fix(core): restore libFuzzer as the CLI default

Make the standalone CLI keep its existing libFuzzer compatibility unless users explicitly opt into LibAFL. This avoids surprising failures for established libFuzzer flag combinations while the LibAFL backend continues to harden.

Author: oetr

docs/fuzz-settings.md

@@ -591,7 +591,7 @@ Instead use the native Jest flag `--testNamePattern` as described above.
 
 ### `engine` : [string]
 
-Default: `"libafl"` in CLI mode, `"libfuzzer"` in Jest mode
+Default: `"libfuzzer"` in CLI mode, `"libfuzzer"` in Jest mode
 
 Select the native fuzzing backend.
 

packages/core/cli.ts

@@ -181,7 +181,7 @@ yargs(process.argv.slice(2))
 					alias: ["backend"],
 					defaultDescription: `${JSON.stringify(defaultCLIOptions.engine)}`,
 					describe:
-						"Fuzzing engine backend. Use 'afl' (alias 'libafl') for the default LibAFL backend or 'libfuzzer' to run the libFuzzer backend.",
+						"Fuzzing engine backend. Use 'libfuzzer' for the default backend or 'afl' (alias 'libafl') to opt into the LibAFL backend.",
 					group: "Fuzzer:",
 					type: "string",
 				})

packages/core/options.test.ts

@@ -31,8 +31,8 @@ import { buildLibAflOptions, spawnsSubprocess } from "./options";
 
 describe("options", () => {
 	describe("merge", () => {
-		it("uses LibAFL as default CLI engine", () => {
-			expect(defaultCLIOptions.engine).toBe("libafl");
+		it("keeps libFuzzer as default CLI engine", () => {
+			expect(defaultCLIOptions.engine).toBe("libfuzzer");
 		});
 
 		it("keeps libFuzzer as default Jest engine", () => {

packages/options/index.ts

@@ -88,7 +88,7 @@ const allowedFuzzTestOptions = [
 export type AllowedFuzzTestOptions = (typeof allowedFuzzTestOptions)[number];
 
 export const defaultCLIOptions: Options = Object.freeze({
-	engine: "libafl",
+	engine: "libfuzzer",
 	coverage: false,
 	coverageDirectory: "coverage",
 	coverageReporters: ["json", "text", "lcov", "clover"],

packages/options/options.test.ts

@@ -71,8 +71,8 @@ describe("options", () => {
 	});
 
 	describe("merge", () => {
-		it("uses LibAFL as default CLI engine", () => {
-			expect(defaultCLIOptions.engine).toBe("libafl");
+		it("keeps libFuzzer as default CLI engine", () => {
+			expect(defaultCLIOptions.engine).toBe("libfuzzer");
 		});
 
 		it("keeps libFuzzer as default Jest engine", () => {