Add helmfile_release_set.skip_diff_on_missing_files (#47)

* Add helmfile_release_set.skip_diff_on_missing_files

Resolves #38

pkg/helmfile/release_set.go

@@ -43,6 +43,14 @@ type ReleaseSet struct {
 	// HelmVersion is the version number or the semver version range for the helm version to use
 	HelmVersion     string
 	HelmDiffVersion string
+
+	// SkipDiffOnMissingFiles is the list of local files. Any file contained in the list but missing on the file system
+	// result in the provider to skip running `helmfile-diff`. Use with Terraform's `depends_on`, so that
+	// you can let another dependent Terraform resource to created required files like kubeconfig or Helmfile values
+	// files to be used by the helmfile_release_set.
+	//
+	// See https://github.com/mumoshu/terraform-provider-helmfile/issues/38 for more information on expected use-cases.
+	SkipDiffOnMissingFiles []string
 }
 
 func NewReleaseSet(d ResourceRead) (*ReleaseSet, error) {
@@ -77,6 +85,16 @@ func NewReleaseSet(d ResourceRead) (*ReleaseSet, error) {
 		f.ValuesFiles = valuesFiles.([]interface{})
 	}
 
+	if vs := d.Get(KeySkipDiffOnMissingFiles); vs != nil {
+		var ss []string
+
+		for _, v := range vs.([]interface{}) {
+			ss = append(ss, v.(string))
+		}
+
+		f.SkipDiffOnMissingFiles = ss
+	}
+
 	f.Values = d.Get(KeyValues).([]interface{})
 	f.ReleasesValues = d.Get(KeyReleasesValues).(map[string]interface{})
 	f.Bin = d.Get(KeyBin).(string)

pkg/helmfile/resource_release_set.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"github.com/hashicorp/terraform-plugin-sdk/helper/schema"
 	"github.com/rs/xid"
+	"golang.org/x/xerrors"
 	"log"
 	"os"
 	"runtime/debug"
@@ -26,6 +27,7 @@ const KeyApplyOutput = "apply_output"
 const KeyDirty = "dirty"
 const KeyConcurrency = "concurrency"
 const KeyReleasesValues = "releases_values"
+const KeySkipDiffOnMissingFiles = "skip_diff_on_missing_files"
 
 const HelmfileDefaultPath = "helmfile.yaml"
 
@@ -46,6 +48,14 @@ var ReleaseSetSchema = map[string]*schema.Schema{
 			Type: schema.TypeString,
 		},
 	},
+	KeySkipDiffOnMissingFiles: {
+		Type:     schema.TypeList,
+		Optional: true,
+		ForceNew: false,
+		Elem: &schema.Schema{
+			Type: schema.TypeString,
+		},
+	},
 	KeySelector: {
 		Type:     schema.TypeMap,
 		Optional: true,
@@ -233,6 +243,14 @@ func resourceReleaseSetDiff(d *schema.ResourceDiff, meta interface{}) (finalErr
 		return nil
 	}
 
+	if v, err := shouldDiff(fs); err != nil {
+		return xerrors.Errorf("checking skip_diff_on_missing_files to determine if the provider needs to run helmfile-diff: %w", err)
+	} else if !v {
+		logf("Skipping helmfile-diff due to that one or more files listed in skip_diff_on_missing_files were missing")
+
+		return nil
+	}
+
 	provider := meta.(*ProviderInstance)
 
 	diff, err := DiffReleaseSet(fs, resourceDiffToFields(d), WithDiffConfig(DiffConfig{

pkg/helmfile/skip_diff.go

@@ -0,0 +1,23 @@
+package helmfile
+
+import (
+	"errors"
+	"golang.org/x/xerrors"
+	"os"
+)
+
+func shouldDiff(rs *ReleaseSet) (bool, error) {
+	for _, path := range rs.SkipDiffOnMissingFiles {
+		if _, err := os.Stat(path); err != nil {
+			if errors.Is(err, os.ErrNotExist) {
+				logf("detected missing file: %s", path)
+
+				return false, nil
+			}
+
+			return false, xerrors.Errorf("failed calling stat: %w", err)
+		}
+	}
+
+	return true, nil
+}