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Add pointing const identifier when emitting E0435 #80012

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Jan 7, 2021
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Add pointing const identifier when emitting E0435 #80012

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f03907b
Add pointing const identifier when emitting E0435
sasurau4 Dec 13, 2020
c9e7045
bless tests
sasurau4 Dec 13, 2020
c71348a
Refine E0435 description
sasurau4 Dec 26, 2020
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6 changes: 6 additions & 0 deletions compiler/rustc_error_codes/src/error_codes/E0435.md
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Expand Up @@ -7,6 +7,12 @@ let foo = 42;
let a: [u8; foo]; // error: attempt to use a non-constant value in a constant
```

'constant' means 'a compile-time value'.

More details can be found in the [Variables and Mutability] section of the book.

[Variables and Mutability]: https://doc.rust-lang.org/book/ch03-01-variables-and-mutability.html#differences-between-variables-and-constants

To fix this error, please replace the value with a constant. Example:

```
Expand Down
8 changes: 7 additions & 1 deletion compiler/rustc_resolve/src/diagnostics.rs
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Expand Up @@ -398,13 +398,19 @@ impl<'a> Resolver<'a> {
err.help("use the `|| { ... }` closure form instead");
err
}
ResolutionError::AttemptToUseNonConstantValueInConstant => {
ResolutionError::AttemptToUseNonConstantValueInConstant(ident, sugg) => {
let mut err = struct_span_err!(
self.session,
span,
E0435,
"attempt to use a non-constant value in a constant"
);
err.span_suggestion(
ident.span,
&sugg,
"".to_string(),
Applicability::MaybeIncorrect,
);
err.span_label(span, "non-constant value");
err
}
Expand Down
38 changes: 28 additions & 10 deletions compiler/rustc_resolve/src/late.rs
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Expand Up @@ -92,6 +92,12 @@ crate enum HasGenericParams {
No,
}

#[derive(Copy, Clone, Debug, Eq, PartialEq)]
crate enum ConstantItemKind {
Const,
Static,
}

/// The rib kind restricts certain accesses,
/// e.g. to a `Res::Local` of an outer item.
#[derive(Copy, Clone, Debug)]
Expand Down Expand Up @@ -119,7 +125,7 @@ crate enum RibKind<'a> {
///
/// The `bool` indicates if this constant may reference generic parameters
/// and is used to only allow generic parameters to be used in trivial constant expressions.
ConstantItemRibKind(bool),
ConstantItemRibKind(bool, Option<(Ident, ConstantItemKind)>),

/// We passed through a module.
ModuleRibKind(Module<'a>),
Expand All @@ -145,7 +151,7 @@ impl RibKind<'_> {
NormalRibKind
| ClosureOrAsyncRibKind
| FnItemRibKind
| ConstantItemRibKind(_)
| ConstantItemRibKind(..)
| ModuleRibKind(_)
| MacroDefinition(_)
| ConstParamTyRibKind => false,
Expand Down Expand Up @@ -634,7 +640,7 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
// Note that we might not be inside of an repeat expression here,
// but considering that `IsRepeatExpr` is only relevant for
// non-trivial constants this is doesn't matter.
self.with_constant_rib(IsRepeatExpr::No, true, |this| {
self.with_constant_rib(IsRepeatExpr::No, true, None, |this| {
this.smart_resolve_path(
ty.id,
qself.as_ref(),
Expand Down Expand Up @@ -843,7 +849,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
| ClosureOrAsyncRibKind
| FnItemRibKind
| ItemRibKind(..)
| ConstantItemRibKind(_)
| ConstantItemRibKind(..)
| ModuleRibKind(..)
| ForwardTyParamBanRibKind
| ConstParamTyRibKind => {
Expand Down Expand Up @@ -970,6 +976,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
this.with_constant_rib(
IsRepeatExpr::No,
true,
None,
|this| this.visit_expr(expr),
);
}
Expand Down Expand Up @@ -1012,11 +1019,19 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
self.with_item_rib(HasGenericParams::No, |this| {
this.visit_ty(ty);
if let Some(expr) = expr {
let constant_item_kind = match item.kind {
ItemKind::Const(..) => ConstantItemKind::Const,
ItemKind::Static(..) => ConstantItemKind::Static,
_ => unreachable!(),
};
// We already forbid generic params because of the above item rib,
// so it doesn't matter whether this is a trivial constant.
this.with_constant_rib(IsRepeatExpr::No, true, |this| {
this.visit_expr(expr)
});
this.with_constant_rib(
IsRepeatExpr::No,
true,
Some((item.ident, constant_item_kind)),
|this| this.visit_expr(expr),
);
}
});
}
Expand Down Expand Up @@ -1118,15 +1133,16 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
&mut self,
is_repeat: IsRepeatExpr,
is_trivial: bool,
item: Option<(Ident, ConstantItemKind)>,
f: impl FnOnce(&mut Self),
) {
debug!("with_constant_rib: is_repeat={:?} is_trivial={}", is_repeat, is_trivial);
self.with_rib(ValueNS, ConstantItemRibKind(is_trivial), |this| {
self.with_rib(ValueNS, ConstantItemRibKind(is_trivial, item), |this| {
this.with_rib(
TypeNS,
ConstantItemRibKind(is_repeat == IsRepeatExpr::Yes || is_trivial),
ConstantItemRibKind(is_repeat == IsRepeatExpr::Yes || is_trivial, item),
|this| {
this.with_label_rib(ConstantItemRibKind(is_trivial), f);
this.with_label_rib(ConstantItemRibKind(is_trivial, item), f);
},
)
});
Expand Down Expand Up @@ -1266,6 +1282,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
this.with_constant_rib(
IsRepeatExpr::No,
true,
None,
|this| {
visit::walk_assoc_item(
this,
Expand Down Expand Up @@ -2200,6 +2217,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
self.with_constant_rib(
is_repeat,
constant.value.is_potential_trivial_const_param(),
None,
|this| {
visit::walk_anon_const(this, constant);
},
Expand Down
40 changes: 32 additions & 8 deletions compiler/rustc_resolve/src/lib.rs
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Expand Up @@ -64,7 +64,7 @@ use tracing::debug;
use diagnostics::{extend_span_to_previous_binding, find_span_of_binding_until_next_binding};
use diagnostics::{ImportSuggestion, LabelSuggestion, Suggestion};
use imports::{Import, ImportKind, ImportResolver, NameResolution};
use late::{HasGenericParams, PathSource, Rib, RibKind::*};
use late::{ConstantItemKind, HasGenericParams, PathSource, Rib, RibKind::*};
use macros::{MacroRulesBinding, MacroRulesScope, MacroRulesScopeRef};

