SERVER-50367 Add IDL support for feature flags

3 files changed, 57 insertions, 0 deletions

diff --git a/buildscripts/idl/idl/binder.py b/buildscripts/idl/idl/binder.py
index 4d9bd3ff79c..8e01fe83b02 100644
--- a/buildscripts/idl/idl/binder.py
+++ b/buildscripts/idl/idl/binder.py
@@ -1005,6 +1005,22 @@ def _bind_server_parameter(ctxt, param):
         return None
 
 
+def _bind_feature_flags(param):
+    # type: (syntax.FeatureFlag) -> ast.ServerParameter
+    """Bind a FeatureFlag as a serverParameter setting."""
+    ast_param = ast.ServerParameter(param.file_name, param.line, param.column)
+    ast_param.name = param.name
+    ast_param.description = param.description
+
+    ast_param.set_at = "ServerParameterType::kStartupOnly"
+
+    ast_param.cpp_vartype = "bool"
+    ast_param.default = _bind_expression(param.default)
+    ast_param.cpp_varname = param.cpp_varname
+
+    return ast_param
+
+
 def _is_invalid_config_short_name(name):
     # type: (str) -> bool
     """Check if a given name is valid as a short name."""
@@ -1168,6 +1184,9 @@ def bind(parsed_spec):
         if not struct.imported:
             bound_spec.structs.append(_bind_struct(ctxt, parsed_spec, struct))
 
+    for feature_flag in parsed_spec.feature_flags:
+        bound_spec.server_parameters.append(_bind_feature_flags(feature_flag))
+
     for server_parameter in parsed_spec.server_parameters:
         bound_spec.server_parameters.append(_bind_server_parameter(ctxt, server_parameter))
 
diff --git a/buildscripts/idl/idl/parser.py b/buildscripts/idl/idl/parser.py
index 7a3a1e376d2..08f76bf0273 100644
--- a/buildscripts/idl/idl/parser.py
+++ b/buildscripts/idl/idl/parser.py
@@ -608,6 +608,25 @@ def _parse_server_parameter(ctxt, spec, name, node):
     spec.server_parameters.append(param)
 
 
+def _parse_feature_flag(ctxt, spec, name, node):
+    # type: (errors.ParserContext, syntax.IDLSpec, str, Union[yaml.nodes.MappingNode, yaml.nodes.ScalarNode, yaml.nodes.SequenceNode]) -> None
+    """Parse a feature_flags section in the IDL file."""
+    if not ctxt.is_mapping_node(node, "feature_flags"):
+        return
+
+    param = syntax.FeatureFlag(ctxt.file_name, node.start_mark.line, node.start_mark.column)
+    param.name = name
+
+    _generic_parser(
+        ctxt, node, "feature_flags", param, {
+            "description": _RuleDesc('scalar', _RuleDesc.REQUIRED),
+            "cpp_varname": _RuleDesc('scalar'),
+            "default": _RuleDesc('scalar_or_mapping', mapping_parser_func=_parse_expression),
+        })
+
+    spec.feature_flags.append(param)
+
+
 def _parse_config_option(ctxt, spec, name, node):
     # type: (errors.ParserContext, syntax.IDLSpec, str, Union[yaml.nodes.MappingNode, yaml.nodes.ScalarNode, yaml.nodes.SequenceNode]) -> None
     """Parse a configs section in the IDL file."""
@@ -727,6 +746,8 @@ def _parse(stream, error_file_name):
             _parse_mapping(ctxt, spec, second_node, "server_parameters", _parse_server_parameter)
         elif first_name == "configs":
             _parse_mapping(ctxt, spec, second_node, "configs", _parse_config_option)
+        elif first_name == "feature_flags":
+            _parse_mapping(ctxt, spec, second_node, "feature_flags", _parse_feature_flag)
         else:
             ctxt.add_unknown_root_node_error(first_node)
 
diff --git a/buildscripts/idl/idl/syntax.py b/buildscripts/idl/idl/syntax.py
index 3c9bb7bedf1..9b3530a7db7 100644
--- a/buildscripts/idl/idl/syntax.py
+++ b/buildscripts/idl/idl/syntax.py
@@ -67,6 +67,7 @@ class IDLSpec(object):
         self.imports = None  # type: Optional[Import]
         self.server_parameters = []  # type: List[ServerParameter]
         self.configs = []  # type: List[ConfigOption]
+        self.feature_flags = []  # type: List[FeatureFlag]
 
 
 def parse_array_type(name):
@@ -527,6 +528,22 @@ class ServerParameter(common.SourceLocation):
         super(ServerParameter, self).__init__(file_name, line, column)
 
 
+class FeatureFlag(common.SourceLocation):
+    """IDL FeatureFlag information."""
+
+    # pylint: disable=too-many-instance-attributes
+
+    def __init__(self, file_name, line, column):
+        # type: (str, int, int) -> None
+        """Construct a FeatureFlag."""
+        self.name = None  # type: str
+        self.description = None  # type: str
+        self.cpp_varname = None  # type: str
+        self.default = None  # type: Expression
+
+        super(FeatureFlag, self).__init__(file_name, line, column)
+
+
 class GlobalInitializer(common.SourceLocation):
     """Initializer details for custom registration/storage."""