[ #1806 ] Add option_env support

[liamnaddell]

Note to reviewers: I do not really get the token stream stuff, I omitted adding a token stream to AST::Fragment, since I wasn't sure how to test the generated token stream.

gcc/rust/ChangeLog:
	* expand/rust-macro-builtins-utility.cc: Add macro expansion for option_env with eager expansion
	* expand/rust-macro-builtins.cc: Add option_env to builtin list
	* expand/rust-macro-builtins.h: Add option_env handler to header file

gcc/testsuite/ChangeLog:
	* rust/compile/option_env1.rs: Add success case for option_env
	* rust/compile/option_env2.rs: Add failure case for option_env
	* rust/execute/torture/builtin_macro_option_env.rs: Add execution case for option_env

Fixes #1806

Addresses #927, #1791

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• Added any relevant test cases to gcc/testsuite/rust/

---

Adds compiler support for option_env, adds eager expansion for option_env, adds tests for option_env

[CohenArthur]

honestly, well done - this isn't an easy part of the codebase, and you did a really good job :) don't worry about the tokenstream stuff, we can think about fixing this later. for the path issue, you're hitting a very frustrating issue which I'm trying to fix in #3068. ideally, we should be able to create paths to lang items (such as Option::Some and Option::None) so that we don't care about the module structure, or the name, or anything - we just care about hitting the proper type from the standard library. good work!

[CohenArthur]

...something like this:

Suggested change

	enum Option<T> {
	Some(T),
	None,
	}
	mod core {
	mod option {
	enum Option<T> {
	Some(T),
	None,
	}
	}
	}

[liamnaddell]

I fixed this for the tests. However, to get the compilation to work, I needed an extra
use core::option::Option;

Is that expected behavior? I would assume this is incorrect behavior, maybe a separate issue?

[CohenArthur]

hmmm... this is weird. you can investigate the generated code by using -frust-dump-all and looking at the generated gccrs.ast-pretty-expanded.dump file. it should show exactly the code you've generated with your macro expansion

[liamnaddell]

This seems like the expected behavior, since we don't have a prelude at the moment:

liam@gentoo ~/option_env2 $ rustc main.rs
error[E0412]: cannot find type `Option2` in this scope
  --> main.rs:23:13
   |
23 |     let _ : Option2< &'_ str > = core2::option2::Option2::Some("/home/liam/option2_env2");
   |             ^^^^^^^
  --> /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/option.rs:571:1
   |
   = note: similarly named enum `Option` defined here
   |
help: an enum with a similar name exists
   |
23 |     let _ : Option< &'_ str > = core2::option2::Option2::Some("/home/liam/option2_env2");
   |             ~~~~~~
help: consider importing this enum
   |
9  + use core2::option2::Option2;
   |

error[E0412]: cannot find type `Option2` in this scope
  --> main.rs:24:13
   |
24 |     let _ : Option2< &'_ str > = core2::option2::Option2::None;
   |             ^^^^^^^
  --> /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/option.rs:571:1
   |
   = note: similarly named enum `Option` defined here
   |
help: an enum with a similar name exists
   |
24 |     let _ : Option< &'_ str > = core2::option2::Option2::None;
   |             ~~~~~~
help: consider importing this enum
   |
9  + use core2::option2::Option2;
   |

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0412`.
liam@gentoo ~/option_env2 $ cat main.rs
//#![feature(rustc_attrs)]
//#[rustc_builtin_macro] macro_rules! option2_env {
//    () => { };
//}

//#[lang = "sized"]
//trait Sized< > { }

pub mod core2 {
    pub mod option2 {
        pub enum Option2< T > {
            Some(T),
            None,
        }

}

}

//use core2::option2::Option2;

fn main() {
    let _ : Option2< &'_ str > = core2::option2::Option2::Some("/home/liam/option2_env2");
    let _ : Option2< &'_ str > = core2::option2::Option2::None;
}

[liamnaddell]

I did mess up the "pub" on the module names in the test though, This is fixed :)

[liamnaddell]

honestly, well done - this isn't an easy part of the codebase, and you did a really good job :)

Thank you :)

[liamnaddell]

@CohenArthur Should I update this PR to use the lang-item paths from #3068 ?

[P-E-P]

@CohenArthur Should I update this PR to use the lang-item paths from #3068 ?

I've been trying to catch up on that issue (sorry for the delay!). We should probably rely on lang item path because right now the tests make use of a core module where it should be the core library (aka technically the file itself since we're defining the builtin macro from within the crate).

[liamnaddell]

@CohenArthur Should I update this PR to use the lang-item paths from #3068 ?

I've been trying to catch up on that issue (sorry for the delay!). We should probably rely on lang item path because right now the tests make use of a core module where it should be the core library (aka technically the file itself since we're defining the builtin macro from within the crate).

Ok, I can wait until the lang items path stuff is usable. If appropriate, we can also revisit some of the other macros then as well to integrate lang items.

[liamnaddell]

Converting to a Draft PR until we have lang items integrated.