Custom import order separation (#12)

Closes #11

This is an adaptation of trivago/prettier-plugin-sort-imports#42 from @atombrenner.  I wasn't able to use most of the commits from the original branch, because our approach is different in this project, but I did pull in his commit with tests.  

The other change I needed to make here was to modify the cloned nodes in `adjustCommentsOnSortedNodes`, rather than mutating the original, which was leading to some strange bugs in the tests.  

* Add test for "local" groups, include newlines in tests

`getSortedNodesByImportOrder` includes a check for `importOrderSeparation`,
and adds newlines when it's true, so we should include that in our tests.

* Add support for custom import group separators

* add tests

* Update snapshots

But the last snapshot is wrong, will fix in next commit

* Copy nodes when adjusting comments

Mutating the original nodes causes strange effects, as seen in the snapshot

* Avoid duplicate newlines

* minor: Remove unused variables

* Update README

Co-authored-by: Christian Rodemeyer <christian.rodemeyer@sz.de>

README.md

@@ -129,7 +129,11 @@ A collection of Regular expressions in string format.
 "importOrder": ["^@core/(.*)$", "^@server/(.*)$", "^@ui/(.*)$", "^[./]"],
 ```
 
-_Default behavior:_ The plugin moves the third party imports to the top which are not part of the `importOrder` list.
+_Default:_ `[]`
+
+By default, this plugin will not move any imports. To separate third party from relative imports, use `["^[./]"]`. This will become the default in the next major version.
+
+The plugin moves the third party imports to the top which are not part of the `importOrder` list.
 To move the third party imports at desired place, you can use `<THIRD_PARTY_MODULES>` to assign third party imports to the appropriate position:
 
