ComposeLens

ComposeLens is a Rust library for reading, understanding, transforming, validating, and rendering real-world Compose documents.

It is designed for tools that need more than strict deserialization: source-aware diagnostics, implementation extensions, optional interpolation, multi-file projects, profiles, and round-trip-safe transformations.

Goals

• Parse Compose YAML without forcing immediate normalization or interpolation.
• Represent syntax, typed Compose concepts, extensions, and unknown fields explicitly.
• Preserve field-specific short and long syntax when their defaults or runtime behavior can differ.
• Preserve enough source information for actionable diagnostics and safe editing.
• Support multi-file project loading, merging, profile selection, and configurable interpolation.
• Model behavior found in real Docker Compose and Podman Compose projects.
• Render deterministic Compose documents.
• Construct new deterministic Compose documents through Compose-owned, parse-back-validated values.
• Preserve, merge, inspect, and generate service metadata labels without exposing sensitive values through debug output.
• Preserve, merge, inspect, and generate explicit runtime container names with field provenance.
• Preserve, merge, inspect, and generate explicit service hostnames with conservative RFC-1123 validation, deferred-expression retention, and no synthesized default.
• Preserve, merge, inspect, and generate service-level restart policies without confusing them with dependency-update or deploy restart settings.
• Preserve, merge, inspect, and generate service image pull policies without inventing provider behavior or discarding schema-only refresh evidence.
• Preserve, merge, inspect, and generate independent service stop signals and raw Compose stop grace periods without normalizing them into another lifecycle manager's units.
• Preserve, merge, inspect, and generate service PID limits without fixed-width parsing, default injection, runtime probing, or conflation with deploy resource limits.
• Preserve, merge, inspect, and safely generate service shared-memory sizes without injecting the Podman default, normalizing provider-dependent values, or inspecting /dev/shm.
• Preserve, merge, inspect, and safely generate service memory limits without fixed-width parsing, provider/runtime enforcement, host/cgroup inspection, or conflation with deploy memory policy.
• Preserve, merge, inspect, and generate service-level tmpfs scalar/list forms, colon-delimited documented or raw options, duplicates, provenance, and sensitivity without conflating volume mounts.
• Preserve, merge, inspect, and safely generate service sysctls mapping/list forms, scalar spelling, order, provenance, and sensitivity without namespace or runtime interpretation.
• Preserve, recursively merge, inspect, and safely generate ordered service ulimits single and soft/hard forms without injecting defaults or claiming runtime enforcement.
• Preserve, merge, inspect, and generate independent ordered service cap_add and cap_drop strings with explicit empty state, exact-case uniqueness, provenance, and no capability whitelist or target normalization.
• Preserve, target-key merge, inspect, and safely generate ordered mixed short/long service devices, including raw CDI/deferred/opaque short forms, explicit empty state, duplicates, nested provenance, and no host-device, permissions, or runtime-access validation.
• Preserve, inspect, and generate ordered service env_file short/long syntax and options; retain interpolation and multi-file provenance without reading environment files.
• Allow callers to choose strict, implementation-specific, or tolerant validation profiles.

Non-goals

• Running a Compose project
• Reimplementing Docker or Podman
• Converting Compose directly to Quadlet or Kubernetes
• Enforcing OCI rules that real Compose implementations do not enforce
• Treating the Compose Specification as the only source of real-world behavior

Cross-format conversion belongs to BoxFerry. Quadlet handling belongs to QuadletLens.

Processing levels

source text
  → loss-aware syntax document
  → typed Compose document
  → loaded multi-file project
  → optional per-file interpolation
  → provenance-preserving merged project
  → optional profile selection and native project view
  → references, paths, defaults, and compatibility
  → validated semantic view
  → rendered Compose document

Callers may stop at any appropriate level. Parsing a document must not implicitly read environment variables or contact a runtime.

Documentation

• Published Rust API documentation
• Documentation index
• Software architecture
• Target project structure
• Processing model
• Preservation-oriented editing
• Render formatting
• Generated documents
• Phase 2 typed model
• Native coverage
• Roadmap and exact specification gaps
• Testing strategy
• Development environment
• Compose implementation conformance
• Real-world fixture corpus
• Cross-repository implementation plan
• API stability policy
• 0.1.14 release notes
• Release process
• Changelog
• Architecture decisions

Repository-specific guidance for coding agents is in AGENTS.md.

Origin

ComposeLens is implemented from scratch. It is not a fork of compose_spec_rs and does not copy or mechanically translate its source code.

Stewardship

ComposeLens is created and maintained by Martin “Becks” Beckert through Strukturpiloten OHG. The project is part of Strukturpiloten's work on open, maintainable, and portable container infrastructure.

License

ComposeLens is licensed under the Mozilla Public License 2.0.