rustc_metadata: don't let LLVM confuse rmeta blobs for COFF object files.

src/librustc_codegen_ssa/lib.rs

@@ -59,7 +59,8 @@ pub struct ModuleCodegen<M> {
     pub kind: ModuleKind,
 }
 
-pub const METADATA_FILENAME: &str = "rust.metadata.bin";
+// FIXME(eddyb) maybe include the crate name in this?
+pub const METADATA_FILENAME: &str = "lib.rmeta";
 pub const RLIB_BYTECODE_EXTENSION: &str = "bc.z";
 
 

src/librustc_metadata/rmeta/mod.rs

@@ -37,18 +37,15 @@
 /// Metadata encoding version.
 /// N.B., increment this if you change the format of metadata such that
 /// the rustc version can't be found to compare with `rustc_version()`.
-const METADATA_VERSION: u8 = 4;
+const METADATA_VERSION: u8 = 5;
 
 /// Metadata header which includes `METADATA_VERSION`.
-/// To get older versions of rustc to ignore this metadata,
-/// there are 4 zero bytes at the start, which are treated
-/// as a length of 0 by old compilers.
 ///
 /// This header is followed by the position of the `CrateRoot`,
 /// which is encoded as a 32-bit big-endian unsigned integer,
 /// and further followed by the rustc version string.
-crate const METADATA_HEADER: &[u8; 12] =
-    &[0, 0, 0, 0, b'r', b'u', b's', b't', 0, 0, 0, METADATA_VERSION];
+crate const METADATA_HEADER: &[u8; 8] =
+    &[b'r', b'u', b's', b't', 0, 0, 0, METADATA_VERSION];
 
 /// Additional metadata for a `Lazy<T>` where `T` may not be `Sized`,
 /// e.g. for `Lazy<[T]>`, this is the length (count of `T` values).

src/test/run-make-fulldeps/invalid-library/Makefile

@@ -1,6 +1,6 @@
 -include ../tools.mk
 
 all:
-	touch $(TMPDIR)/rust.metadata.bin
-	$(AR) crus $(TMPDIR)/libfoo-ffffffff-1.0.rlib $(TMPDIR)/rust.metadata.bin
+	touch $(TMPDIR)/lib.rmeta
+	$(AR) crus $(TMPDIR)/libfoo-ffffffff-1.0.rlib $(TMPDIR)/lib.rmeta
 	$(RUSTC) foo.rs 2>&1 | $(CGREP) "can't find crate for"