support substitutions in provides lists

examples/replacement-provides.yaml

@@ -0,0 +1,13 @@
+package:
+  name: replacement-provides
+  version: 0.0.1
+  description: example using a replacement in provides
+  dependencies:
+    provides:
+      - replacement-provides-version=${{package.version}}
+      - replacement-provides-foo=${{vars.foo}}
+      - replacement-provides-bar=${{vars.bar}}
+
+vars:
+  foo: FOO
+  bar: BAR

pkg/config/config.go

@@ -23,6 +23,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"sort"
+	"strconv"
 	"strings"
 
 	apko_types "chainguard.dev/apko/pkg/build/types"
@@ -33,6 +34,7 @@ import (
 	"gopkg.in/yaml.v3"
 
 	"chainguard.dev/melange/pkg/logger"
+	"chainguard.dev/melange/pkg/util"
 )
 
 type Scriptlets struct {
@@ -115,6 +117,27 @@ func (p Package) PackageURL(distro string) string {
 	)
 }
 
+func (c *Configuration) applySubstitutionsForProvides() error {
+	nw := buildConfigMap(c)
+	for i, prov := range c.Package.Dependencies.Provides {
+		var err error
+		c.Package.Dependencies.Provides[i], err = util.MutateStringFromMap(nw, prov)
+		if err != nil {
+			return fmt.Errorf("failed to apply replacement to provides %q: %w", prov, err)
+		}
+	}
+	for _, sp := range c.Subpackages {
+		for i, prov := range sp.Dependencies.Provides {
+			var err error
+			sp.Dependencies.Provides[i], err = util.MutateStringFromMap(nw, prov)
+			if err != nil {
+				return fmt.Errorf("failed to apply replacement to provides %q: %w", prov, err)
+			}
+		}
+	}
+	return nil
+}
+
 type Copyright struct {
 	// Optional: The license paths, typically '*'
 	Paths []string `yaml:"paths,omitempty"`
@@ -447,9 +470,10 @@ func detectCommit(dirPath string, logger apko_log.Logger) string {
 // buildConfigMap builds a map used to prepare a replacer for variable substitution.
 func buildConfigMap(cfg *Configuration) map[string]string {
 	out := map[string]string{
-		"${{package.name}}":        cfg.Package.Name,
-		"${{package.version}}":     cfg.Package.Version,
-		"${{package.description}}": cfg.Package.Description,
+		SubstitutionPackageName:        cfg.Package.Name,
+		SubstitutionPackageVersion:     cfg.Package.Version,
+		SubstitutionPackageDescription: cfg.Package.Description,
+		SubstitutionPackageEpoch:       strconv.FormatUint(cfg.Package.Epoch, 10),
 	}
 
 	for k, v := range cfg.Vars {
@@ -675,6 +699,10 @@ func ParseConfiguration(configurationFilePath string, opts ...ConfigurationParsi
 
 	cfg.Subpackages = subpackages
 
+	if err := cfg.applySubstitutionsForProvides(); err != nil {
+		return nil, err
+	}
+
 	// Finally, validate the configuration we ended up with before returning it for use downstream.
 	if err = cfg.validate(); err != nil {
 		return nil, fmt.Errorf("validating configuration: %w", err)

pkg/config/config_test.go

@@ -0,0 +1,53 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func Test_applySubstitutionsInProvides(t *testing.T) {
+	fp := filepath.Join(os.TempDir(), "melange-test-applySubstitutionsInProvides")
+	if err := os.WriteFile(fp, []byte(`
+package:
+  name: replacement-provides
+  version: 0.0.1
+  description: example using a replacement in provides
+  dependencies:
+    provides:
+      - replacement-provides-version=${{package.version}}
+      - replacement-provides-foo=${{vars.foo}}
+      - replacement-provides-bar=${{vars.bar}}
+
+vars:
+  foo: FOO
+  bar: BAR
+
+subpackages:
+  - name: subpackage
+    dependencies:
+      provides:
+        - subpackage-version=${{package.version}}
+        - subpackage-foo=${{vars.foo}}
+        - subpackage-bar=${{vars.bar}}
+`), 0644); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := ParseConfiguration(fp)
+	if err != nil {
+		t.Fatalf("failed to parse configuration: %s", err)
+	}
+	require.Equal(t, []string{
+		"replacement-provides-version=0.0.1",
+		"replacement-provides-foo=FOO",
+		"replacement-provides-bar=BAR",
+	}, cfg.Package.Dependencies.Provides)
+
+	require.Equal(t, []string{
+		"subpackage-version=0.0.1",
+		"subpackage-foo=FOO",
+		"subpackage-bar=BAR",
+	}, cfg.Subpackages[0].Dependencies.Provides)
+}

pkg/config/vars.go

@@ -27,6 +27,7 @@ const (
 	SubstitutionPackageName          = "${{package.name}}"
 	SubstitutionPackageVersion       = "${{package.version}}"
 	SubstitutionPackageEpoch         = "${{package.epoch}}"
+	SubstitutionPackageDescription   = "${{package.description}}"
 	SubstitutionTargetsDestdir       = "${{targets.destdir}}"
 	SubstitutionSubPkgDir            = "${{targets.subpkgdir}}"
 	SubstitutionHostTripletGnu       = "${{host.triplet.gnu}}"