C2Rust crashes when transpiling valid C code that includes an anonymous enum inside an anonymous union within a struct, due to the lack of a field name for the enum. While this is standard-compliant C (accepted by GCC and Clang), C2Rust panics with a missing key lookup in its AST processing.

C code:

struct temp {
    union {
        enum {
            VALUE_1,
            VALUE_2
        };
        int int_value;
    } u;
};

int main() {
    struct temp b;
    b.u.int_value = VALUE_2;
    return 0;
}

C2Rust error:

$c2rust-transpile compile_commands.json -e -o transpiled_code --binary runner
Transpiling runner.c
thread 'main' panicked at c2rust-transpile/src/c_ast/mod.rs:653:57:
no entry found for key
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

c2rust version: C2Rust 0.20.0