Modules with same names as built in types causes ICE

[matthewjasper]

Code

mod i32 {}

Meta

Version: gccrs (Compiler-Explorer-Build-gcc-b5c354d038f800695a8d730c56c4a4f744134adb-binutils-2.42) 14.0.1 20240309 (experimental)

Error output

crab1: internal compiler error: in setup_builtin_types, at rust/resolve/rust-late-name-resolver-2.0.cc:97
0x27eb5ec internal_error(char const*, ...)
	???:0
0xaf6cc9 fancy_abort(char const*, int, char const*)
	???:0
0xdbb522 Rust::Resolver2_0::Late::go(Rust::AST::Crate&)
	???:0
0xc4bef0 Rust::Session::compile_crate(char const*)
	???:0
Please submit a full bug report, with preprocessed source (by using -freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler returned: 1

[liamnaddell]

From reading here: https://doc.rust-lang.org/reference/names/namespaces.html

builtins and modules both belong in the Types namespace, however, that can't really be correct, since rustc allows you to name a module i32. I guess the idea is that builtins are resolved separately from other types? Otherwise, how would you prevent NR conflicts here?

[liamnaddell]

Also, look at this error:

liam@newgame ~/projects/gccrs/gccrs-build $ rustc main.rs
...
error[E0605]: non-primitive cast: `i32` as `i32`
 --> main.rs:4:18
  |
4 |     let a: i32 = 0 as i32;
  |                  ^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object

error: aborting due to 1 previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0605`.
liam@newgame ~/projects/gccrs/gccrs-build $ cat main.rs
struct i32 {}

fn main() {
    let a: i32 = 0 as i32;
}
liam@newgame ~/projects/gccrs/gccrs-build $

What happens here is that i32 gets shadowed to the struct, which causes a compile error, since i32 no longer refers to a primative type.

[liamnaddell]

I guess what we are expected to do is remove builtin types from the resolution context when another Item overshadows it

EDIT: I tried this, but then i32 doesn't exist, and this rustc code (which is supposed to compile) no longer compiles:

mod i32 {}

fn main() {
    let a: i32 = 0 as i32;
}

[liamnaddell]

Modules are clearly handled separately from other types like structs. I think modules are somehow part of their own namespace?

EDIT: I checked rustc, structs, builtins, modules, etc are all in the Types namespace, at least at rustc's HIR level. They end up going into different RIB's though. I'm not really sure how you'd make this work yet though

[powerboat9]

It looks like builtins are really supposed to go in a language prelude. That way, module definitions can shadow builtin definitions by virtue of being in a different scope.

[liamnaddell]

It looks like builtins are really supposed to go in a language prelude. That way, module definitions can shadow builtin definitions by virtue of being in a different scope.

Would this be part of a distinct RIB?

[powerboat9]

Yep. Fixing this would probably entail some adjustments to the ForeverStack node hierarchy, and some code for handling descent into prelude nodes (since we'll want multiple preludes).

[liamnaddell]

Yep. Fixing this would probably entail some adjustments to the ForeverStack node hierarchy, and some code for handling descent into prelude nodes (since we'll want multiple preludes).

Wouldn't the prelude end up being handled as an import? I.e. not having a distinct node?

https://github.com/rust-lang/rust/blob/8ad2c9724d983cfb116baab0bb800edd17f31644/compiler/rustc_resolve/src/imports.rs#L75
https://github.com/rust-lang/rust/blob/8ad2c9724d983cfb116baab0bb800edd17f31644/compiler/rustc_resolve/src/lib.rs#L1021

[powerboat9]

There are multiple preludes, some of which should probably have their own nodes

[liamnaddell]

I'm giving this one a try currently. Solving the issue seems easy enough, since you just replace insert with insert_globbed when builtins are added during late resolution.

Some of the secondary problems are more challenging though.

1. You aren't able to use builtin types, since self::i32 isn't supposed to exist (theres a rust spec reference for this, I forgot where though). Of course, if you use std::i32, then you MAY reference self::i32
2. structs and other proper types shadow builtin types for type resolution
3. modules DON'T shadow BUILTIN types for type resolution (this is despite both modules and structs going in the same namespace ;-;)
4. modules cannot coexist with other conflicting items in the same namespace (u can't have struct A and mod A)

I'm trying to see currently how many of these I can solve presently

[powerboat9]

Modules should be inserted into the type namespace, which would solve 4. We might just need a separate rib/node to store builtin types, and some adjustments to path resolution.