编译liquid合约出错

[hongfish]

使用的rust配置：
[source.crates-io]
registry = "https://github.com/rust-lang/crates.io-index"

replace-with = 'ustc' # 如：tuna、sjtu、ustc，或者 rustcc

[source.ustc]
registry = "git://mirrors.ustc.edu.cn/crates.io-index"

[source.sjtu]
registry = "https://mirrors.sjtug.sjtu.edu.cn/git/crates.io-index"

[source.tuna]
registry = "https://mirrors.tuna.tsinghua.edu.cn/git/crates.io-index.git"

[source.rustcc]
registry = "https://code.aliyun.com/rustcc/crates.io-index.git"

1、执行 cargo test 时，出现以下错误：
error[E0635]: unknown feature proc_macro_span_shrink
--> /root/.cargo/registry/src/mirrors.tuna.tsinghua.edu.cn-df7c3c540f42cdbd/proc-macro2-1.0.47/src/lib.rs:92:30
|
92 | feature(proc_macro_span, proc_macro_span_shrink)
| ^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try rustc --explain E0635.
error: could not compile proc-macro2

To learn more, run the command again with --verbose.
warning: build failed, waiting for other jobs to finish...
error: build failed

2、使用清华大学的源
[source.tuna]
registry = "https://mirrors.tuna.tsinghua.edu.cn/git/crates.io-index.git"

执行cargo liquid build时，出现以下错误：
[1/4] 🔍 Collecting crate metadata
ERROR: Error invoking cargo metadata

Caused by:
Error during execution of cargo metadata: Updating https://mirrors.tuna.tsinghua.edu.cn/git/crates.io-index.git index
Updating git repository https://gitee.com/WeBankBlockchain/liquid
Downloading crates ...
error: failed to download once_cell v1.15.0

Caused by:
  unable to get packages from source

Caused by:
  failed to download replaced source registry `https://github.com/rust-lang/crates.io-index`

Caused by:
  failed to parse manifest at `/root/.cargo/registry/src/mirrors.tuna.tsinghua.edu.cn-df7c3c540f42cdbd/once_cell-1.15.0/Cargo.toml`

Caused by:
  feature `edition2021` is required

  consider adding `cargo-features = ["edition2021"]` to the manifest

3、使用中国科学技术大学的源
[source.ustc]
registry = "git://mirrors.ustc.edu.cn/crates.io-index"

执行cargo liquid build时，出现以下错误：
[1/4] 🔍 Collecting crate metadata
ERROR: Error invoking cargo metadata

Caused by:
Error during execution of cargo metadata: Updating git://mirrors.ustc.edu.cn/crates.io-index index
Updating git repository https://gitee.com/WeBankBlockchain/liquid
Downloading crates ...
error: failed to download bumpalo v3.11.1

Caused by:
  unable to get packages from source

Caused by:
  failed to download replaced source registry `https://github.com/rust-lang/crates.io-index`

Caused by:
  failed to parse manifest at `/root/.cargo/registry/src/mirrors.ustc.edu.cn-61ef6e0cd06fb9b8/bumpalo-3.11.1/Cargo.toml`

Caused by:
  feature `edition2021` is required

  consider adding `cargo-features = ["edition2021"]` to the manifest

个人建议，这个编译liquid合约的环境很难配置且容易出错，是否可以提供个docker组件，用户只需要将liquid合约上传到docker容器中，在容器里编译、构建，然后将构建好的Wasm 格式字节码及 ABI拷贝出来使用。

[bxq2011hust]

这个编译出错的原因是liquid当前使用的编译器版本有点旧，而rust发布了新的语言版本2021，有一些依赖库升级语言版本只升级版本号的patch，导致编译报错。
有两种解决办法1. 降低报错的依赖库的版本，到其要求edition2021之前，2. 升级liquid语言使用的rustc版本，需要liquid适配。
我们正在规划升级liquid使用的编译器版本以彻底的解决问题，目前请先尝试降低报错的依赖库版本解决问题

[ethan75]

同样遇到此问题，定位是proc-macro2更新后引起的（https://github.com/dtolnay/proc-macro2）；
查看合约项目中引用proc-macro2的地方都是其他crate，降低proc-macro2的版本好像是可以的，可能要修改多个地方，直接在当前项目指定proc-macro2的版本会导致其他错误；
对比不同版本的proc-macro2，去掉本地库中proc-macro2-1.0.47中proc_macro_span_shrink代码，编译通过，主要修改地方如下（注释掉下面的代码）：
./build.rs:116: && feature_allowed("proc_macro_span_shrink")
./src/lib.rs:92: feature(proc_macro_span, proc_macro_span_shrink)

[ethan75]

希望官方的cargo-liquid和liquid项目能早日适配edition2021，可能那天其他引用的crate更新了，又会导致类似错误。