cnbBuild: allow expansion of buildEnvVars (#4802)

* cnbBuild: allow expansion of `buildEnvVars`

* Update resources/metadata/cnbBuild.yaml

Co-authored-by: Ralf Pannemans <ralf.pannemans@googlemail.com>

---------

Co-authored-by: Ralf Pannemans <ralf.pannemans@googlemail.com>

cmd/cnbBuild.go

@@ -455,6 +455,10 @@ func runCnbBuild(config *cnbBuildOptions, telemetry *buildpacks.Telemetry, image
 	}
 	commonPipelineEnvironment.container.imageNames = append(commonPipelineEnvironment.container.imageNames, imageNameAlias)
 
+	if config.ExpandBuildEnvVars {
+		config.BuildEnvVars = expandEnvVars(config.BuildEnvVars)
+	}
+
 	if config.BuildEnvVars != nil && len(config.BuildEnvVars) > 0 {
 		log.Entry().Infof("Setting custom environment variables: '%v'", config.BuildEnvVars)
 		imageSummary.AddEnv(config.BuildEnvVars)
@@ -619,6 +623,19 @@ func runCnbBuild(config *cnbBuildOptions, telemetry *buildpacks.Telemetry, image
 	return nil
 }
 
+func expandEnvVars(envVars map[string]any) map[string]any {
+	expandedEnvVars := map[string]any{}
+	for key, value := range envVars {
+		valueString, valueIsString := value.(string)
+		if valueIsString {
+			expandedEnvVars[key] = os.ExpandEnv(valueString)
+		} else {
+			expandedEnvVars[key] = value
+		}
+	}
+	return expandedEnvVars
+}
+
 func createInitialTelemetrySegment(config *cnbBuildOptions, utils cnbutils.BuildUtils) *buildpacks.Segment {
 	telemetrySegment := buildpacks.NewSegment()
 	projectPath, _, _ := config.resolvePath(utils)          // ignore error here, telemetry problems should not fail the build

cmd/cnbBuild_generated.go

@@ -30,6 +30,7 @@ type cnbBuildOptions struct {
 	PreBuildpacks             []string                 `json:"preBuildpacks,omitempty"`
 	PostBuildpacks            []string                 `json:"postBuildpacks,omitempty"`
 	BuildEnvVars              map[string]interface{}   `json:"buildEnvVars,omitempty"`
+	ExpandBuildEnvVars        bool                     `json:"expandBuildEnvVars,omitempty"`
 	Path                      string                   `json:"path,omitempty"`
 	ProjectDescriptor         string                   `json:"projectDescriptor,omitempty"`
 	DockerConfigJSON          string                   `json:"dockerConfigJSON,omitempty"`
@@ -238,6 +239,7 @@ func addCnbBuildFlags(cmd *cobra.Command, stepConfig *cnbBuildOptions) {
 	cmd.Flags().StringSliceVar(&stepConfig.PreBuildpacks, "preBuildpacks", []string{}, "Buildpacks to prepend to the groups in the builder's order.")
 	cmd.Flags().StringSliceVar(&stepConfig.PostBuildpacks, "postBuildpacks", []string{}, "Buildpacks to append to the groups in the builder's order.")
 
