fix: TypeError: fs.exists is not a function on read-only file system

lib/eslint/flat-eslint.js

@@ -11,6 +11,7 @@
 
 // Note: Node.js 12 does not support fs/promises.
 const fs = require("fs").promises;
+const { existsSync } = require("fs");
 const path = require("path");
 const findUp = require("find-up");
 const { version } = require("../../package.json");
@@ -766,7 +767,7 @@ class FlatESLint {
                 const errorCode = error && error.code;
 
                 // Ignore errors when no such file exists or file system is read only (and cache file does not exist)
-                if (errorCode !== "ENOENT" && !(errorCode === "EROFS" && !(await fs.exists(cacheFilePath)))) {
+                if (errorCode !== "ENOENT" && !(errorCode === "EROFS" && !existsSync(cacheFilePath))) {
                     throw error;
                 }
             }

tests/lib/eslint/eslint.js

@@ -2711,6 +2711,41 @@ describe("ESLint", () => {
                 assert(!shell.test("-f", cacheFilePath), "the cache for eslint should have been deleted since last run did not use the cache");
             });
 
+            it("should not throw an error if the cache file to be deleted does not exist on a read-only file system", async () => {
+                cacheFilePath = getFixturePath(".eslintcache");
+                doDelete(cacheFilePath);
+                assert(!shell.test("-f", cacheFilePath), "the cache file already exists and wasn't successfully deleted");
+
+                // Simulate a read-only file system.
+                sinon.stub(fs, "unlinkSync").throws(
+                    Object.assign(new Error("read-only file system"), { code: "EROFS" })
+                );
+
+                const eslintOptions = {
+                    useEslintrc: false,
+
+                    // specifying cache true the cache will be created
+                    cache: false,
+                    cacheLocation: cacheFilePath,
+                    overrideConfig: {
+                        rules: {
+                            "no-console": 0,
+                            "no-unused-vars": 2
+                        }
+                    },
+                    extensions: ["js"],
+                    cwd: path.join(fixtureDir, "..")
+                };
+
+                eslint = new ESLint(eslintOptions);
+
+                const file = getFixturePath("cache/src", "test-file.js");
+
+                await eslint.lintFiles([file]);
+
+                assert(fs.unlinkSync.calledWithExactly(cacheFilePath), "Expected attempt to delete the cache was not made.");
+            });
+
             it("should store in the cache a file that has lint messages and a file that doesn't have lint messages", async () => {
                 cacheFilePath = getFixturePath(".eslintcache");
                 doDelete(cacheFilePath);

tests/lib/eslint/flat-eslint.js

@@ -2601,6 +2601,40 @@ describe("FlatESLint", () => {
                 assert(!shell.test("-f", cacheFilePath), "the cache for eslint should have been deleted since last run did not use the cache");
             });
 
+            it("should not throw an error if the cache file to be deleted does not exist on a read-only file system", async () => {
+                cacheFilePath = getFixturePath(".eslintcache");
+                doDelete(cacheFilePath);
+                assert(!shell.test("-f", cacheFilePath), "the cache file already exists and wasn't successfully deleted");
+
+                // Simulate a read-only file system.
+                sinon.stub(fsp, "unlink").rejects(
+                    Object.assign(new Error("read-only file system"), { code: "EROFS" })
+                );
+
+                const eslintOptions = {
+                    overrideConfigFile: true,
+
+                    // specifying cache false the cache will be deleted
+                    cache: false,
+                    cacheLocation: cacheFilePath,
+                    overrideConfig: {
+                        rules: {
+                            "no-console": 0,
+                            "no-unused-vars": 2
+                        }
+                    },
+                    cwd: path.join(fixtureDir, "..")
+                };
+
+                eslint = new FlatESLint(eslintOptions);
+
+                const file = getFixturePath("cache/src", "test-file.js");
+
+                await eslint.lintFiles([file]);
+
+                assert(fsp.unlink.calledWithExactly(cacheFilePath), "Expected attempt to delete the cache was not made.");
+            });
+
             it("should store in the cache a file that has lint messages and a file that doesn't have lint messages", async () => {
                 cacheFilePath = getFixturePath(".eslintcache");
                 doDelete(cacheFilePath);