Add support for custom working directory

README.md

@@ -26,11 +26,12 @@ Then, to install the resulting mixin into PORTER_HOME, execute
 
 ## Mixin Configuration
 
-The Terraform client version can be specified via the `clientVersion` configuration when declaring this mixin.
+When declaring this mixin, the Terraform client version and the working directory can be specified using the `clientVersion` and `workingDirectory` configuration properties:
 
 ```yaml
 - terraform:
     clientVersion: 0.12.17
+    workingDirectory: /cnab/app/terraform
 ```
 
 ## Terraform state

pkg/terraform/build.go

@@ -8,11 +8,12 @@ import (
 )
 
 const dockerfileLines = `ENV TERRAFORM_VERSION=%s
+ENV TERRAFORM_WORKING_DIRECTORY=%s
 RUN apt-get update && apt-get install -y wget unzip && \
  wget https://releases.hashicorp.com/terraform/${TERRAFORM_VERSION}/terraform_${TERRAFORM_VERSION}_linux_amd64.zip && \
  unzip terraform_${TERRAFORM_VERSION}_linux_amd64.zip -d /usr/bin
 COPY . $BUNDLE_DIR
-RUN cd %s && terraform init -backend=false
+RUN cd ${TERRAFORM_WORKING_DIRECTORY} && terraform init -backend=false
 `
 
 // BuildInput represents stdin passed to the mixin for the build command.
@@ -24,8 +25,10 @@ type BuildInput struct {
 // mixins:
 // - terraform:
 //	  version: 0.12.17
+//    workingDir: terraform
 type MixinConfig struct {
-	ClientVersion string `yaml:"clientVersion,omitempty"`
+	ClientVersion    string `yaml:"clientVersion,omitempty"`
+	WorkingDirectory string `yaml:"workingDir,omitempty"`
 }
 
 func (m *Mixin) Build() error {
@@ -42,6 +45,10 @@ func (m *Mixin) Build() error {
 		m.TerraformVersion = input.Config.ClientVersion
 	}
 
+	if input.Config.WorkingDirectory != "" {
+		m.WorkingDir = input.Config.WorkingDirectory
+	}
+
 	fmt.Fprintf(m.Out, dockerfileLines, m.TerraformVersion, m.WorkingDir)
 	return nil
 }

pkg/terraform/build_test.go

@@ -11,26 +11,44 @@ import (
 )
 
 const buildOutputTemplate = `ENV TERRAFORM_VERSION=%s
+ENV TERRAFORM_WORKING_DIRECTORY=%s
 RUN apt-get update && apt-get install -y wget unzip && \
  wget https://releases.hashicorp.com/terraform/${TERRAFORM_VERSION}/terraform_${TERRAFORM_VERSION}_linux_amd64.zip && \
  unzip terraform_${TERRAFORM_VERSION}_linux_amd64.zip -d /usr/bin
 COPY . $BUNDLE_DIR
-RUN cd /cnab/app/terraform && terraform init -backend=false
+RUN cd ${TERRAFORM_WORKING_DIRECTORY} && terraform init -backend=false
 `
 
+const defaultWorkingDirectory = "/cnab/app/terraform"
+
 func TestMixin_Build(t *testing.T) {
 	t.Run("build with the default Terraform version", func(t *testing.T) {
 		m := NewTestMixin(t)
 
 		err := m.Build()
 		require.NoError(t, err)
 
-		wantOutput := fmt.Sprintf(buildOutputTemplate, "0.12.17")
+		wantOutput := fmt.Sprintf(buildOutputTemplate, "0.12.17", defaultWorkingDirectory)
 
 		gotOutput := m.TestContext.GetOutput()
 		assert.Equal(t, wantOutput, gotOutput)
 	})
 
+	t.Run("build with custom working directory", func(t *testing.T) {
+		b, err := ioutil.ReadFile("testdata/build-input-with-working-directory.yaml")
+		require.NoError(t, err)
+
+		m := NewTestMixin(t)
+		m.In = bytes.NewReader(b)
+		err = m.Build()
+		require.NoError(t, err)
+
+		expected := fmt.Sprintf(buildOutputTemplate, "0.12.17", "/cnab/app/custom")
+		actual := m.TestContext.GetOutput()
+
+		assert.Equal(t, expected, actual)
+	})
+
 	t.Run("build with custom Terrafrom version", func(t *testing.T) {
 		b, err := ioutil.ReadFile("testdata/build-input-with-version.yaml")
 		require.NoError(t, err)
@@ -40,7 +58,7 @@ func TestMixin_Build(t *testing.T) {
 		err = m.Build()
 		require.NoError(t, err)
 
-		wantOutput := fmt.Sprintf(buildOutputTemplate, "0.13.0-rc1")
+		wantOutput := fmt.Sprintf(buildOutputTemplate, "0.13.0-rc1", defaultWorkingDirectory)
 
 		gotOutput := m.TestContext.GetOutput()
 		assert.Equal(t, wantOutput, gotOutput)

pkg/terraform/testdata/build-input-with-working-directory.yaml

@@ -0,0 +1,5 @@
+config:
+    workingDirectory: /cnab/app/custom
+    install:
+        - terraform:
+            description: "noop"