fix(code): add missing tag categories to _get_tag()

[sumanjeet0012]

Closes #37.

What was changed:

• Added the 6 missing tag categories (multikey, multisig, nonce, shelter, softhash, vlad) to _get_tag() in multicodec/code.py.
• Reordered the multisig block to precede multihash to ensure correct tag extraction for overlapping names.
• Added comprehensive unit tests in tests/test_code.py to verify each of these new tag categories.

Why the change was needed:

• The Go reference implementation supports these tags, but py-multicodec was previously categorizing these codecs as "<unknown>".
• Ensures feature parity and spec compliance within the Python implementation.

How it was verified:

• Verified by adding new tag classification tests in test_code.py using prefixes like 0xA000, 0xD01300, 0x1A44, 0x123B, 0x511E00, 0xCC01, and 0x1207.
• Executed make pr locally to ensure formatting (ruff), linting (pre-commit), typechecking (mypy), and unit testing (pytest) all pass correctly.

[acul71]

AI PR Review: #49 — fix(code): add missing tag categories to _get_tag()

Reviewer: acul71 (maintainer)
PR: #49
Author: sumanjeet0012
Date: 2026-09-07

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1. Summary of Changes

This PR addresses Closes #37: _get_tag() was missing six category tags present in go-multicodec (multikey, multisig, nonce, shelter, softhash, vlad), so matching codecs returned "<unknown>".

Changes:

• Adds the six missing tag branches to _get_tag() in multicodec/code.py
• Places multisig matching before multihash so names containing both patterns are classified correctly
• Adds unit assertions in tests/test_code.py for each new category

Modules/files: multicodec/code.py, tests/test_code.py
Breaking changes / deprecations: None

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2. Branch Sync Status and Merge Conflicts

Branch Sync Status

• Status: Ahead of origin/master (in sync on the behind axis)
• Details: branch_sync_status.txt = 0 1 → 0 commits behind, 1 commit ahead

Merge Conflict Analysis

• Conflicts Detected: No conflicts
• Test merge against origin/master succeeded (Already up to date / clean abort path)

✅ No merge conflicts detected. The PR branch can be merged cleanly into origin/master.

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3. Strengths

• Directly mirrors the issue’s proposed Go-parity tags with clear comments
• Correct ordering of multisig before multihash (important for -msig / lamport-*-sig names)
• Focused tests covering each new tag with representative codec codes from the issue
• Local CI suite green: lint, typecheck, 689 tests, docs build

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4. Issues Found

Critical

• File: newsfragments/ (missing)
• Line(s): N/A
• Issue: Missing mandatory newsfragment for issue #37
• Suggestion: Add newsfragments/37.bugfix.rst (or 37.misc.rst if preferred) with a short user-facing ReST description ending in a newline, e.g. that Code.tag() now returns the correct categories for multikey/multisig/nonce/shelter/softhash/vlad codecs.

Major

• File: tests/test_code.py
• Line(s): ~120–145
• Issue: New tag checks are appended inside an existing test method rather than a dedicated parametrized test; coverage is spot-check only (one code per category)
• Suggestion: Prefer a parametrized table (as in PR #50) so all codecs in each category can be asserted; at minimum keep this PR’s checks but ensure they do not conflict with #50 when both land

Minor

• File: multicodec/code.py
• Line(s): Multisig / shelter branches
• Issue: Hardcoded name heuristics remain fragile if upstream naming drifts
• Suggestion: Acceptable for parity with Go; longer-term, consider deriving tags from the upstream table when #51’s spec submodule lands

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5. Security Review

No security concerns identified. Changes are pure classification of already-registered codec integers/names; no new I/O, subprocess, or unvalidated external input paths.

• Risk: None material
• Impact: None
• Mitigation: N/A

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6. Documentation and Examples

No public API surface change beyond corrected Code.tag() return values for previously "<unknown>" codecs. Docstring/README updates are not strictly required; a newsfragment is the appropriate user-facing note.

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7. Newsfragment Requirement

⚠️ BLOCKER

• Severity: CRITICAL / BLOCKER
• Issue: No newsfragments/37.*.rst file present; PR correctly references Closes #37
• Impact: Cannot approve until a valid newsfragment exists
• Suggestion:
  1. Issue link is fine (Closes #37)
  2. Add newsfragments/37.bugfix.rst with a user-facing description and trailing newline
• Action Required: Add newsfragment before approval

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8. Tests and Validation

Linting (make lint)

• Exit code: 0
• All pre-commit hooks passed (yaml, toml, EOF, whitespace, pyupgrade, ruff, ruff format, mypy)

Type Checking (make typecheck)

• Exit code: 0 — mypy passed

Test Execution (make test)

• Exit code: 0
• Summary: 689 passed, 0 failed, 0 skipped in ~0.27s
• New tag assertions exercised successfully

Documentation Build (make docs-ci)

• Exit code: 0 — Sphinx HTML build succeeded with -W

GitHub CI

• All reported tox/windows checks on the PR are SUCCESS

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9. Recommendations for Improvement

1. Add newsfragments/37.bugfix.rst (blocker)
2. Coordinate with PR #50 (same files: code.py, test_code.py). #50 expands tag coverage and also patches more unmapped tags. Prefer merge order: land #49 first then rebase #50, or close #49 if #50 fully subsumes these six categories after verification
3. Consider parametrizing the new tests for maintainability

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10. Questions for the Author

1. Have you confirmed these six categories match go-multicodec’s Tag() exactly for all codecs in each category (not only the sample codes)?
2. How do you intend to reconcile this PR with #50, which also edits _get_tag() and tag tests?
3. Is 37.bugfix.rst the intended newsfragment type, or do you prefer misc/internal?

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11. Overall Assessment

• Quality Rating: Good
• Security Impact: None
• Merge Readiness: Needs fixes (missing newsfragment; coordinate with #50)
• Confidence: High

Verdict: REQUEST_CHANGES — solid, focused fix that addresses #37, but blocked on the mandatory newsfragment and should be sequenced with #50.