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"