Static assertions for crate features, with informative errors.
The macros from this crate print which specific features are responsible for the assertion failure.
This example demonstrates the [exactly_one] macro,
which asserts that exactly one of the listed features is enabled.
compile_fail
assert_cfg::exactly_one!{
feature = "foo",
feature = "bar",
feature = "qux",
}
When the "foo" and "bar" features are enabled,
the above code produces this compile-time error:
``text
error[E0080]: evaluation of constant value failed
--> src/lib.rs:15:1
|
4 | / assert_cfg::exactly_one!{
5 | | feature = "foo",
6 | | feature = "bar",
7 | | feature = "qux",
8 | | }
| |_^ the evaluated program panicked at '
too many features were enabled, only one of them can be enabled:
-feature = "foo"
-feature = "bar"`
```
assert_cfg is #![no_std], it can be used anywhere Rust can be used.
This requires Rust 1.57.0, because it uses the panic macro in a const context.