feat(component): Add deterministic component fingerprints

go.mod

@@ -36,6 +36,7 @@ require (
 	github.com/magefile/mage v1.17.1
 	github.com/mark3labs/mcp-go v0.46.0
 	github.com/mattn/go-isatty v0.0.20
+	github.com/mitchellh/hashstructure/v2 v2.0.2
 	github.com/muesli/termenv v0.16.0
 	github.com/nxadm/tail v1.4.11
 	github.com/opencontainers/selinux v1.13.1

go.sum

@@ -231,6 +231,8 @@ github.com/mattn/go-runewidth v0.0.15/go.mod h1:Jdepj2loyihRzMpdS35Xk/zdY8IAYHsh
 github.com/mattn/go-runewidth v0.0.16/go.mod h1:Jdepj2loyihRzMpdS35Xk/zdY8IAYHsh153qUoGf23w=
 github.com/mattn/go-runewidth v0.0.21 h1:jJKAZiQH+2mIinzCJIaIG9Be1+0NR+5sz/lYEEjdM8w=
 github.com/mattn/go-runewidth v0.0.21/go.mod h1:XBkDxAl56ILZc9knddidhrOlY5R/pDhgLpndooCuJAs=
+github.com/mitchellh/hashstructure/v2 v2.0.2 h1:vGKWl0YJqUNxE8d+h8f6NJLcCJrgbhC4NcD46KavDd4=
+github.com/mitchellh/hashstructure/v2 v2.0.2/go.mod h1:MG3aRVU/N29oo/V/IhBX8GR/zz4kQkprJgF2EVszyDE=
 github.com/moby/docker-image-spec v1.3.1 h1:jMKff3w6PgbfSa69GfNg+zN/XLhfXJGnEx3Nl2EsFP0=
 github.com/moby/docker-image-spec v1.3.1/go.mod h1:eKmb5VW8vQEh/BAr2yvVNvuiJuY6UIocYsFu/DxxRpo=
 github.com/moby/go-archive v0.2.0 h1:zg5QDUM2mi0JIM9fdQZWC7U8+2ZfixfTYoHL7rWUcP8=

internal/fingerprint/doc.go

@@ -0,0 +1,13 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+// Package fingerprint computes deterministic identity fingerprints for components.
+// A fingerprint captures all resolved build inputs so that changes to any input
+// (config fields, spec content, overlay files, distro context, upstream refs, or
+// Affects commit count) produce a different fingerprint.
+//
+// The primary entry point is [ComputeIdentity], which takes a resolved
+// [projectconfig.ComponentConfig] and additional context, and returns a
+// [ComponentIdentity] containing the overall fingerprint hash plus a breakdown
+// of individual input hashes for debugging.
+package fingerprint

