feat(component): Add deterministic component fingerprints by dmcilvaney · Pull Request #47 · microsoft/azure-linux-dev-tools

dmcilvaney · 2026-03-31T00:53:41Z

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Copilot

Pull request overview

Adds a new internal fingerprinting utility intended to compute deterministic “component fingerprints” from resolved component configuration plus additional build context.

Changes:

Introduces internal/fingerprint package with ComputeIdentity to produce a SHA256-based fingerprint and an inputs breakdown.
Adds a comprehensive test suite covering many config/input variations.
Exports OpenProjectRepo in synthetic history code and adds hashstructure/v2 dependency.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
internal/fingerprint/fingerprint.go	New fingerprint computation logic (config hashing + overlay file hashing + SHA256 combiner).
internal/fingerprint/fingerprint_test.go	New tests asserting determinism and expected sensitivity/insensitivity to various inputs.
internal/fingerprint/doc.go	Package documentation for the new fingerprint module.
internal/app/azldev/core/sources/synthistory.go	Renames `openProjectRepo` to exported `OpenProjectRepo` and updates call site.
go.mod	Adds `github.com/mitchellh/hashstructure/v2` dependency.
go.sum	Adds checksums for the new dependency.

internal/fingerprint/fingerprint.go

internal/fingerprint/fingerprint_test.go

internal/app/azldev/core/sources/synthistory.go

internal/fingerprint/doc.go

internal/fingerprint/fingerprint.go

Copilot

Pull request overview

Copilot reviewed 5 out of 6 changed files in this pull request and generated 5 comments.

internal/fingerprint/fingerprint.go

internal/fingerprint/fingerprint_test.go

Copilot

Pull request overview

Copilot reviewed 5 out of 6 changed files in this pull request and generated 3 comments.

internal/fingerprint/fingerprint.go

Copilot

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 3 comments.

internal/fingerprint/fingerprint.go

Copilot

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 2 comments.

internal/fingerprint/fingerprint.go

internal/projectconfig/specsource.go

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

reubeno

Apart from the individual comments, my main question... what's your thoughts on how we can ensure that this algorithm stays in sync with the component and overlay definitions as the latter evolve?

reubeno · 2026-04-11T00:07:50Z

internal/fingerprint/fingerprint.go

+	OverlayFileHashes map[string]string `json:"overlayFileHashes,omitempty"`
+	// AffectsCommitCount is the number of "Affects: <component>" commits in the project repo.
+	AffectsCommitCount int `json:"affectsCommitCount"`
+	// Distro is the effective distro name.


Why does this need to be tracked?

reubeno · 2026-04-11T00:09:44Z

internal/fingerprint/fingerprint.go

+func ComputeIdentity(
+	fs opctx.FS,
+	component projectconfig.ComponentConfig,
+	distroRef projectconfig.DistroReference,


Is this the distro that the component is being built for or the distro that the component's spec may have come from? Can we document and clarify?

It should be the effective distro for the component, ie if one is set, pick that, otherwise the global default.

That said, we can probably drop it to just ReleaseVer, that might be the only bit we really care about.

reubeno · 2026-04-11T00:12:19Z

internal/fingerprint/fingerprint.go

+	hashes := make(map[string]string)
+
+	for idx, overlay := range overlays {
+		if overlay.Source == "" {


Since this logic needs to know specific properties of different overlay types -- is there a way for this logic to live closer to the implementation of the overlay types? It otherwise may not occur to someone (AI or human) to keep this in sync.

Sure, I'll have a look

Copilot

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 1 comment.

Copilot · 2026-04-11T00:18:08Z

internal/fingerprint/fingerprint.go

+	// Overlay file hashes in sorted key order for determinism.
+	if len(inputs.OverlayFileHashes) > 0 {
+		keys := make([]string, 0, len(inputs.OverlayFileHashes))
+		for key := range inputs.OverlayFileHashes {
+			keys = append(keys, key)
+		}
+
+		sort.Strings(keys)
+
+		for _, key := range keys {
+			writeField(hasher, "overlay:"+key, inputs.OverlayFileHashes[key])
+		}
+	}


combineInputs sorts overlay indices as strings ("10" comes before "2"), so once there are >= 11 overlays the hash-combination order won’t match overlay order. Consider either writing overlay hashes in slice/index order directly, or sorting by integer index to keep ordering intuitive and stable across multi-digit indices.

I don't think this matters? The fingerprint is an opaque value, so long as its stable and reproducible the exact ordering seems unimportant.

Copilot AI review requested due to automatic review settings March 31, 2026 00:53

Copilot started reviewing on behalf of dmcilvaney March 31, 2026 00:54 View session

dmcilvaney mentioned this pull request Mar 31, 2026

feat(component): Add component change detection #42

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Copilot AI reviewed Mar 31, 2026

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dmcilvaney force-pushed the damcilva/component_change_detection_parts/5 branch from a7d028e to 3fb8df7 Compare March 31, 2026 01:06

Copilot AI review requested due to automatic review settings March 31, 2026 01:07

dmcilvaney force-pushed the damcilva/component_change_detection_parts/5 branch from 3fb8df7 to 759c099 Compare March 31, 2026 01:07

Copilot started reviewing on behalf of dmcilvaney March 31, 2026 01:08 View session

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dmcilvaney marked this pull request as draft March 31, 2026 01:41

dmcilvaney mentioned this pull request Apr 1, 2026

feat(config): Add fingerprint ignore tags to some config fields #46

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dmcilvaney added 2 commits April 10, 2026 15:26

feat(component): Add deterministic component fingerprints

15dcea7

add explicit check that hash is set for components

94e19ff

dmcilvaney force-pushed the damcilva/component_change_detection_parts/5 branch from 0140c52 to 94e19ff Compare April 10, 2026 22:27

Copilot AI review requested due to automatic review settings April 10, 2026 22:27

Copilot AI reviewed Apr 10, 2026

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dmcilvaney added 2 commits April 10, 2026 15:55

feedback: ignore spec dir, use file utils

78e76d5

fix: handle overlay source files better

98422f3

Copilot AI review requested due to automatic review settings April 10, 2026 23:03

feedback: don't need to export repo root func anymore

ce450ef

Copilot AI reviewed Apr 10, 2026

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Copilot started reviewing on behalf of dmcilvaney April 10, 2026 23:13 View session

dmcilvaney added 2 commits April 10, 2026 16:36

fix: handle overlay patch paths

f2c50ee

feedback: force identity, fix comment

cf9d102

Copilot AI review requested due to automatic review settings April 10, 2026 23:43

Copilot started reviewing on behalf of dmcilvaney April 10, 2026 23:45 View session

dmcilvaney marked this pull request as ready for review April 10, 2026 23:48

Copilot AI reviewed Apr 10, 2026

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Update internal/projectconfig/specsource.go

26fd8d3

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings April 11, 2026 00:12

reubeno reviewed Apr 11, 2026

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Copilot started reviewing on behalf of dmcilvaney April 11, 2026 00:15 View session

Copilot AI reviewed Apr 11, 2026

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feedback: use releasever, move overlay logic

561fb1f

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