C++26 + import std 无法通过 mcpp 构建

[skyler-zbt]

环境

• mcpp: 0.0.41
• 工具链: gcc@16.1.0 (xlings-fromsource)
• 系统: Fedora 44, x86_64

项目配置 (mcpp.toml)

[package]
name        = "M3Lib"
version     = "0.1.0"

[targets.M3Lib]
kind = "lib"

[lib]
path = "m3/m3.cppm"

[build]
sources = ["m3/**/*.cppm"]
cxxflags = ["-std=c++26", "-fcontracts"]

[toolchain]
default = "gcc@16.1.0"

实际输出

$ mcpp build
   Resolving toolchain
    Resolved gcc@16.1.0 → @mcpp/registry/data/xpkgs/xim-x-gcc/16.1.0/bin/g++
   Compiling M3Lib v0.1.0 (.)
error: build failed
In module imported at /home/skyler/Dev/M3Lib/m3/detail/alignment_traits.cppm:5:1:
std: error: language dialect differs 'C++23', expected 'C++26/contracts'
std: error: failed to read compiled module: Bad file data
std: note: compiled module file is 'gcm.cache/std.gcm'
std: fatal error: returning to the gate for a mechanical issue
compilation terminated.
In module imported at /home/skyler/Dev/M3Lib/m3/detail/concepts.cppm:7:1:
std: error: language dialect differs 'C++23', expected 'C++26/contracts'
std: error: failed to read compiled module: Bad file data
std: note: compiled module file is 'gcm.cache/std.gcm'
std: fatal error: returning to the gate for a mechanical issue
compilation terminated.

补充信息

GCC 16.x 在 -std=c++26 下隐式启用 contracts：

$ g++ -std=c++26 -E -dM -x c++ - < /dev/null | grep contract
#define __cpp_contracts 202502L

-std=c++26 本身就会让方言变为 C++26/contracts，与 mcpp std 模块的 C++23 不匹配。

纯 C++23 项目（无 -std=c++26 和 -fcontracts）可以正常构建。

[Sunrisepeak]

改功能已经支持, 使用 xlings update mcpp -y 更新到最新版本(0.0.42)即可使用

[package]
standard = "c++26"

具体文档

https://github.com/mcpp-community/mcpp/blob/main/docs/05-mcpp-toml.md#23-build--%E6%9E%84%E5%BB%BA%E9%85%8D%E7%BD%AE

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