rustc-ap-syntax 506.0.0

Automatically published version of the package `syntax` in the rust-lang/rust repository from commit a96ba969156d257e5d5b692946fa8fe40ed6543a The publishing script for this crate lives at: https://github.com/alexcrichton/rustc-auto-publish
fn main() {
    println!("cargo:rerun-if-changed=build.rs");
    println!("cargo:rerun-if-env-changed=CFG_RELEASE_CHANNEL");
    println!("cargo:rerun-if-env-changed=CFG_DISABLE_UNSTABLE_FEATURES");
}