Check dep name to detect it is core

Author: edwin0cheng

crates/ra_hir_expand/src/builtin_derive.rs

@@ -169,11 +169,13 @@ fn find_builtin_crate(db: &dyn AstDatabase, id: LazyMacroId) -> tt::TokenTree {
         }
     };
 
-    // Check whether it has any deps, if not, it should be core:
-    let tt = if cg[*krate].dependencies.is_empty() {
-        quote! { crate }
-    } else {
+    // XXX
+    //  All crates except core itself should have a dependency on core,
+    //  We detect `core` by seeing whether it doesn't have such a dependency.
+    let tt = if cg[*krate].dependencies.iter().any(|dep| dep.name == "core") {
         quote! { core }
+    } else {
+        quote! { crate }
     };
 
     tt.token_trees[0].clone()