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different_lifetimes.rs
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different_lifetimes.rs
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//! Error Reporting for Anonymous Region Lifetime Errors
//! where both the regions are anonymous.
use crate::infer::error_reporting::nice_region_error::find_anon_type::find_anon_type;
use crate::infer::error_reporting::nice_region_error::util::AnonymousParamInfo;
use crate::infer::error_reporting::nice_region_error::NiceRegionError;
use crate::infer::lexical_region_resolve::RegionResolutionError;
use crate::infer::SubregionOrigin;
use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder, ErrorReported};
use rustc_hir as hir;
use rustc_hir::{GenericParamKind, Ty};
use rustc_middle::ty::Region;
impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
/// Print the error message for lifetime errors when both the concerned regions are anonymous.
///
/// Consider a case where we have
///
/// ```no_run
/// fn foo(x: &mut Vec<&u8>, y: &u8) {
/// x.push(y);
/// }
/// ```
///
/// The example gives
///
/// ```text
/// fn foo(x: &mut Vec<&u8>, y: &u8) {
/// --- --- these references are declared with different lifetimes...
/// x.push(y);
/// ^ ...but data from `y` flows into `x` here
/// ```
///
/// It has been extended for the case of structs too.
///
/// Consider the example
///
/// ```no_run
/// struct Ref<'a> { x: &'a u32 }
/// ```
///
/// ```text
/// fn foo(mut x: Vec<Ref>, y: Ref) {
/// --- --- these structs are declared with different lifetimes...
/// x.push(y);
/// ^ ...but data from `y` flows into `x` here
/// }
/// ```
///
/// It will later be extended to trait objects.
pub(super) fn try_report_anon_anon_conflict(&self) -> Option<ErrorReported> {
let (span, sub, sup) = self.regions()?;
if let Some(RegionResolutionError::ConcreteFailure(
SubregionOrigin::ReferenceOutlivesReferent(..),
..,
)) = self.error
{
// This error doesn't make much sense in this case.
return None;
}
// Determine whether the sub and sup consist of both anonymous (elided) regions.
let anon_reg_sup = self.tcx().is_suitable_region(sup)?;
let anon_reg_sub = self.tcx().is_suitable_region(sub)?;
let scope_def_id_sup = anon_reg_sup.def_id;
let bregion_sup = anon_reg_sup.boundregion;
let scope_def_id_sub = anon_reg_sub.def_id;
let bregion_sub = anon_reg_sub.boundregion;
let ty_sup = find_anon_type(self.tcx(), sup, &bregion_sup)?;
let ty_sub = find_anon_type(self.tcx(), sub, &bregion_sub)?;
debug!(
"try_report_anon_anon_conflict: found_param1={:?} sup={:?} br1={:?}",
ty_sub, sup, bregion_sup
);
debug!(
"try_report_anon_anon_conflict: found_param2={:?} sub={:?} br2={:?}",
ty_sup, sub, bregion_sub
);
let (ty_sup, ty_fndecl_sup) = ty_sup;
let (ty_sub, ty_fndecl_sub) = ty_sub;
let AnonymousParamInfo { param: anon_param_sup, .. } =
self.find_param_with_region(sup, sup)?;
let AnonymousParamInfo { param: anon_param_sub, .. } =
self.find_param_with_region(sub, sub)?;
let sup_is_ret_type =
self.is_return_type_anon(scope_def_id_sup, bregion_sup, ty_fndecl_sup);
let sub_is_ret_type =
self.is_return_type_anon(scope_def_id_sub, bregion_sub, ty_fndecl_sub);
let span_label_var1 = match anon_param_sup.pat.simple_ident() {
Some(simple_ident) => format!(" from `{}`", simple_ident),
None => String::new(),
};
let span_label_var2 = match anon_param_sub.pat.simple_ident() {
Some(simple_ident) => format!(" into `{}`", simple_ident),
None => String::new(),
};
let (span_1, span_2, main_label, span_label, future_return_type) =
match (sup_is_ret_type, sub_is_ret_type) {
(None, None) => {
let (main_label_1, span_label_1) = if ty_sup.hir_id == ty_sub.hir_id {
(
"this type is declared with multiple lifetimes...".to_owned(),
