[Fix] no-unused-modules: handle export { default } from syntax

Fixes #1631

Author: richardxia

CHANGELOG.md

@@ -9,6 +9,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 - [`order`]: fix `isExternalModule` detect on windows ([#1651], thanks [@fisker])
 - [`order`]: recognize ".." as a "parent" path ([#1658], thanks [@golopot])
 - [`no-duplicates`]: fix fixer on cases with default import ([#1666], thanks [@golopot])
+- [`no-unused-modules`]: Handle `export { default } from` syntax ([#1631], thanks [@richardxia])
 
 ## [2.20.1] - 2020-02-01
 ### Fixed
@@ -660,6 +661,7 @@ for info on changes for earlier releases.
 [#1658]: https://github.com/benmosher/eslint-plugin-import/pull/1658
 [#1651]: https://github.com/benmosher/eslint-plugin-import/pull/1651
 [#1635]: https://github.com/benmosher/eslint-plugin-import/issues/1635
+[#1631]: https://github.com/benmosher/eslint-plugin-import/issues/1631
 [#1625]: https://github.com/benmosher/eslint-plugin-import/pull/1625
 [#1620]: https://github.com/benmosher/eslint-plugin-import/pull/1620
 [#1619]: https://github.com/benmosher/eslint-plugin-import/pull/1619
@@ -1113,3 +1115,4 @@ for info on changes for earlier releases.
 [@IvanGoncharov]: https://github.com/IvanGoncharov
 [@wschurman]: https://github.com/wschurman
 [@fisker]: https://github.com/fisker
+[@richardxia]: https://github.com/richardxia

src/rules/no-unused-modules.js

@@ -66,8 +66,54 @@ const CLASS_DECLARATION = 'ClassDeclaration'
 const DEFAULT = 'default'
 const TYPE_ALIAS = 'TypeAlias'
 
+/**
+ * List of imports per file.
+ *
+ * Represented by a two-level Map to a Set of identifiers. The upper-level Map
+ * keys are the paths to the modules containing the imports, while the
+ * lower-level Map keys are the paths to the files which are being imported
+ * from. Lastly, the Set of identifiers contains either names being imported
+ * or a special AST node name listed above (e.g ImportDefaultSpecifier).
+ *
+ * For example, if we have a file named foo.js containing:
+ *
+ *   import { o2 } from './bar.js';
+ *
+ * Then we will have a structure that looks like:
+ *
+ *   Map { 'foo.js' => Map { 'bar.js' => Set { 'o2' } } }
+ *
+ * @type {Map<string, Map<string, Set<string>>>}
+ */
 const importList = new Map()
+
+/**
+ * List of exports per file.
+ *
+ * Represented by a two-level Map to an object of metadata. The upper-level Map
+ * keys are the paths to the modules containing the exports, while the
+ * lower-level Map keys are the specific identifiers or special AST node names
+ * being exported. The leaf-level metadata object at the moment only contains a
+ * `whereUsed` propoerty, which contains a Set of paths to modules that import
+ * the name.
+ *
+ * For example, if we have a file named bar.js containing the following exports:
+ *
+ *   const o2 = 'bar';
+ *   export { o2 };
+ *
+ * And a file named foo.js containing the following import:
+ *
+ *   import { o2 } from './bar.js';
+ *
+ * Then we will have a structure that looks like:
+ *
+ *   Map { 'bar.js' => Map { 'o2' => { whereUsed: Set { 'foo.js' } } } }
+ *
+ * @type {Map<string, Map<string, object>>}
+ */
 const exportList = new Map()
+
 const ignoredFiles = new Set()
 const filesOutsideSrc = new Set()
 
@@ -453,9 +499,12 @@ module.exports = {
         }
       }
 
-      const exportStatement = exports.get(exportedValue)
+      // exportsList will always map any imported value of 'default' to 'ImportDefaultSpecifier'
+      const exportsKey = exportedValue === DEFAULT ? IMPORT_DEFAULT_SPECIFIER : exportedValue
+
+      const exportStatement = exports.get(exportsKey)
 
-      const value = exportedValue === IMPORT_DEFAULT_SPECIFIER ? DEFAULT : exportedValue
+      const value = exportsKey === IMPORT_DEFAULT_SPECIFIER ? DEFAULT : exportsKey
 
       if (typeof exportStatement !== 'undefined'){
         if (exportStatement.whereUsed.size < 1) {

tests/files/no-unused-modules/file-0.js

@@ -11,3 +11,4 @@ import {q} from './file-q'
 export * from './file-n'
 export { default, o0, o3 } from './file-o'
 export { p } from './file-p'
+import s from './file-s'

tests/files/no-unused-modules/file-s.js

@@ -0,0 +1 @@
+export { default } from './file-o'

tests/src/rules/no-unused-modules.js

@@ -110,7 +110,8 @@ ruleTester.run('no-unused-modules', rule, {
            import * as l from './file-l'
            export * from './file-n'
            export { default, o0, o3 } from './file-o'
-           export { p } from './file-p'`,
+           export { p } from './file-p'
+           import s from './file-s'`,
            filename: testFilePath('./no-unused-modules/file-0.js'),
            errors: [
              error(`exported declaration 'default' not used within other modules`),
@@ -165,7 +166,11 @@ ruleTester.run('no-unused-modules', rule, {
 
 // // test for export from
 ruleTester.run('no-unused-modules', rule, {
-  valid: [],
+  valid: [
+    test({ options: unusedExportsOptions,
+           code: `export { default } from './file-o'`,
+           filename: testFilePath('./no-unused-modules/file-s.js')}),
+  ],
   invalid: [
     test({ options: unusedExportsOptions,
            code: `export { k } from '${testFilePath('./no-unused-modules/file-k.js')}'`,