--color or HELM_DIFF_COLOR=true to force color (#343)

Resolves #344

Author: mumoshu

README.md

@@ -67,7 +67,7 @@ The Helm Diff Plugin
 
 * Shows a diff explaining what a helm rollback would change:
     This fetches the currently deployed version of a release
-  and compares it to the previously deployed versions of the release, that you 
+  and compares it to the previously deployed version of the release, that you
   want to rollback. This can be used visualize what changes a 
   helm rollback will perform.
 
@@ -83,15 +83,37 @@ Available Commands:
   version     Show version of the helm diff plugin
 
 Flags:
-  -h, --help                   help for diff
-      --no-color               remove colors from the output
-      --reset-values           reset the values to the ones built into the chart and merge in any new values
-      --reuse-values           reuse the last release's values and merge in any new values
-      --set stringArray        set values on the command line (can specify multiple or separate values with commas: key1=val1,key2=val2)
-      --suppress stringArray   allows suppression of the values listed in the diff output
-  -q, --suppress-secrets       suppress secrets in the output
-  -f, --values valueFiles      specify values in a YAML file (can specify multiple) (default [])
-      --version string         specify the exact chart version to use. If this is not specified, the latest version is used
+      --allow-unreleased             enables diffing of releases that are not yet deployed via Helm
+  -a, --api-versions stringArray     Kubernetes api versions used for Capabilities.APIVersions
+      --color                        color output. You can control the value for this flag via HELM_DIFF_COLOR=[true|false]. If both --no-color and --color are unspecified, coloring enabled only when the stdout is a term and TERM is not "dumb"
+  -C, --context int                  output NUM lines of context around changes (default -1)
+      --detailed-exitcode            return a non-zero exit code when there are changes
+      --devel                        use development versions, too. Equivalent to version '>0.0.0-0'. If --version is set, this is ignored.
+      --disable-openapi-validation   disables rendered templates validation against the Kubernetes OpenAPI Schema
+      --disable-validation           disables rendered templates validation against the Kubernetes cluster you are currently pointing to. This is the same validation performed on an install
+      --dry-run                      disables cluster access and show diff as if it was install. Implies --install, --reset-values, and --disable-validation
+  -h, --help                         help for diff
+      --include-tests                enable the diffing of the helm test hooks
+      --install                      enables diffing of releases that are not yet deployed via Helm (equivalent to --allow-unreleased, added to match "helm upgrade --install" command
+      --kubeconfig string            This flag is ignored, to allow passing of this top level flag to helm
+      --no-color                     remove colors from the output. If both --no-color and --color are unspecified, coloring enabled only when the stdout is a term and TERM is not "dumb"
+      --no-hooks                     disable diffing of hooks
+      --normalize-manifests          normalize manifests before running diff to exclude style differences from the output
+      --output string                Possible values: diff, simple, json, template. When set to "template", use the env var HELM_DIFF_TPL to specify the template. (default "diff")
+      --post-renderer string         the path to an executable to be used for post rendering. If it exists in $PATH, the binary will be used, otherwise it will try to look for the executable at the given path
+      --repo string                  specify the chart repository url to locate the requested chart
+      --reset-values                 reset the values to the ones built into the chart and merge in any new values
+      --reuse-values                 reuse the last release's values and merge in any new values. If '--reset-values' is specified, this is ignored
+      --set stringArray              set values on the command line (can specify multiple or separate values with commas: key1=val1,key2=val2)
+      --set-file stringArray         set values from respective files specified via the command line (can specify multiple or separate values with commas: key1=path1,key2=path2)
+      --set-string stringArray       set STRING values on the command line (can specify multiple or separate values with commas: key1=val1,key2=val2)
+      --show-secrets                 do not redact secret values in the output
+      --strip-trailing-cr            strip trailing carriage return on input
+      --suppress stringArray         allows suppression of the values listed in the diff output
+  -q, --suppress-secrets             suppress secrets in the output
+      --three-way-merge              use three-way-merge to compute patch and generate diff output
+  -f, --values valueFiles            specify values in a YAML file (can specify multiple) (default [])
+      --version string               specify the exact chart version to use. If this is not specified, the latest version is used
 
 Additional help topics:
   diff          

cmd/root.go

@@ -2,6 +2,7 @@ package cmd
 
 import (
 	"os"
+	"strconv"
 
 	"github.com/mgutz/ansi"
 	"github.com/spf13/cobra"
@@ -41,9 +42,23 @@ func New() *cobra.Command {
 		Args: chartCommand.Args,
 		// parse the flags and check for actions like suppress-secrets, no-colors
 		PersistentPreRun: func(cmd *cobra.Command, args []string) {
-			if nc, _ := cmd.Flags().GetBool("no-color"); nc {
+			var fc *bool
+
+			if cmd.Flags().Changed("color") {
+				v, _ := cmd.Flags().GetBool("color")
+				fc = &v
+			} else {
+				v, err := strconv.ParseBool(os.Getenv("HELM_DIFF_COLOR"))
+				if err == nil {
+					fc = &v
+				}
+			}
+
+			nc, _ := cmd.Flags().GetBool("no-color")
+
+			if nc || (fc != nil && !*fc) {
 				ansi.DisableColors(true)
-			} else if !cmd.Flags().Changed("no-color") {
+			} else if !cmd.Flags().Changed("no-color") && fc == nil {
 				term := terminal.IsTerminal(int(os.Stdout.Fd()))
 				// https://github.com/databus23/helm-diff/issues/281
 				dumb := os.Getenv("TERM") == "dumb"
@@ -57,7 +72,8 @@ func New() *cobra.Command {
 	}
 
 	// add no-color as global flag
-	cmd.PersistentFlags().Bool("no-color", false, "remove colors from the output")
+	cmd.PersistentFlags().Bool("no-color", false, "remove colors from the output. If both --no-color and --color are unspecified, coloring enabled only when the stdout is a term and TERM is not \"dumb\"")
+	cmd.PersistentFlags().Bool("color", false, "color output. You can control the value for this flag via HELM_DIFF_COLOR=[true|false]. If both --no-color and --color are unspecified, coloring enabled only when the stdout is a term and TERM is not \"dumb\"")
 	// add flagset from chartCommand
 	cmd.Flags().AddFlagSet(chartCommand.Flags())
 	cmd.AddCommand(newVersionCmd(), chartCommand)