"...but data with one lifetime flows into the other here".to_owned(),
)
} else {
(
"these two types are declared with different lifetimes...".to_owned(),
format!("...but data{} flows{} here", span_label_var1, span_label_var2),
)
};
(ty_sup.span, ty_sub.span, main_label_1, span_label_1, None)
}
(Some(ret_span), _) => {
let sup_future = self.future_return_type(scope_def_id_sup);
let (return_type, action) = if sup_future.is_some() {
("returned future", "held across an await point")
} else {
("return type", "returned")
};
(
ty_sub.span,
ret_span,
format!(
"this parameter and the {} are declared with different lifetimes...",
return_type
),
format!("...but data{} is {} here", span_label_var1, action),
sup_future,
)
}
(_, Some(ret_span)) => {
let sub_future = self.future_return_type(scope_def_id_sub);
let (return_type, action) = if sub_future.is_some() {
("returned future", "held across an await point")
} else {
("return type", "returned")
};
(
ty_sup.span,
ret_span,
format!(
"this parameter and the {} are declared with different lifetimes...",
return_type
),
format!("...but data{} is {} here", span_label_var1, action),
sub_future,
)
}
};
let mut err = struct_span_err!(self.tcx().sess, span, E0623, "lifetime mismatch");
err.span_label(span_1, main_label);
err.span_label(span_2, String::new());
err.span_label(span, span_label);
self.suggest_adding_lifetime_params(sub, ty_sup, ty_sub, &mut err);
// TODO: This is only helpful if the lifetime more visible in the impl Future type than in the signature.
if let Some(t) = future_return_type {
let snip = self
.tcx()
.sess
.source_map()
.span_to_snippet(t.span)
.ok()
.and_then(|s| match (&t.kind, s.as_str()) {
(rustc_hir::TyKind::Tup(&[]), "") => Some("()".to_string()),
(_, "") => None,
_ => Some(s),
})
.unwrap_or_else(|| "{unnamed_type}".to_string());
err.span_label(
t.span,
&format!("this `async fn` implicitly returns an `impl Future<Output = {}>`", snip),
);
}
err.emit();
Some(ErrorReported)
}
fn suggest_adding_lifetime_params(
&self,
sub: Region<'tcx>,
ty_sup: &Ty<'_>,
ty_sub: &Ty<'_>,
err: &mut DiagnosticBuilder<'_>,
) {
if let (
hir::Ty { kind: hir::TyKind::Rptr(lifetime_sub, _), .. },
hir::Ty { kind: hir::TyKind::Rptr(lifetime_sup, _), .. },
) = (ty_sub, ty_sup)
{
if lifetime_sub.name.is_elided() && lifetime_sup.name.is_elided() {
if let Some(anon_reg) = self.tcx().is_suitable_region(sub) {
let hir_id = self.tcx().hir().local_def_id_to_hir_id(anon_reg.def_id);
if let hir::Node::Item(&hir::Item {
kind: hir::ItemKind::Fn(_, ref generics, ..),
..
}) = self.tcx().hir().get(hir_id)
{
let (suggestion_param_name, introduce_new) = generics
.params
.iter()
.find(|p| matches!(p.kind, GenericParamKind::Lifetime { .. }))
.and_then(|p| self.tcx().sess.source_map().span_to_snippet(p.span).ok())
.map(|name| (name, false))
.unwrap_or_else(|| ("'a".to_string(), true));
let mut suggestions = vec![
if let hir::LifetimeName::Underscore = lifetime_sub.name {
(lifetime_sub.span, suggestion_param_name.clone())
} else {
(
lifetime_sub.span.shrink_to_hi(),
suggestion_param_name.clone() + " ",
)
},
if let hir::LifetimeName::Underscore = lifetime_sup.name {
(lifetime_sup.span, suggestion_param_name.clone())
} else {
(
lifetime_sup.span.shrink_to_hi(),
suggestion_param_name.clone() + " ",
)
},
];
if introduce_new {
let new_param_suggestion = match &generics.params {
[] => (generics.span, format!("<{}>", suggestion_param_name)),
[first, ..] => (
first.span.shrink_to_lo(),
format!("{}, ", suggestion_param_name),
),
};
suggestions.push(new_param_suggestion);
}
err.multipart_suggestion(
"consider introducing a named lifetime parameter",
suggestions,
Applicability::MaybeIncorrect,
);
err.note(
"each elided lifetime in input position becomes a distinct lifetime",
);
}
}
}
}
}
}