Hologit

Hologit

Overview

Hologit is a Git-native framework for declarative code automation. It projects virtual "holobranches" by combining content from multiple Git sources and applying transformations (lenses), all operating directly on Git's object database without creating intermediate files.

Install: npm install -g hologit Invoke: git holo <command> Requires: Node.js >=20.19.0, Git

Core operation: Define sources, branches, mappings, and lenses in .holo/ TOML config files. Run git holo project <holobranch> to compute a composite output tree.

Key Concepts

Holospace: A workspace defined by .holo/config.toml with a canonical name. The name enables self-references — when a mapping's holosource matches the workspace name, the current workspace tree is used as the source.

Holosource: A named reference to an external Git repository/branch, configured in .holo/sources/<name>.toml. Specifies a url and ref to track. Can optionally project a holobranch within the source via project.holobranch.

Holobranch: A virtual branch defined in .holo/branches/<name>.toml. Declares what content to include (via mappings) and how to transform it (via lenses). Can inherit from another branch using extend.

Holomapping: A content inclusion rule at .holo/branches/<branch>/<key>.toml. Specifies which files from which source to include, where to place them in the output, and ordering via before/after layer constraints.

Hololens: A transformation applied via a Docker container or Habitat package. There are two types:

• Internal lenses (.holo/lenses/<name>.toml): Defined within source content and discovered in the projected composite output tree. These travel with the source — when downstream projects include this source, they inherit its internal lenses. Use for transformations that should apply everywhere the source is consumed.
• External lenses (.holo/branches/<branch>.lenses/<name>.toml): Defined alongside a branch config in the consuming workspace. These are branch-specific and do not travel with sources. Use for transformations applied to external content that shouldn't be inherited downstream.

During projection, internal lenses execute first, then external lenses.

Projection: The process of computing a holobranch's output:

1. Resolve extend chain (parent branches merged first)
2. Composite all mappings in topological order (by before/after)
3. Strip .holo/branches and .holo/sources from output
4. Apply internal lenses (from projected output tree)
5. Apply external lenses (from branch config)
6. Strip .holo/lenses from output
7. Strip empty .holo/ if only config.toml remains

Directory Structure

.holo/
├── config.toml                          # [holospace] name = "my-project"
├── sources/
│   └── <name>.toml                      # [holosource] url, ref
├── branches/
│   ├── <branch>.toml                    # [holobranch] extend, lens
│   ├── <branch>/
│   │   └── <key>.toml                   # [holomapping] holosource, files, root, output
│   └── <branch>.lenses/
│       └── <lens>.toml                  # [hololens] external/branch-specific lens
└── lenses/
    ├── <name>.toml                      # [hololens] internal/inheritable lens
    └── <name>/                          # companion data tree for lens

CLI Quick Reference

Global options: -d/--debug (debug logging), -q/--quiet (errors only)

For complete CLI documentation with all options: references/cli.md

Configuration Quick Reference

All config uses TOML with uppercase section headers matching the config kind.

For complete field schemas with types and defaults: references/toml-configuration.md

Mapping Key Naming Convention

The mapping filename (key) controls default behavior:

• _name.toml (leading underscore): Output merges to the branch root (/). The holosource defaults to name (underscore stripped). Use for sources whose files should be at the top level. Self-reference: if name matches the holospace name from .holo/config.toml, the current workspace tree is used as the source — no holosource field or .holo/sources/ file needed.
• name.toml (no underscore): Output goes to a subdirectory matching the key (/name/). The holosource defaults to name. Use for sources that should be namespaced.
• Nested keys: subdir/name.toml outputs to subdir/name/ (or subdir/ if _name.toml).

The holosource field can use => syntax for in-mapping projection:

• "source-name=>branch-name" — project branch-name within source
• "=>branch-name" — project branch-name within the source derived from the key

Common Workflows

Initialize a workspace

git holo init --name my-project

Creates .holo/config.toml with [holospace] name = "my-project".

Add a remote source

git holo source create https://github.com/org/repo --ref refs/tags/v1.0.0

Creates .holo/sources/repo.toml:

[holosource]
url = "https://github.com/org/repo"
ref = "refs/tags/v1.0.0"

Create a passthrough holobranch

git holo branch create my-branch --template=passthrough

Creates a mapping _<workspace-name>.toml with files = "**" that includes all workspace files.

Filter the current repo to specific paths

The simplest holobranch: select specific paths from the current workspace. Name the mapping _<workspace-name>.toml so the key auto-resolves to the holospace as a self-referencing source — no holosource field or .holo/sources/ file needed.

