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@estebank
estebank committed Sep 28, 2021
1 parent 5c70f25 commit e19d82f
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Showing 2 changed files with 41 additions and 37 deletions.
72 changes: 38 additions & 34 deletions compiler/rustc_typeck/src/check/place_op.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
expr: &hir::Expr<'_>,
base_expr: &'tcx hir::Expr<'tcx>,
base_ty: Ty<'tcx>,
idx_expr: &'tcx hir::Expr<'tcx>,
index_expr: &'tcx hir::Expr<'tcx>,
idx_ty: Ty<'tcx>,
) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
// FIXME(#18741) -- this is almost but not quite the same as the
Expand All @@ -59,12 +59,42 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
let mut autoderef = self.autoderef(base_expr.span, base_ty);
let mut result = None;
while result.is_none() && autoderef.next().is_some() {
result = self.try_index_step(expr, base_expr, &autoderef, idx_ty, idx_expr);
result = self.try_index_step(expr, base_expr, &autoderef, idx_ty, index_expr);
}
self.register_predicates(autoderef.into_obligations());
result
}

fn negative_index(
&self,
ty: Ty<'tcx>,
span: Span,
base_expr: &hir::Expr<'_>,
) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
let ty = self.resolve_vars_if_possible(ty);
let mut err = self.tcx.sess.struct_span_err(
span,
&format!("negative integers cannot be used to index on a `{}`", ty),
);
err.span_label(span, &format!("cannot use a negative integer for indexing on `{}`", ty));
if let (hir::ExprKind::Path(..), Ok(snippet)) =
(&base_expr.kind, self.tcx.sess.source_map().span_to_snippet(base_expr.span))
{
// `foo[-1]` to `foo[foo.len() - 1]`
err.span_suggestion_verbose(
span.shrink_to_lo(),
&format!(
"to access an element starting from the end of the `{}`, compute the index",
ty,
),
format!("{}.len() ", snippet),
Applicability::MachineApplicable,
);
}
err.emit();
Some((self.tcx.ty_error(), self.tcx.ty_error()))
}

/// To type-check `base_expr[index_expr]`, we progressively autoderef
/// (and otherwise adjust) `base_expr`, looking for a type which either
/// supports builtin indexing or overloaded indexing.
Expand All @@ -76,7 +106,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
base_expr: &hir::Expr<'_>,
autoderef: &Autoderef<'a, 'tcx>,
index_ty: Ty<'tcx>,
idx_expr: &hir::Expr<'_>,
index_expr: &hir::Expr<'_>,
) -> Option<(/*index type*/ Ty<'tcx>, /*element type*/ Ty<'tcx>)> {
let adjusted_ty =
self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
Expand All @@ -86,49 +116,23 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
expr, base_expr, adjusted_ty, index_ty
);

let negative_index = || {
let ty = self.resolve_vars_if_possible(adjusted_ty);
let mut err = self.tcx.sess.struct_span_err(
idx_expr.span,
&format!("negative integers cannot be used to index on a `{}`", ty),
);
err.span_label(
idx_expr.span,
&format!("cannot use a negative integer for indexing on `{}`", ty),
);
if let (hir::ExprKind::Path(..), Ok(snippet)) =
(&base_expr.kind, self.tcx.sess.source_map().span_to_snippet(base_expr.span))
{
// `foo[-1]` to `foo[foo.len() - 1]`
err.span_suggestion_verbose(
idx_expr.span.shrink_to_lo(),
&format!(
"if you wanted to access an element starting from the end of the `{}`, you \
must compute it",
ty,
),
format!("{}.len() ", snippet),
Applicability::MachineApplicable,
);
}
err.emit();
Some((self.tcx.ty_error(), self.tcx.ty_error()))
};
if let hir::ExprKind::Unary(
hir::UnOp::Neg,
hir::Expr {
kind: hir::ExprKind::Lit(hir::Lit { node: ast::LitKind::Int(..), .. }),
..
},
) = idx_expr.kind
) = index_expr.kind
{
match adjusted_ty.kind() {
ty::Adt(ty::AdtDef { did, .. }, _)
if self.tcx.is_diagnostic_item(sym::vec_type, *did) =>
{
return negative_index();
return self.negative_index(adjusted_ty, index_expr.span, base_expr);
}
ty::Slice(_) | ty::Array(_, _) => {
return self.negative_index(adjusted_ty, index_expr.span, base_expr);
}
ty::Slice(_) | ty::Array(_, _) => return negative_index(),
_ => {}
}
}
Expand Down
6 changes: 3 additions & 3 deletions src/test/ui/suggestions/negative-literal-index.stderr
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ error: negative integers cannot be used to index on a `Vec<{integer}>`
LL | x[-1];
| ^^ cannot use a negative integer for indexing on `Vec<{integer}>`
|
help: if you wanted to access an element starting from the end of the `Vec<{integer}>`, you must compute it
help: to access an element starting from the end of the `Vec<{integer}>`, compute the index
|
LL | x[x.len() -1];
| +++++++
Expand All @@ -15,7 +15,7 @@ error: negative integers cannot be used to index on a `[{integer}; 3]`
LL | x[-1];
| ^^ cannot use a negative integer for indexing on `[{integer}; 3]`
|
help: if you wanted to access an element starting from the end of the `[{integer}; 3]`, you must compute it
help: to access an element starting from the end of the `[{integer}; 3]`, compute the index
|
LL | x[x.len() -1];
| +++++++
Expand All @@ -26,7 +26,7 @@ error: negative integers cannot be used to index on a `[{integer}; 3]`
LL | x[-1];
| ^^ cannot use a negative integer for indexing on `[{integer}; 3]`
|
help: if you wanted to access an element starting from the end of the `[{integer}; 3]`, you must compute it
help: to access an element starting from the end of the `[{integer}; 3]`, compute the index
|
LL | x[x.len() -1];
| +++++++
Expand Down

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