为什么在生成返回字符串的函数时wasm-opt在wasm-pack构建中失败？

问题描述

我正在这里浏览有关Conway生活游戏的Rust wasm教程：https://rustwasm.github.io/docs/book/game-of-life/implementing.html

文件中最简单的功能之一称为Universe.render（这是用于呈现表示游戏状态的字符串的功能）。运行wasm-pack build时会导致错误：

Fatal: error in validating input
Error: Failed to execute `wasm-opt`: exited with exit code: 1
  full command: "/home/vaer/.cache/.wasm-pack/wasm-opt-4d7a65327e9363b7/wasm-opt" "/home/vaer/src/learn-rust/wasm-game-of-life/pkg/wasm_game_of_life_bg.wasm" "-o" "/home/vaer/src/learn-rust/wasm-game-of-life/pkg/wasm_game_of_life_bg.wasm-opt.wasm" "-O"
To disable `wasm-opt`,add `wasm-opt = false` to your package Metadata in your `Cargo.toml`.

如果我删除该功能，则代码将正确构建。如果我将其替换为以下函数，则构建将失败，并显示相同的错误：

pub fn wtf() -> String {
    String::from("wtf")
}

似乎任何返回String的函数都会导致此错误。为什么？

以下是我的全部代码：

mod utils;

use wasm_bindgen::prelude::*;

// When the `wee_alloc` feature is enabled,use `wee_alloc` as the global
// allocator.
#[cfg(feature = "wee_alloc")]
#[global_allocator]
static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;

// Begin game of life impl

use std::fmt;

#[wasm_bindgen]
#[repr(u8)]
#[derive(Clone,copy,Debug,PartialEq,Eq)]
pub enum Cell {
    Dead = 0,Alive = 1,}

#[wasm_bindgen]
pub struct Universe {
    width: u32,height: u32,cells: Vec<Cell>,}

impl fmt::display for Universe {
    fn fmt(&self,f: &mut fmt::Formatter) -> fmt::Result {
        for line in self.cells.as_slice().chunks(self.width as usize) {
            for &cell in line {
                let symbol = if cell == Cell::Dead { '◻' } else { '◼' };
                write!(f,"{}",symbol)?;
            }
            write!(f,"\n")?;
        }

        Ok(())
    }
}

impl Universe {
    fn get_index(&self,row: u32,column: u32) -> usize {
        (row * self.width + column) as usize
    }

    fn live_neighbor_count(&self,column: u32) -> u8 {
        let mut count = 0;
        for delta_row in [self.height - 1,1].iter().cloned() {
            for delta_col in [self.width - 1,1].iter().cloned() {
                if delta_row == 0 && delta_col == 0 {
                    continue;
                }

                let neighbor_row = (row + delta_row) % self.height;
                let neighbor_col = (column + delta_col) % self.width;
                let idx = self.get_index(neighbor_row,neighbor_col);
                count += self.cells[idx] as u8;
            }
        }
        count
    }
}

/// Public methods,exported to JavaScript.
#[wasm_bindgen]
impl Universe {
    pub fn tick(&mut self) {
        let mut next = self.cells.clone();

        for row in 0..self.height {
            for col in 0..self.width {
                let idx = self.get_index(row,col);
                let cell = self.cells[idx];
                let live_neighbors = self.live_neighbor_count(row,col);

                let next_cell = match (cell,live_neighbors) {
                    // Rule 1: Any live cell with fewer than two live neighbours
                    // dies,as if caused by underpopulation.
                    (Cell::Alive,x) if x < 2 => Cell::Dead,// Rule 2: Any live cell with two or three live neighbours
                    // lives on to the next generation.
                    (Cell::Alive,2) | (Cell::Alive,3) => Cell::Alive,// Rule 3: Any live cell with more than three live
                    // neighbours dies,as if by overpopulation.
                    (Cell::Alive,x) if x > 3 => Cell::Dead,// Rule 4: Any dead cell with exactly three live neighbours
                    // becomes a live cell,as if by reproduction.
                    (Cell::Dead,// All other cells remain in the same state.
                    (otherwise,_) => otherwise,};

                next[idx] = next_cell;
            }
        }

        self.cells = next;
    }

    pub fn new() -> Universe {
        let width = 64;
        let height = 64;

        let cells = (0..width * height)
            .map(|i| {
                if i % 2 == 0 || i % 7 == 0 {
                    Cell::Alive
                } else {
                    Cell::Dead
                }
            })
            .collect();

        Universe {
            width,height,cells,}
    }

    pub fn render(&self) -> String {
        self.to_string()
    }
}

仅删除此文件底部的render函数将使构建成功。用返回render的任何函数替换String函数会导致构建失败。为什么？

解决方法

事实证明这不是预期的行为；相反，它是wasm-pack的错误：https://github.com/rustwasm/wasm-pack/issues/886

现在可以通过将以下内容添加到项目的cargo.toml中来解决该问题：

[package.metadata.wasm-pack.profile.release]
wasm-opt = ["-Oz","--enable-mutable-globals"]