no-unused-modules: support dynamic imports

This is still work in progress but I'd like to receive initial thoughts
on this implementation before I proceed.

This introduces support of dynamic imports for a rule
`no-unused-modules`.

So far only "await" form is implemented:

```js
const a = await import("a")
```
is equivalent to default import
```js
import a from "a"
```

```js
const {a,b,c} = await import("a")
```
is equivalent to named imports
```js
import {a,b,c} from "a"
```

Support import('name').then(a) and import('name').then({a,b,c}) to be
addded soon.

TODO/Open questions

- [ ] Existing code is relying on the fact that all imports/reexports
happen at top level of the file while dynamic import can happen anywhere -
that's why I had to implement visitor against visitor keys of the parser
myself not very happy about it - but couldn't figure out quickly how to
use existing visitor (if any?) supplied by a parser.
I also learned that different parsers have visitor keys defined in
different places so this has to be dealt with as well.

src/ExportMap.js

@@ -6,7 +6,7 @@ import debug from 'debug'
 
 import { SourceCode } from 'eslint'
 
-import parse from 'eslint-module-utils/parse'
+import parse, { visit } from 'eslint-module-utils/parse'
 import resolve from 'eslint-module-utils/resolve'
 import isIgnored, { hasValidExtension } from 'eslint-module-utils/ignore'
 
@@ -351,9 +351,66 @@ ExportMap.parse = function (path, content, context) {
     return m // can't continue
   }
 
-  if (!unambiguous.isModule(ast)) return null
+  let hasDynamicImports = false
 
-  const docstyle = (context.settings && context.settings['import/docstyle']) || ['jsdoc']
+  let declarator = null
+  visit(ast, path, context, {
+    VariableDeclarator(node) {
+      declarator = node
+      if (node.id.type === 'Identifier') {
+        log('Declarator', node.id.name)
+      } else if (node.id.type === 'ObjectPattern') {
+        log('Object pattern')
+      }
+    },
+    'VariableDeclarator:Exit': function() {
+      declarator = null
+    },
+    CallExpression(node) {
+      log('CALL', node.callee.type)
+      // log(JSON.stringify(node))
+      if (node.callee.type === 'Import') {
+        hasDynamicImports = true
+        const p = remotePath(node.arguments[0].value)
+        if (p == null) return null
+        if (declarator) {
+          log('IDDDDDDDD', declarator.id.name)
+        }
+          const importLiteral = node.arguments[0]
+          const importedSpecifiers = new Set()
+        if (declarator) {
+          if (declarator.id.type === 'Identifier') {
+            importedSpecifiers.add('ImportDefaultSpecifier')
+          } else if (declarator.id.type === 'ObjectPattern') {
+            for (const property of declarator.id.properties) {
+              log('ADD PROPERTY', property.key.name)
+              importedSpecifiers.add(property.key.name)
+            }
+          }
+          }
+          const getter = thunkFor(p, context)
+          m.imports.set(p, {
+            getter,
+            source: {
+              // capturing actual node reference holds full AST in memory!
+              value: importLiteral.value,
+              loc: importLiteral.loc,
+            },
+            importedSpecifiers,
+          })
+      }
+    },
+  })
+
+  if (!unambiguous.isModule(ast) && !hasDynamicImports) {
+    log('is not a module', path, hasDynamicImports)
+    return null
+  } else {
+    log('is a module!', path)
+  }
+
+  const docstyle = (context.settings &&
+    context.settings['import/docstyle']) || ['jsdoc']
   const docStyleParsers = {}
   docstyle.forEach(style => {
     docStyleParsers[style] = availableDocStyleParsers[style]

tests/files/no-unused-modules/dynamic-import-default.js

@@ -0,0 +1,3 @@
+async function main() {
+    const value = await import("./exports-for-dynamic")
+}

tests/files/no-unused-modules/dynamic-import-named.js

@@ -0,0 +1,3 @@
+async function main() {
+    const { importMeDynamicallyA, } = await import("./exports-for-dynamic")
+}

tests/files/no-unused-modules/exports-for-dynamic.js

@@ -0,0 +1,4 @@
+export const importMeDynamicallyA = 100;
+const importMeDynamicallyB = 200;
+export const importMeDynamicallyC = 100;
+export default importMeDynamicallayB;

