compiler: split Compile info sub-functions

Also add tests for basic debug info.

pkg/compiler/debug_test.go

@@ -4,8 +4,66 @@ import (
 	"testing"
 
 	"github.com/nspcc-dev/neo-go/pkg/internal/testserdes"
+	"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
+func TestCodeGen_DebugInfo(t *testing.T) {
+	src := `package foo
+func Main(op string) bool {
+	res := methodInt(op)
+	_ = methodString()	
+	_ = methodByteArray()
+	_ = methodArray()
+	_ = methodStruct()
+	return res == 42
+}
+
+func methodInt(a string) int {
+	if a == "get42" {
+		return 42
+	}
+	return 3
+}
+func methodString() string { return "" }
+func methodByteArray() []byte { return nil }
+func methodArray() []bool { return nil }
+func methodStruct() struct{} { return struct{}{} }
+`
+
+	info, err := getBuildInfo(src)
+	require.NoError(t, err)
+
+	pkg := info.program.Package(info.initialPackage)
+	c := newCodegen(info, pkg)
+	require.NoError(t, c.compile(info, pkg))
+
+	buf := c.prog.Bytes()
+	d := c.emitDebugInfo()
+	require.NotNil(t, d)
+
+	t.Run("return types", func(t *testing.T) {
+		returnTypes := map[string]string{
+			"methodInt":    "Integer",
+			"methodString": "String", "methodByteArray": "ByteArray",
+			"methodArray": "Array", "methodStruct": "Struct",
+			"Main": "Boolean",
+		}
+		for i := range d.Methods {
+			name := d.Methods[i].Name.Name
+			assert.Equal(t, returnTypes[name], d.Methods[i].ReturnType)
+		}
+	})
+
+	// basic check that last instruction of every method is indeed RET
+	for i := range d.Methods {
+		index := d.Methods[i].Range.End
+		require.True(t, int(index) < len(buf))
+		require.EqualValues(t, opcode.RET, buf[index])
+	}
+}
+
 func TestDebugInfo_MarshalJSON(t *testing.T) {
 	d := &DebugInfo{
 		EntryPoint: "main",