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Rollup merge of rust-lang#69159 - estebank:use-appropriate-lt-name, r…
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…=ecstatic-morse

Select an appropriate unused lifetime name in suggestion

Follow up to rust-lang#69048.
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Centril authored Feb 18, 2020
2 parents 5e2a095 + 8bafe88 commit 981acd9
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Showing 3 changed files with 71 additions and 13 deletions.
50 changes: 44 additions & 6 deletions src/librustc_typeck/collect.rs
Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ use rustc::ty::{self, AdtKind, Const, ToPolyTraitRef, Ty, TyCtxt};
use rustc::ty::{ReprOptions, ToPredicate, WithConstness};
use rustc_attr::{list_contains_name, mark_used, InlineAttr, OptimizeAttr};
use rustc_data_structures::captures::Captures;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_errors::{struct_span_err, Applicability};
use rustc_hir as hir;
use rustc_hir::def::{CtorKind, DefKind, Res};
Expand Down Expand Up @@ -369,10 +369,12 @@ impl AstConv<'tcx> for ItemCtxt<'tcx> {
hir::ItemKind::Enum(_, generics)
| hir::ItemKind::Struct(_, generics)
| hir::ItemKind::Union(_, generics) => {
// FIXME: look for an appropriate lt name if `'a` is already used
let lt_name = get_new_lifetime_name(self.tcx, poly_trait_ref, generics);
let (lt_sp, sugg) = match &generics.params[..] {
[] => (generics.span, "<'a>".to_string()),
[bound, ..] => (bound.span.shrink_to_lo(), "'a, ".to_string()),
[] => (generics.span, format!("<{}>", lt_name)),
[bound, ..] => {
(bound.span.shrink_to_lo(), format!("{}, ", lt_name))
}
};
let suggestions = vec![
(lt_sp, sugg),
Expand All @@ -387,7 +389,7 @@ impl AstConv<'tcx> for ItemCtxt<'tcx> {
ty::EarlyBoundRegion {
def_id: item_def_id,
index: 0,
name: Symbol::intern("'a"),
name: Symbol::intern(&lt_name),
},
))
})
Expand Down Expand Up @@ -445,6 +447,43 @@ impl AstConv<'tcx> for ItemCtxt<'tcx> {
}
}

/// Synthesize a new lifetime name that doesn't clash with any of the lifetimes already present.
fn get_new_lifetime_name<'tcx>(
tcx: TyCtxt<'tcx>,
poly_trait_ref: ty::PolyTraitRef<'tcx>,
generics: &hir::Generics<'tcx>,
) -> String {
let existing_lifetimes = tcx
.collect_referenced_late_bound_regions(&poly_trait_ref)
.into_iter()
.filter_map(|lt| {
if let ty::BoundRegion::BrNamed(_, name) = lt {
Some(name.as_str().to_string())
} else {
None
}
})
.chain(generics.params.iter().filter_map(|param| {
if let hir::GenericParamKind::Lifetime { .. } = &param.kind {
Some(param.name.ident().as_str().to_string())
} else {
None
}
}))
.collect::<FxHashSet<String>>();

let a_to_z_repeat_n = |n| {
(b'a'..=b'z').map(move |c| {
let mut s = format!("'");
s.extend(std::iter::repeat(char::from(c)).take(n));
s
})
};

// If all single char lifetime names are present, we wrap around and double the chars.
(1..).flat_map(a_to_z_repeat_n).find(|lt| !existing_lifetimes.contains(lt.as_str())).unwrap()
}

/// Returns the predicates defined on `item_def_id` of the form
/// `X: Foo` where `X` is the type parameter `def_id`.
fn type_param_predicates(
Expand Down Expand Up @@ -1588,7 +1627,6 @@ fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
/// Returns a list of user-specified type predicates for the definition with ID `def_id`.
/// N.B., this does not include any implied/inferred constraints.
fn explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
use rustc_data_structures::fx::FxHashSet;
use rustc_hir::*;

debug!("explicit_predicates_of(def_id={:?})", def_id);
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -12,11 +12,12 @@ struct SomeStruct<I: for<'x> Foo<&'x isize>> {
//~^ ERROR cannot extract an associated type from a higher-ranked trait bound in this context
}

enum SomeEnum<I: for<'x> Foo<&'x isize>> {
enum SomeEnum<'b, I: for<'a> Foo<&'a isize>> {
TupleVariant(I::A),
//~^ ERROR cannot extract an associated type from a higher-ranked trait bound in this context
StructVariant { field: I::A },
//~^ ERROR cannot extract an associated type from a higher-ranked trait bound in this context
OkVariant(&'b usize),
}

// FIXME(eddyb) This one doesn't even compile because of the unsupported syntax.
Expand All @@ -26,7 +27,13 @@ enum SomeEnum<I: for<'x> Foo<&'x isize>> {
// }

struct YetAnotherStruct<'a, I: for<'x> Foo<&'x isize>> {
field: <I as Foo<&'a isize>>::A
field: <I as Foo<&'a isize>>::A,
}

struct Why<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, 'j, 'k, 'n, 'o, 'p, 'q, 'r, 's, 't, 'u, 'v, 'w, 'x,
'y, 'z, 'aa, I: for<'l, 'm> Foo<&'l &'m isize>> {
field: I::A,
//~^ ERROR cannot extract an associated type from a higher-ranked trait bound in this context
}

pub fn main() {}
Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,8 @@ LL | TupleVariant(I::A),
|
help: use a fully qualified path with explicit lifetimes
|
LL | enum SomeEnum<'a, I: for<'x> Foo<&'x isize>> {
LL | TupleVariant(<I as Foo<&'a isize>>::A),
LL | enum SomeEnum<'c, 'b, I: for<'a> Foo<&'a isize>> {
LL | TupleVariant(<I as Foo<&'c isize>>::A),
|

error[E0212]: cannot extract an associated type from a higher-ranked trait bound in this context
Expand All @@ -30,11 +30,24 @@ LL | StructVariant { field: I::A },
|
help: use a fully qualified path with explicit lifetimes
|
LL | enum SomeEnum<'a, I: for<'x> Foo<&'x isize>> {
LL | enum SomeEnum<'c, 'b, I: for<'a> Foo<&'a isize>> {
LL | TupleVariant(I::A),
LL |
LL | StructVariant { field: <I as Foo<&'a isize>>::A },
LL | StructVariant { field: <I as Foo<&'c isize>>::A },
|

error: aborting due to 3 previous errors
error[E0212]: cannot extract an associated type from a higher-ranked trait bound in this context
--> $DIR/associated-types-project-from-hrtb-in-struct.rs:35:12
|
LL | field: I::A,
| ^^^^
|
help: use a fully qualified path with explicit lifetimes
|
LL | struct Why<'bb, 'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, 'j, 'k, 'n, 'o, 'p, 'q, 'r, 's, 't, 'u, 'v, 'w, 'x,
LL | 'y, 'z, 'aa, I: for<'l, 'm> Foo<&'l &'m isize>> {
LL | field: <I as Foo<&'bb &'bb isize>>::A,
|

error: aborting due to 4 previous errors

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