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

@@ -71,32 +71,47 @@ ruleTester.run('no-unused-modules', rule, {
 // tests for  exports
 ruleTester.run('no-unused-modules', rule, {
   valid: [
-
     test({ options: unusedExportsOptions,
-           code: 'import { o2 } from "./file-o";export default () => 12',
-           filename: testFilePath('./no-unused-modules/file-a.js')}),
+          code: 'import { o2 } from "./file-o";export default () => 12',
+          filename: testFilePath('./no-unused-modules/file-a.js'),
+          parser: require.resolve('babel-eslint')}),
     test({ options: unusedExportsOptions,
            code: 'export const b = 2',
-           filename: testFilePath('./no-unused-modules/file-b.js')}),
+           filename: testFilePath('./no-unused-modules/file-b.js'),
+           parser: require.resolve('babel-eslint')}),
     test({ options: unusedExportsOptions,
            code: 'const c1 = 3; function c2() { return 3 }; export { c1, c2 }',
-           filename: testFilePath('./no-unused-modules/file-c.js')}),
+           filename: testFilePath('./no-unused-modules/file-c.js'),
+           parser: require.resolve('babel-eslint')}),
     test({ options: unusedExportsOptions,
            code: 'export function d() { return 4 }',
-           filename: testFilePath('./no-unused-modules/file-d.js')}),
+           filename: testFilePath('./no-unused-modules/file-d.js'),
+           parser: require.resolve('babel-eslint')}),
     test({ options: unusedExportsOptions,
            code: 'export class q { q0() {} }',
-           filename: testFilePath('./no-unused-modules/file-q.js')}),
+           filename: testFilePath('./no-unused-modules/file-q.js'),
+           parser: require.resolve('babel-eslint')}),
     test({ options: unusedExportsOptions,
            code: 'const e0 = 5; export { e0 as e }',
-           filename: testFilePath('./no-unused-modules/file-e.js')}),
+           filename: testFilePath('./no-unused-modules/file-e.js'),
+           parser: require.resolve('babel-eslint')}),
     test({ options: unusedExportsOptions,
            code: 'const l0 = 5; const l = 10; export { l0 as l1, l }; export default () => {}',
-           filename: testFilePath('./no-unused-modules/file-l.js')}),
+           filename: testFilePath('./no-unused-modules/file-l.js'),
+           parser: require.resolve('babel-eslint')}),
     test({ options: unusedExportsOptions,
            code: 'const o0 = 0; const o1 = 1; export { o0, o1 as o2 }; export default () => {}',
-           filename: testFilePath('./no-unused-modules/file-o.js')}),
-    ],
+           filename: testFilePath('./no-unused-modules/file-o.js'),
+           parser: require.resolve('babel-eslint')}),
+    test({ options: unusedExportsOptions,
+           code: `
+           export const importMeDynamicallyA = 100;
+           const importMeDynamicallyB = 200;
+           export default importMeDynamicallayB;
+           `,
+           parser: require.resolve('babel-eslint'),
+           filename: testFilePath('./no-unused-modules/exports-for-dynamic.js')}),
+  ],
   invalid: [
     test({ options: unusedExportsOptions,
            code: `import eslint from 'eslint'
@@ -117,11 +132,25 @@ ruleTester.run('no-unused-modules', rule, {
              error(`exported declaration 'o0' not used within other modules`),
              error(`exported declaration 'o3' not used within other modules`),
              error(`exported declaration 'p' not used within other modules`),
-           ]}),
+           ],
+    }),
     test({ options: unusedExportsOptions,
            code: `const n0 = 'n0'; const n1 = 42; export { n0, n1 }; export default () => {}`,
            filename: testFilePath('./no-unused-modules/file-n.js'),
-           errors: [error(`exported declaration 'default' not used within other modules`)]}),
+           errors: [
+             error(`exported declaration 'default' not used within other modules`),
+           ]}),
+    test({ options: unusedExportsOptions,
+           code: `
+           export const importMeDynamicallyC = 100;
+           `,
+           parser: require.resolve('babel-eslint'),
+           filename: testFilePath('./no-unused-modules/exports-for-dynamic.js'),
+           errors: [
+             error(
+               `exported declaration 'importMeDynamicallyC' not used within other modules`,
+             ),
+           ]}),
   ],
 })
 

utils/parse.js

@@ -63,6 +63,39 @@ exports.default = function parse(path, content, context) {
   return parser.parse(content, parserOptions)
 }
 
+function __visit(node, keys, visitorSpec) {
+  if (!node) {
+    return
+  }
+    const type = node.type
+    if (typeof visitorSpec[type] === 'function') {
+      visitorSpec[type](node)
+    }
+    const childFields = keys[type]
+    if (!childFields) {
+      return
+    }
+    for (const fieldName of childFields) {
+      const field = node[fieldName]
+      if (Array.isArray(field)) {
+        for (const item of field) {
+          __visit(item, keys, visitorSpec)
+        }
+      } else {
+        __visit(field, keys, visitorSpec)
+      }
+    }
+    if (typeof visitorSpec[`${type}:Exit`] === 'function') {
+      visitorSpec[`${type}:Exit`](node)
+    }
+}
+
+exports.visit = function (ast, path, context, visitorSpec) {
+  const parserPath = getParserPath(path, context)
+  const keys = moduleRequire(parserPath.replace('index.js', 'visitor-keys.js'))
+  __visit(ast, keys, visitorSpec)
+}
+
 function getParserPath(path, context) {
   const parsers = context.settings['import/parsers']
   if (parsers != null) {

utils/unambiguous.js

@@ -1,8 +1,7 @@
 'use strict'
 exports.__esModule = true
 
-
-const pattern = /(^|;)\s*(export|import)((\s+\w)|(\s*[{*=]))/m
+const pattern = /(^|;)\s*(export|import)((\s+\w)|(\s*[{*=]))|import\(/m
 /**
  * detect possible imports/exports without a full parse.
  *