type Res = def::Res<NodeId>;
Expand Down Expand Up @@ -210,7 +210,7 @@ enum ResolutionError<'a> {
/// Error E0434: can't capture dynamic environment in a fn item.
CannotCaptureDynamicEnvironmentInFnItem,
/// Error E0435: attempt to use a non-constant value in a constant.
AttemptToUseNonConstantValueInConstant,
AttemptToUseNonConstantValueInConstant(Ident, String),
/// Error E0530: `X` bindings cannot shadow `Y`s.
BindingShadowsSomethingUnacceptable(&'static str, Symbol, &'a NameBinding<'a>),
/// Error E0128: type parameters with a default cannot use forward-declared identifiers.
Expand Down Expand Up @@ -1821,14 +1821,16 @@ impl<'a> Resolver<'a> {
// Use the rib kind to determine whether we are resolving parameters
// (macro 2.0 hygiene) or local variables (`macro_rules` hygiene).
let rib_ident = if ribs[i].kind.contains_params() { normalized_ident } else { ident };
if let Some(res) = ribs[i].bindings.get(&rib_ident).cloned() {
if let Some((original_rib_ident_def, res)) = ribs[i].bindings.get_key_value(&rib_ident)
{
// The ident resolves to a type parameter or local variable.
return Some(LexicalScopeBinding::Res(self.validate_res_from_ribs(
i,
rib_ident,
res,
*res,
record_used,
path_span,
*original_rib_ident_def,
ribs,
)));
}
Expand Down Expand Up @@ -2540,6 +2542,7 @@ impl<'a> Resolver<'a> {
mut res: Res,
record_used: bool,
span: Span,
original_rib_ident_def: Ident,
all_ribs: &[Rib<'a>],
) -> Res {
const CG_BUG_STR: &str = "min_const_generics resolve check didn't stop compilation";
Expand Down Expand Up @@ -2586,10 +2589,31 @@ impl<'a> Resolver<'a> {
res_err = Some(CannotCaptureDynamicEnvironmentInFnItem);
}
}
ConstantItemRibKind(_) => {
ConstantItemRibKind(_, item) => {
// Still doesn't deal with upvars
if record_used {
self.report_error(span, AttemptToUseNonConstantValueInConstant);
let (span, resolution_error) =
if let Some((ident, constant_item_kind)) = item {
let kind_str = match constant_item_kind {
ConstantItemKind::Const => "const",
ConstantItemKind::Static => "static",
};
let sugg = format!(
"consider using `let` instead of `{}`",
kind_str
);
(span, AttemptToUseNonConstantValueInConstant(ident, sugg))
} else {
let sugg = "consider using `const` instead of `let`";
(
rib_ident.span,
AttemptToUseNonConstantValueInConstant(
original_rib_ident_def,
sugg.to_string(),
),
)
};
self.report_error(span, resolution_error);
}
return Res::Err;
}
Expand Down Expand Up @@ -2625,7 +2649,7 @@ impl<'a> Resolver<'a> {
in_ty_param_default = true;
continue;
}
ConstantItemRibKind(trivial) => {
ConstantItemRibKind(trivial, _) => {
let features = self.session.features_untracked();
// HACK(min_const_generics): We currently only allow `N` or `{ N }`.
if !(trivial
Expand Down Expand Up @@ -2718,7 +2742,7 @@ impl<'a> Resolver<'a> {
in_ty_param_default = true;
continue;
}
ConstantItemRibKind(trivial) => {
ConstantItemRibKind(trivial, _) => {
let features = self.session.features_untracked();
// HACK(min_const_generics): We currently only allow `N` or `{ N }`.
if !(trivial
Expand Down
2 changes: 2 additions & 0 deletions src/test/ui/error-codes/E0435.stderr
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@@ -1,6 +1,8 @@
error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/E0435.rs:3:17
|
LL | let foo = 42u32;
| --- help: consider using `const` instead of `let`
LL | let _: [u8; foo];
| ^^^ non-constant value

