Closed
Description
env!() is part of the list of builtin macros enumerated here
Its description is as follows:
Inspects an environment variable at compile time
The goal is to fetch environment variables passed to gccrs, and expand them into the user's compiled code.
arthur@platypus ~/G/gccrs (add-assert-macro)> cat test.rs
fn main() {
let s = env!("CUSTOM");
println!("{}", s);
}
arthur@platypus ~/G/gccrs (add-assert-macro)> rustc test.rs
error: environment variable `CUSTOM` not defined
--> test.rs:2:13
|
2 | let s = env!("CUSTOM");
| ^^^^^^^^^^^^^^
|
= note: this error originates in the macro `env` (in Nightly builds, run with -Z macro-backtrace for more info)
error: aborting due to previous error
arthur@platypus ~/G/gccrs (add-assert-macro) [1]> CUSTOM='hi!' rustc test.rs
arthur@platypus ~/G/gccrs (add-assert-macro)> ./test
hi!The macro should not expand to a function call that fetches environment variables during the user's program's execution.
arthur@platypus ~/G/gccrs (add-assert-macro)> ./test
hi!
arthur@platypus ~/G/gccrs (add-assert-macro)> CUSTOM='something else!' ./test
hi!The original macro contains two match arms, including one with a custom error message:
macro_rules! env {
($name:expr $(,)?) => {{ /* compiler built-in */ }};
($name:expr, $error_msg:expr $(,)?) => {{ /* compiler built-in */ }};
}You should try and support the first form first, by simply fetching an environment variable and creating an associated string using the make_string function defined in gcc/rust/expand/rust-macro-builtins.cc
The second form could be implemented in a later PR for simplicity