Chaotic dynamic config codegen

Dynamic configs are runtime-adjustable settings fetched from a config service. Chaotic can generate the C++ type, parser, and variable wrapper for each config variable from a YAML schema file, eliminating hand-written boilerplate.

See Dynamic config for the broader dynamic config system.

Input file format

Each variable lives in its own YAML file. The file contains a JSONSchema object with two top-level keys:

• schema — the schema of the variable value (a full JSONSchema object).
• default — the default value used when the config service does not provide one.

schema may contain a nested definitions section for auxiliary types referenced by $ref.

Example MY_FEATURE_FLAGS.yaml:

# yaml
schema:
    type: object
    additionalProperties: false
    properties:
        enable_new_logic:
            type: boolean
        timeout_ms:
            type: integer
            format: int64
            minimum: 0
    required:
      - enable_new_logic
default:
    enable_new_logic: false
    timeout_ms: 5000

CMake integration

Use userver_target_generate_chaotic_dynamic_configs() to generate a CMake library target from a glob of variable files:

userver_target_generate_chaotic_dynamic_configs(
    myservice-dynconf                           # CMake target name
    ${CMAKE_CURRENT_SOURCE_DIR}/dynconf/*.yaml  # glob for variable YAML files
)
target_link_libraries(myservice myservice-dynconf)

Parameter	Description
First positional (TARGET)	CMake library target name to create.
Second positional (SCHEMAS_REGEX)	Shell glob pattern passed to file(GLOB …) to discover input YAML files.

The macro links the target against userver::core and userver::chaotic automatically.

Generated file layout

For each variable file NAME.yaml the following files are generated under ${CMAKE_CURRENT_BINARY_DIR}/dynamic_configs/:

Generated file	Contents
include/dynamic_config/variables/NAME.types_fwd.hpp	Forward declarations of generated types
include/dynamic_config/variables/NAME.types.hpp	Type definitions
include/dynamic_config/variables/NAME.types_parsers.ipp	DOM / YAML parsers
include/dynamic_config/variables/NAME.hpp	Variable wrapper (dynamic_config::Variable<T>)
src/dynamic_config/variables/NAME.types.cpp	Type definitions source
src/dynamic_config/variables/NAME.cpp	Variable initializer (registers default value)

Include dynamic_config/variables/NAME.hpp to use the variable in C++:

#include <dynamic_config/variables/MY_FEATURE_FLAGS.hpp>
 
// In a handler or task:
auto cfg = config_source.GetSnapshot();
const auto& flags = cfg[dynamic_config::MY_FEATURE_FLAGS];
if (flags.enable_new_logic) { ... }

Direct CLI reference

chaotic-gen-dynamic-configs is the underlying executable.

Flag	Required	Description
-o / --output-dir	yes	Directory for generated files.
file …	yes	One or more YAML variable files.
-I / --include-dir	no (repeatable)	Extra include path for x-usrv-cpp-type header lookup.
--clang-format	no	clang-format binary; set to empty string to disable.

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