fix(sema): reject internal function references in abi.encode* arguments

[aryanbaranwal001]

This PR fixes a compiler panic when an internal function reference is passed as an argument to abi.encode*.

• Fixes Compiler panic in codegen: unreachable!("This type cannot be encoded") when abi-encoding an internal function reference #1862

The root cause is that sema's abi.encode* argument resolution loop at sema/builtin.rs:1403 only guards against mapping and recursive types. It has no guard for Type::InternalFunction. So when a bare internal function reference like f is passed as an argument, sema accepts it without error and stores it in the AST with Type::InternalFunction and put into the args of ast::Expression::Builtin.

codegen/expression.rs:1048 matches ast::Builtin::AbiEncodePacked and calls abi_encode_packed() at codegen/expression.rs:1853.

abi_encode_packed maps expression() over each arg and passes the result to abi_encode() at codegen/expression.rs:1858.

abi_encode calls calculate_size_args() at codegen/encoding/mod.rs:48, which calls get_expr_size() at codegen/encoding/mod.rs:176.

get_expr_size matches on the expression's type. Type::InternalFunction hits the unreachable arm at codegen/encoding/mod.rs:1448–1453:

Type::InternalFunction { .. } | Type::Void | ... => unreachable!("This type cannot be encoded"),

Fix

Add a Type::InternalFunction guard in the arg resolution loop at sema/builtin.rs:1407, that is, immediately after the existing mapping/recursive check:

if matches!(ty, Type::InternalFunction { .. }) {
    diagnostics.push(Diagnostic::error(
        arg.loc(),
        "internal function references cannot be abi encoded".to_string(),
    ));
    return Err(());
}

This makes sema reject internal function references before they reach codegen. The fix covers abi.encode* variants such as abi.encode, abi.encodePacked, abi.encodeWithSelector, and abi.encodeWithSignature, since they all share the same loop at sema/builtin.rs:1403.

Previously panicking inputs:

• abi.encodePacked(f);
• abi.encode(f);

where f is a function in the same contract

Reproduces on polkadot, solana, and evm targets.