_yaml.py: Add node_keys()danielsilverstone-ct/more-yaml-cleanups

There were a number of places where `node_items()` was called and the values
discarded.  Since values can be expensive to compute, this replaces any such
places with a `node_keys()` function call instead

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

3 files changed, 23 insertions, 6 deletions

diff --git a/buildstream/_options/optionpool.py b/buildstream/_options/optionpool.py
index 5b248111f..de3af3e15 100644
--- a/buildstream/_options/optionpool.py
+++ b/buildstream/_options/optionpool.py
@@ -91,7 +91,7 @@ class OptionPool():
     #    node (dict): The loaded YAML options
     #
     def load_yaml_values(self, node, *, transform=None):
-        for option_name, _ in _yaml.node_items(node):
+        for option_name in _yaml.node_keys(node):
             try:
                 option = self._options[option_name]
             except KeyError as e:
diff --git a/buildstream/_project.py b/buildstream/_project.py
index c6d0f29fd..18c2319c0 100644
--- a/buildstream/_project.py
+++ b/buildstream/_project.py
@@ -720,7 +720,7 @@ class Project():
 
         # Perform environment expansion right away
         shell_environment = _yaml.node_get(shell_options, Mapping, 'environment', default_value={})
-        for key, _ in _yaml.node_items(shell_environment):
+        for key in _yaml.node_keys(shell_environment):
             value = _yaml.node_get(shell_environment, str, key)
             self._shell_environment[key] = os.path.expandvars(value)
 
@@ -895,7 +895,7 @@ class Project():
 
             # Store source versions for checking later
             source_versions = _yaml.node_get(origin, Mapping, 'sources', default_value={})
-            for key, _ in _yaml.node_items(source_versions):
+            for key in _yaml.node_keys(source_versions):
                 if key in source_format_versions:
                     raise LoadError(
                         LoadErrorReason.INVALID_YAML,
@@ -904,7 +904,7 @@ class Project():
 
             # Store element versions for checking later
             element_versions = _yaml.node_get(origin, Mapping, 'elements', default_value={})
-            for key, _ in _yaml.node_items(element_versions):
+            for key in _yaml.node_keys(element_versions):
                 if key in element_format_versions:
                     raise LoadError(
                         LoadErrorReason.INVALID_YAML,
@@ -944,11 +944,11 @@ class Project():
             raise LoadError(LoadErrorReason.INVALID_DATA,
                             "Unexpected plugin group: {}, expecting {}"
                             .format(plugin_group, expected_groups))
-        node_keys = [key for key, _ in _yaml.node_items(origin)]
+        node_keys = [key for key in _yaml.node_keys(origin)]
         if plugin_group in node_keys:
             origin_node = _yaml.node_copy(origin)
             plugins = _yaml.node_get(origin, Mapping, plugin_group, default_value={})
-            _yaml.node_set(origin_node, 'plugins', [k for k, _ in _yaml.node_items(plugins)])
+            _yaml.node_set(origin_node, 'plugins', [k for k in _yaml.node_keys(plugins)])
             for group in expected_groups:
                 if _yaml.node_contains(origin_node, group):
                     _yaml.node_del(origin_node, group)
diff --git a/buildstream/_yaml.py b/buildstream/_yaml.py
index 5184485de..15ae5752f 100644
--- a/buildstream/_yaml.py
+++ b/buildstream/_yaml.py
@@ -642,6 +642,23 @@ def node_items(node):
             yield (key, value[0])
 
 
+# node_keys()
+#
+# A convenience generator for iterating over loaded keys
+# in a dictionary loaded from project YAML.
+#
+# Args:
+#    node (dict): The dictionary node
+#
+# Yields:
+#    (str): The key name
+#
+def node_keys(node):
+    if type(node) is not Node:
+        node = Node(node, None, 0, 0)
+    yield from node[0].keys()
+
+
 # node_del()
 #
 # A convenience generator for iterating over loaded key/value