Handle ERR_PACKAGE_PATH_NOT_EXPORTED gracefully

Fixes sveltejs#104
Closes sveltejs#108

index.js

@@ -50,6 +50,10 @@ function tryResolve(pkg, importer) {
 		return relative.resolve(pkg, importer);
 	} catch (err) {
 		if (err.code === 'MODULE_NOT_FOUND') return null;
+		if (err.code === 'ERR_PACKAGE_PATH_NOT_EXPORTED') {
+			console.warn(`WARNING: Could not read svelte config from ${pkg}. Reason: ${err.message}`);
+			return null;
+		}
 		throw err;
 	}
 }

test/test.js

@@ -33,6 +33,22 @@ describe('rollup-plugin-svelte', () => {
 		);
 	});
 
+	it('ignores esm module not exporting package.json', () => {
+		const { resolveId } = plugin();
+		assert.equal(
+			resolveId('esm-module-without-svelte-config', path.resolve('test/foo/main.js')),
+			null
+		);
+	});
+
+	it('resolves esm module exporting package.json', () => {
+		const { resolveId } = plugin();
+		assert.equal(
+			resolveId('esm-widget', path.resolve('test/foo/main.js')),
+			path.resolve('test/node_modules/esm-widget/src/Widget.html')
+		);
+	});
+
 	it('ignores virtual modules', () => {
 		const { resolveId } = plugin();
 		assert.equal(