feat: fuzz gnovm/pkg/transpiler.Transpile (#3457)

Adds a fuzzer for Transpile, which found bugs:
* #3425 in which this following Go program crashed the transpiler
```go
package A
import(""//"
""/***/)
```
* #3426 which generated an input that revealed the fact that Gno
deviates from Go by allowing unused variables yet Go's standard is
strict on unused variables like this program
```go
package main

func main() {
	const c1 = 1 < 8
	main()
	1
}
```
which we shouldn't allow
* partially #3428 which revealed the discrepancy in Gno that the
overflow detection is still lacking as the following program is invalid
Go but Gno allowed it to run
```go
package main

func main() {
	const c1 = int8(1) << 8
	println(c1)
}
```
because 1<<8 (256) is higher than the range of int8 for which the
maximum is `(1<<7) - 1 aka 127`

Updates #3087

Co-authored-by: Nathan Toups <[email protected]>

gnovm/pkg/transpiler/fuzz_test.go

@@ -0,0 +1,80 @@
+package transpiler
+
+import (
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+	"time"
+)
+
+func FuzzTranspiling(f *testing.F) {
+	if testing.Short() {
+		f.Skip("Running in -short mode")
+	}
+
+	// 1. Derive the seeds from our seedGnoFiles.
+	breakRoot := filepath.Join("gnolang", "gno")
+	pc, thisFile, _, _ := runtime.Caller(0)
+	index := strings.Index(thisFile, breakRoot)
+	_ = pc // to silence the pedantic golangci linter.
+	rootPath := thisFile[:index+len(breakRoot)]
+	examplesDir := filepath.Join(rootPath, "examples")
+	ffs := os.DirFS(examplesDir)
+	fs.WalkDir(ffs, ".", func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			panic(err)
+		}
+		if !strings.HasSuffix(path, ".gno") {
+			return nil
+		}
+		file, err := ffs.Open(path)
+		if err != nil {
+			panic(err)
+		}
+		blob, err := io.ReadAll(file)
+		file.Close()
+		if err != nil {
+			panic(err)
+		}
+		f.Add(blob)
+		return nil
+	})
+
+	// 2. Run the fuzzers.
+	f.Fuzz(func(t *testing.T, gnoSourceCode []byte) {
+		// 3. Add timings to ensure that if transpiling takes a long time
+		// to run, that we report this as problematic.
+		doneCh := make(chan bool, 1)
+		readyCh := make(chan bool)
+		go func() {
+			defer func() {
+				r := recover()
+				if r == nil {
+					return
+				}
+
+				sr := fmt.Sprintf("%s", r)
+				if !strings.Contains(sr, "invalid line number ") {
+					panic(r)
+				}
+			}()
+			close(readyCh)
+			defer close(doneCh)
+			_, _ = Transpile(string(gnoSourceCode), "gno", "in.gno")
+			doneCh <- true
+		}()
+
+		<-readyCh
+
+		select {
+		case <-time.After(2 * time.Second):
+			t.Fatalf("took more than 2 seconds to transpile\n\n%s", gnoSourceCode)
+		case <-doneCh:
+		}
+	})
+}

gnovm/pkg/transpiler/testdata/fuzz/FuzzTranspiling/26ec2c0a22e242fc

@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("package\tA\nimport(\"\"//\"\n\"\"/***/)")

gnovm/pkg/transpiler/testdata/fuzz/FuzzTranspiling/54f7287f473abfa5

@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("package A\nimport(\"\"//\"\n\"\"/***/)")

gnovm/pkg/transpiler/testdata/fuzz/FuzzTranspiling/703a1cacabb84c6d

@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("package A\ncon\x12\n\xec|b\x80\xddQst(\n/*\n\n\n\n\n\n\nka\n*/A)")

gnovm/pkg/transpiler/testdata/fuzz/FuzzTranspiling/bcd60839c81ca478

@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("//\"\npackage\tA\nimport(\"\"//\"\n\"\"/***/)")

gnovm/pkg/transpiler/testdata/fuzz/FuzzTranspiling/bf4f7515b25bf71b

@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("//0000\x170000000000:0\npackage A")