fix: compose dropping only.localOS in an only filter (#2173)

## Description

This fixes an issue where compose could drop the `only.localOS` filter
through compose.

## Related Issue

Fixes #2158

## Type of change

- [X] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Other (security config, docs update, etc)

## Checklist before merging

- [X] Test, docs, adr added or updated as needed
- [X] [Contributor Guide
Steps](https://github.com/defenseunicorns/zarf/blob/main/CONTRIBUTING.md#developer-workflow)
followed

---------

Co-authored-by: Lucas Rodriguez <lucas.rodriguez9616@gmail.com>

src/pkg/packager/compose.go

@@ -44,7 +44,7 @@ func (p *Packager) composeComponents() error {
 		if err != nil {
 			return err
 		}
-		components = append(components, composed)
+		components = append(components, *composed)
 
 		// merge variables and constants
 		pkgVars = chain.MergeVariables(pkgVars)

src/pkg/packager/composer/list.go

@@ -216,33 +216,37 @@ func (ic *ImportChain) Migrate(build types.ZarfBuildData) (warnings []string) {
 
 // Compose merges the import chain into a single component
 // fixing paths, overriding metadata, etc
-func (ic *ImportChain) Compose() (composed types.ZarfComponent, err error) {
-	composed = ic.tail.ZarfComponent
+func (ic *ImportChain) Compose() (composed *types.ZarfComponent, err error) {
+	composed = &ic.tail.ZarfComponent
 
 	if ic.tail.prev == nil {
 		// only had one component in the import chain
 		return composed, nil
 	}
 
 	if err := ic.fetchOCISkeleton(); err != nil {
-		return composed, err
+		return nil, err
 	}
 
 	// start with an empty component to compose into
-	composed = types.ZarfComponent{}
+	composed = &types.ZarfComponent{}
 
 	// start overriding with the tail node
 	node := ic.tail
 	for node != nil {
 		fixPaths(&node.ZarfComponent, node.relativeToHead)
 
 		// perform overrides here
-		overrideMetadata(&composed, node.ZarfComponent)
-		overrideDeprecated(&composed, node.ZarfComponent)
-		overrideResources(&composed, node.ZarfComponent)
-		overrideActions(&composed, node.ZarfComponent)
+		err := overrideMetadata(composed, node.ZarfComponent)
+		if err != nil {
+			return nil, err
+		}
+
+		overrideDeprecated(composed, node.ZarfComponent)
+		overrideResources(composed, node.ZarfComponent)
+		overrideActions(composed, node.ZarfComponent)
 
-		composeExtensions(&composed, node.ZarfComponent, node.relativeToHead)
+		composeExtensions(composed, node.ZarfComponent, node.relativeToHead)
 
 		node = node.prev
 	}

src/pkg/packager/composer/list_test.go

@@ -253,7 +253,7 @@ func TestCompose(t *testing.T) {
 			if testCase.returnError {
 				require.Contains(t, err.Error(), testCase.expectedErrorMessage)
 			} else {
-				require.EqualValues(t, testCase.expectedComposed, composed)
+				require.EqualValues(t, &testCase.expectedComposed, composed)
 			}
 		})
 	}

src/pkg/packager/composer/override.go

@@ -5,10 +5,12 @@
 package composer
 
 import (
+	"fmt"
+
 	"github.com/defenseunicorns/zarf/src/types"
 )
 
-func overrideMetadata(c *types.ZarfComponent, override types.ZarfComponent) {
+func overrideMetadata(c *types.ZarfComponent, override types.ZarfComponent) error {
 	c.Name = override.Name
 	c.Default = override.Default
 	c.Required = override.Required
@@ -17,6 +19,16 @@ func overrideMetadata(c *types.ZarfComponent, override types.ZarfComponent) {
 	if override.Description != "" {
 		c.Description = override.Description
 	}
+
+	if override.Only.LocalOS != "" {
+		if c.Only.LocalOS != "" {
+			return fmt.Errorf("component %q \"only.localOS\" %q cannot be redefined as %q during compose", c.Name, c.Only.LocalOS, override.Only.LocalOS)
+		}
+
+		c.Only.LocalOS = override.Only.LocalOS
+	}
+
+	return nil
 }
 
 func overrideDeprecated(c *types.ZarfComponent, override types.ZarfComponent) {

src/test/e2e/09_component_compose_test.go

@@ -20,11 +20,12 @@ type CompositionSuite struct {
 }
 
 var (
-	composeExample     = filepath.Join("examples", "composable-packages")
-	composeExamplePath string
-	composeTest        = filepath.Join("src", "test", "packages", "09-composable-packages")
-	composeTestPath    string
-	relCacheDir        string
+	composeExample        = filepath.Join("examples", "composable-packages")
+	composeExamplePath    string
+	composeTest           = filepath.Join("src", "test", "packages", "09-composable-packages")
+	composeTestPath       string
+	composeTestBadLocalOS = filepath.Join("src", "test", "packages", "09-composable-packages", "bad-local-os")
+	relCacheDir           string
 )
 
 func (suite *CompositionSuite) SetupSuite() {
@@ -87,6 +88,8 @@ func (suite *CompositionSuite) Test_1_FullComposability() {
 - name: test-compose-package
   description: A contrived example for podinfo using many Zarf primitives for compose testing
   required: true
+  only:
+    localOS: linux
 `)
 
 	// Check files
@@ -184,6 +187,14 @@ func (suite *CompositionSuite) Test_1_FullComposability() {
             condition: available`)
 }
 
+func (suite *CompositionSuite) Test_2_ComposabilityBadLocalOS() {
+	suite.T().Log("E2E: Package Compose Example")
+
+	_, stdErr, err := e2e.Zarf("package", "create", composeTestBadLocalOS, "-o", "build", "--zarf-cache", relCacheDir, "--no-color", "--confirm")
+	suite.Error(err)
+	suite.Contains(stdErr, "\"only.localOS\" \"linux\" cannot be\n             redefined as \"windows\" during compose")
+}
+
 func TestCompositionSuite(t *testing.T) {
 	suite.Run(t, new(CompositionSuite))
 }

src/test/packages/09-composable-packages/bad-local-os/zarf.yaml

@@ -0,0 +1,14 @@
+kind: ZarfPackageConfig
+metadata:
+  name: test-compose-package
+  description: A contrived example for localOS compose testing
+
+components:
+  - name: test-compose-package
+    description: A contrived example for localOS compose testing
+    only:
+      localOS: windows
+    required: true
+    import:
+      path: ../sub-package
+      name: test-compose-sub-package

src/test/packages/09-composable-packages/sub-package/zarf.yaml

@@ -6,6 +6,8 @@ metadata:
 
 components:
   - name: test-compose-sub-package
+    only:
+      localOS: linux
     charts:
       - name: podinfo-compose
         releaseName: podinfo-compose