res.compilation.outputs().map(|(k, _)| k.to_owned()).collect::<Vec<_>>();
         out.sort();
         assert_eq!(out, vec!["foo.a", "foo.rlib"]);
     }
 
-    fn hash_key<'a, F>(args: &[OsString], env_vars: &[(OsString, OsString)], pre_func: F)
-                   -> String
+    fn hash_key<'a, F>(f: &TestFixture, args: &[OsString], env_vars: &[(OsString, OsString)],
+                       pre_func: F) -> String
         where F: Fn(&Path) -> Result<()>
     {
-        let f = TestFixture::new();
         let parsed_args = match parse_arguments(args, &f.tempdir.path()) {
             CompilerArguments::Ok(parsed_args) => parsed_args,
             o @ _ => panic!("Got unexpected parse result: {:?}", o),
@@ -2130,33 +2143,49 @@ c:/foo/bar.rs:
             create_file(tempdir, "b.rlib", |mut f| f.write_all(b"this is b.rlib"))?;
             Ok(())
         }
-        assert_eq!(hash_key(&ovec!["--emit", "link", "foo.rs", "--extern", "a=a.rlib", "--out-dir",
+        let f = TestFixture::new();
+        assert_eq!(hash_key(&f, &ovec!["--emit", "link", "foo.rs", "--extern", "a=a.rlib", "--out-dir",
                                    "out", "--crate-name", "foo", "--crate-type", "lib",
                                    "--extern", "b=b.rlib"], &vec![],
                             &mk_files),
-                   hash_key(&ovec!["--extern", "b=b.rlib", "--emit", "link", "--extern", "a=a.rlib",
+                   hash_key(&f, &ovec!["--extern", "b=b.rlib", "--emit", "link", "--extern", "a=a.rlib",
                                    "foo.rs", "--out-dir", "out", "--crate-name", "foo",
                                    "--crate-type", "lib"], &vec![],
                             &mk_files));
     }
 
     #[test]
     fn test_equal_hashes_link_paths() {
-        assert_eq!(hash_key(&ovec!["--emit", "link", "-L", "x=x", "foo.rs", "--out-dir", "out",
+        let f = TestFixture::new();
+        assert_eq!(hash_key(&f, &ovec!["--emit", "link", "-L", "x=x", "foo.rs", "--out-dir", "out",
                                    "--crate-name", "foo", "--crate-type", "lib",
                                    "-L", "y=y"], &vec![], nothing),
-                   hash_key(&ovec!["-L", "y=y", "--emit", "link", "-L", "x=x", "foo.rs",
+                   hash_key(&f, &ovec!["-L", "y=y", "--emit", "link", "-L", "x=x", "foo.rs",
                                    "--out-dir", "out", "--crate-name", "foo",
                                    "--crate-type", "lib"], &vec![], nothing));
     }
 
+    #[test]
+    fn test_equal_hashes_ignored_args() {
+        let f = TestFixture::new();
+        assert_eq!(hash_key(&f, &ovec!["--emit", "link", "-L", "x=x", "foo.rs", "--out-dir", "out",
+                                   "--extern", "a=1", "--crate-name", "foo", "--crate-type", "lib",
+                                   "-L", "y=y"],
+                            &vec![], nothing),
+                   hash_key(&f, &ovec!["-L", "y=a", "--emit", "link", "-L", "x=b", "foo.rs",
+                                   "--extern", "a=2", "--out-dir", "out2", "--crate-name", "foo",
+                                   "--crate-type", "lib"],
+                            &vec![], nothing));
+    }
+
     #[test]
     fn test_equal_hashes_cfg_features() {
-        assert_eq!(hash_key(&ovec!["--emit", "link", "--cfg", "feature=a", "foo.rs", "--out-dir",
+        let f = TestFixture::new();
+        assert_eq!(hash_key(&f, &ovec!["--emit", "link", "--cfg", "feature=a", "foo.rs", "--out-dir",
                                    "out", "--crate-name", "foo", "--crate-type", "lib",
                                    "--cfg", "feature=b"], &vec![],
                             nothing),
-                   hash_key(&ovec!["--cfg", "feature=b", "--emit", "link", "--cfg", "feature=a",
+                   hash_key(&f, &ovec!["--cfg", "feature=b", "--emit", "link", "--cfg", "feature=a",
                                    "foo.rs", "--out-dir", "out", "--crate-name", "foo",
                                    "--crate-type", "lib"], &vec![],
                             nothing));