feat(metadata): deprecate non-SPDX license values

[bepri]

Deprecates non-SPDX license expression values in the top-level license: key.

Any license string is still accepted, and this change is backwards-compatible. This just lets us deprecate it for Snapcraft 10.

SNAPCRAFT-1341

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• I've followed the contribution guidelines.
• I've signed the CLA.
• I've successfully run make lint && make test.
• I've added or updated any relevant documentation.
• In documents I changed, I added a meta description if one was missing.
• I've updated the relevant release notes.

[Copilot]

Pull request overview

This PR adds a deprecation warning when the top-level license: value is not an SPDX license expression (while still accepting and preserving the original value), and documents the change in the Snapcraft 9.0 release notes.

Changes:

• Add a BeforeValidator to Project.license that warns on non-SPDX values via emit.warning.
• Add unit coverage verifying warnings (or lack thereof) and that the parsed license value remains unchanged.
• Add a release-note entry describing the deprecation.

Documentation Review Report

Reviewed: docs/release-notes/snapcraft-9-0.rst
Date: 2026-08-05
Skills Applied: documentation-build, documentation-diataxis, documentation-structure, documentation-verify, documentation-style

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Build Findings (BLOCKING)

Source: documentation-build

• RTD/Sphinx artifacts detected (.readthedocs.yaml, docs/conf.py, docs/Makefile), but the docs build targets could not be executed in this review environment (no command runner available). Build status is unverified.

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Accuracy Findings (CRITICAL)

Source: documentation-verify

• Incorrect: The new release note text states non-SPDX values “must” be SPDX or proprietary, but the implementation only warns and still accepts any string unchanged (snapcraft/models/project.py:323-335), with test evidence (tests/unit/models/test_projects.py:987-1013).

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Diataxis Findings (HIGH)

Source: documentation-diataxis

• Release notes are a hard-to-fit genre (not a strict Diataxis quadrant). Placement under docs/release-notes/ is consistent with the existing structure; no category mismatch identified for the change.

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Structure Findings (MEDIUM)

Source: documentation-structure

• No structural issues found in the edited section (heading level and formatting match surrounding release-notes conventions).

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Style Findings (LOW)

Source: documentation-style

• No style violations found in the edited section based on the repository style guide excerpt reviewed.

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Incomplete Stages

• documentation-build: Could not run make html/linkcheck/spelling/lint-md/vale to confirm the docs build passes.

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Summary

Address the release-note accuracy issue first (it contradicts the implemented behavior), then fix the unit test type annotation mismatch. Docs build should be validated in CI or locally because make html is configured with --fail-on-warning.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
snapcraft/models/project.py	Adds a validator to warn (but accept) non-SPDX license values.
tests/unit/models/test_projects.py	Adds unit coverage for the warning behavior and value preservation.
docs/release-notes/snapcraft-9-0.rst	Adds a release-note entry for the license deprecation (currently overstated vs actual behavior).