Given a workspace named my-project (from .holo/config.toml):

# .holo/branches/my-branch/_my-project.toml
[holomapping]
files = [".claude-plugin/**", "skills/**"]

This projects only .claude-plugin/ and skills/ from the workspace, preserving their original directory structure. Verify with:

git ls-tree -r --name-only $(git holo project my-branch --working)

Since projection produces a git tree hash, it composes with any git command that accepts a tree-ish — for example, creating a distributable archive:

git archive --format=zip $(git holo project my-branch --working) > /tmp/my-project.zip

Add a mapping manually

Create .holo/branches/my-branch/_my-source.toml:

[holomapping]
files = ["src/**", "!test/**"]
root = "packages/core"

This maps packages/core/src/** (excluding tests) from source my-source to the branch root.

Verify configuration

After editing .holo/ config files, run inspect to verify the resolved state before projecting:

git holo inspect my-branch --working

This shows the fully resolved mappings (auto-resolved source names, output paths, layer ordering) and lenses without running a projection. Use it to catch config mistakes early.

Note: Pass --working so hologit reads uncommitted .holo/ files from the working tree. Without it, hologit reads from the git index and won't see unstaged changes. Once .holo/ files are committed, --working is no longer needed.

Project and commit

git holo project my-branch --commit-to=refs/heads/projected --fetch="*"

Fetches all sources, projects the branch, and commits the result.

Add an internal lens (inheritable)

Create .holo/lenses/normalize.toml:

[hololens]
container = "ghcr.io/hologit/lenses/k8s-normalize:latest"
after = "*"

[hololens.input]
files = ["**/*.yaml", "**/*.yml"]

[hololens.output]
merge = "replace"

This lens travels with the source content and applies in any project that consumes it.

Add an external lens (branch-specific)

Create .holo/branches/my-branch.lenses/helm.toml:

[hololens]
container = "ghcr.io/hologit/lenses/helm3:latest"

[hololens.input]
root = "my-chart"
files = "**"

[hololens.output]
merge = "replace"

[hololens.helm]
namespace = "production"
release_name = "my-release"
chart_path = "helm-chart"
value_files = ["values.yaml", "prod-values.yaml"]

This lens only applies to my-branch in the current workspace.

Layer ordering

# .holo/branches/site/_skeleton.toml
[holomapping]
files = "*/**"
before = "*"

# .holo/branches/site/_app.toml
[holomapping]
files = "*/**"
after = "*"

The skeleton layer merges first, app layer merges last (overriding skeleton files).

Branch extension

# .holo/branches/production.toml
[holobranch]
extend = "base"

The production branch inherits all mappings from base, then applies its own.

Lens Caching

Hologit caches lens execution results using Git's own object database, enabling instant reruns and shared caches across machines.

How it works: Before executing a lens, hologit builds a deterministic "spec" — a TOML blob containing the container image's manifest digest, the input tree hash, and lens configuration. The spec blob's git hash becomes the cache key. Results are stored as git refs at refs/holo/lens/<spec-hash>.

Cache lookup flow:

1. Check local ref refs/holo/lens/<spec-hash> → if exists, return cached output tree
2. If miss and --cache-from is set, fetch the ref from the remote → if found, return it
3. If still no hit, execute the lens in its container, save output to local ref
4. If --cache-to is set, push the ref to the remote for other machines to use

Why it's deterministic: Container images are pinned by manifest digest (queried from the registry via docker buildx imagetools inspect), not by mutable tags. The same input tree + same image digest + same config always produces the same spec hash, guaranteeing cache correctness even when :latest tags are updated.

CLI options:

• --cache-from <remote> (default: origin) — pull cached lens results before executing
• --cache-to <remote> — push cached lens results after executing
• Also configurable via HOLO_CACHE_FROM / HOLO_CACHE_TO environment variables

CI/CD pattern: Use --cache-from=origin --cache-to=origin so the first CI run computes and pushes results, and subsequent runs with identical inputs get instant cache hits:

git holo project my-branch --commit-to=projected --fetch="*" --cache-from=origin --cache-to=origin

Environment Variables

Key overrides (see references/environment-variables.md):

• HOLO_SOURCE_<NAME> — Override source URL/ref/holobranch
• HOLO_FETCH — Sources to fetch during projection (* for all)
• HOLO_CACHE_FROM / HOLO_CACHE_TO — Cache remotes for lens results

Reference Files

• references/cli.md — Complete CLI command documentation with all options and defaults
• references/toml-configuration.md — Complete TOML schema for all configuration file types
• references/stock-lenses.md — All 8 stock lenses (helm3, kustomize, k8s-normalize, k8s-patch, npm-install, npm-run, mkdocs, shell) with full configuration options
• references/environment-variables.md — Environment variable overrides and debug options
• references/github-action.md — GitHub Action for CI/CD projection workflows