repolish 0.1.0

Maintain consistency across repositories

repolish

Repolish is a hybrid of templating and diff/patch systems, useful for maintaining repo consistency while allowing local customizations. It uses templates with placeholders that can be filled from a context, and regex patterns to preserve existing local content in files.

Why this exists

Teams often need to enforce repository-level conventions (CI config, build tools, metadata, common docs) while letting individual projects keep local customizations. The naive approaches are painful:

• Copying templates into many repos means drift over time and manual syncs.
• Running destructive templating can overwrite local changes developers rely on.

Repolish solves this by combining templating (to generate canonical files) with a set of careful, reversible operations that preserve useful local content. Instead of blindly replacing files, Repolish can:

• Fill placeholders from provider-supplied context.
• Apply anchor-driven replacements to keep developer-customized sections.
• Track provider-specified deletions and record provenance so reviewers can see why a path was requested for deletion.

Design overview

Key concepts:

• Providers (templates): Each provider lives in a template directory and may include a repolish.py module that exports create_context(), create_anchors(), and/or create_delete_files() helpers. Providers supply cookiecutter context and may indicate files that should be removed from a project.
• Anchors: A small markup syntax placed in templates (and optionally in project files) that marks blocks or regex lines to preserve. Examples:
  • Block anchors: ## repolish-start[readme] ... repolish-end[readme]
  • Regex anchors: ## repolish-regex[keep]: ^important=.* The processors use these anchors to replace or merge the template content with the local project file while preserving the parts marked with anchors.
• Delete semantics: Providers can request deletions using POSIX-style paths. A ! prefix acts as a negation (keep). Config-level delete_files are applied last and recorded in provenance.
• Provenance: Repolish records a delete_history mapping that stores, for each candidate path, a list of decisions (which provider or config requested a delete or a keep). This helps reviewers and automation understand why a path was flagged.

How it works (high level)

1. Load providers configured in repolish.yaml (or the default config).
2. Merge provider contexts; config-level context overrides provider values.
3. Merge anchors from providers and config.
4. Stage all provider template directories into a single cookiecutter template (adjacent to the config under .repolish/setup-input).
5. Preprocess staged templates by applying anchor-driven replacements using local project files (looked up relative to the config location).
6. Render the merged cookiecutter template once into .repolish/setup-output.
7. In --check mode: compare generated files to project files and report either diffs, missing files, or paths that providers wanted deleted but which are still present.
8. In apply mode: copy generated files into the project and apply deletions as the final step.

Example usage

repolish.yaml (simple example):

directories:
  - ./templates/template_a
  - ./templates/template_b
context: {}
anchors: {}
delete_files: []

Run a dry-run check (useful for CI):

repolish --check --config repolish.yaml

This will produce structured logs that include:

• The merged provider context and delete_paths (so you can see what was requested).
• A check_result listing per-path diffs or deletion warnings like PRESENT_BUT_SHOULD_BE_DELETED.

Processor story (anchors)

We iterated on preserving local file semantics and landed on a simple, explicit anchor-based system. Anchors are easy for template authors to add and for maintainers to reason about:

• Block anchors allow entire sections of a file to be preserved or replaced while keeping the surrounding template-driven structure.
• Regex anchors can mark single lines or patterns to keep (useful for maintainer-inserted keys or comments that should survive templating).

Anchors are processed in staging before cookiecutter runs, so the generated output already reflects local overrides while still taking canonical values from templates when needed.

How do I add anchors?

Anchors are intentionally simple so template authors and maintainers can reason about them easily. There are two primary forms:

• Block anchors mark a named section to preserve or replace between repolish-start[...] and repolish-end[...] markers. Use them for multi-line sections such as README snippets, install blocks, or long descriptions.
• Regex anchors mark single-line patterns to keep using a regular expression. They are useful when you want to preserve a line that follows a predictable pattern (version lines, keys, simple single-line edits).

Below are two practical examples you can copy into templates and projects.

