go-hiera — a pure-Go reimplementation of Puppet's Hiera 5 hierarchical data-lookup engine, no cgo

go-hiera is a pure-Go (no cgo) reimplementation of Hiera 5, the hierarchical data-lookup engine behind Puppet's lookup(). It loads a hiera.yaml version-5 config — defaults plus an ordered hierarchy of levels (path, paths, glob, globs, mapped_paths) — reads data through yaml_data and json_data backends, and assembles the result with Hiera's four merge behaviours (first, unique, hash, deep) driven by lookup_options. Full %{...} interpolation — facts, trusted, scope(), lookup() / hiera(), whole-value alias() and literal() — is resolved with interpolation-loop detection. The variable / fact Scope is a pluggable interface the caller injects, so go-facter (facts) and the Ruby binding go-ruby-hiera plug in without a hard dependency. Faithful to Hiera 5 so it can back Puppet's lookup() — CGO-free, 100% coverage, green across 6 arches.

go-hiera/hiera core · engine

The Hiera 5 data-lookup engine: hiera.yaml v5 loader, yaml_data / json_data backends (pluggable via RegisterDataHash), the first / unique / hash / deep merge engine with lookup_options, dotted-key dig, and full %{...} interpolation. go get github.com/go-hiera/hiera

hiera.yaml v5 loader ready

Parses hiera.yaml version 5 — the defaults block and the ordered hierarchy of levels, with every path form: path / paths, glob / globs, and mapped_paths. Each level resolves its datadir, data_hash backend and per-level options exactly as Hiera 5 does.

yaml / json backends ready

The yaml_data backend reads through go-ruby-yaml’s pure-Go, Psych-faithful loader so YAML parses byte-for-byte the way MRI’s Ruby does; json_data reads JSON. Backends are pluggable via RegisterDataHash, so eyaml / HOCON slot in later without touching the engine.

merge engine + lookup_options ready

All four merge behaviours — first, unique, hash and deep — driven by lookup_options (per-key and ^regex keys), honouring knockout_prefix and merge_hash_arrays. The value assembled across every matching hierarchy level is the one Puppet’s lookup() would return.

%{...} interpolation + loop detection ready

Full %{...} interpolation: %{facts.x}, %{trusted.x}, %{scope('x')}, %{lookup('x')} / %{hiera('x')}, the whole-value %{alias('x')}, and %{literal('%')} — with interpolation-loop detection that stops a key that resolves back through itself.

dotted dig + defaults ready

Dotted keys (a.b.c) dig into structured hashes and arrays, and lookups fall through to caller-supplied default values / default blocks when no level matches — the same digging and defaulting semantics Puppet exposes on lookup().

Ruby surface planned

Downstream, not part of this engine module: the Ruby Hiera class and Puppet’s lookup() / automatic data-binding surface are mapped onto this engine by the go-ruby-hiera consumer. This library is the data-lookup engine; the binding is the Ruby face.

ready capability complete (exit criteria met, nothing material left)
active in progress (substantial work shipped, not yet finished)
planned not started yet (or downstream by design)

A faithful port of Puppet's Hiera 5 in pure Go, cgo disabled, so it cross-compiles and embeds anywhere. It reads hiera.yaml v5 through yaml_data (via the pure-Go, Psych-faithful go-ruby-yaml loader) and json_data, applies the first / unique / hash / deep merge behaviours with lookup_options, knockout_prefix and merge_hash_arrays, and resolves every %{...} interpolation with loop detection. The variable/fact Scope is a pluggable interface, so go-facter and the Ruby binding go-ruby-hiera — which maps Ruby's Hiera and Puppet's lookup() onto this engine — plug in downstream. Part of the sibling org github.com/go-hiera.