dns fuzz targets: smith corpus, llvm-backed fuzz artifact

build.zig

@@ -18,6 +18,7 @@ pub fn build(b: *std.Build) void {
 
     const integration = b.option(bool, "integration", "Run hermetic integration tests (loopback sockets only)") orelse false;
     const live = b.option(bool, "live", "Run tests that reach external network hosts") orelse false;
+    const fuzz = b.option(bool, "fuzz", "Build the fuzz targets with the LLVM backend (required for --fuzz)") orelse false;
     const version_string = b.option([]const u8, "version-string", "Version reported by `nxdns version`") orelse "0.1.0-dev";
     const git_commit = b.option([]const u8, "git-commit", "Git commit reported by `nxdns version`") orelse "unknown";
 
@@ -52,7 +53,31 @@ pub fn build(b: *std.Build) void {
     tests.root_module.addAnonymousImport("test_fixtures", .{
         .root_source_file = b.path("tests/fixtures/fixtures.zig"),
     });
-    b.step("test", "Run the test suite").dependOn(&b.addRunArtifact(tests).step);
+    const test_step = b.step("test", "Run the test suite");
+    test_step.dependOn(&b.addRunArtifact(tests).step);
+
+    // Fuzz targets compile as a second test artifact with `dns` as a named module
+    // (a file belongs to one module per compilation; the aggregator keeps owning
+    // the in-file tests). `-Dfuzz` opts into the LLVM backend, which `--fuzz`
+    // needs for sanitizer coverage; stock 0.16.0 also requires a patched
+    // test_runner.zig for fuzz mode — see specs/milestone-2.md.
+    const dns_mod = b.createModule(.{
+        .root_source_file = b.path("src/dns/dns.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    const fuzz_mod = b.createModule(.{
+        .root_source_file = b.path("tests/fuzz/dns_fuzz.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    fuzz_mod.addImport("dns", dns_mod);
+    const fuzz_tests = b.addTest(.{
+        .name = "fuzz",
+        .use_llvm = if (fuzz) true else null,
+        .root_module = fuzz_mod,
+    });
+    test_step.dependOn(&b.addRunArtifact(fuzz_tests).step);
 
     const cross = b.step("cross", "Build static musl executables for every deploy target");
     for (cross_targets) |triple| {