Prevent glob importing from failing with empty dir

In some circumstances it can be useful to already import the contents of
a directory (e.g. `@import 'objects/**/*.scss'`) although the directory
is empty, because there might be files added later in the process. Up
until now this was not possible and node-sass was throwing an error.
With this patch, empty directories are ignored and no error is thrown.

Fixes #161

packages/node-sass-glob-importer/src/index.ts

@@ -13,7 +13,7 @@ export = function globImporter() {
 
     const filePaths = resolveGlobUrl(url, includePaths);
 
-    if (filePaths.length) {
+    if (filePaths) {
       const contents = filePaths
         .map((x: string) => `@import '${x}';`)
         .join(`\n`);

packages/node-sass-magic-importer/src/functions/resolve-glob-url.spec.ts

@@ -25,7 +25,7 @@ describe(`resolveGlobUrl()`, () => {
     const result = resolveGlobUrl(`test/url`);
 
     expect(globMock.hasMagic).toBeCalled();
-    expect(result).toEqual([]);
+    expect(result).toEqual(null);
   });
 
   test(`It should return found glob file paths.`, () => {

packages/node-sass-magic-importer/src/functions/resolve-glob-url.ts

@@ -19,8 +19,10 @@ export function resolveGlobUrlFactory(
           .split(`\\`).join(`/`));
         });
       });
+
+      return [...filePaths];
     }
 
-    return [...filePaths];
+    return null;
   };
 }

packages/node-sass-magic-importer/src/index.ts

@@ -119,7 +119,7 @@ export = function magicImporter(userOptions?: IMagicImporterOptions) {
       filterPrefix = `${url.split(` from `)[0]} from `;
     }
 
-    if (globFilePaths.length) {
+    if (globFilePaths) {
       const contents = globFilePaths
         .filter((x) => !store.has(getStoreId(x, selectorFilters, nodeFilters)))
         .map((x) => `@import '${filterPrefix}${x}';`)

packages/node-sass-magic-importer/src/interfaces/IResolveGlobUrl.ts

@@ -1,4 +1,4 @@
 export type IResolveGlobUrl = (
   url: string,
   includePaths?: string[],
-) => string[];
+) => string[]|null;

test/files/glob-import-empty-dir.scss

@@ -0,0 +1 @@
+@import 'empty-dir/*.scss';

test/glob-importer.test.ts

@@ -19,6 +19,17 @@ describe(`globImporter()`, () => {
     expect(result).toBe(expectedResult);
   });
 
+  test(`Should not fail when dir is empty.`, () => {
+    const expectedResult = ``;
+
+    const result = sass.renderSync({
+      file: `test/files/glob-import-empty-dir.scss`,
+      importer: globImporter(),
+    }).css.toString();
+
+    expect(result).toBe(expectedResult);
+  });
+
   test(`It should import glob files via CLI.`, async () => {
     // tslint:disable-next-line max-line-length
     const cmd = `node node_modules/.bin/node-sass --importer packages/node-sass-glob-importer/dist/cli.js test/files/glob-import.scss`;