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annotate #[allow(unreachable_code)] to tail expr #43

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annotate #[allow(unreachable_code)] to tail expr #43

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58eb203
annotate #[allow(unreachable_code)] to tail expr
ubnt-intrepid Apr 18, 2020
f3ab630
keep attributes when the tail expr is explicit
ubnt-intrepid Apr 18, 2020
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32 changes: 23 additions & 9 deletions fehler-macros/src/throws.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -101,8 +101,8 @@ impl Fold for Throws {

fn fold_expr_return(&mut self, i: syn::ExprReturn) -> syn::ExprReturn {
let ok = match &i.expr {
Some(expr) => ok(expr),
None => ok_unit(),
Some(expr) => ok(expr, false),
None => ok_unit(false),
};
syn::ExprReturn { expr: Some(Box::new(ok)), ..i }
}
Expand All @@ -117,13 +117,13 @@ fn modify_tail(is_unit_fn: bool, stmts: &mut Vec<syn::Stmt>) {
let new = syn::parse2(quote::quote!(#e;)).unwrap();
stmts.pop();
stmts.push(new);
stmts.push(syn::Stmt::Expr(ok_unit()));
stmts.push(syn::Stmt::Expr(ok_unit(true)));
}
Some(syn::Stmt::Expr(e)) => {
*e = ok(e);
*e = ok(e, true);
}
_ if is_unit_fn => {
stmts.push(syn::Stmt::Expr(ok_unit()));
stmts.push(syn::Stmt::Expr(ok_unit(true)));
}
_ => { }
}
Expand All @@ -141,10 +141,24 @@ fn is_unit_fn(i: &syn::ReturnType) -> bool {
}
}

fn ok(expr: &syn::Expr) -> syn::Expr {
syn::parse2(quote::quote!(<_ as ::fehler::__internal::_Succeed>::from_ok(#expr))).unwrap()
fn ok(expr: &syn::Expr, is_tail: bool) -> syn::Expr {
if is_tail {
syn::parse_quote! {
#[allow(unreachable_code)]
<_ as ::fehler::__internal::_Succeed>::from_ok(#expr)
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@dtolnay dtolnay Apr 18, 2020

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It's not great that this ends up suppressing legitimate unreachable_code lints inside the user's tail expr (which might be a big complicated match or something). Is there a different way?

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@ubnt-intrepid ubnt-intrepid Apr 18, 2020

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Adding here is certainly wrong (I was confused with the case of unit return).
It seems to be desirable to add the attribute only on an implicit unit, and inherit the original attributes when an explicit tail expr is provided.

}
} else {
syn::parse_quote!(<_ as ::fehler::__internal::_Succeed>::from_ok(#expr))
}
}

fn ok_unit() -> syn::Expr {
syn::parse2(quote::quote!(<_ as ::fehler::__internal::_Succeed>::from_ok(()))).unwrap()
fn ok_unit(is_tail: bool) -> syn::Expr {
if is_tail {
syn::parse_quote! {
#[allow(unreachable_code)]
<_ as ::fehler::__internal::_Succeed>::from_ok(())
}
} else {
syn::parse_quote!(<_ as ::fehler::__internal::_Succeed>::from_ok(()))
}
}