Fix: ensure --stdin flag works when stdin is piped asynchronously (eslint#10393)

Author: not-an-aardvark

bin/eslint.js

@@ -56,7 +56,15 @@ process.once("uncaughtException", err => {
 });
 
 if (useStdIn) {
-    process.exitCode = cli.execute(process.argv, fs.readFileSync(process.stdin.fd, "utf8"));
+
+    /*
+     * Note: `process.stdin.fd` is not used here due to https://github.com/nodejs/node/issues/7439.
+     * Accessing the `process.stdin` property seems to modify the behavior of file descriptor 0, resulting
+     * in an error when stdin is piped in asynchronously.
+     */
+    const STDIN_FILE_DESCRIPTOR = 0;
+
+    process.exitCode = cli.execute(process.argv, fs.readFileSync(STDIN_FILE_DESCRIPTOR, "utf8"));
 } else if (init) {
     const configInit = require("../lib/config/config-initializer");
 

tests/bin/eslint.js

@@ -152,6 +152,17 @@ describe("bin/eslint.js", () => {
             }
         );
 
+        it("successfully reads from an asynchronous pipe", () => {
+            const child = runESLint(["--stdin", "--no-eslintrc"]);
+
+            child.stdin.write("var foo = bar;\n");
+            return new Promise(resolve => setTimeout(resolve, 300)).then(() => {
+                child.stdin.write("var baz = qux;\n");
+                child.stdin.end();
+
+                return assertExitCode(child, 0);
+            });
+        });
     });
 
     describe("running on files", () => {