Why can't I import `std::assert` via `use` while it works for other macros from std? - rust

Question

With Rust 2018, this code works (Playground):
use std::panic;
use std::format;
use std::assert_eq;
But this:
use std::assert;
Results in this error:
error[E0432]: unresolved import `std::assert`
--> src/lib.rs:4:5
|
4 | use std::assert;
| ^^^^^^^^^^^ no `assert` in the root
I read the edition guide about this topic and it says that use should work with macro_rules! macros and procedural macros. Thus, I'm confused.

Answer 1

use should work with macro_rules! macros and procedural macros
Except assert is neither of those:
/// Built-in macros to the compiler itself.
///
/// These macros do not have any corresponding definition with a `macro_rules!`
/// macro, but are documented here. Their implementations can be found hardcoded
/// into libsyntax itself.
It is a compiler built-in:
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_doc_only_macro]
macro_rules! assert {
($cond:expr) => ({ /* compiler built-in */ });
($cond:expr,) => ({ /* compiler built-in */ });
($cond:expr, $($arg:tt)+) => ({ /* compiler built-in */ });
}
Other faux-macros include:
compile_error
format_args
env
option_env
concat_idents
concat
line
column
file
stringify
include_str
include_bytes
module_path
cfg
include
The actual definition of assert is buried much lower in libsyntax_ext/assert.rs
Stabilize uniform paths on Rust 2018 (#56417) does mention these in passing:
Built-in macros, for example use env.
Currently an error due to some (fixable) implementation details of built-in macros.
No known issues to resolve before stabilization (after the error is removed).