feat: add type-import-style rule (#320)

Author: danwang

.README/README.md

@@ -168,6 +168,7 @@ When `true`, only checks files with a [`@flow` annotation](http://flowtype.org/d
 {"gitdown": "include", "file": "./rules/space-before-generic-bracket.md"}
 {"gitdown": "include", "file": "./rules/space-before-type-colon.md"}
 {"gitdown": "include", "file": "./rules/type-id-match.md"}
+{"gitdown": "include", "file": "./rules/type-import-style.md"}
 {"gitdown": "include", "file": "./rules/union-intersection-spacing.md"}
 {"gitdown": "include", "file": "./rules/use-flow-type.md"}
 {"gitdown": "include", "file": "./rules/valid-syntax.md"}

.README/rules/type-import-style.md

@@ -0,0 +1,22 @@
+### `type-import-style`
+
+_The `--fix` option on the command line automatically fixes problems reported by this rule._
+
+Enforces a particular style for type imports:
+
+```
+// 'identifier' style
+import {type T, type U, type V} from '...';
+
+// 'declaration' style
+import type {T, U, V} from '...';
+```
+
+The rule has a string option:
+
+* `"identifier"` (default): Enforces that type imports are all in the
+  'identifier' style.
+* `"declaration"`: Enforces that type imports are all in the 'declaration'
+  style.
+
+<!-- assertions typeImportStyle -->

src/index.js

@@ -26,6 +26,7 @@ import spaceAfterTypeColon from './rules/spaceAfterTypeColon';
 import spaceBeforeGenericBracket from './rules/spaceBeforeGenericBracket';
 import spaceBeforeTypeColon from './rules/spaceBeforeTypeColon';
 import typeIdMatch from './rules/typeIdMatch';
+import typeImportStyle from './rules/typeImportStyle';
 import unionIntersectionSpacing from './rules/unionIntersectionSpacing';
 import useFlowType from './rules/useFlowType';
 import validSyntax from './rules/validSyntax';
@@ -58,6 +59,7 @@ const rules = {
   'space-before-generic-bracket': spaceBeforeGenericBracket,
   'space-before-type-colon': spaceBeforeTypeColon,
   'type-id-match': typeIdMatch,
+  'type-import-style': typeImportStyle,
   'union-intersection-spacing': unionIntersectionSpacing,
   'use-flow-type': useFlowType,
   'valid-syntax': validSyntax
@@ -98,6 +100,7 @@ export default {
     'space-before-generic-bracket': 0,
     'space-before-type-colon': 0,
     'type-id-match': 0,
+    'type-import-style': 0,
     'union-intersection-spacing': 0,
     'use-flow-type': 0,
     'valid-syntax': 0

src/rules/typeImportStyle.js

@@ -0,0 +1,53 @@
+const schema = [
+  {
+    enum: ['declaration', 'identifier'],
+    type: 'string'
+  }
+];
+
+const create = (context) => {
+  if (context.options[0] === 'declaration') {
+    return {
+      ImportDeclaration (node) {
+        if (node.importKind !== 'type') {
+          node.specifiers.forEach((specifier) => {
+            if (specifier.importKind === 'type') {
+              context.report({
+                message: 'Unexpected type import',
+                node
+              });
+            }
+          });
+        }
+      }
+    };
+  } else {
+    // Default to 'identifier'
+    return {
+      ImportDeclaration (node) {
+        if (node.importKind === 'type') {
+          context.report({
+            fix (fixer) {
+              const imports = node.specifiers.map((specifier) => {
+                return 'type ' + specifier.local.name;
+              });
+              const source = node.source.value;
+
+              return fixer.replaceText(node,
+                'import {' + imports.join(', ') + '} from \'' + source + '\';'
+              );
+            },
+            message: 'Unexpected "import type"',
+            node
+          });
+        }
+      }
+    };
+  }
+};
+
+export default {
+  create,
+  schema
+};
+

tests/rules/assertions/typeImportStyle.js

@@ -0,0 +1,38 @@
+export default {
+  invalid: [
+    {
+      code: 'import type {A, B} from \'a\';',
+      errors: [{message: 'Unexpected "import type"'}],
+      output: 'import {type A, type B} from \'a\';'
+    },
+    {
+      code: 'import type {A, B} from \'a\';',
+      errors: [{message: 'Unexpected "import type"'}],
+      options: ['identifier'],
+      output: 'import {type A, type B} from \'a\';'
+    },
+    {
+      code: 'import {type A, type B} from \'a\';',
+      errors: [
+        {message: 'Unexpected type import'},
+        {message: 'Unexpected type import'}
+      ],
+      options: ['declaration']
+    }
+  ],
+  valid: [
+    {
+      code: 'import {type A, type B} from \'a\';'
+    },
+    {
+      code: 'import {type A, type B} from \'a\';',
+      options: ['identifier']
+    },
+    {
+      code: 'import type {A, B} from \'a\';',
+      options: ['declaration']
+    }
+  ]
+};
+
+

tests/rules/index.js

@@ -36,6 +36,7 @@ const reportingRules = [
   'space-before-generic-bracket',
   'space-before-type-colon',
   'type-id-match',
+  'type-import-style',
   'union-intersection-spacing',
   'use-flow-type',
   'valid-syntax'