+	cmd.Flags().BoolVar(&stepConfig.ExpandBuildEnvVars, "expandBuildEnvVars", false, "Expand environment variables used in `buildEnvVars`.\nExample:\n```yaml\nexpandBuildEnvVars: true\nbuildEnvVars:\n  foo: ${BAR}\n```\n")
 	cmd.Flags().StringVar(&stepConfig.Path, "path", os.Getenv("PIPER_path"), "Glob that should either point to a directory with your sources or one artifact in zip format.\nThis property determines the input to the buildpack.\n")
 	cmd.Flags().StringVar(&stepConfig.ProjectDescriptor, "projectDescriptor", `project.toml`, "Relative path to the project.toml file.\nSee [buildpacks.io](https://buildpacks.io/docs/reference/config/project-descriptor/) for the reference.\nParameters passed to the cnbBuild step will take precedence over the parameters set in the project.toml file, except the `env` block.\nEnvironment variables declared in a project descriptor file, will be merged with the `buildEnvVars` property, with the `buildEnvVars` having a precedence.\n\n*Note*: The project descriptor path should be relative to what is set in the [path](#path) property. If the `path` property is pointing to a zip archive (e.g. jar file), project descriptor path will be relative to the root of the workspace.\n\n*Note*: Inline buildpacks (see [specification](https://buildpacks.io/docs/reference/config/project-descriptor/#build-_table-optional_)) are not supported yet.\n")
 	cmd.Flags().StringVar(&stepConfig.DockerConfigJSON, "dockerConfigJSON", os.Getenv("PIPER_dockerConfigJSON"), "Path to the file `.docker/config.json` - this is typically provided by your CI/CD system. You can find more details about the Docker credentials in the [Docker documentation](https://docs.docker.com/engine/reference/commandline/login/).")
@@ -371,6 +373,15 @@ func cnbBuildMetadata() config.StepData {
 						Mandatory:   false,
 						Aliases:     []config.Alias{},
 					},
+					{
+						Name:        "expandBuildEnvVars",
+						ResourceRef: []config.ResourceReference{},
+						Scope:       []string{"PARAMETERS", "STAGES", "STEPS"},
+						Type:        "bool",
+						Mandatory:   false,
+						Aliases:     []config.Alias{},
+						Default:     false,
+					},
 					{
 						Name:        "path",
 						ResourceRef: []config.ResourceReference{},

cmd/cnbBuild_test.go

@@ -238,16 +238,17 @@ func TestRunCnbBuild(t *testing.T) {
 		assert.Equal(t, "my-image:0.0.1", commonPipelineEnvironment.container.imageNameTag)
 	})
 
-	t.Run("success case (custom buildpacks and custom env variables, renaming docker conf file, additional tag)", func(t *testing.T) {
-		t.Parallel()
+	t.Run("success case (custom buildpacks and custom env variables with expand, renaming docker conf file, additional tag)", func(t *testing.T) {
+		t.Setenv("BAR", "BAZZ")
 		config := cnbBuildOptions{
 			ContainerImageName:   "my-image",
 			ContainerImageTag:    "0.0.1",
 			ContainerRegistryURL: imageRegistry,
 			DockerConfigJSON:     "/path/to/test.json",
 			Buildpacks:           []string{"test"},
+			ExpandBuildEnvVars:   true,
 			BuildEnvVars: map[string]interface{}{
-				"FOO": "BAR",
+				"FOO": "${BAR}",
 			},
 			AdditionalTags: []string{"latest"},
 		}
@@ -269,6 +270,8 @@ func TestRunCnbBuild(t *testing.T) {
 
 		copiedFileExists, _ := utils.FileExists("/tmp/config.json")
 		assert.True(t, copiedFileExists)
+
+		assetBuildEnv(t, utils, "FOO", "BAZZ")
 	})
 
 	t.Run("success case (custom buildpacks, pre and post buildpacks and custom env variables, renaming docker conf file, additional tag)", func(t *testing.T) {
@@ -281,8 +284,9 @@ func TestRunCnbBuild(t *testing.T) {
 			PreBuildpacks:        []string{"pre-test"},
 			PostBuildpacks:       []string{"post-test"},
 			Buildpacks:           []string{"test"},
+			ExpandBuildEnvVars:   false,
 			BuildEnvVars: map[string]interface{}{
-				"FOO": "BAR",
+				"FOO": "${BAR}",
 			},
 			AdditionalTags: []string{"latest"},
 		}
@@ -304,6 +308,8 @@ func TestRunCnbBuild(t *testing.T) {
 
 		copiedFileExists, _ := utils.FileExists("/tmp/config.json")
 		assert.True(t, copiedFileExists)
+
+		assetBuildEnv(t, utils, "FOO", "${BAR}")
 	})
 
 	t.Run("success case (custom pre and post buildpacks and custom env variables, renaming docker conf file, additional tag)", func(t *testing.T) {

resources/metadata/cnbBuild.yaml

@@ -138,6 +138,21 @@ spec:
           - PARAMETERS
           - STAGES
           - STEPS
+      - name: expandBuildEnvVars
+        type: "bool"
+        default: false
+        description: |
+          Expand environment variables used in `buildEnvVars`.
+          Example:
+          ```yaml
+          expandBuildEnvVars: true
+          buildEnvVars:
+            foo: ${BAR}
+          ```
+        scope:
+          - PARAMETERS
+          - STAGES
+          - STEPS
       - name: path
         type: string
         description: |