 ```json
@@ -149,6 +153,18 @@ between sorted import declarations group. The separation takes place according t
 "importOrderSeparation": true,
 ```
 
+_Note:_ If you want greater control over which groups are separated from others, you can add an empty string to your `importOrder` array to signify newlines. For example:
+
+```js
+"importOrderSeparation": false,
+"importOrder": [
+   "^react", // React will be placed at the top of third-party modules
+    "<THIRD_PARTY_MODULES>",
+    "",  // use empty strings to separate groups with empty lines
+    "^[./]"
+],
+```
+
 #### `importOrderSortSpecifiers`
 
 **type**: `boolean`

src/utils/__tests__/adjust-comments-on-sorted-nodes.spec.ts

@@ -1,13 +1,12 @@
-import { ImportDeclaration } from '@babel/types';
-
+import type { ImportOrLine } from '../../types';
 import { adjustCommentsOnSortedNodes } from '../adjust-comments-on-sorted-nodes';
 import { getImportNodes } from '../get-import-nodes';
 
-function leadingComments(node: ImportDeclaration): string[] {
+function leadingComments(node: ImportOrLine): string[] {
     return node.leadingComments?.map((c) => c.value) ?? [];
 }
 
-function trailingComments(node: ImportDeclaration): string[] {
+function trailingComments(node: ImportOrLine): string[] {
     return node.trailingComments?.map((c) => c.value) ?? [];
 }
 
@@ -21,14 +20,14 @@ test('it preserves the single leading comment for each import declaration', () =
     `);
     expect(importNodes).toHaveLength(3);
     const finalNodes = [importNodes[2], importNodes[1], importNodes[0]];
-    adjustCommentsOnSortedNodes(importNodes, finalNodes);
-    expect(finalNodes).toHaveLength(3);
-    expect(leadingComments(finalNodes[0])).toEqual([' comment a']);
-    expect(trailingComments(finalNodes[0])).toEqual([]);
-    expect(leadingComments(finalNodes[1])).toEqual([' comment b']);
-    expect(trailingComments(finalNodes[1])).toEqual([]);
-    expect(leadingComments(finalNodes[2])).toEqual([]);
-    expect(trailingComments(finalNodes[2])).toEqual([]);
+    const adjustedNodes = adjustCommentsOnSortedNodes(importNodes, finalNodes);
+    expect(adjustedNodes).toHaveLength(3);
+    expect(leadingComments(adjustedNodes[0])).toEqual([' comment a']);
+    expect(trailingComments(adjustedNodes[0])).toEqual([]);
+    expect(leadingComments(adjustedNodes[1])).toEqual([' comment b']);
+    expect(trailingComments(adjustedNodes[1])).toEqual([]);
+    expect(leadingComments(adjustedNodes[2])).toEqual([]);
+    expect(trailingComments(adjustedNodes[2])).toEqual([]);
 });
 
 test('it preserves multiple leading comments for each import declaration', () => {
@@ -45,22 +44,22 @@ test('it preserves multiple leading comments for each import declaration', () =>
     `);
     expect(importNodes).toHaveLength(3);
     const finalNodes = [importNodes[2], importNodes[1], importNodes[0]];
-    adjustCommentsOnSortedNodes(importNodes, finalNodes);
-    expect(finalNodes).toHaveLength(3);
-    expect(leadingComments(finalNodes[0])).toEqual([
+    const adjustedNodes = adjustCommentsOnSortedNodes(importNodes, finalNodes);
+    expect(adjustedNodes).toHaveLength(3);
+    expect(leadingComments(adjustedNodes[0])).toEqual([
         ' comment a1',
         ' comment a2',
         ' comment a3',
     ]);
-    expect(trailingComments(finalNodes[0])).toEqual([]);
-    expect(leadingComments(finalNodes[1])).toEqual([
+    expect(trailingComments(adjustedNodes[0])).toEqual([]);
+    expect(leadingComments(adjustedNodes[1])).toEqual([
         ' comment b1',
         ' comment b2',
         ' comment b3',
     ]);
-    expect(trailingComments(finalNodes[1])).toEqual([]);
-    expect(leadingComments(finalNodes[2])).toEqual([]);
-    expect(trailingComments(finalNodes[2])).toEqual([]);
+    expect(trailingComments(adjustedNodes[1])).toEqual([]);
+    expect(leadingComments(adjustedNodes[2])).toEqual([]);
+    expect(trailingComments(adjustedNodes[2])).toEqual([]);
 });
 
 test('it does not move comments at before all import declarations', () => {
@@ -73,17 +72,17 @@ test('it does not move comments at before all import declarations', () => {
     `);
     expect(importNodes).toHaveLength(3);
     const finalNodes = [importNodes[2], importNodes[1], importNodes[0]];
-    adjustCommentsOnSortedNodes(importNodes, finalNodes);
-    expect(finalNodes).toHaveLength(3);
-    expect(leadingComments(finalNodes[0])).toEqual([
+    const adjustedNodes = adjustCommentsOnSortedNodes(importNodes, finalNodes);
+    expect(adjustedNodes).toHaveLength(3);
+    expect(leadingComments(adjustedNodes[0])).toEqual([
         ' comment c1',
         ' comment c2',
     ]);
-    expect(trailingComments(finalNodes[0])).toEqual([]);
-    expect(leadingComments(finalNodes[1])).toEqual([]);
-    expect(trailingComments(finalNodes[1])).toEqual([]);
-    expect(leadingComments(finalNodes[2])).toEqual([]);
-    expect(trailingComments(finalNodes[2])).toEqual([]);
+    expect(trailingComments(adjustedNodes[0])).toEqual([]);
+    expect(leadingComments(adjustedNodes[1])).toEqual([]);
+    expect(trailingComments(adjustedNodes[1])).toEqual([]);
+    expect(leadingComments(adjustedNodes[2])).toEqual([]);
+    expect(trailingComments(adjustedNodes[2])).toEqual([]);
 });
 
 test('it does not affect comments after all import declarations', () => {
@@ -96,12 +95,12 @@ test('it does not affect comments after all import declarations', () => {
     `);
     expect(importNodes).toHaveLength(3);
     const finalNodes = [importNodes[2], importNodes[1], importNodes[0]];
-    adjustCommentsOnSortedNodes(importNodes, finalNodes);
-    expect(finalNodes).toHaveLength(3);
-    expect(leadingComments(finalNodes[0])).toEqual([]);
-    expect(trailingComments(finalNodes[0])).toEqual([]);
-    expect(leadingComments(finalNodes[1])).toEqual([]);
-    expect(trailingComments(finalNodes[1])).toEqual([]);
-    expect(leadingComments(finalNodes[2])).toEqual([]);
-    expect(trailingComments(finalNodes[2])).toEqual([]);
+    const adjustedNodes = adjustCommentsOnSortedNodes(importNodes, finalNodes);
+    expect(adjustedNodes).toHaveLength(3);
+    expect(leadingComments(adjustedNodes[0])).toEqual([]);
+    expect(trailingComments(adjustedNodes[0])).toEqual([]);
+    expect(leadingComments(adjustedNodes[1])).toEqual([]);
+    expect(trailingComments(adjustedNodes[1])).toEqual([]);
+    expect(leadingComments(adjustedNodes[2])).toEqual([]);
+    expect(trailingComments(adjustedNodes[2])).toEqual([]);
 });