fix(v2): avoid duplicated imports in npm2yarn plugin (#4964)

* fix(v2): avoid duplicated imports in npm2yarn plugin

* Better testing

packages/docusaurus-remark-plugin-npm2yarn/src/__tests__/__snapshots__/index.test.js.snap

@@ -1,5 +1,61 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`npm2yarn plugin test: already imported tabs components above are not re-imported 1`] = `
+"import Tabs from '@theme/Tabs';
+
+import TabItem from '@theme/TabItem';
+
+<Tabs defaultValue=\\"npm\\" values={[
+    { label: 'npm', value: 'npm', },
+    { label: 'Yarn', value: 'yarn', },
+  ]}
+>
+<TabItem value=\\"npm\\">
+
+\`\`\`bash
+  $ npm install --global docusaurus
+\`\`\`
+
+</TabItem>
+<TabItem value=\\"yarn\\">
+
+\`\`\`bash
+  $ yarn add --global docusaurus
+\`\`\`
+
+</TabItem>
+</Tabs>
+"
+`;
+
+exports[`npm2yarn plugin test: already imported tabs components below are not re-imported 1`] = `
+"<Tabs defaultValue=\\"npm\\" values={[
+    { label: 'npm', value: 'npm', },
+    { label: 'Yarn', value: 'yarn', },
+  ]}
+>
+<TabItem value=\\"npm\\">
+
+\`\`\`bash
+  $ npm install --global docusaurus
+\`\`\`
+
+</TabItem>
+<TabItem value=\\"yarn\\">
+
+\`\`\`bash
+  $ yarn add --global docusaurus
+\`\`\`
+
+</TabItem>
+</Tabs>
+
+import Tabs from '@theme/Tabs';
+
+import TabItem from '@theme/TabItem';
+"
+`;
+
 exports[`npm2yarn plugin test: installation file 1`] = `
 "import Tabs from '@theme/Tabs';
 import TabItem from '@theme/TabItem';

packages/docusaurus-remark-plugin-npm2yarn/src/__tests__/fixtures/import-tabs-above.md

@@ -0,0 +1,7 @@
+import Tabs from '@theme/Tabs';
+
+import TabItem from '@theme/TabItem';
+
+```bash npm2yarn
+  $ npm install --global docusaurus
+```

packages/docusaurus-remark-plugin-npm2yarn/src/__tests__/fixtures/import-tabs-below.md

@@ -0,0 +1,7 @@
+```bash npm2yarn
+  $ npm install --global docusaurus
+```
+
+import Tabs from '@theme/Tabs';
+
+import TabItem from '@theme/TabItem';

packages/docusaurus-remark-plugin-npm2yarn/src/__tests__/index.test.js

@@ -50,4 +50,20 @@ describe('npm2yarn plugin', () => {
 
     expect(result).toMatchSnapshot();
   });
+
+  test('test: already imported tabs components above are not re-imported', async () => {
+    const result = await processFixture('import-tabs-above', {
+      staticDir,
+    });
+
+    expect(result).toMatchSnapshot();
+  });
+
+  test('test: already imported tabs components below are not re-imported', async () => {
+    const result = await processFixture('import-tabs-below', {
+      staticDir,
+    });
+
+    expect(result).toMatchSnapshot();
+  });
 });

packages/docusaurus-remark-plugin-npm2yarn/src/index.js

@@ -57,7 +57,11 @@ const nodeForImport = {
 module.exports = (options = {}) => {
   const {sync = false} = options;
   let transformed = false;
+  let alreadyImported = false;
   const transformer = (node) => {
+    if (node.type === 'import' && node.value.includes('@theme/Tabs')) {
+      alreadyImported = true;
+    }
     if (matchNode(node)) {
       transformed = true;
       return transformNode(node, sync);
@@ -74,7 +78,7 @@ module.exports = (options = {}) => {
         }
       }
     }
-    if (node.type === 'root' && transformed) {
+    if (node.type === 'root' && transformed && !alreadyImported) {
       node.children.unshift(nodeForImport);
     }
     return null;