internal/fingerprint/fingerprint.go

@@ -0,0 +1,174 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+package fingerprint
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"sort"
+	"strconv"
+
+	"github.com/microsoft/azure-linux-dev-tools/internal/global/opctx"
+	"github.com/microsoft/azure-linux-dev-tools/internal/projectconfig"
+	"github.com/mitchellh/hashstructure/v2"
+)
+
+// hashstructureTagName is the struct tag name used by hashstructure to determine
+// field inclusion. Fields tagged with `fingerprint:"-"` are excluded.
+const hashstructureTagName = "fingerprint"
+
+// ComponentIdentity holds the computed fingerprint for a single component plus
+// a breakdown of individual input hashes for debugging.
+type ComponentIdentity struct {
+	// Fingerprint is the overall SHA256 hash combining all inputs.
+	Fingerprint string `json:"fingerprint"`
+	// Inputs provides the individual input hashes that were combined.
+	Inputs ComponentInputs `json:"inputs"`
+}
+
+// ComponentInputs contains the individual input hashes that comprise a component's
+// fingerprint.
+type ComponentInputs struct {
+	// ConfigHash is the hash of the resolved component config fields (uint64 from hashstructure).
+	ConfigHash uint64 `json:"configHash"`
+	// SourceIdentity is the opaque identity string for the component's source.
+	// For local specs this is a content hash; for upstream specs this is a commit hash.
+	SourceIdentity string `json:"sourceIdentity,omitempty"`
+	// OverlayFileHashes maps overlay index (as string) to a combined hash of the
+	// source file's basename and content. Keyed by index rather than path to avoid
+	// checkout-location dependence.
+	OverlayFileHashes map[string]string `json:"overlayFileHashes,omitempty"`
+	// AffectsCommitCount is the number of "Affects: <component>" commits in the project repo.
+	AffectsCommitCount int `json:"affectsCommitCount"`
+	// ReleaseVer is the distro's formal releasever (e.g., "4.0"), which feeds into
+	// RPM macros like %{dist}. Different release versions produce different package
+	// NEVRAs even with identical specs.
+	ReleaseVer string `json:"releaseVer"`
+}
+
+// IdentityOptions holds additional inputs for computing a component's identity
+// that are not part of the component config itself.
+type IdentityOptions struct {
+	// AffectsCommitCount is the number of "Affects: <component>" commits.
+	AffectsCommitCount int
+	// SourceIdentity is the opaque identity string from a [sourceproviders.SourceIdentityProvider].
+	// For upstream components this is the resolved commit hash; for local components this is a
+	// content hash of the spec directory.
+	//
+	// This is caller-provided because resolving it requires network access (upstream clone) or
+	// filesystem traversal (local content hash). [ComputeIdentity] is a pure combiner — it does
+	// not perform I/O beyond reading overlay files. Callers should resolve source identity via
+	// SourceManager.ResolveSourceIdentity before calling [ComputeIdentity].
+	SourceIdentity string
+}
+
+// ComputeIdentity computes the fingerprint for a component from its resolved config
+// and additional context. The fs parameter is used to read overlay source file
+// contents for hashing; spec content identity is provided via [IdentityOptions.SourceIdentity].
+//
+// This function is a deterministic combiner: given the same resolved inputs it always
+// produces the same fingerprint. It does not resolve source identity or count commits —
+// those are expected to be pre-resolved by the caller and passed via opts.
+func ComputeIdentity(
+	fs opctx.FS,
+	component projectconfig.ComponentConfig,
+	releaseVer string,
+	opts IdentityOptions,
+) (*ComponentIdentity, error) {
+	inputs := ComponentInputs{
+		AffectsCommitCount: opts.AffectsCommitCount,
+		SourceIdentity:     opts.SourceIdentity,
+		ReleaseVer:         releaseVer,
+	}
+
+	// 1. Require source identity when the component has a spec source that
+	//    contributes content. Without it the fingerprint cannot detect spec
+	//    content changes (Spec.Path is excluded from the config hash).
+	if opts.SourceIdentity == "" && component.Spec.SourceType != "" {
+		return nil, fmt.Errorf(
+			"source identity is required for component with source type %#q; "+
+				"resolve it via SourceManager.ResolveSourceIdentity before calling ComputeIdentity",
+			component.Spec.SourceType)
+	}
+
+	// 2. Verify all source files have a hash. Without a hash the fingerprint
+	//    cannot detect content changes, so we refuse to compute one.
+	for i := range component.SourceFiles {
+		if component.SourceFiles[i].Hash == "" {
+			return nil, fmt.Errorf(
+				"source file %#q has no hash; cannot compute a deterministic fingerprint",
+				component.SourceFiles[i].Filename,
+			)
+		}
+	}
+
+	// 3. Hash the resolved config struct (excluding fingerprint:"-" fields).
+	configHash, err := hashstructure.Hash(component, hashstructure.FormatV2, &hashstructure.HashOptions{
+		TagName: hashstructureTagName,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("hashing component config:\n%w", err)
+	}
+
+	inputs.ConfigHash = configHash
+
+	// 4. Hash overlay source file contents. Each overlay owns its identity
+	//    computation via [projectconfig.ComponentOverlay.SourceContentIdentity].
+	overlayHashes := make(map[string]string)
+
+	for idx := range component.Overlays {
+		identity, overlayErr := component.Overlays[idx].SourceContentIdentity(fs)
+		if overlayErr != nil {
+			return nil, fmt.Errorf("hashing overlay %d source:\n%w", idx, overlayErr)
+		}
+
+		if identity != "" {
+			overlayHashes[strconv.Itoa(idx)] = identity
+		}
+	}
+
+	inputs.OverlayFileHashes = overlayHashes
+
+	// 5. Combine all inputs into the overall fingerprint.
+	return &ComponentIdentity{
+		Fingerprint: combineInputs(inputs),
+		Inputs:      inputs,
+	}, nil
+}
+
+// combineInputs deterministically combines all input hashes into a single SHA256 fingerprint.
+func combineInputs(inputs ComponentInputs) string {
+	hasher := sha256.New()
+
+	// Write each input in a fixed order with field labels for domain separation.
+	writeField(hasher, "config_hash", strconv.FormatUint(inputs.ConfigHash, 10))
+	writeField(hasher, "source_identity", inputs.SourceIdentity)
+	writeField(hasher, "affects_commit_count", strconv.Itoa(inputs.AffectsCommitCount))
+	writeField(hasher, "release_ver", inputs.ReleaseVer)
+
+	// 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])
+		}
+	}
+
+	return "sha256:" + hex.EncodeToString(hasher.Sum(nil))
+}
+
+// writeField writes a labeled value to the hasher for domain separation.
+func writeField(writer io.Writer, label string, value string) {
+	// Length-prefix both label and value to prevent injection of fake field records
+	// via values containing newlines.
+	fmt.Fprintf(writer, "%d:%s=%d:%s\n", len(label), label, len(value), value)
+}