_yaml.py::node_get(): Only construct path on errorkinnison/cleanups

We don't need to spend the CPU constructing path except when there is
an error which needs it, so don't.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

1 files changed, 6 insertions, 2 deletions

diff --git a/buildstream/_yaml.py b/buildstream/_yaml.py
index 519d91b34..5184485de 100644
--- a/buildstream/_yaml.py
+++ b/buildstream/_yaml.py
@@ -452,7 +452,6 @@ _sentinel = object()
 def node_get(node, expected_type, key, indices=None, *, default_value=_sentinel, allow_none=False):
     assert type(node) is Node
 
-    path = key
     if indices is None:
         if default_value is _sentinel:
             value = node[0].get(key, Node(default_value, None, 0, 0))
@@ -471,7 +470,6 @@ def node_get(node, expected_type, key, indices=None, *, default_value=_sentinel,
             value = value[0][index]
             if type(value) is not Node:
                 value = (value,)
-            path += '[{:d}]'.format(index)
 
     # Optionally allow None as a valid value for any type
     if value[0] is None and (allow_none or default_value is None):
@@ -499,6 +497,12 @@ def node_get(node, expected_type, key, indices=None, *, default_value=_sentinel,
                 raise ValueError()
         except (ValueError, TypeError):
             provenance = node_get_provenance(node, key=key, indices=indices)
+            if indices:
+                path = [key]
+                path.extend("[{:d}]".format(i) for i in indices)
+                path = "".join(path)
+            else:
+                path = key
             raise LoadError(LoadErrorReason.INVALID_DATA,
                             "{}: Value of '{}' is not of the expected type '{}'"
                             .format(provenance, path, expected_type.__name__))