fix issues in --reset-values and --reuse-values on helm v3

Closes #157

Author: mumoshu

cmd/helm3.go

@@ -62,27 +62,32 @@ func (d *diffCmd) template() ([]byte, error) {
 	if d.namespace != "" {
 		flags = append(flags, "--namespace", d.namespace)
 	}
-	if !d.resetValues {
-		if d.reuseValues {
-			tmpfile, err := ioutil.TempFile("", "existing-values")
-			if err != nil {
-				return nil, err
-			}
-			defer os.Remove(tmpfile.Name())
-			flags = append(flags, "--values", tmpfile.Name())
+	// Helm automatically enable --reuse-values when there's no --set, --set-string, --set-values, --set-file present.
+	// Let's simulate that in helm-diff.
+	// See https://medium.com/@kcatstack/understand-helm-upgrade-flags-reset-values-reuse-values-6e58ac8f127e
+	shouldDefaultReusingValues := len(d.values) > 0 && len(d.stringValues) > 0 && len(d.valueFiles) > 0 && len(d.fileValues) > 0
+	if (d.reuseValues || shouldDefaultReusingValues) && !d.resetValues {
+		tmpfile, err := ioutil.TempFile("", "existing-values")
+		if err != nil {
+			return nil, err
 		}
-		for _, value := range d.values {
-			flags = append(flags, "--set", value)
-		}
-		for _, stringValue := range d.stringValues {
-			flags = append(flags, "--set-string", stringValue)
-		}
-		for _, valueFile := range d.valueFiles {
-			flags = append(flags, "--values", valueFile)
-		}
-		for _, fileValue := range d.fileValues {
-			flags = append(flags, "--set-file", fileValue)
+		defer os.Remove(tmpfile.Name())
+		if err := d.writeExistingValues(tmpfile); err != nil {
+			return nil, err
 		}
+		flags = append(flags, "--values", tmpfile.Name())
+	}
+	for _, value := range d.values {
+		flags = append(flags, "--set", value)
+	}
+	for _, stringValue := range d.stringValues {
+		flags = append(flags, "--set-string", stringValue)
+	}
+	for _, valueFile := range d.valueFiles {
+		flags = append(flags, "--values", valueFile)
+	}
+	for _, fileValue := range d.fileValues {
+		flags = append(flags, "--set-file", fileValue)
 	}
 
 	args := []string{"template", d.release, d.chart}
@@ -91,8 +96,8 @@ func (d *diffCmd) template() ([]byte, error) {
 	return outputWithRichError(cmd)
 }
 
-func (d *diffCmd) existingValues(f *os.File) error {
-	cmd := exec.Command(os.Getenv("HELM_BIN"), "get", "values", d.release, "--all")
+func (d *diffCmd) writeExistingValues(f *os.File) error {
+	cmd := exec.Command(os.Getenv("HELM_BIN"), "get", "values", d.release, "--all", "--output", "yaml")
 	debugPrint("Executing %s", strings.Join(cmd.Args, " "))
 	defer f.Close()
 	cmd.Stdout = f

cmd/upgrade.go

@@ -86,7 +86,7 @@ func newChartCommand() *cobra.Command {
 	f.StringArrayVar(&diff.values, "set", []string{}, "set values on the command line (can specify multiple or separate values with commas: key1=val1,key2=val2)")
 	f.StringArrayVar(&diff.stringValues, "set-string", []string{}, "set STRING values on the command line (can specify multiple or separate values with commas: key1=val1,key2=val2)")
 	f.StringArrayVar(&diff.fileValues, "set-file", []string{}, "set values from respective files specified via the command line (can specify multiple or separate values with commas: key1=path1,key2=path2)")
-	f.BoolVar(&diff.reuseValues, "reuse-values", false, "reuse the last release's values and merge in any new values")
+	f.BoolVar(&diff.reuseValues, "reuse-values", false, "reuse the last release's values and merge in any new values. If '--reset-values' is specified, this is ignored")
 	f.BoolVar(&diff.resetValues, "reset-values", false, "reset the values to the ones built into the chart and merge in any new values")
 	f.BoolVar(&diff.allowUnreleased, "allow-unreleased", false, "enables diffing of releases that are not yet deployed via Helm")
 	f.BoolVar(&diff.noHooks, "no-hooks", false, "disable diffing of hooks")