Add INVALID_CRATE CrateNum constant.

Author: michaelwoerister

src/librustc/hir/def_id.rs

@@ -36,7 +36,10 @@ pub const LOCAL_CRATE: CrateNum = CrateNum(0);
 
 /// Virtual crate for builtin macros
 // FIXME(jseyfried): this is also used for custom derives until proc-macro crates get `CrateNum`s.
-pub const BUILTIN_MACROS_CRATE: CrateNum = CrateNum(!0);
+pub const BUILTIN_MACROS_CRATE: CrateNum = CrateNum(u32::MAX);
+
+/// A CrateNum value that indicates that something is wrong.
+pub const INVALID_CRATE: CrateNum = CrateNum(u32::MAX - 1);
 
 impl CrateNum {
     pub fn new(x: usize) -> CrateNum {

src/libsyntax_pos/lib.rs

@@ -494,7 +494,9 @@ impl Decodable for FileMap {
                 name: name,
                 name_was_remapped: name_was_remapped,
                 // `crate_of_origin` has to be set by the importer.
-                crate_of_origin: 0xEFFF_FFFF,
+                // This value matches up with rustc::hir::def_id::INVALID_CRATE.
+                // That constant is not available here unfortunately :(
+                crate_of_origin: ::std::u32::MAX - 1,
                 start_pos: start_pos,
                 end_pos: end_pos,
                 src: None,