feat: support TypeScript code in eval flag

src/cli.ts

@@ -1,4 +1,5 @@
 import { cli } from 'cleye';
+import { transformSync } from '@esbuild-kit/core-utils';
 import { version } from '../package.json';
 import { run } from './run';
 import { watchCommand } from './watch';
@@ -36,6 +37,11 @@ cli({
 			alias: 'h',
 			description: 'Show help',
 		},
+		eval: {
+			type: String,
+			alias: 'e',
+			description: 'Evaluate code inside the eval flag',
+		},
 	},
 	help: false,
 	ignoreArgv: ignoreAfterArgument(),
@@ -49,8 +55,31 @@ cli({
 		console.log(`${'-'.repeat(45)}\n`);
 	}
 
+	const argvsToRun = removeArgvFlags(tsxFlags);
+
+	if (argv.flags.eval) {
+		const transformed = transformSync(
+			argv.flags.eval,
+			'/tmp/tsx_temporarily_stored_cache_file_for_the_code.ts',
+			{
+				loader: 'ts',
+				tsconfigRaw: {
+					compilerOptions: {
+						preserveValueImports: true,
+					},
+				},
+				define: {
+					require: 'global.require',
+				},
+				banner: '',
+				footer: '',
+			},
+		);
+		argvsToRun[1] = transformed.code;
+	}
+
 	const childProcess = run(
-		removeArgvFlags(tsxFlags),
+		argvsToRun,
 		{
 			noCache: Boolean(argv.flags.noCache),
 			tsconfigPath: argv.flags.tsconfig,

tests/specs/cli.ts

@@ -59,6 +59,37 @@ export default testSuite(({ describe }, fixturePath: string) => {
 			});
 		});
 
+		describe('eval', ({ test }) => {
+			test('evaluates TypeScript code inside the eval flag', async () => {
+				const tsxProcess = await tsx({
+					args: ['--eval', 'const thing: string = "hi!!!"; console.log(thing);'],
+				});
+
+				expect(tsxProcess.exitCode).toBe(0);
+				expect(tsxProcess.stdout).toMatch('hi!!!');
+				expect(tsxProcess.stderr).toBe('');
+			});
+
+			test('works expectedly with --input-type=module', async () => {
+				const tsxProcess = await tsx({
+					args: ['--eval', 'console.log(import.meta.url);', '--input-type=module'],
+				});
+
+				expect(tsxProcess.exitCode).toBe(0);
+				expect(tsxProcess.stdout).toMatch('undefined');
+				expect(tsxProcess.stderr).toBe('');
+			});
+
+			test('fails to access __dirname with --input-type=module', async () => {
+				const tsxProcess = await tsx({
+					args: ['--eval', 'console.log(__dirname);', '--input-type=module'],
+				});
+
+				expect(tsxProcess.exitCode).toBe(1);
+				expect(tsxProcess.stderr).toMatch('ReferenceError: __dirname is not defined in ES module scope');
+			});
+		});
+
 		test('Node.js test runner', async () => {
 			const tsxProcess = await tsx({
 				args: [