Expand Down
16 changes: 12 additions & 4 deletions src/test/ui/impl-trait/bindings.stderr
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Expand Up @@ -2,25 +2,33 @@ error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/bindings.rs:5:29
|
LL | const foo: impl Clone = x;
| ^ non-constant value
| --- ^ non-constant value
| |
| help: consider using `let` instead of `const`

error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/bindings.rs:11:33
|
LL | const foo: impl Clone = x;
| ^ non-constant value
| --- ^ non-constant value
| |
| help: consider using `let` instead of `const`

error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/bindings.rs:18:33
|
LL | const foo: impl Clone = x;
| ^ non-constant value
| --- ^ non-constant value
| |
| help: consider using `let` instead of `const`

error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/bindings.rs:25:33
|
LL | const foo: impl Clone = x;
| ^ non-constant value
| --- ^ non-constant value
| |
| help: consider using `let` instead of `const`

warning: the feature `impl_trait_in_bindings` is incomplete and may not be safe to use and/or cause compiler crashes
--> $DIR/bindings.rs:1:12
Expand Down
4 changes: 3 additions & 1 deletion src/test/ui/issues/issue-27433.stderr
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Expand Up @@ -2,7 +2,9 @@ error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/issue-27433.rs:3:23
|
LL | const FOO : u32 = foo;
| ^^^ non-constant value
| --- ^^^ non-constant value
| |
| help: consider using `let` instead of `const`

error: aborting due to previous error

Expand Down
4 changes: 3 additions & 1 deletion src/test/ui/issues/issue-3521-2.stderr
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Expand Up @@ -2,7 +2,9 @@ error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/issue-3521-2.rs:4:23
|
LL | static y: isize = foo + 1;
| ^^^ non-constant value
| - ^^^ non-constant value
| |
| help: consider using `let` instead of `static`

error: aborting due to previous error

Expand Down
3 changes: 3 additions & 0 deletions src/test/ui/issues/issue-3521.stderr
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@@ -1,6 +1,9 @@
error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/issue-3521.rs:6:15
|
LL | let foo = 100;
| --- help: consider using `const` instead of `let`
...
LL | Bar = foo
| ^^^ non-constant value

Expand Down
4 changes: 3 additions & 1 deletion src/test/ui/issues/issue-3668-2.stderr
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Expand Up @@ -2,7 +2,9 @@ error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/issue-3668-2.rs:2:27
|
LL | static child: isize = x + 1;
| ^ non-constant value
| ----- ^ non-constant value
| |
| help: consider using `let` instead of `static`

error: aborting due to previous error

Expand Down
4 changes: 3 additions & 1 deletion src/test/ui/issues/issue-3668.stderr
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Expand Up @@ -2,7 +2,9 @@ error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/issue-3668.rs:8:34
|
LL | static childVal: Box<P> = self.child.get();
| ^^^^ non-constant value
| -------- ^^^^ non-constant value
| |
| help: consider using `let` instead of `static`

error: aborting due to previous error

Expand Down
4 changes: 4 additions & 0 deletions src/test/ui/issues/issue-42060.stderr
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@@ -1,12 +1,16 @@
error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/issue-42060.rs:3:23
|
LL | let thing = ();
| ----- help: consider using `const` instead of `let`
LL | let other: typeof(thing) = thing;
| ^^^^^ non-constant value

error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/issue-42060.rs:9:13
|
LL | let q = 1;
| - help: consider using `const` instead of `let`
LL | <typeof(q)>::N
| ^ non-constant value

Expand Down
3 changes: 3 additions & 0 deletions src/test/ui/issues/issue-44239.stderr
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@@ -1,6 +1,9 @@
error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/issue-44239.rs:6:26
|
LL | let n = 0;
| - help: consider using `const` instead of `let`
...
LL | const N: usize = n;
| ^ non-constant value

Expand Down
2 changes: 2 additions & 0 deletions src/test/ui/non-constant-expr-for-arr-len.stderr
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@@ -1,6 +1,8 @@
error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/non-constant-expr-for-arr-len.rs:5:22
|
LL | fn bar(n: usize) {
| - help: consider using `const` instead of `let`
LL | let _x = [0; n];
| ^ non-constant value

Expand Down
2 changes: 2 additions & 0 deletions src/test/ui/repeat_count.stderr
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@@ -1,6 +1,8 @@
error[E0435]: attempt to use a non-constant value in a constant
--> $DIR/repeat_count.rs:5:17
|
LL | let n = 1;
| - help: consider using `const` instead of `let`
LL | let a = [0; n];
| ^ non-constant value

Expand Down
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