Dockerfile (block anchor)

Template (templates/template_a/Dockerfile):

# base image
FROM python:3.11-slim

## repolish-start[install]
# install system deps
RUN apt-get update && apt-get install -y build-essential libssl-dev
## repolish-end[install]

# copy + install python deps
COPY pyproject.toml .
RUN pip install --no-cache-dir .

Project Dockerfile (local override) — developer has custom install needs:

FROM python:3.11-slim

## repolish-start[install]
# custom build deps for project X
RUN apt-get update && apt-get install -y locales libpq-dev
## repolish-end[install]

# copy + install python deps
COPY pyproject.toml .
RUN pip install --no-cache-dir .

When Repolish runs its preprocessing, the install block from the local project will be preserved in the staged template (so the generated output keeps the local custom RUN command), while the rest of the Dockerfile comes from the template.

pyproject.toml (regex anchor + block anchor)

Template (templates/template_a/pyproject.toml):

[tool.poetry]
name = "{{ cookiecutter.package_name }}"
version = "0.1.0"
## repolish-regex[keep]: ^version\s*=\s*".*"

description = "A short description"

## repolish-start[extra-deps]
# optional extra deps (preserved when present)
## repolish-end[extra-deps]

Project pyproject.toml (developer bumped version and added extras):

[tool.poetry]
name = "myproj"
version = "0.2.0"

description = "Local project description"

## repolish-start[extra-deps]
requests = "^2.30"
## repolish-end[extra-deps]

In this example the ## repolish-regex[keep]: ^version\s*=\s*".*" anchor ensures the local version = "0.2.0" line is preserved instead of being replaced by the template's 0.1.0. The extra-deps block is preserved whole-cloth when present, letting projects keep local dependency additions.

Notes and tips

• Use meaningful anchor names (e.g., install, readme, extra-deps) so reviewers immediately understand the preserved section's intent.
• Regex anchors are applied line-by-line; prefer anchoring to a simple, easy to read pattern to avoid surprises.
• Anchors are processed before cookiecutter rendering, so template substitutions still work around preserved sections.

Where anchors are declared and uniqueness

Anchors can come from three places (and are merged in this order):

1. Provider templates: any ## repolish-start[...] / ## repolish-regex[...] markers present inside the provider's template files.
2. Provider code: a provider's create_anchors() callable can return an anchors mapping (key -> replacement text) used during preprocessing.
3. Config-level anchors: the anchors mapping in repolish.yaml applies last and can be used to override or add anchor values.

When anchors are merged, later sources override earlier ones (config wins). Anchor keys must be unique across the whole merged template set — keys are global identifiers used to find matching repolish-start[...] blocks or repolish-regex[...] declarations. If two different template files (or providers) use the same anchor key, the later provider's value will override the earlier one, which can produce surprising results.

Example conflict

Two provider templates accidentally use the same anchor key init:

• templates/a/Dockerfile contains ## repolish-start[init] … ## repolish-end[init]
• templates/b/README.md also contains ## repolish-start[init] … ## repolish-end[init]

Because anchor keys are merged globally, the init block from the provider that is processed later will replace (or be used in place of) the other one. That may not be what you want — for predictable behavior, choose anchor keys scoped to the file or the provider, e.g. docker-install or readme-intro.

Best practice: prefix anchor keys with the file or provider name when the content is file-scoped. This avoids accidental collisions when multiple providers contribute templates that contain similarly-named sections.

Why this is useful

• Safe consistency: teams get centralized templates without forcing destructive, manual rollouts.
• Clear explainability: the delete_history provenance makes it easy to review why a file was targeted for deletion or kept.
• CI-friendly: --check can be run in CI to detect drift; logs and diffs make it straightforward to require PRs to run repolish before merging.

Final notes

Repolish is intentionally small and composable. If you need per-file log artifacts, or slightly different merge rules, the processors and cookiecutter helpers are isolated so you can adapt them safely.

Contributions and issues are welcome — see the test-suite for practical examples of how the system behaves.