Improve error message for buildcaches (#37626)

2 files changed, 23 insertions, 6 deletions

diff --git a/lib/spack/spack/binary_distribution.py b/lib/spack/spack/binary_distribution.py
index ca69695f11..06ed2ff5a5 100644
--- a/lib/spack/spack/binary_distribution.py
+++ b/lib/spack/spack/binary_distribution.py
@@ -193,10 +193,17 @@ class BinaryCacheIndex(object):
             db_root_dir = os.path.join(tmpdir, "db_root")
             db = spack_db.Database(None, db_dir=db_root_dir, enable_transaction_locking=False)
 
-            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)
+            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 @@ class FetchIndexError(Exception):
             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")
 
 
diff --git a/lib/spack/spack/database.py b/lib/spack/spack/database.py
index 9fa041ea35..47cdb51774 100644
--- a/lib/spack/spack/database.py
+++ b/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"The expected database version is '{expected}', but '{found}' was found."
+            f"you need a newer Spack version to read the DB in '{database.root}'. "
+            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."