Prevent potential bug resulting from changing crate_hash query name

Author: tgnottingham

Diff for: compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -47,7 +47,8 @@ macro_rules! provide {
                 // External query providers call `crate_hash` in order to register a dependency
                 // on the crate metadata. The exception is `crate_hash` itself, which obviously
                 // doesn't need to do this (and can't, as it would cause a query cycle).
-                if stringify!($name) != "crate_hash" && $tcx.dep_graph.is_fully_enabled() {
+                use rustc_middle::dep_graph::DepKind;
+                if DepKind::$name != DepKind::crate_hash && $tcx.dep_graph.is_fully_enabled() {
                     $tcx.ensure().crate_hash($def_id.krate);
                 }
 

Diff for: compiler/rustc_middle/src/query/mod.rs

@@ -1220,6 +1220,8 @@ rustc_queries! {
             eval_always
             desc { "looking up the disambiguator a crate" }
         }
+        // The macro which defines `rustc_metadata::provide_extern` depends on this query's name.
+        // Changing the name should cause a compiler error, but in case that changes, be aware.
         query crate_hash(_: CrateNum) -> Svh {
             eval_always
             desc { "looking up the hash a crate" }