feat(cli): show help without any option

Closes #349

Author: gregberge

packages/cli/src/__snapshots__/index.test.js.snap

@@ -124,6 +124,22 @@ Array [
 ]
 `;
 
+exports[`cli should support stdin filepath 1`] = `
+"import React from 'react'
+
+function SvgFile(props) {
+  return (
+    <svg width={48} height={1} {...props}>
+      <path d=\\"M0 0h48v1H0z\\" fill=\\"#063855\\" fillRule=\\"evenodd\\" />
+    </svg>
+  )
+}
+
+export default SvgFile
+
+"
+`;
+
 exports[`cli should support various args: --expand-props none 1`] = `
 "import React from 'react'
 

packages/cli/src/fileCommand.js

@@ -17,15 +17,21 @@ async function fileCommand(program, filenames, config) {
     })
 
     process.stdin.on('end', () => {
-      output(convert(code, config))
+      output(convert(code, config, { filePath: program.stdinFilepath }))
     })
   }
 
-  if (filenames.length === 0) {
+  if (program.stdin || (filenames.length === 0 && !process.stdin.isTTY)) {
     stdin()
     return
   }
 
+  if (filenames.length === 0) {
+    // eslint-disable-next-line no-console
+    console.log(program.helpInformation())
+    return
+  }
+
   if (filenames.length > 1) {
     exitError('Please specify only one filename or use `--out-dir` option.')
     return

packages/cli/src/index.js

@@ -88,6 +88,11 @@ program
   )
   .option('--no-svgo', 'disable SVGO')
   .option('--silent', 'suppress output')
+  .option('--stdin', 'force reading input from stdin')
+  .option(
+    '--stdin-filepath',
+    'path to the file to pretend that stdin comes from',
+  )
 
 program.on('--help', () => {
   console.log(`

packages/cli/src/index.test.js

@@ -48,6 +48,13 @@ describe('cli', () => {
     expect(result).toMatchSnapshot()
   }, 10000)
 
+  it('should support stdin filepath', async () => {
+    const result = await cli(
+      '--stdin-filepath __fixtures__/simple/file.svg < __fixtures__/simple/file.svg',
+    )
+    expect(result).toMatchSnapshot()
+  }, 10000)
+
   it('should transform a whole directory and output relative destination paths', async () => {
     const result = await cli('--out-dir __fixtures_build__/whole __fixtures__')
     const sorted = result