terraform: add Input API to ResourceProvider

terraform/resource_provider.go

@@ -4,6 +4,15 @@ package terraform
 // resource provider: the thing that creates and manages the resources in
 // a Terraform configuration.
 type ResourceProvider interface {
+	// Input is called to ask the provider to ask the user for input
+	// for completing the configuration if necesarry.
+	//
+	// This may or may not be called, so resource provider writers shouldn't
+	// rely on this being available to set some default values for validate
+	// later. Example of a situation where this wouldn't be called is if
+	// the user is not using a TTY.
+	Input(UIInput, *ResourceConfig) (*ResourceConfig, error)
+
 	// Validate is called once at the beginning with the raw configuration
 	// (no interpolation done) and can return a list of warnings and/or
 	// errors.

terraform/resource_provider_mock.go

@@ -12,6 +12,11 @@ type MockResourceProvider struct {
 	// Anything you want, in case you need to store extra data with the mock.
 	Meta interface{}
 
+	InputCalled                  bool
+	InputInput                   UIInput
+	InputConfig                  *ResourceConfig
+	InputReturnConfig            *ResourceConfig
+	InputReturnError             error
 	ApplyCalled                  bool
 	ApplyInfo                    *InstanceInfo
 	ApplyState                   *InstanceState
@@ -51,6 +56,14 @@ type MockResourceProvider struct {
 	ValidateResourceReturnErrors []error
 }
 
+func (p *MockResourceProvider) Input(
+	input UIInput, c *ResourceConfig) (*ResourceConfig, error) {
+	p.InputCalled = true
+	p.InputInput = input
+	p.InputConfig = c
+	return p.InputReturnConfig, p.InputReturnError
+}
+
 func (p *MockResourceProvider) Validate(c *ResourceConfig) ([]string, []error) {
 	p.Lock()
 	defer p.Unlock()