rustc_metadata: Privatize `CrateMetadata::extern_crate`

src/librustc/middle/cstore.rs

@@ -146,6 +146,13 @@ impl ExternCrate {
     pub fn is_direct(&self) -> bool {
         self.dependency_of == LOCAL_CRATE
     }
+
+    pub fn rank(&self) -> impl PartialOrd {
+        // Prefer:
+        // - direct extern crate to indirect
+        // - shorter paths to longer
+        (self.is_direct(), !self.path_len)
+    }
 }
 
 #[derive(Copy, Clone, Debug, HashStable)]

src/librustc_metadata/creader.rs

@@ -400,36 +400,12 @@ fn update_extern_crate(&self,
         if !visited.insert((cnum, extern_crate.is_direct())) { return }
 
         let cmeta = self.cstore.get_crate_data(cnum);
-        let mut old_extern_crate = cmeta.extern_crate.borrow_mut();
-
-        // Prefer:
-        // - something over nothing (tuple.0);
-        // - direct extern crate to indirect (tuple.1);
-        // - shorter paths to longer (tuple.2).
-        let new_rank = (
-            true,
-            extern_crate.is_direct(),
-            cmp::Reverse(extern_crate.path_len),
-        );
-        let old_rank = match *old_extern_crate {
-            None => (false, false, cmp::Reverse(usize::max_value())),
-            Some(ref c) => (
-                true,
-                c.is_direct(),
-                cmp::Reverse(c.path_len),
-            ),
-        };
-        if old_rank >= new_rank {
-            return; // no change needed
-        }
-
-        *old_extern_crate = Some(extern_crate);
-        drop(old_extern_crate);
-
-        // Propagate the extern crate info to dependencies.
-        extern_crate.dependency_of = cnum;
-        for &dep_cnum in cmeta.dependencies().iter() {
-            self.update_extern_crate(dep_cnum, extern_crate, visited);
+        if cmeta.update_extern_crate(extern_crate) {
+            // Propagate the extern crate info to dependencies.
+            extern_crate.dependency_of = cnum;
+            for &dep_cnum in cmeta.dependencies().iter() {
+                self.update_extern_crate(dep_cnum, extern_crate, visited);
+            }
         }
     }
 

src/librustc_metadata/rmeta/decoder.rs

@@ -112,7 +112,7 @@
 
     /// Information about the `extern crate` item or path that caused this crate to be loaded.
     /// If this is `None`, then the crate was injected (e.g., by the allocator).
-    crate extern_crate: Lock<Option<ExternCrate>>,
+    extern_crate: Lock<Option<ExternCrate>>,
 }
 
 /// Holds information about a syntax_pos::SourceFile imported from another crate.
@@ -1525,6 +1525,15 @@ fn get_crate_dep_node_index(&self, tcx: TyCtxt<'tcx>) -> DepNodeIndex {
     crate fn add_dependency(&self, cnum: CrateNum) {
         self.dependencies.borrow_mut().push(cnum);
     }
+
+    crate fn update_extern_crate(&self, new_extern_crate: ExternCrate) -> bool {
+        let mut extern_crate = self.extern_crate.borrow_mut();
+        let update = Some(new_extern_crate.rank()) > extern_crate.as_ref().map(ExternCrate::rank);
+        if update {
+            *extern_crate = Some(new_extern_crate);
+        }
+        update
+    }
 }
 
 // Cannot be implemented on 'ProcMacro', as libproc_macro