A Rust implementation of HCL v2 — HashiCorp Configuration Language. v2 only; the v1 API is out of scope.

Status: early. src/ is API-shaped stubs by design — every public signature exists (so the conformance suite compiles), every body is todo!(). The Go→Rust API correspondence is documented in docs/api-mapping.md.

Not published to crates.io. Depend on it by git URL:

hcl = { git = "https://github.com/DanielMSchmidt/rust-hcl", tag = "v0.1.0" }

A learning project: a from-scratch Rust port of HCL, working toward an alternative Terraform implementation. Every line of the implementation is written by hand, deliberately. AI assistance here is limited to research, test porting, and debugging help — it does not write the implementation.

The upstream Go test suite is the specification. Tests under tests/conformance/ are transcribed from it, with expected values taken as literals from upstream so they specify behavior rather than mirror this implementation. Each file carries the upstream path(s) and pinned commit SHA (6abbb088cdb82416d1b3d9fcbaab29534133567a), and each test a permalink to the func Test* it was ported from. Go-only cases (nil zero values, pointer identity, reflection shapes) are kept in place as NOTE(port) comments rather than silently dropped.

Every test starts marked #[ignore = "not yet implemented"]; that is the backlog. As behavior lands, run the backlog with cargo test -- --ignored, and delete the #[ignore] from tests that now pass — from then on they gate CI like any other test. cargo test -- --include-ignored runs everything.

HCL also ships an implementation-agnostic spec suite that drives an implementation through an hcldec-compatible executable rather than the Go API; it maps case-by-case onto the HCL spec. Its fixtures are copied under tests/testdata/specsuite/ and driven by the conformance_specsuite test target (ignored like everything else, one test per fixture). Once this crate ships an hcldec-compatible executable, the upstream harness also runs against it unmodified — its pass rate is the compliance number that counts.

The gohcl package's struct-tag reflection is ported via the hcl-derive workspace crate: #[derive(FromBody)] / #[derive(EncodeBody)] with #[hcl(...)] field attributes mirroring the Go hcl:"..." tags (grammar in docs/api-mapping.md). The derives accept the grammar so annotated structs compile; their emitted bodies are todo!() like everything else.

Original work in this repository — everything under src/, hcl-derive/, docs/, and the build/CI scaffolding — is MIT licensed (see LICENSE).

hashicorp/hcl is MPL-2.0, and the transcribed test files are derivative works of its test code, as are the copied fixtures. Therefore every file under tests/conformance/ and tests/testdata/ is licensed MPL-2.0 (see LICENSE-MPL-2.0) and carries an MPL-2.0 notice plus a provenance header naming the upstream file and pinned commit. If you redistribute this repository, both licenses apply, each to its part.

cargo test

Toolchain is pinned in rust-toolchain.toml.

To build against a local cty working copy instead of the pinned git revision, with both repos checked out as siblings:

cp .cargo/config.toml.example .cargo/config.toml