store the rustc version in metadata and check it

This prevents ICEs when old crates are used with a new version of
rustc. Currently, the linking of crates compiled with different
versions of rustc is completely unsupported.

Fixes rust-lang#28700

Author: Ariel Ben-Yehuda

src/librustc/diagnostics.rs

@@ -2074,4 +2074,5 @@ register_diagnostics! {
     E0495, // cannot infer an appropriate lifetime due to conflicting requirements
     E0496, // .. name `..` shadows a .. name that is already in scope
     E0498, // malformed plugin attribute
+    E0514, // metadata version mismatch
 }

src/librustc/metadata/common.rs

@@ -259,3 +259,11 @@ pub const tag_defaulted_trait: usize = 0xa4;
 pub const tag_impl_coerce_unsized_kind: usize = 0xa5;
 
 pub const tag_items_data_item_constness: usize = 0xa6;
+
+pub const tag_rustc_version: usize = 0x10f;
+pub fn rustc_version() -> String {
+    format!(
+        "rustc {}",
+        option_env!("CFG_VERSION").unwrap_or("unknown version")
+    )
+}

src/librustc/metadata/creader.rs

@@ -15,6 +15,7 @@
 use back::svh::Svh;
 use session::{config, Session};
 use session::search_paths::PathKind;
+use metadata::common::rustc_version;
 use metadata::cstore;
 use metadata::cstore::{CStore, CrateSource, MetadataBlob};
 use metadata::decoder;
@@ -270,6 +271,24 @@ impl<'a> CrateReader<'a> {
         return ret;
     }
 
+    fn verify_rustc_version(&self,
+                            name: &str,
+                            span: Span,
+                            metadata: &MetadataBlob) {
+        let crate_rustc_version = decoder::crate_rustc_version(metadata.as_slice());
+        if crate_rustc_version != Some(rustc_version()) {
+            span_err!(self.sess, span, E0514,
+                      "the crate `{}` has been compiled with {}, which is \
+                       incompatible with this version of rustc",
+                      name,
+                      crate_rustc_version
+                          .as_ref().map(|s|&**s)
+                          .unwrap_or("an old version of rustc")
+            );
+            self.sess.abort_if_errors();
+        }
+    }
+
     fn register_crate(&mut self,
                       root: &Option<CratePaths>,
                       ident: &str,
@@ -279,6 +298,8 @@ impl<'a> CrateReader<'a> {
                       explicitly_linked: bool)
                       -> (ast::CrateNum, Rc<cstore::crate_metadata>,
                           cstore::CrateSource) {
+        self.verify_rustc_version(name, span, &lib.metadata);
+
         // Claim this crate number and cache it
         let cnum = self.next_crate_num;
         self.next_crate_num += 1;

src/librustc/metadata/decoder.rs

@@ -77,6 +77,11 @@ pub fn load_index(data: &[u8]) -> index::Index {
     index::Index::from_buf(index.data, index.start, index.end)
 }
 
+pub fn crate_rustc_version(data: &[u8]) -> Option<String> {
+    let doc = rbml::Doc::new(data);
+    reader::maybe_get_doc(doc, tag_rustc_version).map(|s| s.as_str())
+}
+
 #[derive(Debug, PartialEq)]
 enum Family {
     ImmStatic,             // c

src/librustc/metadata/encoder.rs

@@ -1923,6 +1923,10 @@ fn encode_hash(rbml_w: &mut Encoder, hash: &Svh) {
     rbml_w.wr_tagged_str(tag_crate_hash, hash.as_str());
 }
 
+fn encode_rustc_version(rbml_w: &mut Encoder) {
+    rbml_w.wr_tagged_str(tag_rustc_version, &rustc_version());
+}
+
 fn encode_crate_name(rbml_w: &mut Encoder, crate_name: &str) {
     rbml_w.wr_tagged_str(tag_crate_crate_name, crate_name);
 }
@@ -2051,6 +2055,7 @@ fn encode_metadata_inner(wr: &mut Cursor<Vec<u8>>,
 
     let mut rbml_w = Encoder::new(wr);
 
+    encode_rustc_version(&mut rbml_w);
     encode_crate_name(&mut rbml_w, &ecx.link_meta.crate_name);
     encode_crate_triple(&mut rbml_w, &tcx.sess.opts.target_triple);
     encode_hash(&mut rbml_w, &ecx.link_meta.crate_hash);