bjoernager/rust
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suggest MAX constant if -1 is assigned to unsigned type

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This commit is contained in:
Andy Russell 2020-10-05 12:23:36 -04:00
parent a585aaefb6
commit ced11a83cb
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GPG key ID: BE2221033EDBC374
4 changed files with 70 additions and 1 deletions
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25
compiler/rustc_typeck/src/check/op.rs
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@ -2,6 +2,7 @@
use super::method::MethodCallee;
use super::FnCtxt;
use rustc_ast as ast;
use rustc_errors::{self, struct_span_err, Applicability, DiagnosticBuilder};
use rustc_hir as hir;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
@ -13,6 +14,7 @@ use rustc_middle::ty::TyKind::{Adt, Array, Char, FnDef, Never, Ref, Str, Tuple,
use rustc_middle::ty::{
self, suggest_constraining_type_param, Ty, TyCtxt, TypeFoldable, TypeVisitor,
};
use rustc_span::source_map::Spanned;
use rustc_span::symbol::{sym, Ident};
use rustc_span::Span;
use rustc_trait_selection::infer::InferCtxtExt;
@ -673,6 +675,29 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
match actual.kind() {
Uint(_) if op == hir::UnOp::UnNeg => {
err.note("unsigned values cannot be negated");
if let hir::ExprKind::Unary(
_,
hir::Expr {
kind:
hir::ExprKind::Lit(Spanned {
node: ast::LitKind::Int(1, _),
..
}),
..
},
) = ex.kind
{
err.span_suggestion(
ex.span,
&format!(
"you may have meant the maximum value of `{}`",
actual
),
format!("{}::MAX", actual),
Applicability::MaybeIncorrect,
);
}
}
Str | Never | Char | Tuple(_) | Array(_, _) => {}
Ref(_, ref lty, _) if *lty.kind() == Str => {}