refactor: rename format flag to stdout-format

ci/release/changelogs/next.md

@@ -4,6 +4,7 @@
 - Connections now support `link` [#1955](https://github.com/terrastruct/d2/pull/1955)
 - Vars: vars in markdown blocks are substituted [#2218](https://github.com/terrastruct/d2/pull/2218)
 - Markdown: Github-flavored tables work in `md` blocks [#2221](https://github.com/terrastruct/d2/pull/2221)
+- CLI: PNG output to stdout is supported using `--stdout-format png -` [#2260](https://github.com/terrastruct/d2/pull/2260)
 
 #### Improvements 🧹
 

d2cli/export.go

@@ -3,6 +3,7 @@ package d2cli
 import (
 	"fmt"
 	"path/filepath"
+	"strings"
 )
 
 type exportExtension string
@@ -15,20 +16,20 @@ const SVG exportExtension = ".svg"
 
 var SUPPORTED_EXTENSIONS = []exportExtension{SVG, PNG, PDF, PPTX, GIF}
 
-func getOutputFormat(formatFlag *string, outputPath string) (exportExtension, error) {
+var STDOUT_FORMAT_MAP = map[string]exportExtension{
-	var formatMap = map[string]exportExtension{
+	"png": PNG,
-		"png":  PNG,
+	"svg": SVG,
-		"svg":  SVG,
+}
-		"pdf":  PDF,
-		"pptx": PPTX,
-		"gif":  GIF,
-	}
 
-	if *formatFlag != "" {
+var SUPPORTED_STDOUT_FORMATS = []string{"png", "svg"}
-		if format, ok := formatMap[*formatFlag]; ok {
+
-			return format, nil
+func getOutputFormat(stdoutFormatFlag *string, outputPath string) (exportExtension, error) {
+	if *stdoutFormatFlag != "" {
+		format := strings.ToLower(*stdoutFormatFlag)
+		if ext, ok := STDOUT_FORMAT_MAP[format]; ok {
+			return ext, nil
 		}
-		return "", fmt.Errorf("unsupported format: %s", *formatFlag)
+		return "", fmt.Errorf("%s is not a supported format. Supported formats are: %s", *stdoutFormatFlag, SUPPORTED_STDOUT_FORMATS)
 	}
 	return getExportExtension(outputPath), nil
 }

d2cli/export_test.go

@@ -8,7 +8,7 @@ import (
 
 func TestOutputFormat(t *testing.T) {
 	type testCase struct {
-		formatFlag                string
+		stdoutFormatFlag          string
 		outputPath                string
 		extension                 exportExtension
 		supportsDarkTheme         bool
@@ -43,7 +43,7 @@ func TestOutputFormat(t *testing.T) {
 			requiresPngRender:         false,
 		},
 		{
-			formatFlag:                "png",
+			stdoutFormatFlag:          "png",
 			outputPath:                "-",
 			extension:                 PNG,
 			supportsDarkTheme:         false,
@@ -88,7 +88,7 @@ func TestOutputFormat(t *testing.T) {
 	for _, tc := range testCases {
 		tc := tc
 		t.Run(tc.outputPath, func(t *testing.T) {
-			extension, err := getOutputFormat(&tc.formatFlag, tc.outputPath)
+			extension, err := getOutputFormat(&tc.stdoutFormatFlag, tc.outputPath)
 			assert.NoError(t, err)
 			assert.Equal(t, tc.extension, extension)
 			assert.Equal(t, tc.supportsAnimation, extension.supportsAnimation())

d2cli/main.go

@@ -103,7 +103,7 @@ func Run(ctx context.Context, ms *xmain.State) (err error) {
 	if err != nil {
 		return err
 	}
-	formatFlag := ms.Opts.String("", "format", "f", "", "stdout output format (svg, png)")
+	stdoutFormatFlag := ms.Opts.String("", "stdout-format", "", "", "output format when writing to stdout (svg, png). Usage: d2 input.d2 --stdout-format png - > output.png")
 	if err != nil {
 		return err
 	}
@@ -219,7 +219,7 @@ func Run(ctx context.Context, ms *xmain.State) (err error) {
 		return xmain.UsageErrorf("D2 does not support ppt exports, did you mean \"pptx\"?")
 	}
 
-	outputFormat, err := getOutputFormat(formatFlag, outputPath)
+	outputFormat, err := getOutputFormat(stdoutFormatFlag, outputPath)
 	if err != nil {
 		return xmain.UsageErrorf("%v", err)
 	}