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[fine] Check the return type of functions

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A function returns what it says it does, the check is that the body
returns the right value.
This commit is contained in:
John Doty 2024-01-15 07:46:20 -08:00
parent 257a7e64c2
commit d893002ec2
5 changed files with 70 additions and 14 deletions
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42
fine/src/semantics.rs
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@ -657,6 +657,7 @@ impl<'a> Semantics<'a> {
TreeKind::Identifier => self.type_of_identifier(t, tree),
TreeKind::FunctionDecl => self.type_of_function_decl(tree),
TreeKind::ReturnType => self.type_of_return_type(tree),
_ => self.internal_compiler_error(Some(t), "asking for a nonsense type"),
};
@ -1021,6 +1022,11 @@ impl<'a> Semantics<'a> {
Some(Type::Function(parameter_types, return_type))
}
fn type_of_return_type(&self, tree: &Tree) -> Option<Type> {
assert_eq!(tree.kind, TreeKind::ReturnType);
Some(self.type_of(tree.nth_tree(1)?)) // type expression
}
fn type_of_if_statement(&self, tree: &Tree) -> Option<Type> {
Some(self.type_of(tree.nth_tree(0)?))
}
@ -1101,9 +1107,7 @@ pub fn check(s: &Semantics) {
match tree.kind {
TreeKind::Error => {} // already reported
TreeKind::File => {}
TreeKind::FunctionDecl => {
let _ = s.environment_of(t);
}
TreeKind::FunctionDecl => check_function_decl(s, t, tree),
TreeKind::ParamList => {}
TreeKind::Parameter => {}
TreeKind::TypeExpression => {
@ -1138,6 +1142,38 @@ pub fn check(s: &Semantics) {
}
}
fn check_function_decl(s: &Semantics, t: TreeRef, tree: &Tree) {
assert_eq!(tree.kind, TreeKind::FunctionDecl);
let _ = s.environment_of(t);
let return_type_tree = tree.child_of_kind(s.syntax_tree, TreeKind::ReturnType);
let return_type = return_type_tree
.map(|t| s.type_of(t))
.unwrap_or(Type::Nothing);
if let Some(body) = tree.child_of_kind(s.syntax_tree, TreeKind::Block) {
let body_type = s.type_of(body);
if !body_type.compatible_with(&return_type) {
// Just work very hard to get an appropriate error span.
let (start, end) = return_type_tree
.map(|t| {
let rtt = &s.syntax_tree[t];
(rtt.start_pos, rtt.end_pos)
})
.unwrap_or_else(|| {
let start = tree.start_pos;
let end_tok = tree
.nth_token(1)
.unwrap_or_else(|| tree.nth_token(0).unwrap());
let end_pos = end_tok.start + end_tok.as_str().len();
(start, end_pos)
});
s.report_error_span(start, end, format!("the body of this function yields a value of type `{body_type}`, but callers expect this function to produce a `{return_type}`"));
}
}
}
#[cfg(test)]
mod tests {
use super::*;