Crate swc_feature_flags 

SWC Feature Flags

A two-phase feature flag system for SWC:

1. Build-time: Mark feature flag usage with __SWC_FLAGS__ markers
2. Runtime: Substitute flag values and eliminate dead code

Example

use swc_feature_flags::{build_time_pass, runtime_pass, BuildTimeConfig, RuntimeConfig};
use std::collections::HashMap;

// Build-time configuration
let mut libraries = HashMap::new();
libraries.insert(
    "@their/library".to_string(),
    LibraryConfig {
        functions: vec!["useExperimentalFlags".to_string()],
    },
);

let build_config = BuildTimeConfig {
    libraries,
    marker_object: "__SWC_FLAGS__".to_string(),
};

// Apply build-time pass
let program = program.apply(build_time_pass(build_config));

// Runtime configuration
let mut flag_values = HashMap::new();
flag_values.insert("featureA".to_string(), true);
flag_values.insert("featureB".to_string(), false);

let runtime_config = RuntimeConfig {
    flag_values,
    remove_markers: true,
    collect_stats: true,
    marker_object: "__SWC_FLAGS__".to_string(),
};

// Apply runtime pass
let program = program.apply(runtime_pass(runtime_config));

Re-exports

pub use build_time::BuildTimeTransform;

pub use config::BuildTimeConfig;

pub use config::FeatureFlagsConfig;

pub use config::LibraryConfig;

pub use config::RuntimeConfig;

pub use config::TransformMode;

pub use runtime::RuntimeTransform;

pub use stats::TransformStats;

Modules

build_time

config

runtime

stats

Functions

build_time_pass

Create a build-time pass that marks feature flags with __SWC_FLAGS__ markers

feature_flags_pass

Create a unified feature flags pass based on the configured mode

runtime_pass

Create a runtime pass that substitutes flag values and eliminates dead code