[heft-lint] Fix autofixer (#5171)

Co-authored-by: David Michon <dmichon-msft@users.noreply.github.com>

Author: dmichon-msft

common/changes/@rushstack/heft-lint-plugin/fix-eslint-fix_2025-03-24-22-49.json

@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@rushstack/heft-lint-plugin",
+      "comment": "Fix the `--fix` argument when the file only contains fixable issues.",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@rushstack/heft-lint-plugin"
+}

heft-plugins/heft-lint-plugin/src/Eslint.ts

@@ -178,7 +178,12 @@ export class Eslint extends LinterBase<TEslint.ESLint.LintResult> {
 
     const trimmedLintResults: TEslint.ESLint.LintResult[] = [];
     for (const lintResult of lintResults) {
-      if (lintResult.messages.length > 0 || lintResult.warningCount > 0 || lintResult.errorCount > 0) {
+      if (
+        lintResult.messages.length > 0 ||
+        lintResult.warningCount > 0 ||
+        lintResult.errorCount > 0 ||
+        fixMessages.length > 0
+      ) {
         trimmedLintResults.push(lintResult);
       }
     }