feat(yarn): ignore yarn-path if binary does not exist

lib/manager/npm/post-update/__snapshots__/yarn.spec.ts.snap

@@ -31,6 +31,13 @@ Object {
 }
 `;
 
+exports[`manager/npm/post-update/yarn checkYarnrc() returns offline mirror and no yarn path for non-existant yarn-path binary 1`] = `
+Object {
+  "offlineMirror": false,
+  "yarnPath": null,
+}
+`;
+
 exports[`manager/npm/post-update/yarn checkYarnrc() returns offline mirror and yarn path 1`] = `
 Object {
   "offlineMirror": true,

lib/manager/npm/post-update/yarn.spec.ts

@@ -223,6 +223,12 @@ describe('manager/npm/post-update/yarn', () => {
 
   describe('checkYarnrc()', () => {
     it('returns offline mirror and yarn path', async () => {
+      fs.exists.mockImplementation((path) => {
+        if (path === './.yarn/cli.js') {
+          return new Promise<boolean>((resolve) => resolve(true));
+        }
+        return new Promise<boolean>((resolve) => resolve(false));
+      });
       fs.readFile.mockImplementation((filename, encoding) => {
         if (filename.endsWith('.yarnrc')) {
           return new Promise<string>((resolve) =>
@@ -238,6 +244,12 @@ describe('manager/npm/post-update/yarn', () => {
     });
 
     it('returns no offline mirror and unquoted yarn path', async () => {
+      fs.exists.mockImplementation((path) => {
+        if (path === './.yarn/cli.js') {
+          return new Promise<boolean>((resolve) => resolve(true));
+        }
+        return new Promise<boolean>((resolve) => resolve(false));
+      });
       fs.readFile.mockImplementation((filename, encoding) => {
         if (filename.endsWith('.yarnrc')) {
           return new Promise<string>((resolve) =>
@@ -249,5 +261,24 @@ describe('manager/npm/post-update/yarn', () => {
       // FIXME: explicit assert condition
       expect(await _yarnHelper.checkYarnrc('/tmp/renovate')).toMatchSnapshot();
     });
+
+    it('returns offline mirror and no yarn path for non-existant yarn-path binary', async () => {
+      let yarnrcContents = 'yarn-path ./.yarn/cli.js\n';
+      fs.writeFile.mockImplementation((filename, fileContents) => {
+        if (filename.endsWith('.yarnrc')) {
+          yarnrcContents = fileContents;
+        }
+        return new Promise<void>((resolve) => resolve());
+      });
+      fs.readFile.mockImplementation((filename, encoding) => {
+        if (filename.endsWith('.yarnrc')) {
+          return new Promise<string>((resolve) => resolve(yarnrcContents));
+        }
+        return new Promise<string>((resolve) => resolve(''));
+      });
+      // FIXME: explicit assert condition
+      expect(await _yarnHelper.checkYarnrc('/tmp/renovate')).toMatchSnapshot();
+      expect(yarnrcContents).not.toContain('yarn-path');
+    });
   });
 });

lib/manager/npm/post-update/yarn.ts

@@ -11,7 +11,7 @@ import { id as npmId } from '../../../datasource/npm';
 import { logger } from '../../../logger';
 import { ExternalHostError } from '../../../types/errors/external-host-error';
 import { ExecOptions, exec } from '../../../util/exec';
-import { readFile, remove } from '../../../util/fs';
+import { exists, readFile, remove, writeFile } from '../../../util/fs';
 import { regEx } from '../../../util/regex';
 import type { PostUpdateConfig, Upgrade } from '../../types';
 import { getNodeConstraint } from './node-version';
@@ -35,6 +35,15 @@ export async function checkYarnrc(
       if (pathLine) {
         yarnPath = pathLine.replace(regEx(/^yarn-path\s+"?(.+?)"?$/), '$1');
       }
+      const yarnBinaryExists = await exists(yarnPath);
+      if (!yarnBinaryExists) {
+        const scrubbedYarnrc = yarnrc.replace(
+          regEx(/^yarn-path\s+"?.+?"?$/gm),
+          ''
+        );
+        await writeFile(`${cwd}/.yarnrc`, scrubbedYarnrc);
+        yarnPath = null;
+      }
     }
   } catch (err) /* istanbul ignore next */ {
     // not found