添加println!导致Rust OpenGL程序无法渲染三角形？

我用Rust开发了一个在屏幕上绘制彩色三角形的简单OpenGL程序，原本运行正常，三角形能按预期渲染：

之后我尝试对代码做抽象：把VAO、VBO和ShaderProgram封装成结构体，处理绑定、着色器附加等逻辑，这部分工作正常。但在抽象顶点属性时遇到了问题：

我给ShaderProgram结构体加了两个方法，目的是不用硬编码步长（stride）或属性起始指针就能启用顶点属性：

pub fn add_attribute(&mut self, name: &'a str, length: i32) {
    let mut props = VertexAttributeProps::new(name, length);
    self.attributes.push(props);
}
pub fn apply_attributes(&self) {
    const GL_FLOAT_SIZE: i32 = mem::size_of::<gl::types::GLfloat>() as i32;
    let stride = self
        .attributes
        .iter()
        .fold(0, |prev, attr| prev + attr.length)
        * GL_FLOAT_SIZE;

    let mut current_pos: i32 = 0;
    for attr_options in self.attributes.iter() {
        // println!("{:?}", current_pos);
        unsafe {
            let attribute = VertexAttribute::new(
                location,
                attr_options.length,
                gl::FLOAT,
                gl::FALSE,
                stride,
                (current_pos * GL_FLOAT_SIZE) as *const c_void,
            );
            attribute.enable();
        }
        current_pos = current_pos + attr_options.length;
    }
}

我希望通过以下方式添加属性：

shader_program.add_attribute("position", 2);
shader_program.add_attribute("color", 3);
shader_program.apply_attributes();

替代原本冗长的代码块：

let posAttrib: GLuint;
unsafe {
    posAttrib = gl::GetAttribLocation(
        shader_program.program_handle,
        "position".as_ptr() as *const i8,
    ) as u32;
    gl::EnableVertexAttribArray(posAttrib);
    gl::VertexAttribPointer(
        posAttrib,
        2,
        gl::FLOAT,
        gl::FALSE,
        5 * mem::size_of::<gl::types::GLfloat>() as i32,
        0 as *const c_void,
    )
}

let colAttrib: GLuint;
unsafe {
    colAttrib =
        gl::GetAttribLocation(shader_program.program_handle, "color".as_ptr() as *const i8)
            as u32;
    gl::EnableVertexAttribArray(colAttrib);
    gl::VertexAttribPointer(
        colAttrib,
        3,
        gl::FLOAT,
        gl::FALSE,
        5 * mem::size_of::<gl::types::GLfloat>() as i32,
        (2 * mem::size_of::<gl::types::GLfloat>()) as *const c_void,
    )
}

但这种抽象方式无法正常工作。于是我尝试调试，在原本可行的冗长代码中添加了println!语句：

let posAttrib: GLuint;
unsafe {
    posAttrib = gl::GetAttribLocation(
        shader_program.program_handle,
        "position".as_ptr() as *const i8,
    ) as u32;

    // ???????
    println!("{}", posAttrib);
    // ???????

    gl::EnableVertexAttribArray(posAttrib);
    gl::VertexAttribPointer(
        posAttrib,
        2,
        gl::FLOAT,
        gl::FALSE,
        5 * mem::size_of::<gl::types::GLfloat>() as i32,
        0 as *const c_void,
    )
}

结果三角形停止渲染，移除该语句后三角形又能正常显示。为何一个简单的println!会导致这种问题？是时序问题导致程序异常吗？

内容的提问来源于stack exchange，提问作者DerAnonyme