117 lines
5.1 KiB
Markdown
117 lines
5.1 KiB
Markdown
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# Capability Resolution & Installer Shadowing
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## Layer Hierarchy
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```
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┌───────────────────────────┐ Highest layer
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│ OS-PACKAGES │ (PKGBUILD / debian / rpm)
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└───────────▲───────────────┘
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│ shadows lower layers
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┌───────────┴───────────────┐
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│ NIX │ (flake.nix)
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└───────────▲───────────────┘
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│ shadows lower layers
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┌───────────┴───────────────┐
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│ PYTHON │ (pyproject.toml)
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└───────────▲───────────────┘
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│ shadows lower layers
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┌───────────┴───────────────┐
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│ MAKEFILE │ (Makefile)
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└────────────────────────────┘ Lowest layer
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```
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---
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## Scenario Matrix
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| Scenario | Makefile | Python | Nix | OS-Pkgs | Test Name |
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| -------------------------- | -------- | ------ | --- | ------- | ----------------------------- |
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| 1) Only Makefile | ✔ | – | – | – | `only_makefile` |
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| 2) Python + Makefile | ✔ | ✔ | – | – | `python_and_makefile` |
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| 3) Python shadows Makefile | ✗ | ✔ | – | – | `python_shadows_makefile` |
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| 4) Nix shadows Py & MF | ✗ | ✗ | ✔ | – | `nix_shadows_python_makefile` |
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| 5) OS-Pkgs shadow all | ✗ | ✗ | ✗ | ✔ | `os_packages_shadow_all` |
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Legend:
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✔ = installer runs
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✗ = installer skipped (shadowed by upper layer)
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– = no such layer present
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---
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## What the Integration Test Confirms
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**Goal:** Validate that the capability-shadowing mechanism correctly determines *which installers actually run* for a given repository layout.
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### 1) Only Makefile
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* Makefile provides `make-install`.
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* No higher layers → MakefileInstaller runs.
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### 2) Python + Makefile
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* Python provides `python-runtime`.
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* Makefile additionally provides `make-install`.
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* No capability overlap → both installers run.
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### 3) Python shadows Makefile
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* Python also provides `make-install`.
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* Makefile’s capability is fully covered → MakefileInstaller is skipped.
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### 4) Nix shadows Python & Makefile
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* Nix provides all capabilities below it.
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* Only NixInstaller runs.
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### 5) OS-Packages shadow all
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* PKGBUILD/debian/rpm provide all capabilities.
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* Only the corresponding OS package installer runs.
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---
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## Capability Processing Flowchart
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```
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┌────────────────────────────┐
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│ Start │
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└───────────────┬────────────┘
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│
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provided_capabilities = ∅
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│
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▼
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┌──────────────────────────────────────────────┐
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│ For each installer in layer order (low→high) │
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└───────────────────┬──────────────────────────┘
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│
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supports(ctx)?│
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┌─────────┴──────────┐
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│ no │
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│ → skip installer │
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└─────────┬──────────┘
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│ yes
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▼
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caps = detect_capabilities(layer)
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│
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caps ⊆ provided_capabilities ?
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┌─────────────┬─────────────┐
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│ yes │ no │
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│ skip │ run installer│
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└─────────────┴──────────────┘
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│
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▼
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provided_capabilities ∪= caps
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│
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▼
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┌────────────────────────┐
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│ End of installer list │
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└────────────────────────┘
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```
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---
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## Core Principle (one sentence)
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**A layer only executes if it provides at least one capability not already guaranteed by any higher layer.**
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