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//! Function-body and return-statement checking.
//!
//! `check_fn_body` is the standard entry point for any callable body
//! (fn / tool / pipeline / closure) — it bumps `fn_depth` so `try*`
//! diagnostics know they have somewhere to rethrow to. `check_return_type`
//! recursively walks return statements and `if`/`else` arms to verify
//! every reachable return matches the declared return type.
use crate::ast::*;
use crate::diagnostic_codes::Code;
use harn_lexer::Span;
use super::super::format::format_type;
use super::super::scope::TypeScope;
use super::super::TypeChecker;
impl TypeChecker {
pub(in crate::typechecker) fn callable_return_type(
is_stream: bool,
return_type: &Option<TypeExpr>,
body: &[SNode],
) -> Option<TypeExpr> {
if is_stream {
return Some(
return_type
.clone()
.unwrap_or_else(|| TypeExpr::Stream(Box::new(TypeExpr::Named("any".into())))),
);
}
if Self::body_contains_yield(body) {
return Some(
return_type.clone().unwrap_or_else(|| {
TypeExpr::Generator(Box::new(TypeExpr::Named("any".into())))
}),
);
}
return_type.clone()
}
pub(in crate::typechecker) fn body_contains_yield(nodes: &[SNode]) -> bool {
nodes
.iter()
.any(|node| Self::node_contains_yield(&node.node))
}
fn node_contains_yield(node: &Node) -> bool {
match node {
Node::YieldExpr { .. } => true,
Node::FnDecl { .. } | Node::Closure { .. } => false,
Node::Block(body)
| Node::SpawnExpr { body }
| Node::Retry { body, .. }
| Node::CostRoute { body, .. }
| Node::DeferStmt { body }
| Node::MutexBlock { body }
| Node::Parallel { body, .. }
| Node::TryExpr { body } => Self::body_contains_yield(body),
Node::IfElse {
then_body,
else_body,
..
} => {
Self::body_contains_yield(then_body)
|| else_body
.as_ref()
.is_some_and(|body| Self::body_contains_yield(body))
}
Node::ForIn { body, .. } | Node::WhileLoop { body, .. } => {
Self::body_contains_yield(body)
}
Node::TryCatch {
has_catch: _,
body,
catch_body,
finally_body,
..
} => {
Self::body_contains_yield(body)
|| Self::body_contains_yield(catch_body)
|| finally_body
.as_ref()
.is_some_and(|body| Self::body_contains_yield(body))
}
Node::MatchExpr { arms, .. } => {
arms.iter().any(|arm| Self::body_contains_yield(&arm.body))
}
_ => false,
}
}
pub(in crate::typechecker) fn check_fn_body(
&mut self,
type_params: &[TypeParam],
params: &[TypedParam],
return_type: &Option<TypeExpr>,
body: &[SNode],
where_clauses: &[WhereClause],
is_stream: bool,
expected_span: Span,
) {
self.fn_depth += 1;
let saved_stream_depth = self.stream_fn_depth;
let saved_stream_emit_types = self.stream_emit_types.clone();
if is_stream {
self.stream_fn_depth += 1;
self.stream_emit_types
.push(Self::stream_emit_type(return_type));
} else {
self.stream_fn_depth = 0;
self.stream_emit_types.clear();
}
self.check_fn_body_inner(
type_params,
params,
return_type,
body,
where_clauses,
is_stream,
expected_span,
);
if is_stream {
self.stream_emit_types.pop();
}
self.stream_fn_depth = saved_stream_depth;
self.stream_emit_types = saved_stream_emit_types;
self.fn_depth -= 1;
}
fn stream_emit_type(return_type: &Option<TypeExpr>) -> Option<TypeExpr> {
match return_type {
Some(TypeExpr::Stream(inner)) => Some((**inner).clone()),
_ => None,
}
}
fn check_fn_body_inner(
&mut self,
type_params: &[TypeParam],
params: &[TypedParam],
return_type: &Option<TypeExpr>,
body: &[SNode],
where_clauses: &[WhereClause],
is_stream: bool,
expected_span: Span,
) {
let mut fn_scope = self.scope.child();
// Register generic type parameters so they are treated as compatible
// with any concrete type during type checking.
