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Make nested impl Trait a hard error

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This commit is contained in:
Taylor Cramer 2018-02-08 15:40:27 -08:00
parent 4d2d3fc5da
commit 75f72c0de1
8 changed files with 138 additions and 83 deletions
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69
src/librustc_passes/ast_validation.rs
View File

@ -420,6 +420,75 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
}
}
// Bans nested `impl Trait`, e.g. `impl Into<impl Debug>`.
// Nested `impl Trait` _is_ allowed in associated type position,
// e.g `impl Iterator<Item=impl Debug>`
struct NestedImplTraitVisitor<'a> {
session: &'a Session,
outer_impl_trait: Option<Span>,
}
impl<'a> NestedImplTraitVisitor<'a> {
fn with_impl_trait<F>(&mut self, outer_impl_trait: Option<Span>, f: F)
where F: FnOnce(&mut NestedImplTraitVisitor<'a>)
{
let old_outer_impl_trait = self.outer_impl_trait;
self.outer_impl_trait = outer_impl_trait;
f(self);
self.outer_impl_trait = old_outer_impl_trait;
}
}
impl<'a> Visitor<'a> for NestedImplTraitVisitor<'a> {
fn visit_ty(&mut self, t: &'a Ty) {
if let TyKind::ImplTrait(_) = t.node {
if let Some(outer_impl_trait) = self.outer_impl_trait {
struct_span_err!(self.session, t.span, E0666,
"nested `impl Trait` is not allowed")
.span_label(outer_impl_trait, "outer `impl Trait`")
.span_label(t.span, "devilishly nested `impl Trait` here")
.emit();
}
self.with_impl_trait(Some(t.span), |this| visit::walk_ty(this, t));
} else {
visit::walk_ty(self, t);
}
}
fn visit_path_parameters(&mut self, _: Span, path_parameters: &'a PathParameters) {
match *path_parameters {
PathParameters::AngleBracketed(ref params) => {
for type_ in &params.types {
self.visit_ty(type_);
}
for type_binding in &params.bindings {
// Type bindings such as `Item=impl Debug` in `Iterator<Item=Debug>`
// are allowed to contain nested `impl Trait`.
self.with_impl_trait(None, |this| visit::walk_ty(this, &type_binding.ty));
}
}
PathParameters::Parenthesized(ref params) => {
for type_ in &params.inputs {
self.visit_ty(type_);
}
if let Some(ref type_) = params.output {
// `-> Foo` syntax is essentially an associated type binding,
// so it is also allowed to contain nested `impl Trait`.
self.with_impl_trait(None, |this| visit::walk_ty(this, type_));
}
}
}
}
}
pub fn check_crate(session: &Session, krate: &Crate) {
visit::walk_crate(
&mut NestedImplTraitVisitor {
session,
outer_impl_trait: None,
}, krate);
visit::walk_crate(&mut AstValidator { session: session }, krate)
}

1
src/librustc_passes/diagnostics.rs
View File

@ -320,4 +320,5 @@ register_diagnostics! {
E0567, // auto traits can not have generic parameters
E0568, // auto traits can not have super traits
E0642, // patterns aren't allowed in methods without bodies
E0666, // nested `impl Trait` is illegal
}

