prettier: support read code from stdin and output to stdout

prettier/main.ts

@@ -11,7 +11,7 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 // This script formats the given source files. If the files are omitted, it
 // formats the all files in the repository.
-const { args, exit, readFile, writeFile, stdout } = Deno;
+const { args, exit, readFile, writeFile, stdout, stdin, readAll } = Deno;
 import { glob, isGlob, GlobOptions } from "../fs/glob.ts";
 import { walk, WalkInfo } from "../fs/walk.ts";
 import { parse } from "../flags/mod.ts";
@@ -26,6 +26,7 @@ Options:
  -H, --help Show this help message and exit.
  --check Check if the source files are formatted.
  --write Whether to write to the file, otherwise it will output to stdout, Defaults to false.
+ --from-stdin Read the typescript/javascript code from stdin and output formatted code to stdout.
  --ignore <path> Ignore the given path(s).
 
 JS/TS Styling Options:
@@ -227,6 +228,19 @@ async function formatSourceFiles(
  exit(0);
 }
 
+/**
+ * Format source code
+ */
+function format(text: string, prettierOpts: PrettierOptions): string {
+ const formatted: string = prettier.format(text, {
+ ...prettierOpts,
+ parser: selectParser("stdin.ts"),
+ plugins: prettierPlugins
+ });
+
+ return formatted;
+}
+
 /**
  * Get the files to format.
  * @param selectors The glob patterns to select the files.
@@ -306,6 +320,15 @@ async function main(opts): Promise<void> {
  write: opts["write"]
  };
 
+ const isReadFromStdin: boolean = opts["from-stdin"];
+
+ if (isReadFromStdin) {
+ const byte = await readAll(stdin);
+ const formattedCode = format(new TextDecoder().decode(byte), prettierOpts);
+ stdout.write(new TextEncoder().encode(formattedCode));
+ return;
+ }
+
  if (help) {
  console.log(HELP_MESSAGE);
  exit(0);
@@ -348,7 +371,8 @@ main(
  "use-tabs",
  "single-quote",
  "bracket-spacing",
- "write"
+ "write",
+ "from-stdin"
  ],
  default: {
  ignore: [],
@@ -362,7 +386,8 @@ main(
  "arrow-parens": "avoid",
  "prose-wrap": "preserve",
  "end-of-line": "auto",
- write: false
+ write: false,
+ "from-stdin": false
  },
  alias: {
  H: "help"