fix!: handle --output-file for empty output when saving to disk (#1…

…7957)

* fix!: handle -output-file for empty output when saving to disk

* docs: update migration guide

* Update tests/lib/cli.js

Co-authored-by: Milos Djermanovic <milos.djermanovic@gmail.com>

* docs: update migration guide

---------

Co-authored-by: Milos Djermanovic <milos.djermanovic@gmail.com>

docs/src/use/migrate-to-9.0.0.md

@@ -30,6 +30,7 @@ The lists below are ordered roughly by the number of users each change is expect
 * [Stricter `/* exported */` parsing](#exported-parsing)
 * [`"eslint:recommended"` and `"eslint:all"` strings no longer accepted in flat config](#string-config)
 * [`varsIgnorePattern` option of `no-unused-vars` no longer applies to catch arguments](#vars-ignore-pattern)
+* [`--output-file` now writes a file to disk even with an empty output](#output-file)
 
 ### Breaking changes for plugin developers
 
@@ -299,6 +300,14 @@ try {
 
 **Related issue(s):** [#17540](https://github.com/eslint/eslint/issues/17540)
 
+## <a name="output-file"></a> `--output-file` now writes a file to disk even with an empty output
+
+Prior to ESLint v9.0.0, the `--output-file` flag would skip writing a file to disk if the output was empty. However, in ESLint v9.0.0, `--output-file` now consistently writes a file to disk, even when the output is empty. This update ensures a more consistent and reliable behavior for `--output-file`.
+
+**To address:** Review your usage of the `--output-file` flag, especially if your processes depend on the file's presence or absence based on output content. If necessary, update your scripts or configurations to accommodate this change.
+
+**Related Issues(s):** [#17660](https://github.com/eslint/eslint/issues/17660)
+
 ## <a name="removed-context-methods"></a> Removed multiple `context` methods
 
 ESLint v9.0.0 removes multiple deprecated methods from the `context` object and moves them onto the `SourceCode` object:

lib/cli.js

@@ -285,25 +285,23 @@ async function printResults(engine, results, format, outputFile, resultsMeta) {
 
     const output = await formatter.format(results, resultsMeta);
 
-    if (output) {
-        if (outputFile) {
-            const filePath = path.resolve(process.cwd(), outputFile);
+    if (outputFile) {
+        const filePath = path.resolve(process.cwd(), outputFile);
 
-            if (await isDirectory(filePath)) {
-                log.error("Cannot write to output file path, it is a directory: %s", outputFile);
-                return false;
-            }
+        if (await isDirectory(filePath)) {
+            log.error("Cannot write to output file path, it is a directory: %s", outputFile);
+            return false;
+        }
 
-            try {
-                await mkdir(path.dirname(filePath), { recursive: true });
-                await writeFile(filePath, output);
-            } catch (ex) {
-                log.error("There was a problem writing the output file:\n%s", ex);
-                return false;
-            }
-        } else {
-            log.info(output);
+        try {
+            await mkdir(path.dirname(filePath), { recursive: true });
+            await writeFile(filePath, output);
+        } catch (ex) {
+            log.error("There was a problem writing the output file:\n%s", ex);
+            return false;
         }
+    } else if (output) {
+        log.info(output);
     }
 
     return true;

tests/lib/cli.js

@@ -1006,6 +1006,19 @@ describe("cli", () => {
                 assert.isTrue(log.info.notCalled);
             });
 
+            // https://github.com/eslint/eslint/issues/17660
+            it(`should write the file and create dirs if they don't exist even when output is empty with configType:${configType}`, async () => {
+                const filePath = getFixturePath("single-quoted.js");
+                const code = `${flag} --rule 'quotes: [1, single]' --o tests/output/eslint-output.txt ${filePath}`;
+
+                // TODO: fix this test to: await cli.execute(code, null, useFlatConfig);
+                await cli.execute(code, "var a = 'b'", useFlatConfig);
+
+                assert.isTrue(fs.existsSync("tests/output/eslint-output.txt"));
+                assert.strictEqual(fs.readFileSync("tests/output/eslint-output.txt", "utf8"), "");
+                assert.isTrue(log.info.notCalled);
+            });
+
             it(`should return an error if the path is a directory with configType:${configType}`, async () => {
                 const filePath = getFixturePath("single-quoted.js");
                 const code = `${flag} --rule 'quotes: [1, double]' --o tests/output ${filePath}`;