feat(format): fuzz targets for the parser and formatter

Assisted-by: GLM 5.3 Flash

parser/fuzz_test.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package parser
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// FuzzParse hammers the parser with arbitrary input.  The contract: no panic,
+// and always a usable file, whether or not diagnostics were reported.  The
+// seed corpus carries the repository's kernels, so a plain `go test` run
+// replays every seed as a regression case and CI exercises them without any
+// fuzzing budget.
+func FuzzParse(f *testing.F) {
+	for _, pattern := range []string{
+		"../testdata/*.s",
+		"../testdata/verify/*.s",
+	} {
+		files, _ := filepath.Glob(pattern)
+		for _, path := range files {
+			if b, err := os.ReadFile(path); err == nil {
+				f.Add(string(b))
+			}
+		}
+	}
+	f.Add("TEXT ·f(SB), NOSPLIT, $0\n\tRET\n")
+	f.Add("garbage ### ??? ::: \xff\xfe\n")
+	f.Add("#define A(x) x+1\nTEXT ·f(SB), $0\n\tA(2)\n\tRET\n")
+	f.Add("DATA t<>+0(SB)/8, $1\nGLOBL t<>(SB), RODATA, $8\n")
+	f.Add("TEXT ·f(SB), $0\n\tJMP (AX)\n\tCALL (BX)\n\tRET\n")
+
+	f.Fuzz(func(t *testing.T, src string) {
+		file, _ := Parse("fuzz.s", src)
+		if file == nil {
+			t.Fatal("Parse returned a nil file")
+		}
+	})
+}