feat(cli): Add component identity sub-command

Author: dmcilvaney

internal/app/azldev/cmds/component/component.go

@@ -26,6 +26,7 @@ components defined in the project configuration.`,
 	addOnAppInit(app, cmd)
 	buildOnAppInit(app, cmd)
 	diffSourcesOnAppInit(app, cmd)
+	identityOnAppInit(app, cmd)
 	listOnAppInit(app, cmd)
 	prepareOnAppInit(app, cmd)
 	queryOnAppInit(app, cmd)

internal/app/azldev/cmds/component/identity.go

@@ -0,0 +1,131 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+package component
+
+import (
+	"fmt"
+	"log/slog"
+
+	"github.com/microsoft/azure-linux-dev-tools/internal/app/azldev"
+	"github.com/microsoft/azure-linux-dev-tools/internal/app/azldev/core/components"
+	"github.com/microsoft/azure-linux-dev-tools/internal/app/azldev/core/sources"
+	"github.com/microsoft/azure-linux-dev-tools/internal/fingerprint"
+	"github.com/microsoft/azure-linux-dev-tools/internal/projectconfig"
+	"github.com/spf13/cobra"
+)
+
+// Options for computing component identity fingerprints.
+type IdentityComponentOptions struct {
+	// Standard filter for selecting components.
+	ComponentFilter components.ComponentFilter
+}
+
+func identityOnAppInit(_ *azldev.App, parentCmd *cobra.Command) {
+	parentCmd.AddCommand(NewComponentIdentityCommand())
+}
+
+// Constructs a [cobra.Command] for "component identity" CLI subcommand.
+func NewComponentIdentityCommand() *cobra.Command {
+	options := &IdentityComponentOptions{}
+
+	cmd := &cobra.Command{
+		Use:   "identity",
+		Short: "Compute identity fingerprints for components",
+		Long: `Compute a deterministic identity fingerprint for each selected component.
+
+The fingerprint captures all resolved build inputs (config fields, spec file
+content, overlay source files, distro context, and Affects commit count).
+A change to any input produces a different fingerprint.
+
+Use this with 'component diff-identity' to determine which components need
+rebuilding between two commits.`,
+		Example: `  # All components, JSON output for CI
+  azldev component identity -a -O json > identity.json
+
+  # Single component, table output for dev
+  azldev component identity -p curl
+
+  # Components in a group
+  azldev component identity -g core`,
+		RunE: azldev.RunFuncWithExtraArgs(func(env *azldev.Env, args []string) (interface{}, error) {
+			options.ComponentFilter.ComponentNamePatterns = append(
+				args, options.ComponentFilter.ComponentNamePatterns...,
+			)
+
+			return ComputeComponentIdentities(env, options)
+		}),
+		ValidArgsFunction: components.GenerateComponentNameCompletions,
+	}
+
+	azldev.ExportAsMCPTool(cmd)
+	components.AddComponentFilterOptionsToCommand(cmd, &options.ComponentFilter)
+
+	return cmd
+}
+
+// ComponentIdentityResult is the per-component output for the identity command.
+type ComponentIdentityResult struct {
+	// Component is the component name.
+	Component string `json:"component" table:",sortkey"`
+	// Fingerprint is the overall identity hash string.
+	Fingerprint string `json:"fingerprint"`
+	// Inputs provides the individual input hashes (shown in JSON output).
+	Inputs fingerprint.ComponentInputs `json:"inputs" table:"-"`
+}
+
+// ComputeComponentIdentities computes fingerprints for all selected components.
+func ComputeComponentIdentities(
+	env *azldev.Env, options *IdentityComponentOptions,
+) ([]ComponentIdentityResult, error) {
+	resolver := components.NewResolver(env)
+
+	comps, err := resolver.FindComponents(&options.ComponentFilter)
+	if err != nil {
+		return nil, fmt.Errorf("failed to resolve components:\n%w", err)
+	}
+
+	distroRef := env.Config().Project.DefaultDistro
+
+	results := make([]ComponentIdentityResult, 0, comps.Len())
+
+	for _, comp := range comps.Components() {
+		config := comp.GetConfig()
+		componentName := comp.GetName()
+
+		// Count Affects commits for this component.
+		affectsCount := countAffectsCommits(config, componentName)
+
+		identity, identityErr := fingerprint.ComputeIdentity(
+			env.FS(), *config, distroRef, affectsCount,
+		)
+		if identityErr != nil {
+			return nil, fmt.Errorf("computing identity for component %#q:\n%w",
+				componentName, identityErr)
+		}
+
+		results = append(results, ComponentIdentityResult{
+			Component:   componentName,
+			Fingerprint: identity.Fingerprint,
+			Inputs:      identity.Inputs,
+		})
+	}
+
+	return results, nil
+}
+
+// countAffectsCommits counts the number of "Affects: <componentName>" commits in the
+// project repo. Returns 0 if the count cannot be determined (e.g., no git repo).
+func countAffectsCommits(
+	config *projectconfig.ComponentConfig, componentName string,
+) int {
+	commits, err := sources.CountAffectsCommits(config, componentName)
+	if err != nil {
+		slog.Debug("Could not count Affects commits; defaulting to 0",
+			"component", componentName, "error", err)
+
+		return 0
+	}
+
+	return commits
+}

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

@@ -82,6 +82,30 @@ func FindAffectsCommits(repo *gogit.Repository, componentName string) ([]CommitM
 	return matches, nil
 }
 
+// CountAffectsCommits returns the number of "Affects: <componentName>" commits in the
+// project repository that contains the component's config file. Returns 0 and an error
+// if the repository cannot be opened or the config file path is unavailable.
+func CountAffectsCommits(
+	config *projectconfig.ComponentConfig, componentName string,
+) (int, error) {
+	configFilePath, err := resolveConfigFilePath(config, componentName)
+	if err != nil {
+		return 0, fmt.Errorf("resolving config file path:\n%w", err)
+	}
+
+	projectRepo, _, err := openProjectRepo(configFilePath)
+	if err != nil {
+		return 0, fmt.Errorf("opening project repo:\n%w", err)
+	}
+
+	commits, err := FindAffectsCommits(projectRepo, componentName)
+	if err != nil {
+		return 0, fmt.Errorf("finding Affects commits:\n%w", err)
+	}
+
+	return len(commits), nil
+}
+
 // CommitSyntheticHistory stages all pending working tree changes and creates synthetic
 // commits in the provided git repository. The first commit captures all file changes;
 // subsequent commits are created as empty commits to preserve the commit count for