diff --git a/compiler/rustc_typeck/src/check/expr.rs b/compiler/rustc_typeck/src/check/expr.rs index 8a69e0a737d..09aeb62fc02 100644 --- a/compiler/rustc_typeck/src/check/expr.rs +++ b/compiler/rustc_typeck/src/check/expr.rs @@ -2136,7 +2136,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { idx_t } else { let base_t = self.structurally_resolved_type(base.span, base_t); - match self.lookup_indexing(expr, base, base_t, idx_t) { + match self.lookup_indexing(expr, base, base_t, idx, idx_t) { Some((index_ty, element_ty)) => { // two-phase not needed because index_ty is never mutable self.demand_coerce(idx, idx_t, index_ty, None, AllowTwoPhase::No); diff --git a/compiler/rustc_typeck/src/check/place_op.rs b/compiler/rustc_typeck/src/check/place_op.rs index 055072d3a1d..e5a5066544a 100644 --- a/compiler/rustc_typeck/src/check/place_op.rs +++ b/compiler/rustc_typeck/src/check/place_op.rs @@ -1,5 +1,7 @@ use crate::check::method::MethodCallee; use crate::check::{has_expected_num_generic_args, FnCtxt, PlaceOp}; +use rustc_ast as ast; +use rustc_errors::Applicability; use rustc_hir as hir; use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; use rustc_infer::infer::InferOk; @@ -47,6 +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>, 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 @@ -56,7 +59,7 @@ 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); + result = self.try_index_step(expr, base_expr, &autoderef, idx_ty, idx_expr); } self.register_predicates(autoderef.into_obligations()); result @@ -73,6 +76,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { base_expr: &hir::Expr<'_>, autoderef: &Autoderef<'a, 'tcx>, index_ty: Ty<'tcx>, + idx_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)); @@ -82,6 +86,53 @@ 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 + { + match adjusted_ty.kind() { + ty::Adt(ty::AdtDef { did, .. }, _) + if self.tcx.is_diagnostic_item(sym::vec_type, *did) => + { + return negative_index(); + } + ty::Slice(_) | ty::Array(_, _) => return negative_index(), + _ => {} + } + } + for unsize in [false, true] { let mut self_ty = adjusted_ty; if unsize { diff --git a/src/test/ui/suggestions/negative-literal-index.fixed b/src/test/ui/suggestions/negative-literal-index.fixed new file mode 100644 index 00000000000..e52714cf97f --- /dev/null +++ b/src/test/ui/suggestions/negative-literal-index.fixed @@ -0,0 +1,22 @@ +// run-rustfix + +use std::ops::Index; +struct X; +impl Index for X { + type Output = (); + + fn index(&self, _: i32) -> &() { + &() + } +} + +fn main() { + let x = vec![1, 2, 3]; + x[x.len() -1]; //~ ERROR negative integers cannot be used to index on a + let x = [1, 2, 3]; + x[x.len() -1]; //~ ERROR negative integers cannot be used to index on a + let x = &[1, 2, 3]; + x[x.len() -1]; //~ ERROR negative integers cannot be used to index on a + let _ = x; + X[-1]; +} diff --git a/src/test/ui/suggestions/negative-literal-index.rs b/src/test/ui/suggestions/negative-literal-index.rs new file mode 100644 index 00000000000..d88b66e679e --- /dev/null +++ b/src/test/ui/suggestions/negative-literal-index.rs @@ -0,0 +1,22 @@ +// run-rustfix + +use std::ops::Index; +struct X; +impl Index for X { + type Output = (); + + fn index(&self, _: i32) -> &() { + &() + } +} + +fn main() { + let x = vec![1, 2, 3]; + x[-1]; //~ ERROR negative integers cannot be used to index on a + let x = [1, 2, 3]; + x[-1]; //~ ERROR negative integers cannot be used to index on a + let x = &[1, 2, 3]; + x[-1]; //~ ERROR negative integers cannot be used to index on a + let _ = x; + X[-1]; +} diff --git a/src/test/ui/suggestions/negative-literal-index.stderr b/src/test/ui/suggestions/negative-literal-index.stderr new file mode 100644 index 00000000000..f5ea980048b --- /dev/null +++ b/src/test/ui/suggestions/negative-literal-index.stderr @@ -0,0 +1,35 @@ +error: negative integers cannot be used to index on a `Vec<{integer}>` + --> $DIR/negative-literal-index.rs:15:7 + | +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 + | +LL | x[x.len() -1]; + | +++++++ + +error: negative integers cannot be used to index on a `[{integer}; 3]` + --> $DIR/negative-literal-index.rs:17:7 + | +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 + | +LL | x[x.len() -1]; + | +++++++ + +error: negative integers cannot be used to index on a `[{integer}; 3]` + --> $DIR/negative-literal-index.rs:19:7 + | +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 + | +LL | x[x.len() -1]; + | +++++++ + +error: aborting due to 3 previous errors +