Support inline package manifest for git dependencies without mcpp.toml

[ZheFeng7110]

Problem

Currently, when specifying a dependency via git, mcpp strictly requires the cloned repository to contain an mcpp.toml at its root. If the upstream project does not use mcpp (which is common for third-party C/C++ libraries), the build fails immediately with:

git dependency 'xxx' (at '...') has no mcpp.toml

This is different from version-based dependencies, where mcpp can fall back to synthesizing a manifest from the index descriptor (mcpp = { ... } block in the .lua file). Git (and path) dependencies have no such fallback mechanism.

Use Case

I want to depend on a third-party library directly from its upstream Git repository (e.g., to track a specific commit or fork before it is published to the mcpp index). The library does not have mcpp.toml, but I know enough about its layout to describe it: source globs, include directories, target kind, etc.

Right now, the only workaround is to fork the repository and add an mcpp.toml manually, which adds maintenance burden and fragments upstream tracking.

Proposed Feature

Allow the consumer to provide an inline package description directly inside the dependency spec in their own mcpp.toml. When the fetched git repository lacks an mcpp.toml, mcpp should use this inline description as an overlay / synthesized manifest.

Example syntax:

[dependencies]
mylib = { 
    git = "https://github.com/user/mylib.git", 
    tag = "v1.0.0",
    # Inline manifest keys used when upstream has no mcpp.toml
    name = "mylib",
    version = "1.0.0",
    sources = ["src/**/*.cpp", "include/**/*.h"],
    include_dirs = ["include"],
    targets = { mylib = { kind = "lib" } }
}

Or alternatively, under a dedicated sub-table to avoid key conflicts:

[dependencies.mylib]
git = "https://github.com/user/mylib.git"
tag = "v1.0.0"

[dependencies.mylib.manifest]
name = "mylib"
version = "1.0.0"
sources = ["src/**/*.cpp"]
include_dirs = ["include"]

Benefits

• Lowers the barrier to adopting mcpp with existing third-party code.
• Avoids unnecessary forks just to add a 10-line mcpp.toml.
• Keeps the dependency declaration self-contained in the consumer's manifest.
• Aligns with the existing descriptor-synthesis concept already used for index packages.

Additional Context

The relevant strict check lives in src/build/prepare.cppm around line 2967:

if (spec.isPath() || spec.isGit()) {
    if (!std::filesystem::exists(dep_root / "mcpp.toml")) {
        return std::unexpected(std::format(
            "%s dependency '%s' (at '%s') has no mcpp.toml",
            spec.isGit() ? "git" : "path", name, dep_root.string()));
    }

For version dependencies, loadVersionDep already knows how to synthesize a manifest via synthesize_from_xpkg_lua when no mcpp.toml is present. A similar synthesis path could be added for git/path dependencies that carry an inline descriptor.

[Sunrisepeak]

这个功能实际上已经支持, 而且可以避免 mcpp.toml 内嵌多个复杂包描述。
通过自定义 indexrepo 统一描述然后 mcpp.toml 中使用

• https://github.com/Sunrisepeak/mbun/blob/6dad3b1d7a75047119e0068da387e4603df40961/mcpp.toml#L49
• https://github.com/Sunrisepeak/mbun/tree/rewrite_bun_in_mcpp/mcpp
• https://github.com/mcpp-community/mcpp/archive/refs/tags/v2026.7.29.2.tar.gz

[ZheFeng7110]

ok，谢谢