Improve error message for buildcaches (#37626)

lib/spack/spack/binary_distribution.py

@@ -193,10 +193,17 @@ def _associate_built_specs_with_mirror(self, cache_key, mirror_url):
             db_root_dir = os.path.join(tmpdir, "db_root")
             db = spack_db.Database(None, db_dir=db_root_dir, enable_transaction_locking=False)
 
+            try:
                 self._index_file_cache.init_entry(cache_key)
                 cache_path = self._index_file_cache.cache_path(cache_key)
                 with self._index_file_cache.read_transaction(cache_key):
                     db._read_from_file(cache_path)
+            except spack_db.InvalidDatabaseVersionError as e:
+                msg = (
+                    f"you need a newer Spack version to read the buildcache index for the "
+                    f"following mirror: '{mirror_url}'. {e.database_version_message}"
+                )
+                raise BuildcacheIndexError(msg) from e
 
             spec_list = db.query_local(installed=False, in_buildcache=True)
 
@@ -2429,6 +2436,10 @@ def __str__(self):
             return "{}, due to: {}".format(self.args[0], self.args[1])
 
 
+class BuildcacheIndexError(spack.error.SpackError):
+    """Raised when a buildcache cannot be read for any reason"""
+
+
 FetchIndexResult = collections.namedtuple("FetchIndexResult", "etag hash data fresh")
 
 

lib/spack/spack/database.py

@@ -1654,8 +1654,14 @@ class InvalidDatabaseVersionError(SpackError):
     """Exception raised when the database metadata is newer than current Spack."""
 
     def __init__(self, database, expected, found):
+        self.expected = expected
+        self.found = found
         msg = (
-            f"you need a newer Spack version to read the database in '{database.root}'. "
+            f"you need a newer Spack version to read the DB in '{database.root}'. "
-            f"The expected database version is '{expected}', but '{found}' was found."
+            f"{self.database_version_message}"
         )
         super(InvalidDatabaseVersionError, self).__init__(msg)
+
+    @property
+    def database_version_message(self):
+        return f"The expected DB version is '{self.expected}', but '{self.found}' was found."