bugfix: tests trying to ignore package changes should use build_hash

- [x] update test to use `build_hash` instead of `dag_hash`, as we're testing for
      graph structure, and specifically NOT testing for package changes.
- [x] make hash descriptors callable on specs to simplify syntax for invoking them
- [x] make `Spec.spec_hash()` public

lib/spack/spack/hash_types.py

@@ -33,6 +33,10 @@ def attr(self):
         """Private attribute stored on spec"""
         return '_' + self.name
 
+    def __call__(self, spec):
+        """Run this hash on the provided spec."""
+        return spec.spec_hash(self)
+
 
 #: Spack's deployment hash. Includes all inputs that can affect how a package is built.
 dag_hash = SpecHashDescriptor(

lib/spack/spack/spec.py

@@ -1754,7 +1754,7 @@ def prefix(self):
     def prefix(self, value):
         self._prefix = spack.util.prefix.Prefix(pth.convert_to_platform_path(value))
 
-    def _spec_hash(self, hash):
+    def spec_hash(self, hash):
         """Utility method for computing different types of Spec hashes.
 
         Arguments:
@@ -1771,7 +1771,7 @@ def _spec_hash(self, hash):
     def _cached_hash(self, hash, length=None):
         """Helper function for storing a cached hash on the spec.
 
-        This will run _spec_hash() with the deptype and package_hash
+        This will run spec_hash() with the deptype and package_hash
         parameters, and if this spec is concrete, it will store the value
         in the supplied attribute on this spec.
 
@@ -1779,13 +1779,13 @@ def _cached_hash(self, hash, length=None):
             hash (spack.hash_types.SpecHashDescriptor): type of hash to generate.
         """
         if not hash.attr:
-            return self._spec_hash(hash)[:length]
+            return self.spec_hash(hash)[:length]
 
         hash_string = getattr(self, hash.attr, None)
         if hash_string:
             return hash_string[:length]
         else:
-            hash_string = self._spec_hash(hash)
+            hash_string = self.spec_hash(hash)
             if self.concrete:
                 setattr(self, hash.attr, hash_string)
 

lib/spack/spack/test/concretize.py

@@ -16,6 +16,7 @@
 import spack.compilers
 import spack.concretize
 import spack.error
+import spack.hash_types as ht
 import spack.platforms
 import spack.repo
 import spack.variant as vt
@@ -1287,7 +1288,12 @@ def test_reuse_installed_packages_when_package_def_changes(
 
         new_root_without_reuse = Spec('root').concretized()
 
-        assert root.dag_hash() == new_root_with_reuse.dag_hash()
+        # validate that the graphs are the same with reuse, but not without
+        assert ht.build_hash(root) == ht.build_hash(new_root_with_reuse)
+        assert ht.build_hash(root) != ht.build_hash(new_root_without_reuse)
+
+        # package hashes are different, so dag hashes will be different
+        assert root.dag_hash() != new_root_with_reuse.dag_hash()
         assert root.dag_hash() != new_root_without_reuse.dag_hash()
 
     @pytest.mark.regression('20784')