70
src/libsyntax/feature_gate.rs
View File

@ -432,9 +432,6 @@ declare_features! (
// `foo.rs` as an alternative to `foo/mod.rs`
(active, non_modrs_mods, "1.24.0", Some(44660)),
// Nested `impl Trait`
(active, nested_impl_trait, "1.24.0", Some(34511)),
// Termination trait in main (RFC 1937)
(active, termination_trait, "1.24.0", Some(43301)),
@ -1352,73 +1349,8 @@ fn contains_novel_literal(item: &ast::MetaItem) -> bool {
}
}
// Bans nested `impl Trait`, e.g. `impl Into<impl Debug>`.
// Nested `impl Trait` _is_ allowed in associated type position,
// e.g `impl Iterator<Item=impl Debug>`
struct NestedImplTraitVisitor<'a> {
context: &'a Context<'a>,
is_in_impl_trait: bool,
}
impl<'a> NestedImplTraitVisitor<'a> {
fn with_impl_trait<F>(&mut self, is_in_impl_trait: bool, f: F)
where F: FnOnce(&mut NestedImplTraitVisitor<'a>)
{
let old_is_in_impl_trait = self.is_in_impl_trait;
self.is_in_impl_trait = is_in_impl_trait;
f(self);
self.is_in_impl_trait = old_is_in_impl_trait;
}
}
impl<'a> Visitor<'a> for NestedImplTraitVisitor<'a> {
fn visit_ty(&mut self, t: &'a ast::Ty) {
if let ast::TyKind::ImplTrait(_) = t.node {
if self.is_in_impl_trait {
gate_feature_post!(&self, nested_impl_trait, t.span,
"nested `impl Trait` is experimental"
);
}
self.with_impl_trait(true, |this| visit::walk_ty(this, t));
} else {
visit::walk_ty(self, t);
}
}
fn visit_path_parameters(&mut self, _: Span, path_parameters: &'a ast::PathParameters) {
match *path_parameters {
ast::PathParameters::AngleBracketed(ref params) => {
for type_ in &params.types {
self.visit_ty(type_);
}
for type_binding in &params.bindings {
// Type bindings such as `Item=impl Debug` in `Iterator<Item=Debug>`
// are allowed to contain nested `impl Trait`.
self.with_impl_trait(false, |this| visit::walk_ty(this, &type_binding.ty));
}
}
ast::PathParameters::Parenthesized(ref params) => {
for type_ in &params.inputs {
self.visit_ty(type_);
}
if let Some(ref type_) = params.output {
// `-> Foo` syntax is essentially an associated type binding,
// so it is also allowed to contain nested `impl Trait`.
self.with_impl_trait(false, |this| visit::walk_ty(this, type_));
}
}
}
}
}
impl<'a> PostExpansionVisitor<'a> {
fn whole_crate_feature_gates(&mut self, krate: &ast::Crate) {
visit::walk_crate(
&mut NestedImplTraitVisitor {
context: self.context,
is_in_impl_trait: false,
}, krate);
fn whole_crate_feature_gates(&mut self, _krate: &ast::Crate) {
for &(ident, span) in &*self.context.parse_sess.non_modrs_mods.borrow() {
if !span.allows_unstable() {
let cx = &self.context;

4
src/test/compile-fail/impl-trait/where-allowed.rs
View File

@ -10,7 +10,7 @@
//! A simple test for testing many permutations of allowedness of
//! impl Trait
#![feature(conservative_impl_trait, nested_impl_trait, universal_impl_trait, dyn_trait)]
#![feature(conservative_impl_trait, universal_impl_trait, dyn_trait)]
use std::fmt::Debug;
// Allowed
@ -60,6 +60,7 @@ fn in_dyn_Fn_return_in_return() -> &'static dyn Fn() -> impl Debug { panic!() }
// Disallowed
fn in_impl_Fn_parameter_in_parameters(_: &impl Fn(impl Debug)) { panic!() }
//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
//~^^ ERROR nested `impl Trait` is not allowed
// Disallowed
fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() }
@ -68,6 +69,7 @@ fn in_impl_Fn_return_in_parameters(_: &impl Fn() -> impl Debug) { panic!() }
// Disallowed
fn in_impl_Fn_parameter_in_return() -> &'static impl Fn(impl Debug) { panic!() }
//~^ ERROR `impl Trait` not allowed outside of function and inherent method return types
//~^^ ERROR nested `impl Trait` is not allowed
// Disallowed
fn in_impl_Fn_return_in_return() -> &'static impl Fn() -> impl Debug { panic!() }

11
src/test/run-pass/impl-trait/lifetimes.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![feature(conservative_impl_trait, underscore_lifetimes, universal_impl_trait, nested_impl_trait)]
#![feature(conservative_impl_trait, underscore_lifetimes, universal_impl_trait)]
#![allow(warnings)]
use std::fmt::Debug;
@ -55,12 +55,11 @@ fn pass_through_elision_with_fn_ptr(x: &fn(&u32) -> &u32) -> impl Into<&fn(&u32)
fn pass_through_elision_with_fn_path<T: Fn(&u32) -> &u32>(
x: &T
) -> impl Into<&impl Fn(&u32) -> &u32> { x }
) -> &impl Fn(&u32) -> &u32 { x }
fn foo(x: &impl Debug) -> impl Into<&impl Debug> { x }
fn foo_explicit_lifetime<'a>(x: &'a impl Debug) -> impl Into<&'a impl Debug> { x }
fn foo_no_outer_impl(x: &impl Debug) -> &impl Debug { x }
fn foo_explicit_arg<T: Debug>(x: &T) -> impl Into<&impl Debug> { x }
fn foo(x: &impl Debug) -> &impl Debug { x }
fn foo_explicit_lifetime<'a>(x: &'a impl Debug) -> &'a impl Debug { x }
fn foo_explicit_arg<T: Debug>(x: &T) -> &impl Debug { x }
fn mixed_lifetimes<'a>() -> impl for<'b: 'a> Fn(&'b u32) { |_| () }
fn mixed_as_static() -> impl Fn(&'static u32) { mixed_lifetimes() }