for tp in type_params {
fn_scope.generic_type_params.insert(tp.name.clone());
}
// Store where-clause constraints for definition-site checking
for wc in where_clauses {
fn_scope
.where_constraints
.insert(wc.type_name.clone(), wc.bound.clone());
}
for param in params {
let param_type = if param.rest {
param
.type_expr
.clone()
.map(|inner| TypeExpr::List(Box::new(inner)))
} else {
param.type_expr.clone()
};
let has_annotation = param.type_expr.is_some();
fn_scope.define_var(¶m.name, param_type);
if has_annotation {
fn_scope.mark_annotated(¶m.name);
}
fn_scope.clear_nil_widenable(¶m.name);
if let Some(default) = ¶m.default_value {
self.check_node(default, &mut fn_scope);
}
}
self.check_block(body, &mut fn_scope);
if is_stream && !matches!(return_type, None | Some(TypeExpr::Stream(_))) {
if let Some(actual) = return_type {
self.error_at(
Code::ReturnTypeMismatch,
format!(
"`gen fn` must return Stream<T>, found {}",
format_type(actual)
),
Span::dummy(),
);
}
}
// Check return statements against the declared return type using the
// post-body scope so locally-bound `let` values are visible, with any
// outstanding narrowings rolled back so a parameter typed (e.g.) `T?`
// is still seen as `T?` here even when the body narrowed it inside a
// conditional that fell through.
if let Some(ret_type) = return_type {
let mut ret_scope = fn_scope.clone();
ret_scope.restore_narrowed_vars();
for stmt in body {
self.check_return_type(stmt, ret_type, expected_span, &mut ret_scope);
}
}
}
pub(in crate::typechecker) fn check_return_type(
&mut self,
snode: &SNode,
expected: &TypeExpr,
expected_span: Span,
scope: &mut TypeScope,
) {
match &snode.node {
Node::ReturnStmt { value: Some(val) } => {
let inferred = self.infer_type(val, scope);
if let Some(actual) = &inferred {
if !self.types_compatible(expected, actual, scope) {
self.type_mismatch_at(
Code::ReturnTypeMismatch,
"return value",
expected,
actual,
val.span,
(
Some((expected_span, "return type declared here".to_string())),
Some(val.span),
),
scope,
);
}
}
// Returning an `owned<T>` binding by name silently disables
// the auto-drop: the value escapes the scope where the
// synthetic `defer { drop(x) }` would have fired. Surface
// this as `HARN-OWN-003` so the author can either change the
// return signature to `owned<T>` (declaring an ownership
// transfer) or pick a different value.
if let Node::Identifier(name) = &val.node {
if let Some(Some(declared)) = scope.get_var(name) {
if matches!(declared, TypeExpr::Owned(_))
&& !matches!(expected, TypeExpr::Owned(_))
{
self.warning_at(
Code::OwnershipEscape,
format!(
"owned binding `{name}` escapes its scope via `return`; \
either return `owned<…>` to transfer ownership or drop \
the value before returning"
),
val.span,
);
}
}
}
}
Node::IfElse {
condition,
then_body,
else_body,
} => {
let refs = Self::extract_refinements(condition, scope);
let mut then_scope = scope.child();
refs.apply_truthy(&mut then_scope);
for stmt in then_body {
self.check_return_type(stmt, expected, expected_span, &mut then_scope);
}
if let Some(else_body) = else_body {
let mut else_scope = scope.child();
refs.apply_falsy(&mut else_scope);
for stmt in else_body {
self.check_return_type(stmt, expected, expected_span, &mut else_scope);
}
// Post-branch narrowing for return type checking
if Self::block_definitely_exits(then_body)
&& !Self::block_definitely_exits(else_body)
{
refs.apply_falsy(scope);
} else if Self::block_definitely_exits(else_body)
&& !Self::block_definitely_exits(then_body)
{
refs.apply_truthy(scope);
}
} else {
// No else: if then-body always exits, apply falsy after
if Self::block_definitely_exits(then_body) {
refs.apply_falsy(scope);
}
}
}
_ => {}
}
}
}