metadata_dep_env test

This package contains end-to-end tests for metadata forwarding through cargo_build_script for both syntax forms:

• modern syntax: cargo::metadata=KEY=VALUE
• legacy syntax: cargo:KEY=VALUE

What it verifies

1. producer_build_rs emits both:
   • cargo::metadata=modern_version_1_10_0=1
   • cargo:legacy_version_1_10_0=2
2. rules_rust converts that to a dependent build-script env var:
   • DEP_PRODUCER_MODERN_VERSION_1_10_0=1
   • DEP_PRODUCER_LEGACY_VERSION_1_10_0=1
3. consumer_build_rs reads both and exports:
   • cargo:rustc-env=METADATA_MODERN_VALUE=1
   • cargo:rustc-env=METADATA_LEGACY_VALUE=2
4. Two rust_test targets assert each value independently:
   • metadata_dep_env_modern_test: env!("METADATA_MODERN_VALUE") == "1"
   • metadata_dep_env_legacy_test: env!("METADATA_LEGACY_VALUE") == "2"

Why producer_lib.rs exists

cargo_build_script targets cannot directly depend on other cargo_build_script targets. To model a realistic dependency edge, we attach producer_build_rs to a tiny Rust library (producer_lib), and the consumer build script depends on that library via link_deps.