esm: --type=auto should throw syntax errors directly

lib/internal/errors.js

@@ -816,7 +816,8 @@ E('ERR_INVALID_SYNC_FORK_INPUT',
 E('ERR_INVALID_THIS', 'Value of "this" must be of type %s', TypeError);
 E('ERR_INVALID_TUPLE', '%s must be an iterable %s tuple', TypeError);
 E('ERR_INVALID_TYPE_FLAG',
-  'Type flag must be one of "auto", "commonjs", or "module". Received --type=%s',
+  'Type flag must be one of "auto", "commonjs", or "module". ' +
+  'Received --type=%s',
   TypeError);
 E('ERR_INVALID_URI', 'URI malformed', URIError);
 E('ERR_INVALID_URL', 'Invalid URL: %s', TypeError);

lib/internal/main/check_syntax.js

@@ -58,7 +58,8 @@ function checkSyntax(source, filename) {
     if (filename === '[stdin]' || filename === '[eval]') {
       const { typeFlag } = require('internal/process/esm_loader');
       isModule = typeFlag === 'module' || (typeFlag === 'auto' &&
-        require('internal/modules/esm/detect_type')(source) === 'module');
+        require('internal/modules/esm/detect_type')(source, filename) ===
+          'module');
     } else {
       const resolve = require('internal/modules/esm/default_resolve');
       const { format } = resolve(pathToFileURL(filename).toString());

lib/internal/main/eval_stdin.js

@@ -21,7 +21,7 @@ readStdin((code) => {
   process._eval = code;
   if (typeFlag === 'module' ||
     (typeFlag === 'auto' &&
-    require('internal/modules/esm/detect_type')(code) === 'module'))
+    require('internal/modules/esm/detect_type')(code, '[stdin]') === 'module'))
     evalModule(process._eval);
   else
     evalScript('[stdin]', process._eval, process._breakFirstLine);

lib/internal/main/eval_string.js

@@ -16,7 +16,7 @@ addBuiltinLibsToObject(global);
 markBootstrapComplete();
 if (typeFlag === 'module' ||
   (typeFlag === 'auto' &&
-  require('internal/modules/esm/detect_type')(source) === 'module'))
+  require('internal/modules/esm/detect_type')(source, '[eval]') === 'module'))
   evalModule(source);
 else
   evalScript('[eval]', source, process._breakFirstLine);

lib/internal/modules/esm/default_resolve.js

@@ -102,8 +102,9 @@ function getModuleFormat(url, isMain, parentURL) {
 
   // --type=auto detects an ESM .js file within a CommonJS scope.
   if (isMain && format === 'commonjs' && asyncESM.typeFlag === 'auto') {
-    const source = readFileSync(fileURLToPath(url), 'utf8');
-    format = require('internal/modules/esm/detect_type')(source);
+    const filename = fileURLToPath(url);
+    const source = readFileSync(filename, 'utf8');
+    format = require('internal/modules/esm/detect_type')(source, filename);
   }
 
   return format;

lib/internal/modules/esm/detect_type.js

@@ -1,6 +1,9 @@
 'use strict';
 
 const acorn = require('internal/deps/acorn/acorn/dist/acorn');
+const {
+  stripShebang, stripBOM
+} = require('internal/modules/cjs/helpers');
 
 // Detect the module type of a file: CommonJS or ES module.
 // An ES module, for the purposes of this algorithm, is defined as any
@@ -9,7 +12,9 @@ const acorn = require('internal/deps/acorn/acorn/dist/acorn');
 // full parse; we can detect import or export statements just from the tokens.
 // Also as of this writing, Acorn doesn't support import() expressions as they
 // are only Stage 3; yet Node already supports them.
-function detectType(source) {
+function detectType(source, filename) {
+  source = stripShebang(source);
+  source = stripBOM(source);
   try {
     let prevToken, prevPrevToken;
     for (const { type: token } of acorn.tokenizer(source)) {
@@ -30,7 +35,10 @@ function detectType(source) {
       prevToken = token;
     }
   } catch {
-    return 'commonjs';
+    // If the tokenizer threw, there's a syntax error.
+    // Compile the script, this will throw with an informative error.
+    const vm = require('vm');
+    new vm.Script(source, { displayErrors: true, filename });
   }
   return 'commonjs';
 }

test/es-module/test-esm-type-auto.js

@@ -19,7 +19,10 @@ expect('cjs-with-string-containing-import.js', version);
 expect('print-version.js', version);
 expect('ambiguous-with-import-expression.js', version);
 
-function expect(file, want) {
+expect('syntax-error-1.js', 'SyntaxError', true);
+expect('syntax-error-2.js', 'SyntaxError', true);
+
+function expect(file, want, wantsError = false) {
   const argv = [
     require.resolve(`../fixtures/es-modules/type-auto-scope/${file}`)
   ];
@@ -32,6 +35,11 @@ function expect(file, want) {
     };
     exec(process.execPath, argv, opts,
          common.mustCall((err, stdout, stderr) => {
+           if (wantsError) {
+             stdout = stderr;
+           } else {
+             assert.ifError(err);
+           }
            if (stdout.includes(want)) return;
            assert.fail(
              `For ${file}, failed to find ${want} in: <\n${stdout}\n>`);

test/fixtures/es-modules/type-auto-scope/syntax-error-1.js

@@ -0,0 +1 @@
+export

test/fixtures/es-modules/type-auto-scope/syntax-error-2.js

@@ -0,0 +1,2 @@
+const str = 'import
+var foo = 3;