Problem
Example can be found at example
I defined a no_std compatible crate as bellow
[package]
name = "static-dep"
[lib]
crate-type = ["staticlib", "cdylib", "rlib"] # Can not compile successfully
# crate-type = ["rlib"] # Compile successfully
and use it in a seperate crate
[package]
name = "using"
[dependencies]
static-dep = { version = "0.1.0"}
Although I have implemented a global allocator in crate using, cargo build still fail:
warning: dropping unsupported crate type `cdylib` for target `armv7a-none-eabi`
error: no global memory allocator found but one is required; link to std or add `#[global_allocator]` to a static item that implements the GlobalAlloc trait
error: `#[panic_handler]` function required, but not found
warning: `static-dep` (lib) generated 1 warning
error: could not compile `static-dep` (lib) due to 2 previous errors; 1 warning emitted
This is because when building the static-deps dependency, its static library will be built, and building a static library requires it to have a GlobalAllocator. I think it makes no sense to build a static library when using a library as a dependency. If you want a static library of this library, you should build the library directly instead of expecting it to be a product of a build process.
Why not cargo rustc --crate-type=<staticlib/cdylib> ?
I noticed that it's recommanded to use cargo rustc --crate-type=staticlib to replace the crate-type defined in Cargo.toml. But in some tools, like wasm-pack, they just simply use cargo build and there is no way to use customized commands. And there is no way other than specify crate-type in Cargo.toml to make wasm-pack works. Further more, the action of building a staticlib of a dependency is meaningless. Using cargo rustc --crate-type is just an incorrect but effective shortcut
Proposed Solution
When a crate is used as a dependency, do not pass dylib, staticlib, cdylib, or bin as the crate type during compilation, so that it is used only as an rlib