6
src/test/ui/error-codes/E0657.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![allow(warnings)]
#![feature(conservative_impl_trait, nested_impl_trait)]
#![feature(conservative_impl_trait)]
trait Id<T> {}
trait Lt<'a> {}
@ -17,7 +17,7 @@ impl<'a> Lt<'a> for () {}
impl<T> Id<T> for T {}
fn free_fn_capture_hrtb_in_impl_trait()
-> impl for<'a> Id<impl Lt<'a>>
-> Box<for<'a> Id<impl Lt<'a>>>
//~^ ERROR `impl Trait` can only capture lifetimes bound at the fn or impl level [E0657]
{
()
@ -26,7 +26,7 @@ fn free_fn_capture_hrtb_in_impl_trait()
struct Foo;
impl Foo {
fn impl_fn_capture_hrtb_in_impl_trait()
-> impl for<'a> Id<impl Lt<'a>>
-> Box<for<'a> Id<impl Lt<'a>>>
//~^ ERROR `impl Trait` can only capture lifetimes bound at the fn or impl level
{
()

10
src/test/compile-fail/feature-gate-nested_impl_trait.rs → src/test/ui/nested_impl_trait.rs
View File

@ -14,18 +14,19 @@ use std::fmt::Debug;
fn fine(x: impl Into<u32>) -> impl Into<u32> { x }
fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
//~^ ERROR nested `impl Trait` is experimental
//~^ ERROR nested `impl Trait` is not allowed
fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
//~^ ERROR nested `impl Trait` is experimental
//~^ ERROR nested `impl Trait` is not allowed
//~^^ `impl Trait` not allowed
fn bad_in_arg_position(_: impl Into<impl Debug>) { }
//~^ ERROR nested `impl Trait` is experimental
//~^ ERROR nested `impl Trait` is not allowed
struct X;
impl X {
fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
//~^ ERROR nested `impl Trait` is experimental
//~^ ERROR nested `impl Trait` is not allowed
}
fn allowed_in_assoc_type() -> impl Iterator<Item=impl Fn()> {
@ -33,6 +34,7 @@ fn allowed_in_assoc_type() -> impl Iterator<Item=impl Fn()> {
}
fn allowed_in_ret_type() -> impl Fn() -> impl Into<u32> {
//~^ `impl Trait` not allowed
|| 5
}

50
src/test/ui/nested_impl_trait.stderr Normal file
View File

@ -0,0 +1,50 @@
error[E0666]: nested `impl Trait` is not allowed
--> $DIR/nested_impl_trait.rs:16:56
|
16 | fn bad_in_ret_position(x: impl Into<u32>) -> impl Into<impl Debug> { x }
| ----------^^^^^^^^^^-
| | |
| | devilishly nested `impl Trait` here
| outer `impl Trait`
error[E0666]: nested `impl Trait` is not allowed
--> $DIR/nested_impl_trait.rs:19:42
|
19 | fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
| ----------^^^^^^^^^^-
| | |
| | devilishly nested `impl Trait` here
| outer `impl Trait`
error[E0666]: nested `impl Trait` is not allowed
--> $DIR/nested_impl_trait.rs:23:37
|
23 | fn bad_in_arg_position(_: impl Into<impl Debug>) { }
| ----------^^^^^^^^^^-
| | |
| | devilishly nested `impl Trait` here
| outer `impl Trait`
error[E0666]: nested `impl Trait` is not allowed
--> $DIR/nested_impl_trait.rs:28:44
|
28 | fn bad(x: impl Into<u32>) -> impl Into<impl Debug> { x }
| ----------^^^^^^^^^^-
| | |
| | devilishly nested `impl Trait` here
| outer `impl Trait`
error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
--> $DIR/nested_impl_trait.rs:19:32
|
19 | fn bad_in_fn_syntax(x: fn() -> impl Into<impl Debug>) {}
| ^^^^^^^^^^^^^^^^^^^^^
error[E0562]: `impl Trait` not allowed outside of function and inherent method return types
--> $DIR/nested_impl_trait.rs:36:42
|
36 | fn allowed_in_ret_type() -> impl Fn() -> impl Into<u32> {
| ^^^^^^^^^^^^^^
error: aborting due to 6 previous errors