kernel config hash: ignore modifications the source config already declares

[iav]

Description

A hook that sets a kernel config option to the value the source config already carries
produces a byte-identical .config, yet still moves artifact_version — cutting the board
off from the published kernel debs. Compare each announced OPTION=value against the
config text before hashing and drop the ones that match.

Announcements are canonicalized to the CONFIG_ prefix first: scripts/config accepts an
option name either way, so both spellings have to collapse to one key before the
last-assignment-wins reduction.

Every kernel family changes version once: even with no extension in play, the core hooks
re-announce options the config file already carries — 237 of 334 announcements dropped on
odroidn2/edge. One rebuild, then versions settle.

Not covered: an option that ends up enabled through a Kconfig dependency rather than a
literal line. Detecting that needs make, which version calculation deliberately runs
without.

How Has This Been Tested?

• ./compile.sh artifact-config-dump-json WHAT=kernel BOARD=odroidn2 BRANCH=edge, with and
  without an extension setting IP_PNP=y, TUN=y, NFS_FS=m — the exact values already in
  linux-meson64-edge.config. Before: .config hook hash 1c3a9337c4583b24 without the
  extension, 029b15474d885e57 with it. After: 76b3aeb8f7fb12d7 in both.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

Summary by CodeRabbit

• Bug Fixes
  • Improved kernel configuration change handling by standardizing option updates.
  • Prevented redundant configuration changes from being included when they already match the existing system configuration.
  • Preserved meaningful differences while removing duplicate or unnecessary modifications.

[coderabbitai]

📝 Walkthrough

Walkthrough

Kernel configuration modification hashing now canonicalizes assignments, removes entries matching the source configuration, and then reduces the remaining modifications before calculating the hash.

Changes

Kernel configuration hash normalization

Layer / File(s)	Summary
Modification normalization and filtering lib/functions/compilation/kernel-config.sh	Adds helpers that prefix assignments with CONFIG_, preserve non-assignment markers, parse source values, and remove matching announcements.
Hash input preparation lib/functions/artifacts/artifact-kernel.sh	Prepares a copied modification list by canonicalizing and filtering entries before last-assignment reduction and hashing.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Suggested reviewers: rpardini

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: excluding source-config modifications from the kernel configuration hash.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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