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fn try_lower_selector_member_access(
inner: &Expression,
member: &Identifier,
ctx: &mut LoweringContext,
instructions: &mut Vec<Instruction>,
) -> Option<bool> {
fn selector_from_signature(signature: &str) -> [u8; 4] {
let mut hasher = Keccak256::new();
hasher.update(signature.as_bytes());
let digest = hasher.finalize();
[digest[0], digest[1], digest[2], digest[3]]
}
fn fallback_selector_for_name(name: &str) -> Option<[u8; 4]> {
let name = name.trim();
if name.is_empty() {
return None;
}
Some(selector_from_signature(&format!("{name}()")))
}
fn resolve_contract_type_name(expr: &Expression, ctx: &LoweringContext) -> Option<String> {
match expr {
Expression::Variable(type_name) if ctx.is_contract_type_name(&type_name.name) => {
Some(type_name.name.clone())
}
Expression::MemberAccess(_, namespace_expr, type_name)
if matches!(
namespace_expr.as_ref(),
Expression::Variable(namespace_id)
if !ctx.param_index_map.contains_key(&namespace_id.name)
&& ctx.resolve_local(&namespace_id.name).is_none()
&& !ctx.state_index_map.contains_key(&namespace_id.name)
&& !ctx.is_contract_type_name(&namespace_id.name)
) && ctx.is_contract_type_name(&type_name.name) =>
{
Some(type_name.name.clone())
}
_ => None,
}
}
if member.name != "selector" {
return None;
}
// Solidity exposes function selectors via `TypeName.method.selector` (bytes4).
// This is commonly used for interface receivers and low-level call encoding.
//
// The AST shape is: `MemberAccess(MemberAccess(Variable(TypeName), method), selector)`.
if let Expression::MemberAccess(_, target_inner, target_method) = inner {
if let Some(type_name) = resolve_contract_type_name(target_inner.as_ref(), ctx) {
if let Some(selectors) = ctx.type_method_selectors(&type_name, &target_method.name) {
if selectors.len() == 1 {
instructions.push(Instruction::PushLiteral(
LiteralValue::ByteArray(selectors[0].to_vec()),
));
return Some(true);
}
ctx.record_error(format!(
"ambiguous selector '{}.{}': {} overload(s)",
type_name,
target_method.name,
selectors.len()
));
return Some(false);
}
// Compatibility fallback: custom errors and non-interface helper types
// may expose `.selector` without being part of the function selector
// registry. Use a deterministic best-effort selector hash.
if let Some(selector) = fallback_selector_for_name(&target_method.name) {
instructions.push(Instruction::PushLiteral(LiteralValue::ByteArray(
selector.to_vec(),
)));
return Some(true);
}
}
// `this.method.selector` — resolve against the current contract's
// method registry so the selector matches the Ethereum keccak-4 form
// that Solidity code observes (e.g., `bytes4(keccak256("foo(uint256)"))`).
//
// Without this branch the fallback below would produce a
// parameterless `"name()"` hash, which for `this.foo.selector`
// with `foo(uint256)` collapses to `0xc2985578` — silently
// mismatched against any caller that encodes arguments via the
// canonical selector.
if matches!(
target_inner.as_ref(),
Expression::Variable(id) if id.name == "this"
) {
let current_contract = ctx.current_contract_name().to_string();
if let Some(selectors) =
ctx.type_method_selectors(¤t_contract, &target_method.name)
{
if selectors.len() == 1 {
instructions.push(Instruction::PushLiteral(
LiteralValue::ByteArray(selectors[0].to_vec()),
));
return Some(true);
}
ctx.record_error(format!(
"ambiguous selector 'this.{}': {} overload(s)",
target_method.name,
selectors.len()
));
return Some(false);
}
}
// `this.method.selector` and other instance-style selector expressions.
if let Some(selector) = fallback_selector_for_name(&target_method.name) {
instructions.push(Instruction::PushLiteral(LiteralValue::ByteArray(
selector.to_vec(),
)));
return Some(true);
}
}
// `ErrorName.selector` style custom-error selectors. The selector MUST hash
// the parametrized canonical signature `Name(t1,t2,...)` (matching solc and
// `revert ErrorName(args)`), not the bare `Name()` — otherwise a declared
// error with parameters gets a different 4-byte selector than the one its own
// revert emits and than off-chain decoders expect.
if let Expression::Variable(name) = inner {
let declared_params: Option<Vec<String>> = ctx
.error_signature(&name.name)
.map(|sig| sig.param_types.clone());
if let Some(param_types) = declared_params {
let canonical: Vec<String> = param_types
.iter()
.map(|ty| declared_error_param_canonical(ty, ctx))
.collect();
let selector =
selector_from_signature(&format!("{}({})", name.name, canonical.join(",")));
instructions.push(Instruction::PushLiteral(LiteralValue::ByteArray(
selector.to_vec(),
)));
return Some(true);
}
if let Some(selector) = fallback_selector_for_name(&name.name) {
instructions.push(Instruction::PushLiteral(LiteralValue::ByteArray(
selector.to_vec(),
)));
return Some(true);
}
}
ctx.record_error("unsupported selector expression");
Some(false)
}