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Add better diagnostic for missing where clause

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Previously, it's not clear what exactly should be added in the suggested where clause,
so this adds an example to demonstrate.
This commit is contained in:
kadmin 2021-01-30 03:45:18 +00:00
parent 04caa632dd
commit 65256717f2
7 changed files with 93 additions and 18 deletions
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30
compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
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@ -16,8 +16,7 @@
use rustc_middle::mir::abstract_const::{Node, NodeId};
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::mir::{self, Rvalue, StatementKind, TerminatorKind};
use rustc_middle::ty::subst::Subst;
use rustc_middle::ty::subst::SubstsRef;
use rustc_middle::ty::subst::{Subst, SubstsRef};
use rustc_middle::ty::{self, TyCtxt, TypeFoldable};
use rustc_session::lint;
use rustc_span::def_id::{DefId, LocalDefId};
@ -43,10 +42,6 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
for pred in param_env.caller_bounds() {
match pred.kind().skip_binder() {
ty::PredicateKind::ConstEvaluatable(b_def, b_substs) => {
debug!(
"is_const_evaluatable: caller_bound={:?}, {:?}",
b_def, b_substs
);
if b_def == def && b_substs == substs {
debug!("is_const_evaluatable: caller_bound ~~> ok");
return Ok(());
@ -100,15 +95,24 @@ enum FailureKind {
}
FailureKind::MentionsParam => {
// FIXME(const_evaluatable_checked): Better error message.
infcx
.tcx
.sess
.struct_span_err(span, "unconstrained generic constant")
.span_help(
let mut err =
infcx.tcx.sess.struct_span_err(span, "unconstrained generic constant");
let const_span = tcx.def_span(def.did);
// FIXME(const_evaluatable_checked): Update this suggestion once
// explicit const evaluatable bounds are implemented.
if let Ok(snippet) = infcx.tcx.sess.source_map().span_to_snippet(const_span)
{
err.span_help(
tcx.def_span(def.did),
&format!("try adding a `where` bound using this expression: where [u8; {}]: Sized", snippet),
);
} else {
err.span_help(
const_span,
"consider adding a `where` bound for this expression",
)
.emit();
);
}
err.emit();
return Err(ErrorHandled::Reported(ErrorReported));
}
FailureKind::Concrete => {

8
src/test/ui/const-generics/const_evaluatable_checked/cross_crate_predicate.stderr
View File

@ -4,7 +4,7 @@ error: unconstrained generic constant
LL | let _ = const_evaluatable_lib::test1::<T>();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: consider adding a `where` bound for this expression
help: try adding a `where` bound using this expression: where [u8; std::mem::size_of::<T>() - 1]: Sized
--> $DIR/auxiliary/const_evaluatable_lib.rs:6:10
|
LL | [u8; std::mem::size_of::<T>() - 1]: Sized,
@ -16,7 +16,7 @@ error: unconstrained generic constant
LL | let _ = const_evaluatable_lib::test1::<T>();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: consider adding a `where` bound for this expression
help: try adding a `where` bound using this expression: where [u8; std::mem::size_of::<T>() - 1]: Sized
--> $DIR/auxiliary/const_evaluatable_lib.rs:4:27
|
LL | pub fn test1<T>() -> [u8; std::mem::size_of::<T>() - 1]
@ -28,7 +28,7 @@ error: unconstrained generic constant
LL | let _ = const_evaluatable_lib::test1::<T>();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: consider adding a `where` bound for this expression
help: try adding a `where` bound using this expression: where [u8; std::mem::size_of::<T>() - 1]: Sized
--> $DIR/auxiliary/const_evaluatable_lib.rs:6:10
|
LL | [u8; std::mem::size_of::<T>() - 1]: Sized,
@ -40,7 +40,7 @@ error: unconstrained generic constant
LL | let _ = const_evaluatable_lib::test1::<T>();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: consider adding a `where` bound for this expression
help: try adding a `where` bound using this expression: where [u8; std::mem::size_of::<T>() - 1]: Sized
--> $DIR/auxiliary/const_evaluatable_lib.rs:4:27
|
LL | pub fn test1<T>() -> [u8; std::mem::size_of::<T>() - 1]

2
src/test/ui/const-generics/const_evaluatable_checked/different-fn.stderr
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@ -4,7 +4,7 @@ error: unconstrained generic constant
LL | [0; size_of::<Foo<T>>()]
| ^^^^^^^^^^^^^^^^^^^
|
help: consider adding a `where` bound for this expression
help: try adding a `where` bound using this expression: where [u8; size_of::<Foo<T>>()]: Sized
--> $DIR/different-fn.rs:10:9
|
LL | [0; size_of::<Foo<T>>()]

14
src/test/ui/const_evaluatable/needs_where_clause.rs Normal file
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@ -0,0 +1,14 @@
#![crate_type = "lib"]
#![feature(const_generics, const_evaluatable_checked)]
#![allow(incomplete_features)]
const fn complex_maths<T>(n : usize) -> usize {
2 * n + 1
}
struct Example<T, const N: usize> {
a: [f32; N],
b: [f32; complex_maths::<T>(N)],
//~^ ERROR unconstrained
c: T,
}

14
src/test/ui/const_evaluatable/needs_where_clause.stderr Normal file
View File

@ -0,0 +1,14 @@
error: unconstrained generic constant
--> $DIR/needs_where_clause.rs:11:6
|
LL | b: [f32; complex_maths::<T>(N)],
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: try adding a `where` bound using this expression: where [u8; complex_maths::<T>(N)]: Sized
--> $DIR/needs_where_clause.rs:11:12
|
LL | b: [f32; complex_maths::<T>(N)],
| ^^^^^^^^^^^^^^^^^^^^^
error: aborting due to previous error

29
src/test/ui/const_evaluatable/no_where_clause.rs Normal file
View File

@ -0,0 +1,29 @@
#![feature(const_generics, const_evaluatable_checked)]
#![allow(incomplete_features, unused)]
const fn complex_maths(n : usize) -> usize {
2 * n + 1
}
pub struct Example<const N: usize> {
a: [f32; N],
b: [f32; complex_maths(N)],
//~^ ERROR unconstrained generic
}
impl<const N: usize> Example<N> {
pub fn new() -> Self {
Self {
a: [0.; N],
b: [0.; complex_maths(N)],
}
}
}
impl Example<2> {
pub fn sum(&self) -> f32 {
self.a.iter().sum::<f32>() + self.b.iter().sum::<f32>()
}
}
fn main() {}

14
src/test/ui/const_evaluatable/no_where_clause.stderr Normal file
View File

@ -0,0 +1,14 @@
error: unconstrained generic constant
--> $DIR/no_where_clause.rs:10:6
|
LL | b: [f32; complex_maths(N)],
| ^^^^^^^^^^^^^^^^^^^^^^^
|
help: try adding a `where` bound using this expression: where [u8; complex_maths(N)]: Sized
--> $DIR/no_where_clause.rs:10:12
|
LL | b: [f32; complex_maths(N)],
| ^^^^^^^^^^^^^^^^
error: aborting due to previous error