refutable pattern in local binding - [E0005]

[MahadMuhammad]

Refutable pattern in local binding - E0005

Patterns used to bind names must be irrefutable, that is, they must guarantee that a name will be extracted in all cases.

• You can view the same on compiler-explorer

---

I tried this code from E0005:

#![allow(unused)]
fn main() {
let x = Some(1);
let Some(y) = x;
// error: refutable pattern in local binding: `None` not covered
}

• Also this - godbolt

#![allow(unused)]
fn main() {
let x = Some(1);

match x {
    Some(y) => {
        // do something
    },
    None => {}
}

// or:

if let Some(y) = x {
    // do something
}
}

---

I expected to see this happen:

• Give error like rustc i.e.,

error[E0005]: refutable pattern in local binding: `None` not covered

---

Instead, this happened:

• Give wrong message & error code

➜  gccrs-build gcc/crab1 ../mahad-testsuite/E0005.rs 
../mahad-testsuite/E0005.rs:3:9: error: Cannot find path ‘Some’ in this scope [E0433]
    3 | let x = Some(1);
      |         ^~~~
../mahad-testsuite/E0005.rs:4:5: error: Cannot find path ‘Some’ in this scope [E0433]
    4 | let Some(y) = x;
      |     ^~~~

Meta

• What version of Rust GCC were you using, git sha 6c63150
• gccrs (Compiler-Explorer-Build-gcc-dba8bc5bf8247161b6eff4f738b6479382f770f2-binutils-2.40) 13.0.1 20230417 (experimental)

Fixing this issue will also help this #2301 to emit error codes similiar to rustc.

[CohenArthur]

The error you got is due to the standard prelude not being included by gccrs, as we cannot yet compile Rust's core library (which defines the Option type and its two None and Some variants). Here is a testcase which does not depend on core:

enum AnEnum {
    VariantA(i32),
    VariantB(f32),
}

fn main() {
    let x = AnEnum::VariantA(15);
    let AnEnum::VariantA(x_inner) = x;
}

which errors out with

arthur@platypus ~/G/r/gccrs (nr2.0-early-name-resolver) [1]> build/gcc/crab1 test.rs
test.rs:8:9: sorry, unimplemented: tuple-struct pattern let statements not supported
    8 |     let AnEnum::VariantA(x_inner) = x;
      |         ^~~~~~