rust-lang/rust · critical

Unexpected type {:?}

Error message

Unexpected type {:?}

What it means

Panics in extract_value when the aggregate value is neither an array, a vector, nor a struct. The message prints the offending value_type, indicating rustc asked the backend to extract a field from a value whose GCC type the backend does not recognise as an aggregate kind.

Source

Thrown at compiler/rustc_codegen_gcc/src/builder.rs:1544

    fn extract_value(&mut self, aggregate_value: RValue<'gcc>, idx: u64) -> RValue<'gcc> {
        // FIXME(antoyo): it would be better if the API only called this on struct, not on arrays.
        assert_eq!(idx as usize as u64, idx);
        let value_type = aggregate_value.get_type();

        if value_type.dyncast_array().is_some() {
            let index = self
                .context
                .new_rvalue_from_long(self.u64_type, i64::try_from(idx).expect("i64::try_from"));
            let element = self.context.new_array_access(self.location, aggregate_value, index);
            element.get_address(self.location)
        } else if value_type.dyncast_vector().is_some() {
            panic!();
        } else if let Some(struct_type) = value_type.is_struct() {
            aggregate_value
                .access_field(self.location, struct_type.get_field(idx as i32))
                .to_rvalue()
        } else {
            panic!("Unexpected type {:?}", value_type);
        }
    }

    fn insert_value(
        &mut self,
        aggregate_value: RValue<'gcc>,
        value: RValue<'gcc>,
        idx: u64,
    ) -> RValue<'gcc> {
        // FIXME(antoyo): it would be better if the API only called this on struct, not on arrays.
        assert_eq!(idx as usize as u64, idx);
        let value_type = aggregate_value.get_type();

        let new_val = self.current_func().new_local(None, value_type, "aggregate_value");
        self.block.add_assignment(None, new_val, aggregate_value);

        let lvalue = if value_type.dyncast_array().is_some() {
            let index = self

View on GitHub (pinned to 22057b88b0)

Solutions

1. Reproduce with the failing crate, capture the printed value_type, and report it upstream so the missing type kind can be handled.
2. Update rustc_codegen_gcc to a commit that recognises the additional aggregate type and routes it correctly.
3. As a temporary local workaround, lower the offending construct differently in the source crate (e.g. avoid the type/representation that triggers extract_value on it).

Example fix

// before
} else {
    panic!("Unexpected type {:?}", value_type);
}
// after
} else {
    bug!("extract_value on unsupported aggregate type {:?}", value_type);
}

use gccjit::Type;

#[derive(Debug)]
enum SupportedAggregate { Array, Struct }

fn classify_for_extract_value(ty: Type<'_>) -> Option<SupportedAggregate> {
    if ty.dyncast_array().is_some() {
        Some(SupportedAggregate::Array)
    } else if ty.is_struct().is_some() {
        Some(SupportedAggregate::Struct)
    } else {
        None // vector, union, opaque, fn, etc. -> would hit "Unexpected type"
    }
}

// guard before extract_value:
match classify_for_extract_value(aggregate_value.get_type()) {
    Some(kind) => extract_value(aggregate_value, idx),
    None => return Err(format!("extract_value: unsupported aggregate kind")),
}

When it happens

Trigger: extract_value is called on a RValue whose value_type returns None for dyncast_array, dyncast_vector, and is_struct. This occurs when a non-aggregate (e.g. a scalar, pointer, or opaque libgccjit type) reaches the aggregate-extraction code path.

Common situations: Arises after rustc internals change how certain types are represented, or when libgccjit returns an unexpected type kind for a fat-pointer/unsized value. Crates exercising DSTs, trait-object fat pointers, or exotic representations are common triggers.

Related errors

• i64::try_from
• vector type
• mask should be of struct type
• Size::bits: {bytes} bytes in bits doesn't fit in u64
• Size::add: {} + {} doesn't fit in u64

AI-assisted analysis of rust-lang/rust@22057b88b0 (2026-08-03). Data as JSON: /data/errors/a09e7222fff0d935.json. Report an issue: GitHub.