feat: HELM_DIFF_USE_UPGRADE_DRY_RUN (#330)

Resolves #253

Author: mumoshu

README.md

@@ -120,8 +120,14 @@ Examples:
 
   # Set HELM_DIFF_IGNORE_UNKNOWN_FLAGS=true to ignore unknown flags
   # It's useful when you're using `helm-diff` in a `helm upgrade` wrapper.
+  # See https://github.com/databus23/helm-diff/issues/278 for more information.
   HELM_DIFF_IGNORE_UNKNOWN_FLAGS=true helm diff upgrade my-release stable/postgres --wait
 
+  # Set HELM_DIFF_USE_UPGRADE_DRY_RUN=true to
+  # use `helm upgrade --dry-run` instead of `helm template` to render manifests from the chart.
+  # See https://github.com/databus23/helm-diff/issues/253 for more information.
+  HELM_DIFF_USE_UPGRADE_DRY_RUN=true helm diff upgarde my-release datadog/datadog
+
 Flags:
       --allow-unreleased             enables diffing of releases that are not yet deployed via Helm
   -a, --api-versions stringArray     Kubernetes api versions used for Capabilities.APIVersions

cmd/helm3.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"bytes"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -129,26 +130,63 @@ func (d *diffCmd) template(isUpgrade bool) ([]byte, error) {
 		flags = append(flags, "--set-file", fileValue)
 	}
 
-	if !d.disableValidation && !d.dryRun {
-		flags = append(flags, "--validate")
-	}
-
-	if isUpgrade {
-		flags = append(flags, "--is-upgrade")
-	}
-
 	if d.disableOpenAPIValidation {
 		flags = append(flags, "--disable-openapi-validation")
 	}
 
-	for _, a := range d.extraAPIs {
-		flags = append(flags, "--api-versions", a)
+	var (
+		subcmd string
+		filter func([]byte) []byte
+	)
+
+	if d.useUpgradeDryRun {
+		if d.dryRun {
+			return nil, fmt.Errorf("`diff upgrade --dry-run` conflicts with HELM_DIFF_USE_UPGRADE_DRY_RUN_AS_TEMPLATE. Either remove --dry-run to enable cluster access, or unset HELM_DIFF_USE_UPGRADE_DRY_RUN_AS_TEMPLATE to make cluster access unnecessary")
+		}
+
+		flags = append(flags, "--dry-run")
+		subcmd = "upgrade"
+		filter = func(s []byte) []byte {
+			if len(s) == 0 {
+				return s
+			}
+
+			i := bytes.Index(s, []byte("MANIFEST:"))
+			s = s[i:]
+			i = bytes.Index(s, []byte("---"))
+			s = s[i:]
+			i = bytes.Index(s, []byte("\nNOTES:"))
+			if i != -1 {
+				s = s[:i+1]
+			}
+			return s
+		}
+	} else {
+		if !d.disableValidation && !d.dryRun {
+			flags = append(flags, "--validate")
+		}
+
+		if isUpgrade {
+			flags = append(flags, "--is-upgrade")
+		}
+
+		for _, a := range d.extraAPIs {
+			flags = append(flags, "--api-versions", a)
+		}
+
+		subcmd = "template"
+
+		filter = func(s []byte) []byte {
+			return s
+		}
 	}
 
-	args := []string{"template", d.release, d.chart}
+	args := []string{subcmd, d.release, d.chart}
 	args = append(args, flags...)
+
 	cmd := exec.Command(os.Getenv("HELM_BIN"), args...)
-	return outputWithRichError(cmd)
+	out, err := outputWithRichError(cmd)
+	return filter(out), err
 }
 
 func (d *diffCmd) writeExistingValues(f *os.File) error {

cmd/upgrade.go

@@ -61,6 +61,7 @@ type diffCmd struct {
 	normalizeManifests       bool
 	threeWayMerge            bool
 	extraAPIs                []string
+	useUpgradeDryRun         bool
 }
 
 func (d *diffCmd) isAllowUnreleased() bool {
@@ -95,7 +96,13 @@ func newChartCommand() *cobra.Command {
 			"",
 			"  # Set HELM_DIFF_IGNORE_UNKNOWN_FLAGS=true to ignore unknown flags",
 			"  # It's useful when you're using `helm-diff` in a `helm upgrade` wrapper.",
+			"  # See https://github.com/databus23/helm-diff/issues/278 for more information.",
 			"  HELM_DIFF_IGNORE_UNKNOWN_FLAGS=true helm diff upgrade my-release stable/postgres --wait",
+			"",
+			"  # Set HELM_DIFF_USE_UPGRADE_DRY_RUN=true to ",
+			"  # use `helm upgrade --dry-run` instead of `helm template` to render manifests from the chart.",
+			"  # See https://github.com/databus23/helm-diff/issues/253 for more information.",
+			"  HELM_DIFF_USE_UPGRADE_DRY_RUN=true helm diff upgarde my-release datadog/datadog",
 		}, "\n"),
 		Args: func(cmd *cobra.Command, args []string) error {
 			return checkArgsLength(len(args), "release name", "chart path")
@@ -107,6 +114,9 @@ func newChartCommand() *cobra.Command {
 			// Suppress the command usage on error. See #77 for more info
 			cmd.SilenceUsage = true
 
+			// See https://github.com/databus23/helm-diff/issues/253
+			diff.useUpgradeDryRun = os.Getenv("HELM_DIFF_USE_UPGRADE_DRY_RUN") == "true"
+
 			if q, _ := cmd.Flags().GetBool("suppress-secrets"); q {
 				diff.suppressedKinds = append(diff.suppressedKinds, "Secret")
 			}